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115 HVAC and Ventilation Strategies 7.1 Introduction The primary goal of FAA-funded SIPs is to reduce the adverse impacts of airport-related noise that negatively affect so-called sensitive receptor building types such as residences, schools, churches, and others, as described in Chapter 2 of these guidelines. A core strategy of acoustical treatments is to seal noise paths into the habitable portions of the affected buildings and pro- vide mechanical systems to accommodate the comfort and health of the occupants. Generally, exterior envelope treatments involve installation of acoustical windows and doors that result in a structure that is tightened against both sound and air infiltration. Following treatment, struc- tures typically require HVAC systems to condition and ventilate the space for occupancy. Condi- tioning is not limited to heating and coolingâit also includes humidity control, ventilation air, exhaust air, and indoor air quality. As a result, SIPs are multidisciplinary and require knowledge from many design professionals, construction trades, standards writing organizations, and code compliance agencies. It is recognized by the design professionals involved in specifying SIP treatments that changes to the building envelope, reduction of intrusion points, and lowered infiltration can affect occu- pant health and comfort. Significant building envelope changes typically require the addition of mechanical ventilation to maintain indoor air quality, proper moisture levels, and comfort. Any replacement products and treatments required to meet program objectives must meet the current governing construction standards, energy standards, federal and state code compliance standards, Title 24 in California, and any local codes or requirements that apply. Please note that this guide does not replace professional guidance from design professionals or engineers. 7.2 Regulatory Environment 7.2.1 Code Compliance Building codes specify the minimum acceptable design and construction criteria for public safety and enduring functionality. The main purposes of building codes are public health, safety, and general welfare as related to the construction and occupancy of buildings and structures. Building codes become law in particular jurisdictions when formally enacted by the appropriate governing authority. Design professionals are some of the primary users of building codes, using the criteria in the design process to ensure conformance to the minimum standard, or, as necessary, designing to a more stringent standard that may be required for particular projects. It is necessary for all design personnel to be familiar with the codes related to their work. In addition, building codes affect all aspects of construction involving environmental scientists, developers, contractors and C H A P T E R 7
116 Guidelines for Airport Sound Insulation Programs subcontractors, manufacturers of building products and materials, facility managers, building owners, occupants, and inspection officials. The International Code Council (ICC) publishes the International Building Codes, used by most jurisdictions in the United States. They have 14 sets of codes, including the IBC, the Interna- tional Residential Code, the Existing Building Code, the International Fire Code, the International Energy Conservation Code (IECC), the International Plumbing Code, and the International Mechanical Code (IMC). There are instances where states and local jurisdictions choose to develop their own building codes. In the past, all major cities in the United States had their own building codes; however, due to the increasing complexity and cost of developing building regulations, virtually all munici- palities in the country have chosen to adopt model codes instead, commonly based on the IBC. The design process defines the code compliance needed for any project. Sometimes it is dif- ficult to determine the hierarchy of code enforcement, but traditionally the local code enforce- ment agency is the final arbiter. In most cases, SIPs will use the highest jurisdictional standard as the minimum acceptable parameters for design solutions. Since state, county, and, in many cases, city code requirements will vary, it is critical for SIP teams to investigate the presiding require- ments for each project or individual site. SIPs will receive their final construction approval from local county or municipality code enforcement inspectors. Energy Codes. National building codes and the air conditioning, refrigeration, and ventila- tion industry standards recognize the impact of residential and commercial buildings on national energy usage and future planning. As a result, building codes are requiring greater efficiency with each new revision. Efficiency requirements affect both the construction of the building envelope and the equipment that conditions and services the occupied spaces. States set the minimum standards that municipalities and counties use and administer within their jurisdictions. Many states have adopted the ICCâs model code and require buildings to be constructed in accordance with ICCâs family of codes, including the IBC, the IMC, and the IECC. In addition to the ICC, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and other industry associations provide significant information regarding design criteria. Newer standards and codes have an increased focus on sustainability and energy-conscious building construction. LEED in particular is receiving wide-ranging approval and implementation. A new voluntary International Green Construction Code (IgCC) has been promulgated to provide guidelines on sustainable design and construction. The IECC and the ASHRAE Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, are the major references for energy compliance. The IECC is a model energy code, but it is written in mandatory, enforceable language, so that state and local jurisdic- tions can easily adopt the model as their energy code. These codes take into account local climate, geography, and other regional factors. The significance of energy standards affects the type and ratings of aperture treatments and mechanical equipment used to complete SIPs. Any upgraded or replaced equipment must meet or exceed the localityâs current standard. Changing energy standards, combined with locality requirements, may cause significant cost variations and affect SIP treatments. The resulting projects will necessitate the SIP managerâs diligent involvement to maintain productivity, expenditure, and schedule control. 7.2.2 Standards for Ventilation To understand ventilation requirements, a few concepts need to be defined to properly under- stand the regulations. The regulations described in the following refer to air changes per hour, fresh air, outdoor air, and air exchange rate. These terms are not interchangeable in the lexicon of HVAC
HVAC and Ventilation Strategies 117 design, and the terms are often redefined as the standards evolve. The term air changes per hour (ACH) is changing to air change rate (ACR) and is a volume measurement for air moving from a space measured against the total volume of the space. There is a separate standard, ASHRAE Stan- dard 136-1993 (RA 2006), A Method of Determining Air Change Rates in Detached Dwellings, for calculating the ACR that works in conjunction with the other ventilation standards. The term fresh air is no longer used to mean air pulled directly from the outside. The HVAC industry now refers to fresh air as outdoor air, with the understanding that in many areas of the country, the air being introduced from outside is not fresh due to airborne pollutants. The term air exchange rate is now referred to as ventilation and is the process of supplying outdoor air or removing indoor air, or both (see Section 7.3.4 on pressurization for full discussion). Because there are sometimes years between the posting of a new standard and the ratifica- tion by other agencies, there are some changes that have not reached the local level of code enforcement but will in the future. One such example is the term ventilation, which in ASHRAE Standard 62.1-2007, Ventilation for Accessible Indoor Air Quality, was defined as âthe process of treating air to meet the requirements of a conditioned space by controlling temperature, humidity, and distribution.â The 2010 update to the standard provides the definition, âventila- tion (is) the process of supplying outdoor air to or removing indoor air from a dwelling by natu- ral or mechanical means.â Therefore, for the purpose of this document, the term ventilation is intended to mean the process described in the latest standard. This point is very important since most SIP treatments will include ventilation air. A. International Residential Code Residential sound insulation treatments start with the IRC as the minimum standard for resi- dential ventilation. Section 303.1 of the IRC-2012 states that: Habitable rooms shall have an aggregate glazing (window) area of not less than 8% of the floor area of such rooms. 1. Natural ventilation shall be through windows, doors, louvers, or other approved openings to the out- door air. . . . 2. The minimum open area of a window to the outdoors shall be four percent of the floor area being ventilated. This standard allows for the following exception: Windows are not required to be operable if they are not required for emergency egress and a mechani- cal ventilation system is present that meets the conditions of Chapter 15 of the IRC-2012. However, the acoustical improvements provided by SIPs require that windows and doors be kept closed to provide the sound insulation benefits. As such, FAA guidelines acknowledge the need for ventilation air and stipulate the provision of air-changeâcompliant designs. IRC-2012 and all ICC model codes structure their regulations on the recommendations of industry groups such as ASHRAE. To develop these guidelines for SIPs, ASHRAE standards provide the basis for recommendations. B. ASHRAE Ventilation Standards In response to increasing concerns regarding residential indoor air quality, ASHRAE devel- oped a new standard for ventilation, ASHRAE 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. Added to the standard are two appendices to clarify questions regarding existing buildings and outline addenda. The standard addresses the need to control indoor air quantity and quality via mechanical systems rather than infiltration and operable windows. The standard provides basic recommendations, sometimes adopted by code officials as requirements. It is important to remember that local codes have precedence over any standards
118 Guidelines for Airport Sound Insulation Programs unless otherwise stated in the local codes. Additionally, there is often a multiyear delay between ASHRAE publication and local adoption. The removal of indoor air pollution can be addressed by three principal methods: â¢ Whole-house ventilation is intended to dilute unavoidable contaminant emissions from people, from materials, and from background processes. â¢ Local exhaust is intended to remove contaminants from those specific rooms (e.g., kitchens and bath- rooms) that, because of their design function, are expected to contain sources of contaminants. â¢ Other source control measures are included to deal with those sources that can be reasonably anticipated to be found in a residence1 [such as from combustion appliances and garages]. Section 4 of the standard provides tables for whole-house ventilation rates and equations for calculations based on square footage of living space and the number of bedrooms. Ventilation is best accomplished by exhausting indoor air and supplying outdoor air, pos- sibly through an energy (or enthalpy) recovery ventilator (ERV) or a heat recovery ventilator (HRV). It is important to remember that air cannot be moved into or out of a structure without pressurization changes. Therefore, it is necessary to have a means to relieve building pressure if outdoor air is forced in. Bathroom exhaust fans with a low-speed continuous-operation mode or intermittent operation of a kitchen exhaust hood are inexpensive solutions that can meet ven- tilation rate objectives but will be an issue for occupants. Occupants will turn off or disconnect fans that run continuously to stop the noise, eliminate the energy consumption, or stop drafts, regardless of the impact on the overall system objectives. Outdoor air intakes ducted to return- side HVAC distribution systems can be used as a ventilation air solution. Air distribution can be managed with a simple switch that controls operation functions such as intermittent (during seasons that require minimal heating and cooling), continuous (for continuous operation dur- ing high occupancy), or off. The standard also takes into account differing climates. Some mild climates do not require whole-house ventilation (though the assumption is that the windows are operable and used). Extremely cold, hot, or humid climates, as defined by the standard (see ASHRAE 62.2, Section 8), have limitations on ventilation rates so that conditioning systems can maintain proper comfort. It is important to note that ASHRAE 62.2 does not address ventilation systems as a require- ment for providing temperature and humidity control (i.e., comfort cooling or heating); that information is contained in ASHRAE Standard 55-2010, Thermal Environmental Conditions for Human Occupancy. Ventilation systems are additionally not designed as indoor air quality (IAQ) systems, even though they often contain limited filtration. C. FAA AIP Guidance The FAAâs AIP Handbook, Chapter 812, as replaced by PGL 12-09, acknowledges central air ventilation systems as a noise insulation measure if the structure does not already have a central air ventilation system.2 It further acknowledges that âthe sponsor may recommend an air- conditioning system in lieu of ventilation only.â3 Note: It is important to ascertain whether new or existing air conditioning systems provide supplementary outdoor air to meet ASHRAE requirements. Older and many current residential air conditioning systems are not typically designed to provide outdoor air. Therefore, homes with existing ducted air conditioning systems will need to be inspected to determine if they pro- vide outdoor air. Introduction of outdoor air into the existing system will need to be reviewed for humidity, air quality, and thermal impact to the system. 1 ASHRAE 62.2-2010, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, Foreword, p. 2. 2 U.S. DOT, FAA, PGL 12-09, August 17, 2012, Attachment 1, Â§812 (c)(1), Table 1 p. 1-4. 3 U.S. DOT, FAA, PGL 12-09, August 17, 2012, Attachment 1, Â§812 (d), Table 4 p. 1-13.
HVAC and Ventilation Strategies 119 Table 7.1, taken from ASHRAE 62.2-2010, states the ventilation rates for some typical dwelling sizes and is by no means exhaustive or correct in every instance. Full examination of the ASHRAE standards is required to set up specific projects; they include 136-1993, 119-1988, 55-2010, and 62.2-2010. As an example, 62.2 is a good starting location for calculations. In addition to Table 7.1, Section 4.1.3 of ASHRAE 62.2-2010 discusses an infiltration credit that is allowed on homes that were constructed prior to January 2010, when the newest standard was adopted. The credit is for infiltration with a value of 2 cfm per 100 ft2 of a dwelling. Table 7.1 assumes that this amount [(2 cfm)(square feet of conditioned space/100)] of infiltration will occur in addition to any mechanical ventilation in homes that are not extraordinarily treated against infiltration (i.e., standard building stock). It may be necessary to increase the mechani- cal ventilation rate of a home that has extraordinary treatments such as those provided by SIPs. (This is because the assumed infiltration rate built into the table may not occur.) The only true way to know the acceptable measures to undertake is to perform actual testing, such as blower- door tests, on each structure. Whole-house ventilation systems discussed in the AIP Handbook are conceived as comfort systems, where air is filtered, conditioned, or partially exchanged with outdoor air. Calculating the design differences between the two criteria reveals that the previous FAA goal4 (now super- seded by ASHRAE) of two ACH (48 air changes per day) would far exceed the new ASHRAE IAQ standard and increase operational costs for building owners. The following is an example in compliance with ASHRAE 62.2-2010 for a standard-construction, stick-built, 1500-ft2 dwelling with 8-ft ceilings, two to three occupants, and 45 cfm of continuous exhaust: â¢ Total cubic feet of air in the dwelling: 1500 ft2 Ã 8 ft = 12,000 ft3 â¢ Total ventilation per the standard: 45 cfm Ã 60 min/hr Ã 12 hr/day = 32,400 cfm per day â¢ Total air change rate: 32,400/12,000 = 2.7 ACR per day It is clear that the cost for ventilation can be substantial. For a ventilated home of this size to meet the ASHRAE standard, all the air would need to be replaced 2.7 times a day. The require- ment to heat or cool this air can be offset by the use of an ERV [discussed in Sec tion 7.7.2 (D)]. It is a best practice recommendation of these guidelines to use the most current ASHRAE standard for ventilation as the policy for SIPs, even if it is more stringent than standards the local jurisdic- tion has adopted. At the time of this publication the current standard is 62.2-2010. Floor Area (ft2) Bedrooms (cfm*) 0â1 2â3 4â5 6â7 >7 <1500 30* 45 60 75 90 1501â3000 45 60 75 90 105 3001â4500 60 75 90 105 120 4501â6000 75 90 105 120 135 6001â7500 90 105 120 135 150 >7500 105 120 135 150 165 * cfm of infiltration applies to all numbers in chart. Table 7.1. Ventilation air requirements (ASHRAE 62.2-2010). 4 U.S. DOT, FAA, Report No. DOT/FAA/PP-92-5, Guidelines for the Sound Insulation of Residences Exposed to Aircraft Operations, October 1992, Â§126.96.36.199, p. 3-45.
120 Guidelines for Airport Sound Insulation Programs PGL 12-09 stipulates that plans and specifications must âconform to the local building code.â5 Local building codes vary considerably depending on location. For a program that has a national scope and is trying to achieve some measure of consistency in treatments, it is not unusual to adopt standards higher than those set at the local level. The federal govern- ment has taken a leadership position in designing and constructing projects in a manner that is energy efficient. ASHRAE standards for designing ventilation and air conditioning systems conform to this intent, but these standards are not uniformly adopted across the country. Some jurisdictions take several years to become up to date with new standards. Restricting treatments to the lower standards found in some local codes will reduce the increased energy efficiency available to sound insulation projects. Program sponsors and consultants are advised to consult with their local ADOs for further clarification. D. Makeup Air As mentioned previously, ventilation air will come from somewhere, whether it is through con- trolled mechanical systems or from infiltration through existing roofs, floors, walls, and their open- ings. SIPs aim to control the source of ventilation air. Air and noise will make it into the house through the path of least resistance. It is undesirable for the unintended path to be from uncondi- tioned crawl spaces, attics, wall sections, doors, windows, or other penetration points. As much as possible, the path of outside air should be through the ventilation system. The FAA requirement for âcontinuous positive ventilation airâ is a good idea as long as it is controlled and has a suitable intake point. The location for intake grills needs to be selected carefully to prevent the intake of air from areas prone to dust, dirt, or other contaminants. Intake louvers should be mounted high enough on the wall to avoid dust and ground clippings from mowing operations, far enough from exhaust systems to prevent recirculation, and distant from combustion gas exhaust as specified in applicable building codes. It is also better for the occupants if the ventilation air passes through some filtration. 5 See note 2. Attachment 1, Â§812 (c)(1), p. 1-5. 7.2.3 Best Practice Recommendations: Code Compliance 1. Use the highest jurisdictional standard as the minimum acceptable parameters for design solutions. Investigate the presiding requirements for each project or indi- vidual site. 2. Use the most current ASHRAE, IECC, IBC, and other jurisdictional standards for design of HVAC systems. Use the most current ASHRAE standard for ventilation as the policy for SIPs, even if it is more stringent than standards the local jurisdiction has adopted. 3. Specify an outdoor air component for residential air conditioning units in order to comply with AIP guidance to provide residences with outdoor air changes. 7.3 Residential Indoor Air/Environment Quality 7.3.1 Sealing of Homes for Air Infiltration IAQ is a significant issue that must be addressed as part of the design of sound insulation treatments. The reduction of infiltration and naturally occurring ventilation rates can intensify the effects of indoor air pollutants. Pollutants are chemical, physical, and biologicalâspecifically,
HVAC and Ventilation Strategies 121 radon, molds and allergens, carbon monoxide (CO) and carbon dioxide (CO2), volatile organic compounds (VOCs), and other airborne contaminants that become trapped and recirculated in homes. The resultant lower ventilation rates, infiltration rates, and changes to indoor contami- nation are not specific to SIPs but rather are issues that need to be addressed in any structure with a tight exterior envelope. A. Background In a study conducted in the Midwest, blower-door testing established a baseline infiltra- tion rate for each representative home before any project-related sealing or insulating was performed. Blower-door testing pulls a small negative pressure on a home using a doorway- mounted blower assembly, and simultaneously tracks airflow measurements and differen- tial pressure. The studyâs measurements supplied researchers with a close approximation of natural infiltration. Results showed that newer homes (no date available) were sounderâthat is, they had less measurable airflow at equivalent pressures than older homes. With measure- ments in hand, the necessity to address reduced infiltration resulted in the development of crite- ria to ensure that minimum ventilation air was included in the treatments, along with measures to ensure sufficient combustion air and venting for fuel-burning appliances. It is important to remember that combustion air is not part of ventilation air and must be considered sepa- rately. ASHRAE weighed in on the subject: Residential ventilation was traditionally not a major concern, because it was understood that between operable windows and envelope leakage, people were getting enough (outside) air. In the quarter of a century since the first oil crisis, houses have become more energy efficient. At the same time, the materials and functionality of houses have changed in response to peopleâs evolving needs. People are also becoming more environmentally conscious, not only about the resources they consume but also about the environment in which they live. These factors contribute to an increasing level of public concern regarding residential indoor air quality and ventilation. Where once there was an easy feeling about the residential indoor environment, there is now a desire to define levels of acceptability and performance.6 ASHRAE produces a standard for use in achieving good indoor air quality, ASHRAE Standard 24-2008, Ventilation and Indoor Air Quality in Low-Rise Residential Buildings. The purpose of the standard is to provide information for good air quality and âprovide information relevant to ventilation and IAQ on envelope and system design, material selection, commissioning, and installation, operation and maintenance.â7 Filtration is one of the biggest issues for IAQ; there- fore, ASHRAE continues to increase filtration recommendations. B. Combustion Air Combustion appliances can be deadly sources of CO if not properly maintained or vented, especially for non-vented space heaters, wood stoves, and open fireplaces. Proper installation of fuel-burning appliances is addressed in the National Fuel Gas Code and the IRC and is therefore not part of ASHRAE Standard 62.2. The standard does not cover the proper opera- tion and maintenance of existing combustion appliances assumed to be operating properly. However, in SIPs that affect the construction and permeability of a structure, it is important that the design team recognize the combustion air requirements of existing equipment. In addition, if electric HVAC equipment inside the home is replaced by an SIP with fuel-burning equipment, provisions will need to be made to bring combustion air to the location of the new equipment. 6 ASHRAE 62.2-2003, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. 7 ASHRAE Standard 24-2008, Ventilation and Indoor Air Quality in Low-Rise Residential Buildings. Section 1.2.
122 Guidelines for Airport Sound Insulation Programs 7.3.2 Testing for Indoor Environmental Quality A. SIP Blower-Door Testing A thoughtfully planned SIP can address indoor air quality concerns for sponsors and building owners. For the most part, the solutions to tightness issues are not overly complex or expensive. Sampling and analysis of homes to establish baseline conditions can be instituted when devel- oping design solutions and program policies. Similar to acoustical testing before and after con- struction, this sampling would strive to achieve designs applicable to the specific housing stock and conditions for each community, thereby avoiding repetitive and expensive house-by-house testing. A best practice recommendation is to test and inspect existing mechanical and ducting systems when they are to be reused. Blower-door testing (see Figure 7.1) is used to provide empirical data on a structureâs infiltra- tion rate. Blower-door testing can measure the buildingâs negative pressurization when exhaust fans are operating. The measurements obtained through this type of testing can help determine the potential for back-drafting of combustion appliances, the overall infiltration of a structure, and the integrity of any existing HVAC systems. It can also be used as a base for a particular dwelling type within a given area if ASHRAE has no existing suitable data. B. Existing Duct Pressure Testing Duct pressurization tests of any existing ductwork will help determine the need for addi- tional air volume or treatment of ducts. There is great potential for reduction in the required amount of outside air reaching occupants and for loss of energy efficiency into attics or other unconditioned space from leaky ductwork. SIPs are advised to incorporate this testing as part of premodification design. Figure 7.1. Blower-door test equipment.
HVAC and Ventilation Strategies 123 7.3.3 Indoor Air Pollution Indoor air pollution is created by building materials, furnishings, wall and floor coverings, and occupants. Buildings generate pollutants from plastics and synthetic fabrics that off-gas VOCs, combustion appliances that are poorly adjusted or vented, plumbing and building envelope leaks that lead to mold growth, or dust from multiple sources, including ones that may contain asbestos or lead. Indoor pollution originates from common household sources such as cleaning products, hobby materials, smoking tobacco, cooking odors, pet dander, odors from people, and any constituent of air that reduces acceptability. Even sources and products from outside migrate indoors, such as radon, pesticides, car exhaust, and myriad outdoor pollutants. Indoor pollution can be controlled by reducing pollution at the sources and by diluting the indoor air with outdoor air. Some pollution may be controlled by eliminating the source from the start by selecting nonpolluting cleaners, smoking outside away from building inlets, and adjust- ing improperly functioning appliances. Pollutants such as off-gassing construction materials are not as easily controlled once the building is constructed. Purchasing furnishing and coverings made from natural materials may reduce out-gassing. Reducing or eliminating behavior-caused pollution should always be a first strategy for reducing indoor air pollution. Properly ventilating a building is the critical second step since human behavior devised to reduce pollution will vary and behavioral change will have little effect on building-generated pollution. Ultraviolet (UV) lights, which have been used in hospitals for years, have moved into the resi- dential market. UV light is powerful as a measure for defeating bacterial and microbial growth in air handlers and moist areas within HVAC systems. These systems require switching to prevent exposure to people, but the systems normally come with a door kill switch as part of the package. One of the newer systems features a sweeping UV light that prevents overexposure to internal parts. Filtration is another method for eliminating some forms of indoor contaminants. Filters range in efficiency and cost, from the very basic throwaway from the local hardware store to the very costly HEPA, electronic, or 90%+ efficiency pleated media. In some cases, combinations of these filtration methods are used. No matter the method for filtration used to protect equipment and people, there are maintenance considerations. Filters must be accessible and removable, and possibly be cleanable. ASHRAE is preparing several addenda to 62.1 and 62.2 for clarification of filtration initiatives. 7.3.4 Pressurization Mechanical equipment can cause pressurization differences within buildings. Negative pres- sures within the building envelope can prevent flues and furnaces from operating properly, allowing combustion gases to back-draft into the house. Even small pressure differences can push humid air through leakage paths in the building envelope, allowing condensation to form within walls and ceilings. Pressurization must be taken into account when designing and providing a ventilation system. The design requires more stringent duct sealing and leakage consideration if the mechanical equipment or ducting is outside the building envelope since untreated outdoor air, moisture, or other contaminants may be pulled into the airstream. Open windows and infiltration historically provided sufficient air changes in residential dwell- ings. Figure 7.2 shows a few typical infiltration patterns. Open windows obviously create breaks in the building envelope and allow free exchange of air and noise. SIPs provide windows and doors with low rates of infiltration. These windows must be kept closed to achieve FAA goals for noise reduction. Infiltration involves more than just windows and doors and is determined using a variety of factors, including average indoor temperature, degree-day measurements, average wind conditions, and average building envelope construction.
124 Guidelines for Airport Sound Insulation Programs According to research done by the Lawrence Berkeley Laboratories at the University of Cali- fornia, most housing stock in the United States is relatively leaky.8 (Leaky, by loose definition, is where infiltration exceeds the current ASHRAE Standard 119 for a particular class of home or geographical area.) When existing test homes were upgraded, intending to meet the standards for new construction homes, the homes were still leaky. ASHRAE Standard 119, Air Leakage Performance for Detached Single-Family Residential Buildings, calculates and tabulates the aver- age leak rates for homes in hundreds of geographical areas within the United States. Although the composite average leak rate based on the tables is approximately 140 cubic ft/min, each geo- graphical area must be considered individually. There are two methods to determine whether a structure complies with the standard for a given area: the first is to perform blower-door testing, and the second is to measure and perform the complex calculations listed in the standard. Without testing to specifically measure a structureâs infiltration rate, it can be assumed, based on ASHRAE 119, Section 4, Paragraph 2, that houses in known areas meet the standard for that location. After sound insulation treatments are installed and the major noise and air paths are sealed, the structure loses permeability. Since the post-treatment infiltration rate is now lower than the standard, infiltration cannot be relied on to consistently provide appropriate air exchanges. As a result, mechanical systems must intake outside air to fulfill ASHRAE 62.2-2010 requirements. ASHRAE 119-1988 states: Although ASHRAE Standard 62.2 is to be considered as the reference for determining the sufficiency of ventilation (outdoor air), Appendix Table B.1a can be used to help estimate the contribution of infil- tration in meeting ventilation requirements. For structures in (the first three) classes, infiltration will almost never be sufficient to achieve adequate indoor air quality; specific mechanical ventilation will probably be required at all times (in which the windows are closed). For structures in (the next set of classes), infiltration may or may not be sufficient, depending on circumstances; mechanical ventilation may be required in some cases, but existing inter- mittent mechanical ventilation (i.e., bathroom/kitchen exhaust fans) may be sufficient. For structures in (the finial classes), infiltration will normally be sufficient to meet ventilation requirements; additional mechanical ventilation will usually not be required. Courtesy of the Office of Energy Efficiency (OEE) Natural Resources Canada (NRCAN). Figure 7.2. Typical infiltration patterns. 8 Max Sherman and Nance Matson, Residential Ventilation and Energy Characteristics, Nance Lawrence Berkeley Labora- tory, 1997.
HVAC and Ventilation Strategies 125 7.4 Evaluating Existing Residential Systems 7.4.1 Standard Types of Residential HVAC Systems HVAC systems are as complex and varied as the homes and buildings they service and the geographical locations in which they are built. Buildings can be heated by straight electric strip heaters like baseboard heaters, radiant heat coils embedded in floors or ceilings, or strips in an air handling system. (Straight electric heat is the least desirable, most expensive choice to oper- ate.) Buildings can also be heated by boilers that operate with electricity (expensive), natural gas, liquefied petroleum (LP) gas, fuel oil, or other fuel-burning appliances that hydronically trans- port heated water or steam to the conditioned space. Fuel-burning appliances are not limited to hydronics; indirect combustion in furnaces warm a heat exchanger that then heats the occupied space. Air conditioning is limited to two basic types: direct expansion and chilled water. Direct expansion is a system where refrigerant is used to carry heat between the condenser and evapo- rator and is typically used on smaller systems (most residential systems). Chilled water systems involve a chiller that produces cold water and a piping system that moves water to air handlers equipped with water-based heat exchangers; they are typically for commercial systems. There is some crossover of chilled water systems to residential, but it is rare. Both systems require air to move over the heat exchangers to condition the occupied space. Air movement is a common component of nearly all HVAC systems. Therefore, it is necessary to have a method to move air through the temperature-producing sections of the system. To put it simply, there generally needs to be a primary mover (blower) and a distribution (duct) system. As a part of the design of treatments for SIPs, existing systems need to be evaluated for viability and sizing. Additionally, existing systems need to be examined to determine their compatibility with current energy standards. Given the comprehensive nature of SIPs, the reduction of infiltra- tion, and the installation of some sort of forced outdoor ventilation, few existing ventilation and It is important to remember that when infiltration is the key mechanism for supply ventilation, window opening during periods of low driving forces (wind, temperature differential, or humidity differential) will be necessary for adequate indoor air quality. Even if the average ventilation rate over the season is adequate to supply all ventilation needs, extended periods of low temperature difference may not supply sufficient ventilation. Thus for all leakage classes and in all climates, there will be times when infiltration is insuf- ficient to meet ventilation requirements unless natural ventilation (i.e., window opening) or mechanical ventilation is used to augment the infiltration.9 7.3.5 Best Practice Recommendations: Indoor Air/Environment Quality 1. When considering ventilation solutions, such as in relation to continuous venting via bathroom or kitchen fans, recognize the role occupants playâspecifically, the pos- sibility of tenants shutting off equipment, to the detriment of planned ventilation. 2. Where required, install combustion air ducting and CO detectors to deal with the potential impact of combustion appliances as sources of CO. 3. Test existing building air infiltration and ducting system leakages to facilitate proper system design. 9 ASHRAE 119-1988 (RA2004), Air Leakage Performance for Detached Single-Family Residential Buildings, Ventilation Recommendations, p. 8.
126 Guidelines for Airport Sound Insulation Programs distributions systems will be adequate. This typically means, at a minimum, equipment replace- ment, and at a maximum, a complete reengineering of the buildingâs HVAC system. Duct or distribution systems vary by size, material, and location. The systems listed in the fol- lowing illustrate some of the variances in the equipment that are used in HVAC systems. A. Outdoor Air Ventilation Fresh air ventilation, currently known as outdoor air ventilation, is one method of improv- ing interior conditions in occupied spaces. Outdoor air ventilation is different from natural ventilation because it is accomplished by mechanical means as opposed to simple pressure dif- ferential. It is uncommon to have distribution systems specifically for ventilation air in homes except in northern or low-humidity, temperate climates where air conditioning is uncommon or unneeded. B. Central Heating: Furnaces One of the most common residential systems is the centralized system. Central systems offer distribution to all conditioned living spaces and a ducted centralized return of air to the air handler or furnace. Forced-air furnaces using fossil fuels are popular central systems in colder climates. C. Heat Pumps and Split Systems Heat pumps, or reverse-cycle air conditioners, are central air conditioning systems that use a reverse cycle to heat. Using an air conditioner in this way to produce heat is significantly more cost-effective than electric resistance heating. Resistance heating is typically used as a backup for heat pumps. There are limitations in the geographical climate regions where heat pumps are most effective. A heat pump is basically a heat transfer machine, conveying heat from the indoors to the outdoors in the cooling season and vice versa in the heating season. The issue is that there is limited heat available to transfer when the outdoor temperature drops sufficiently. At some point, the outdoor section will not pick up enough heat to increase the indoor temperature, and some form of supplementary system will need to be used. Split systems are systems where the air handler and the condensing section are not assembled into one unit like package units. D. Package Units Many configurations of package units are available from the major manufacturers. Packaged units can be electric heat pumps, strictly air conditioners, or gas furnace/air conditioner com- binations. The main consideration is that there is no need for an interior air handler. They can be ground-mounted, platform-mounted, or roof-mounted. Roof-mounted package units are typically used in commercial buildings. Many years ago, package units made the transition to the residential market. Rooftop locations provide free flow of air for unit operation and decrease vandalism. There are some areas in the western United States where the rooftop is used com- monly for air conditioning equipment. Ductwork openings to the outdoor unit must be evalu- ated for noise intrusion and treated accordingly. Access for service may be a consideration in design of structures when moving units to this location. E. Ductless Mini-Split Systems Ductless mini-split systems are available in both straight air-conditioning and heat pump models. They are for single room conditioning, with some systems capable of conditioning up to three zones with three separate air handlers served by one condenser. Typically, the air handler/evaporator is mounted in the room itself on a wall or ceiling, while the small con- denser, about the size of a medium suitcase, is mounted outside. The systems do not have ducting. The air handler/evaporator is located in or near the desired space, and air is recir-
HVAC and Ventilation Strategies 127 culated within the conditioned space; therefore, outside ventilation air must be introduced by another means. These systems are used by SIPs where it is impractical to use existing ductwork or install new ductwork. F. Adding Outdoor Air FAA and ASHRAE guidelines require outdoor air to be mechanically provided in occupied structures if infiltration rates in the structure are insufficient to meet minimum standards for occupancy. Following the SIP treatments, structures typically will not meet minimum infiltra- tion requirements, and outdoor ventilation will be required. G. Energy Recovery Systems Energy recovery ventilation systems provide a controlled way of ventilating a home while minimizing energy loss. They reduce the costs of heating ventilation air in the winter by transfer- ring heat from the warm exhaust air to the cold outside supply air. In the summer, the inside air cools the warmer supply air to reduce ventilation cooling costs. There are two types of energy recovery systems: HRVs and ERVs. Both types include a heat exchanger, one or more fans to push air through the machine, and some controls. The bulk of SIPs install or adapt central, whole-house ventilation systems with dedicated distribution sys- tems or shared ductwork with the heating/cooling system. The primary difference between an HRV and an ERV is the way the heat exchanger works. ERVs have limited-permeability heat exchangers that transfer some moisture along with heat energy, while HRVs only transfer heat. Transferring moisture from exhaust air to incoming outdoor air or vice versa allows the structure to maintain more consistent humidity levels. When used in conjunction with a central cooling system, ERVs generally offer better humidity control. Some controversy exists regarding the use of ventilation systems during humid, but not overly hot, summer weather. It may be necessary to install an enthalpy control to maintain indoor humidity. Most energy recovery ventilation systems can recover 70% to 80% of the energy in the exiting air and deliver that energy to the incoming air. However, they are most cost-effective in climates with extreme winters or summers and where fuel costs are high. In mild climates, the cost of the additional electricity consumed by the system fans may exceed the energy savings from not having to condition the supply air.10 7.4.2 Regional Differences Since sound insulation programs occur in all eight major climate zones in the United States, there is no one way to design indoor environmental systems to meet all of these conditions. Study of local engineering practice and codes will be required in each zone. A. Energy Code Climate Zones The 2004 IECC supplement was the first model energy code to adopt a new set of climate zones (see Figure 7.3). The older IECC zones were based only on heating degree days and did not account for cooling energy. The new climate zones were developed based on analysis of the 4,775 National Oceanic and Atmospheric Administration (NOAA) weather sites and statistical analysis of regional information. 10 Energy Efficiency & Renewable Energy, U.S. Department of Energy, accessed January 2012, www.energysavers.gov/ your_home/insulation_airsealing/index.cfm/mytopic=11900.
128 Guidelines for Airport Sound Insulation Programs The new climate zones are entirely set by county boundaries and are accepted and adopted by many other standards and organizations, including: â¢ ASHRAE 90.1, â¢ ASHRAE 90.2, â¢ ASHRAE Advanced Energy Design Guide for Small Office Buildings, â¢ Building America (modified), and â¢ Energy Star. The important issue with energy code climate zones is that they illustrate significant differ- ences between the eight regions within the United States that need to be taken into account when designing an SIP. The new zone jurisdictions are by county and take into account differences within each major zone. A full outline of this topic is discussed in the Building America Best Practices Series, Volume 7.1, High-Performance Home Technologies: Guide to Determining Cli- mate Regions by County, available at http://apps1.eere.energy.gov/buildings/publications/pdfs/ building_america/ba_climateguide_7_1.pdf. B. Californiaâs Title 24 Title 24 Part 6 of the California Code of Regulations is the California Building Energy Effi- ciency Standards; it was legislated into law in 1978, with the current 2008 standards in effect and enforced since 2010. It is an energy guide designed to help building owners, architects, Â©ASHRAE, www.ashrae.org. (2007) ASHRAE Standardâ(90-1). Figure 7.3. National climate zones (2004 IECC supplement).
HVAC and Ventilation Strategies 129 engineers, designers, energy consultants, builders, enforcement agencies, contractors, installers, and manufacturers. The document sets standards for residential and nonresidential buildings and is written as both a reference and an instructional guide for anyone who is directly or indi- rectly involved in the construction of buildings. The guide is intended to supplement several other documents that are available from the California Energy Commission: the 2008 California Building Energy Efficiency Standards, reference appendices for the standards, and the Residential Alternative Calculation Method Manual. (The standards are not always but frequently are at a higher level than general industry.) The technical chapters cover building envelope, mechanical/ HVAC, water heating (including swimming pool system requirements), and interior and exterior lighting permanently attached to the building. Mandatory measures, prescriptive requirements, and compliance options are described within each technical area, subsystem, or component. Other subjects that are covered are the compliance and enforcement process, including design and preparation of compliance documentation through field verification and diagnostic testing; computer performance approach; additions, alterations, and repairs; New Solar Home Partner- ship (NSHP) requirements; and Home Energy Rating System (HERS) raters.11 7.4.3 Condition of Systems Except for homes in the most temperate of climates, such as Hawaii or Californiaâs central and southern coastal areas, most residences will have existing heating or cooling systems. Before adapting an existing system to meet the requirements for SIPs, assess the condition of the sys- tem. In numerous SIPs, mechanical engineers inspect existing systems to determine the age and condition of the system and whether it has a projected service life that would at least equal the warranty period on most of the other acoustical treatments, which is 10 years. Depending on its condition, mechanical equipment older than 10 years may need to be replaced. In terms of system age, as a rule of thumb, a 20-year-old air conditioner is at the end of its useful life. A heat pump that is 15 years old can be equivalent to a 30-year-old air conditioner. Since most residential systems do not provide outdoor air, existing systems must be evaluated for their ability to accept the added load of tempering the outdoor air to meet the ASHRAE 62.2 standard. Systems unable to accept this alteration may need to be replaced. Cooling efficiency of residential air conditioners and heat pumps is measured using the Sea- sonal Energy Efficiency Ratio (SEER). Builders of homes are only required to meet the current standard at the time of construction; unless a homeowner has replaced an existing system, the system in the home was the builderâs choice. SEER ratings have changed dramatically in the last 40 years. In the 1980s there was a loose standard that was changed to 10 SEER in the 1990s. The minimum standard was changed to 13 SEER in January of 2006. Energy Starâqualified central air conditioners must have a SEER of at least 14. This rating continues to increase as technology advances. Furnace efficiencies have not changed much in the last 20 years because combustion technol- ogy is limited to the physical properties of the fuel and combustion materials. Annual fuel utiliza- tion efficiency (AFUE) is the recognized efficiency measure for combustion appliances. AFUE is a measure of the combustion efficiency of the device and does not measure electrical efficiency. Standard efficiencies for todayâs natural gas and LP furnaces range from 78% (the minimum standard) to 96%. Some ultra high-end units reach above this level, with significantly higher prices. Many older systems may have an AFUE in the 60% range; this would be a natural draft 11 2008 Building Energy Efficiency Standards for Residential and Nonresidential Buildings, The California Energy Commission, p. 3, http://www.energy.ca.gov/2008publications/CEC-400-2008-001/CEC-400-2008-001-CMF.PDF.
130 Guidelines for Airport Sound Insulation Programs unit and cannot meet current standards. Standard systems today have forced-draft combustion (a small blower in the exhaust system to motivate combustion gases to exit, preventing stagna- tion that steals efficiency) and will be used in SIPs. Existing furnaces and other HVAC systems will be evaluated on a case-by-case basis to deter- mine adaptability and their remaining life span. The issuance of PGL 12-09 has raised the question of whether the replacement of furnaces is an allowable treatment. While the FAA has not issued a definitive policy statement regarding this, it should be noted that the 1992 guidelines describe six system types that programs might need to adapt to provide ventilation air. The 1992 guidelines acknowledge that the condition and type of the existing furnace may necessitate its replacement in order to provide the required ventilation/ air conditioning.12 Program sponsors and consultants are advised to consult with their local ADO for further clarification. 7.4.4 ACRP Project 02-31, âAssessment of Sound Insulation Treatmentsâ At the time of the publication of these guidelines, the Airport Cooperative Research Program began ACRP Project 02-31, âAssessment of Sound Insulation Treatments,â to conduct research and provide evaluation of the performance of acoustical products and treatments in previous SIPs, including the proper maintenance required to ensure the longevity of the installed acousti- cal treatments. It is recommended that users of these guidelines review the results and recom- mendations of ACRP Project 02-31 for further information regarding sustainable and effective noise reduction products and treatment strategies. 12 See note 4. Â§188.8.131.52, p. 3-47. 7.4.5 Best Practice Recommendations: Evaluating Existing Systems 1. Design of preferred ventilation and mechanical systems is heavily dependent on geographically defined environmental conditions. 2. California has special issues in regard to Title 24 that require additional con- siderations. 3. Issues like remaining life span, outside air adaptability, and ductwork sizes of exist- ing systems are critical to determining the need for a new or retrofitted mechanical system for SIP-treated homes. 7.5 System Design 7.5.1 Sizing of HVAC Systems A. Manual J: The Correct Way to Size a System Correct HVAC system sizing requires many considerations; simply replacing an existing sys- tem with a similarly sized newer system will rarely fulfill the new requirements of a home after sound insulation improvements. In order to accurately meet the contemporary design needs of HVAC systems for SIPs, designers must use a standardized system for load calculations. The Air Conditioning Contractors of America (ACCA) produces the most widely recognized sizing
HVAC and Ventilation Strategies 131 method for residential systems and load calculations: Manual J. (The latest update is version 8.) In addition to Manual J, ACCA produces a commercial system sizing guide (Manual N), a duct sizing guide (Manual D), and an equipment selection guide (Manual T). Discussion of these additional guides follows. The most common considerations for proper system sizing are: â¢ Local climate; â¢ Size, shape, and orientation of the house; â¢ Insulation levels; â¢ Window area, location, and type; â¢ Air infiltration rates; â¢ Number and ages of occupants; â¢ Occupant comfort preferences; â¢ Types and efficiencies of lights and major home appliances; and â¢ Ancillary heat sources. Manual J, version 8 (MJ-8) provides calculations and load sizing in printed and software versions for single-family detached homes, small multi-unit structures, condominiums, town- houses, and modular and manufactured homes (trailers). In addition to these standard construc- tion types, the MJ-8 software13 can accommodate HVAC design in homes that have exceptional architectural features and lifestyle amenities, such as: â¢ Dwellings that have limited exposure or no exposure diversity, â¢ Homes with large south-facing glass area or rooms with unusually large glass area, â¢ A thermally isolated solarium, â¢ Customized internal load estimates, and â¢ Fenestration loads for glass rated by the National Fenestration Rating Council (NFRC).14 The latest version of the software can also incorporate the following geographical, physical, and operational characteristics in the calculations for final sizing: â¢ Improved duct load models; â¢ Improved methods for estimating the effects of internal and external shading devices, includ- ing insect screens; â¢ Infiltration estimated based on blower-door test; â¢ Sensitivity to latitude and altitude; â¢ Sensitivity to skylight glazing material, curb construction, and light shaft construction; and â¢ Heat gain sensitivity to roofing material, roof color, and the use of a radiant barrier.15 The software will also calculate heat loss and gain for log walls, structural foam panels, aerated autoclaved concrete block, insulated concrete panels, brick walls, concrete walls, wood founda- tion walls, and any other type of wall and insulation option.16 B. Additional Steps and Data In addition to the previous lists, calculations require measurements of walls, ceilings, floor space, and windows to determine the room volumes. Confirmation of insulation R-values; window size, type, and location; and building materials will be necessary to complete the load calculations. A close estimate of the buildingâs air leakage is also necessary; using results from a blower-door test is highly recommended. An inspection and description of the air distribution systems will 13 https://www.acca.org/industry/system-design/software. 14 https://www.acca.org/store/product.php?pid=172. 15 https://www.acca.org/store/product.php?pid=172. 16 See Air Conditioning Contractors of America website, acca.org.
132 Guidelines for Airport Sound Insulation Programs also be necessary. These should include the placement of supply and return registers. This information will be necessary when confirming whether the existing system will support the new objectives. Consider the architectural design of the house: are there large overhangs, extensive shading, large skylights, and so forth? Overhangs can reduce solar gain through windows. The house orientation will affect heat gain and heat loss through windows. Use the correct design tempera- tures and humidity for the geographical location of the building. Using an incorrect number or estimate will result in improper sizing. After all the data are entered into the computer, the result can be printed out with all the mea- surements, calculations, and assumptions listed for later review. 7.5.2 Incorrect Sizing Methods Simply replacing an existing system with another similarly designed system is not likely to yield the best results. Just checking the existing nameplate [the label on the unit that has the British thermal unit (BTU) per hour output, among other things] of a system is discouraged. The data from such a check should be used as only one factor in determining proper sizing or to determine natural gas or electrical capacity. One type of guesstimate is the rule of thumb method. This method is based on generalities that are typically geographically specific and loosely based on the size, age, and location of a home. This method has many variations, all of which are not recommended by these guidelines, nor are they in the best interest of SIP participants. Therefore, guesses and rules of thumb should not be used in SIPs. The best practice recommendation for new HVAC system design is to use computer-generated load calculations based on Manual J software or a similarly accepted and recognized alternative. A. Why Most Older Systems Are Oversized Before the first worldwide energy crunch in the early 1970s, homes suffered high infiltration, had poor sealing of windows and openings, and generally were leaky (as discussed in Section 7.3.4). During that era of loose construction, it was not uncommon to find furnaces and air con- ditioners that were (and still are) significantly oversized. In addition to owner efforts to reduce energy consumption, SIP treatments consist of energy-efficient doors and windows, which sig- nificantly reduce infiltration and building loads. Therefore, using the old nameplate data to size new equipment is likely to result in an oversized system. B. Sizing Heating and Cooling Systems Correctly sizing a system is critical for achieving maximum efficiency and comfort while low- ering life-cycle maintenance and operating costs. Equipment oversizing is the most common issue with un-engineered systems. It causes higher system installation costs, inefficient operation, more frequent breakdowns, and higher costs. Certain limitations are built into system sizing and design for residential systems. Air conditioners and heat pumps are limited to half-ton incre- ments up to 4 tons in capacity for most manufacturers. Anything over 4 tons for residences is limited to 5 tons. Due to the electrical construction of such units, anything over this capacity is a commercial unit with commercial power (3 phase) requirements. Oversized air conditioners and heat pumps short cycle, meaning they run long enough to cap- ture the sensible load, but not the latent load. Sensible heat is the heat measured by degrees on a thermometer. Latent heat is the heat within the moisture or humidity suspended in the air. The total amount of humidity in air varies by temperature; the warmer the air, the more moisture it can hold. Generally stated, a space with 50% to 60% humidity is considered comfortable. One of the benefits of an air conditioning system is that it also removes humidity from air as it cools.
HVAC and Ventilation Strategies 133 The big issue with oversized systems is that the air temperature changes quickly without much humidity condensing on the evaporator coil before the system cycles off. The result is a space where the temperature drops but the humidity rises above the comfort level. The space then feels cool, but moist or clammy like the inside of a cave. The analogy is further supported in extreme conditions because surfaces within a home condense moisture as the inside dew point rises with high relative humidity. This is undesirable not only for the comfort of the occupants but also for their health. A high humidity condition over a prolonged period will cause unhealthy mold and bacterial growth within the duct system, air handler, or home materials. Oversized heating equipment is also a problem for similar reasons. Capacities for furnaces tend to run in increments of 20,000 BTUs, starting at 40,000. In addition to combustion limita- tions, there are airflow limitations with each size. The smaller capacities tend to have air blowers capable of supporting air conditioners of 1 to 2 tons. Each size thereafter is capable of support- ing a few different sizes of air conditioners. Manufacturers make units generically to cover the entire country; this leads to standardization of heating capacities that will span the gamut of conditions. A system for a seacoast home in Maine will need more heat and less air condition- ing than a farmhouse in Georgia. Since most manufacturers would rather err on the high side regarding heat capacity, it is more common for a system to have more heat than it needs rather than too much airflow. Therefore, when a system that has high air-conditioning demand and low heat demand is needed, the higher capacity units will be used to achieve the airflow neces- sary to drive the air conditioner, and the heat will cycle more than is desirable. Caution needs to be exercised to not oversize since it can cause uncomfortably large heating temperature swings within a building. It is best to size equipment as closely as possible to the load calculations for the most efficient operation. For a brief discussion of proper sizing of air distribution ductwork in addition to equipment sizing, refer to Section 7.5.4. C. Last Note on Sizing It may be prudent in certain projects to exceed design standards both within the envelope and when choosing the equipment serving the building. This is apparent when considering the impact of west-facing glass and multi-pane, heat-absorbing glass, as well as when designing for localities with extreme ambient conditions. In all cases, it is advised that the SIP team consider several factors before finalizing system design: up-front costs, long-term effects for minimizing envelope permeability, maximizing the aesthetic, and gaining maximum efficiency. 7.5.3 Standard Systems A. Outdoor Air Ventilation Only This option can be considered for regions where the climate is temperate throughout most of the year, where mechanical cooling is not required on a regular basis, and in buildings that have existing functional heating systems. For example, coastal regions that do not experience signifi- cant humidity can be a good fit for the consideration of ventilation. Adding ERVs can enhance the overall effectiveness of a ventilation-only system. Ventilation systems typically make use of a fan (ventilator) that draws outside air into the building through ductwork and pressurizes the interior of the building. Positive building pres- sure causes air to be pushed out of the building through sound-attenuated exterior openings (louvers) at the same rate that outdoor air is being brought in. Alternatively, the ventilator can exhaust air from the building, and by doing so, induce outdoor air to enter the building through weatherproof and sound-attenuated openings. Filtration of the outside air is required. Remov- able filters are typically located within the ventilator package for positive pressure systems; exhaust systems would require filters to be installed at all outside air openings.
134 Guidelines for Airport Sound Insulation Programs B. Full Central Heat and Air (Split Systems) For regions that experience relatively warm summers, high humidity levels, colder winters, or any combination of these, a complete central HVAC system should be considered. The system is made up of a central forced-air unit (FAU) paired with an outdoor air conditioner that distrib- utes heated or refrigerated air to occupied spaces through a network of ducts. This approach is particularly appropriate for buildings or homes that have old, inefficient, or ineffective heating systems. The heating source could be either natural gas or electricity. Split-type direct expansion (DX) refrigerant-based air conditioning would provide cooling. Full central air conditioning systems make use of an indoor furnace or FAU, which typically serves to push air throughout the supply ductwork system as well as to provide heating via a gas burner and heat exchanger. The indoor furnace or FAU is paired with an outdoor condensing unit. The condensing unit produces the mechanical cooling and is connected to the indoor FAU via a pair of refrigeration pipesâone for supplying liquid refrigerant to the FAU and the other for returning vapor refrigerant to the condenser. C. All-Electric/Heat Pump Systems Similar to full central heating/air conditioning systems, central heat pump systems are suitable for regions that experience hot or cold weather and for buildings that lack efficient or effective heating systems. Central heat pump systems are all-electric. Both cooling and heating are pro- vided by mechanical means, namely DX refrigerant being pumped by a compressor. Full central heat pump systems make use of an indoor FAU or fan coil, which typically serves to push either hot or cold air throughout the supply ductwork system. The indoor FAU is paired with an outdoor condensing unit or split heat pump. The condensing unit produces both mechanical cooling and heating and is connected to the indoor FAU via a pair refrigeration pipes, one carrying liquid refrigerant and the other carrying vapor refrigerant. D. Ductless Mini-Split in Conjunction with Outdoor Air Ductless mini-split systems (sometimes referred to as ductless wall-mounted systems) pro- vide spot cooling or heating in rooms that do not have adequate space (either above the ceiling or below the floor) to install ductwork for proper air distribution. Instead, ductless mini-split systems tend to be installed within the conditioned space, either on a wall or hung from the ceil- ing, and circulate air within the room while simultaneously cooling or heating the air. They are capable of providing cooling or both cooling and heating in heat pump configuration. Ductless mini-splits need to be paired with an outdoor component, typically referred to as an outdoor condensing unit. Since ductless mini-splits are typically not capable of introducing outdoor air into the occupied spaces, they should be installed in conjunction with an outdoor air system. See Section 7.7.2 for further discussion. E. Add Outdoor Air to Existing Central Heat and Air System Some buildings have an existing, functioning central cooling and heating system already installed, but no provision for outside air or ventilation. In such instances, outdoor air can be ducted into the central air conditioning system to provide ASHRAE-required minimum outside air rates. F. Roof-Mounted Package Systems Packaged air conditioning systems (whether gas/electric or heat pump) have all the heat- ing, cooling, and fan equipment in a single box or package. They can be installed with gas heating or in heat pump configuration (mechanical cooling and heating). They can be con- sidered for buildings with adequate roof space available for mounting the packaged air con- ditioning unit. Buildings on which they are installed should typically have adequate ceiling or
HVAC and Ventilation Strategies 135 attic space available for installing air distribution ductwork. In instances where no attic space is available, ductwork can be installed on the roof; however, care should be given to properly seal all points where ducts penetrate into the interior space. A factor that can influence the practicality of roof-mounted packaged air conditioning systems is whether the region in consideration has high levels of seismic activity. In such regions, local building codes typically require structural and seismic calculations for most roof-mounted equipment, which can be an added cost factor. In addition, local ordinances may limit the installation of roof-mounted equipment for aesthetic purposes. Energy Recovery Ventilators. Regardless of the system type chosen for a particular SIP, some additional energy recovery may be needed to present an acceptable package to decision makers. ERV units have risen in popularity in localities with extreme ambient conditions and provide a means to recover energy before it is rejected from the building. ERVs are generally suitable for commercial applications with high occupancy rates, but they are making an appear- ance in new residential construction. Most manufacturers of fan systems now offer some level of ERV for residential use. Energy recovery occurs as conditioned air is rejected to the outdoors through one side of a heat exchanger; ventilation air passes through the opposite side of the same heat exchanger, thus exchanging energy between the two sections into the passing air. The now-tempered air enters the mechanical system or moves directly to the living space. Refer to Section 7.7.2 for information regarding common types of heat exchangers. Consideration of an ERV must include the energy used to push or pull air through the outdoor air heat exchanger as well as the thermal savings from transfer. Just as infiltration increases with large disparities in temperature and humidity, greater energy recovery occurs in an ERV when there are large differ- ences in temperature or humidity. Therefore, higher differentials across an ERV equate to higher efficiency and cost-effectiveness. ERVs are a viable option for ventilation in areas where dwellings experience a high average differential between indoor and outdoor temperature. Controls. Each HVAC system or zone requires thermostatic control to maintain room tem- perature. It is preferable, and occasionally required by IECC and local codes, to install program- mable controls. Programmable controls offer the opportunity to adjust set points for optimum temperatures during disparate occupied modes. Programmable thermostats often compare closely to standard thermostats in cost and can be packaged with new equipment. It is a good idea to include them in the design checklist to avoid any oversight. 7.5.4 Ductwork Achieving occupant satisfaction is the principal goal of any HVAC design and an impor- tant goal of SIPs. In a perfect world, duct systems would deliver fully conditioned air to the desired space, in the desired volume, at the desired rate, and only for the duration necessary for space conditioning and occupancy comfort. Unfortunately, this is not the case, especially in existing systems. A. Existing Systems Depending on geographic location, age of the home, and local standards, it is possible for existing systems to be made up of almost anything as far as ductwork is concerned. The system could be made of galvanized steel, steel, aluminum, or even stainless steel, and of any gauge from 30 to 20, depending on the dimension and tonnage of the system. The system could be made of spun fiberglass sheets with a paper/foil barrier (duct board) cut and fitted together. There are numerous thicknesses and varieties of duct board. It is also possible to have wooden ducts due to joist panning where a joist has sheet metal nailed to the bottom of two adjacent joists to
136 Guidelines for Airport Sound Insulation Programs form an air path. Return air systems can be all of the previously mentioned materials or flexible duct. There could be no return ducting, open plenums, and louvered doors. Branch ducts are often flexible class-one insulated duct, metal, duct board, or some combination. In conditioned space, uninsulated class-one duct or connector duct can also be used. That being said, it is readily evident that examination, measurement, and careful consideration should be exercised before simply putting new equipment on an existing distribution system. B. Air Leakage To say that existing duct systems in homes leak is an understatement. Unless a particular home has a custom-installed system by a conscientious contractor, it is unlikely that the joints, takeoffs, and outlets were sealed by mastic, which is the current standard. These unsealed mechanical joints, tap ins, or connections can lose considerable air or draw in the air surrounding ducting. As discussed in Section 7.3.4, pressure differences cause air movement. Similar to other forms of pressurization and infiltration, the forced air of a mechanical system can cause unwanted issues. All leaks rob mechanical systems of energy, but inward leaks pull in pollutants and contaminate the inside of ductwork. C. Heat Conduction System efficiency is critical for homeowners, yet few existing systems are sufficiently insulated. Conduction of heat occurs when the temperature difference between the interior and exterior of the duct is sufficiently high. Metal ducts with no insulation conduct the most heat, those with little insulation a little less, and so on. Some existing systems that are heat only do not have vapor barriers on the insulation. Systems without vapor barriers on the insulation cannot be used for cooling. Some duct-board systems use board that is too thin and subsequently have low R-values, which can cause problems beyond conduction, especially in high vapor pressure areas like crawl spaces. During cooling operation, the cold interior of the duct can cause condensation on the surface of the ducts and saturate the material. This can lead to microbial growth and eventually destruction of the duct. Low R-value insulation on metal ducts can also cause condensation and moisture problems. One significant issue with existing systems is flex duct. There are many types of flex duct. Some of the earliest manufacturers used rubber-based products in the liner, which deteriorate over time. Other manufactures used glues to bind layers of material together in the liner, which separate with age. Still others used polyvinylchloride- (PVC-) based exteriors, which dehydrate and split with heat and age. Another issue with flex duct is improper sizing. The earlier prod- ucts had low R-value insulation; products are now required to be R-6 or R-8. The interior and exterior materials are also significantly better, with fused Mylar liners and a Mylar/fiberglass mesh reinforced/foil exterior. Conduction becomes an issue when flex duct comes into contact with disparately tempered surfaces. The most significant problem occurs when sagging flex duct contacts the ground, which causes moisture problems, including puddles of condensation within the duct. The many issues with conduction reveal the need for thorough examination of existing duct systems. D. New Systems New system installations must meet specific standards; SMACNA, ANSI, and ACCA are the most recognized organizations with standards for duct construction. ANSI recognizes both the SMACNA and ACCA standards. The current standards are SMACNAâs HVAC Duct Con- struction Standards â Metal and Flexible and ACCA Manual D Residential Duct Systems. The SMACNA standard covers all duct systems while ACCA is specific to residences. Few existing systems will meet the current standards for airflow, proper sizing, proper sealing, and the many other components of the standards.
HVAC and Ventilation Strategies 137 The third edition of ANSI/ACCA Manual D uses Manual J (ANSI/ACCA, Eighth Edition) for heating and cooling loads and to determine space air delivery requirements for low-rise, residential-use buildings. By matching sizing requirements to duct system resistances (pressure drop) and blower performance (as defined by manufacturerâs blower performance tables), the entire system will perform the most efficiently. This ensures that appropriate airflow is delivered to all rooms and spaces and that system airflow is compatible with the operating range of pri- mary equipment. Advantages of designing with Manual J are: â¢ Updated and expanded variable air volume (VAV) guidance, with detailed examples; â¢ Impacts of excess length, sag, and compression in flexible ducts; â¢ New equivalent length values for flex duct junction boxes; â¢ A single set of ANSI-recognized duct sizing principles and calculations that apply to all duct materials; â¢ System operating point (supply cfm and external static pressure) and airway sizing for single- speed and multispeed blowers; â¢ A method for determining the impact of duct friction and fitting pressure drop on blower performance and air delivery; and â¢ The most comprehensive equivalent length data ever published. Although it is unlikely that all of the options of Manual D will be used in SIPs, Manual D is the proper standard to apply to systems requiring ducting. Designers can apply the Manual D procedure to constant volume systems and zoned variable air volume systems using a full range of duct construction materials. Manual D includes a number of informative appendices related to air distribution systems (e.g., equipment and air-side components; controlling excess air when VAV dampers close; duct loads, duct leakage, and duct system efficiency; air quality issues; noise control; minimum air velocity for ducts; codes, standards, and best practice issues; and commissioning issues). As mentioned previously, HVAC systems outside the building envelope require careful sealing of joints and ducting. This includes attics, garages, and crawl spaces. It follows that, wherever possible, HVAC systems should be installed within the envelope. 7.5.5 System Operation Costs The AIP Handbook identifies the issues of ongoing operation and maintenance of mechani- cal systems as a cost issue for property owners. The FAA advises that SIPs provide an operation and maintenance cost projection for the new system as part of the process of design and pre- sentation of the scope of work to the homeowners. Once the systems have been installed as part of the sound insulation project, the upkeep becomes the responsibility of the owner. The AIP Handbook states: Two caveats should be discussed with sponsors and recipients who receive air conditioning or a con- tinuous positive ventilation system: (a) The recipient will be expected to operate the system installed under the AIP grant to preserve the noise attenuation benefits achieved with the insulation project. Failure to use the installed system will negate the benefits and will not be grounds for making complaints about noise levels. (b) Property owners and residents should be presented with information about utility and maintenance costs for the installed equipment. Increased utility costs are to be expected. Also, routine maintenance costs should be planned to keep the system operating at peak efficiency. Maintenance service contracts tend to minimize disruptions by providing regular checks of the installed system. The costs of these con- tracts are a responsibility of the property owner.17 17 U.S. DOT, FAA, FAA Order 5100.38C, Airport Improvement Program Handbook, June 28, 2005.
138 Guidelines for Airport Sound Insulation Programs 7.6 Developing Program Policies There is no one-size-fits-all approach to designing mechanical systems. It is important when establishing policies for SIP HVAC systems to answer these questions: â¢ What are the standard types of mechanical systems in the buildings to be treated? â¢ What level of energy efficiency will the program provide? Minimum code? (These guidelines recommend Energy Star practices and products for SIPs.) â¢ What condition does the existing system have to be in to be replaced? â¢ What protocols will be decided for ductwork? â¢ How will outdoor air be provided to meet ASHRAE standards? There are many factors to consider when creating policies for retrofitting buildings to receive updated HVAC systems. Many programs find pilot programs useful to ascertain existing condi- tions and to design policies after the initial assessment of existing conditions. 7.6.1 Impact of PGL 12-09 PGL 12-09 advises that continuous ventilation systems can be provided where interior noise levels are less than 45-dB DNL and where there is no existing ventilation system and ventilation depends on having windows open. It states that âa Continuous Positive Ventilation System is the allowable package for these residences. . . . The sponsor may recommend an air conditioning system in lieu of ventilation only.â18 Questions have been raised by program sponsors and consultants regarding whether a contin- uous ventilation system is considered a secondary treatment and whether this type of treatment is limited to a specific number or percentage of homes. Program sponsors and consultants are advised to consult with their local ADO for further clarification. 7.5.6 Best Practice Recommendations: System Design 1. Use computer-generated load calculations based on Manual J software or a similarly accepted and recognized surrogate. 2. Be aware of practices and assumptions that lead to incorrect sizing methods, oversized units, and poor air quality for occupants. 3. Consider several factors before finalizing system design: up-front costs, long-term effects for minimizing envelope permeability, maximizing the aesthetic, and gaining maximum efficiency. 4. Examination, measurement, and careful consideration of ductwork should be exer- cised before installing new equipment on an existing distribution system. 5. Install HVAC systems within the envelope, whenever possible. 6. For design purposes, the minimum energy standard for all SIP-associated equipment is Energy Star. 7. Programs are advised to present property owners and residents with information about utility and maintenance costs for the installed equipment. 18 See note 2. Attachment 1, Â§812 (d), p. 1-13.
HVAC and Ventilation Strategies 139 7.6.2 Establishment of Policies A. Air Quality Programs need to examine several air quality and environmental issues when establishing policies. Issues include managing existing hazardous materials such as lead and asbestos, evalu- ating new material hazards and VOCs, providing appropriate levels of ventilation, controlling moisture and humidity, and checking the installation and operation of HVAC systems and fuel- burning appliances (see Figure 7.4). Potentially, a number of homes will have existing air qual- ity problems, the correction of which is typically outside the scope of most SIPs. A minimum practical objective would be to not make things worse. In many cases, a modest expenditure on treatments can ensure a minimum level of performance and reduce the risk of problems. B. Combustion Air SIPs may also include fuel-burning appliance testing, testing by the sponsor under the pro- gram policy, or simple system maintenance in the construction package. Other recommenda- tions include: â¢ Understand ASHRAE 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Resi- dential Buildings, and create design solutions that meet this standard. â¢ Review how new air handling systems relate to air quality. Look at leakage of ductwork in unconditioned spaces, the effect of climate on system design, and changes in air pressure dif- ferentials that move moist air through walls. â¢ Add operable, low-noise bathroom exhaust fans, and make sure existing ones vent to the outside. Maintain kitchen exhaust fan operation. (They should not be made into recirculating types.) Dryers must be vented directly to the outside. â¢ Make sure each homeowner knows the purpose of the exhaust system and the importance of its use. Courtesy of the Office of Energy Efficiency (OEE) Natural Resources Canada (NRCAN). Figure 7.4. Home ventilation pathways.
140 Guidelines for Airport Sound Insulation Programs C. Moisture Control Abating existing excess moisture/leaks in buildings is generally outside the scope of SIPs. With the exception of ventilating for habitation and air quality, there are methods for preventing non- behavioral sources of moisture: â¢ Ensure that window installation conforms to requirements to preclude water leakage. â¢ Examine conditions that require penetration of the roof or exterior walls that may leak. â¢ Look for pre-existing conditions that may affect the participation of a home in the program, such as the presence of mold, crawl spaces without moisture barriers, and poor drainage. These conditions may require remediation by the homeowner prior to sound treatments. â¢ Provide information to owners regarding control of interior humidity, the types of activities that cause excess humidity, and steps to reduce humidity. â¢ Provide adequate intake and exhaust ventilation in attics. The approach for evaluation of fuel-burning appliances may vary significantly by climatic region, program policy, and type of housing stock. Issues to consider/tasks to perform include: â¢ Replacement heating systems that incorporate new combustion technology, including sealed- combustion systems (systems that intake outside air directly to the combustion intake, not the space). â¢ Check local code compliance of existing systems for combustion air venting and adequacy. Include draft inducer fans where necessary to overcome negative pressurization or flue inad- equacies, or add required venting. Venting for combustion air may come from adjacent rooms, unconditioned space, or outdoor air. â¢ Evaluate existing appliances for possible reduction of carbon monoxide emissions. Adjustments can be included in the general contract, or the systems can be tested during the design phase. 7.6.3 Specifying Manufacturers Many programs provide HVAC systems with warranties that extend beyond what is standard. Not all HVAC equipment is of a quality to provide the desired length of warranty. In addition, programs endeavor to provide equipment that building owners will recognize as a quality prod- uct. Setting the standards for bidding specifications to fulfill these expectations is an important early step in design. 7.6.4 Best Practice Recommendations: Program Policies 1. Recognize that air quality changes from home to home and space to space. There is no one-size-fits-all or rule-of-thumb approach to designing mechanical systems. 2. Document pre-existing conditions of moisture control problems that may need to be remediated by the homeowner prior to conducting any work in the house. 3. Specify high-efficiency and industry-recognized, quality equipment whenever possible. 7.7 Emerging Energy Design 7.7.1 ASHRAE 90.2, Energy-Efficient Design ASHRAE 90.2-2007, Energy-Efficient Design of Low-Rise Residential Buildings, has raised the minimum efficiencies and minimum requirements for new residential construction to qualify as an energy-efficient design for new construction of residential buildings. The basic criteria within
HVAC and Ventilation Strategies 141 the standard are aimed at reducing total building energy. The method for achieving the stan- dard involves higher efficiency equipment, appliances, and materials for all buildings, including existing dwelling units and new additions. The goal of the standard is to have a greater scope than merely the installation of higher efficiency equipment. Meeting the annual energy cost compliance requirements for the entire residential dwelling involves proper thermal insulation for walls, roofs, and windows. Design teams should review the requirements for the individual components of a structure to ensure total envelope compliance where local codes include these standards. Design teams need also be mindful that treatments eligible for reimbursement from the FAA are those that contribute to meeting FAA acoustical goals; however, meeting those goals with Energy Star practices and products can maximize the achievement of federal goals for energy efficiency. 7.7.2 Options for Energy-Efficient Ventilation A. Making a Choice As federal regulations and local energy code requirements dictate higher overall energy effi- ciency, it is necessary for the design team to review and consider various methods for compli- ance with both the codes and ASHRAE standards. Particular care is needed where the IECC is an adopted component of the local building codes because they have directives that may override certain design criteria. In many western states, more stringent energy code requirements necessi- tate design team analysis for the most cost-effective solution. The solution needs to comply with requirements for ventilation yet be cognizant of the operational cost shouldered by the building owner. Clearly, the designed solution must consider the impact of ventilation strategies and the associated operational costs. It is possible to overcome the advantages of higher efficiency equipment with ventilation strategies that require constant introduction of outdoor air. As an example, exhaust fans that operate continuously offer a host of issues for end users, including energy cost concerns, life-cycle costs, uncontrolled infiltration due to negative pressurization, and increased dust and dirt within grills and ducting. Many of the following equipment types are available in package configurations, essentially a plug-and-play type of finished product. These products can be installed in series with other mechanical systems or stand alone, depending on design criteria. One area of concern for these and many other systems is the architectural consideration of fitting another piece of mechanical equipment into dwellings that typically have limited space for mechanical systems. B. Outdoor Air Economizers As SIPs tighten homes to prevent the intrusion of noise, mechanical systems become a neces- sity rather than an extravagant program extra. Additionally, as demand for conformity to effi- ciency standards becomes more stringent, houses become less permeable, and forced ventilation becomes more commonplace. Although this seems counterintuitive, to bring in outdoor air after sealing infiltration points, standards for indoor air quality must be maintained. The benefit of mechanical ventilation is the ability to measure and control outdoor air to a minimum standard. The addition of outside air, even under control, may drive overall system efficiency downward; therefore, the treatment of outside air will become necessary. Treatment of outside air can be achieved through many means, including outside air economizers (OAEs), various types of heat exchangers, permeable membranes, desiccant wheels, and heat tubes. In commercial or insti- tutional buildings, OAEs are prevalent; in homes, however, outdoor air issues and their vari- ous solutions are emerging. The recommended purpose of ancillary ventilation equipment is, therefore, to transfer heat, humidity, and other building energy to incoming air, thereby reducing operational costs. Each treatment type has inherent costs and benefits; their cost impacts will need to be evaluated on a case-by-case basis in order to determine their suitability. Geographical location and local codes will affect which choice is optimum for each site.
142 Guidelines for Airport Sound Insulation Programs C. Dedicated Outside Air Systems â Demand-Controlled Ventilation Dedicated outside air systems (DOAS) or demand-controlled ventilation (DCV) systems are typically used in commercial or institutional buildings where the outdoor air requirements can consume upward of 50% of a buildingâs energy requirement. As outside air requirements moved into the residential market, residential-scale versions of these systems were developed. These systems are designed to control specific volumes of outdoor air. Some standards allow the option to choose the specific amount of ventilation air required for a residence based on the occupant load of a residence as opposed to the building load. That choice will be driven by the expected increase in operational costs if the minimum ventilation for the structure significantly exceeds the minimum ventilation for the maximum normal occupancy. Such a case could occur in a home with high or vaulted ceilings, which would significantly increase the total cubic feet of air within the structure. Reduced ventilation is also allowable during unoccupied hours. How- ever, when mechanical ventilation is code-mandated, it is generally required to be continuous. Controls are available to determine the occupancy status and toggle the requirement for ventila- tion if intermittent operation is permitted. Specifically, CO2 sensors have proven to be effective measurement devices for triggering specific modes of ventilation. This method of operation may allow for a reduction in unneeded outside air and a subsequent reduction in operational costs. D. Installation of HRV or ERV Systems Both HRV and ERV units are used to remove stale indoor air from homes and replace it with outdoor air. The basic difference between the two is the exchange of moisture; ERV is full energy recovery (heat and moisture), whereas an HRV only exchanges heat. The installation of these two units is practically identical and will be discussed as one type of unit, an ERV, unless specified. The basic installation types are stand alone and integrated. Figure 7.5 is a representational image of a typical HRV; the important difference between an HRV and an ERV is in the materials in the heat exchanger core. The materials of an ERV allow the permeation of moisture through to the spaceâs supply air, and an HRV only exchanges temperature. The exchange of moisture can help with humidity control, especially in situations where extreme differences in interior and exterior moisture levels occur. In humid, cooling- Courtesy of the Office of Energy Efficiency (OEE) Natural Resources Canada (NRCAN). Figure 7.5. Components of an HRV.
HVAC and Ventilation Strategies 143 dominated climates, it is important to dry out incoming ventilation air to prevent mildew or mold from occurring in the ductwork. However, keep in mind that ERVs are not dehumidi- fiers; their moisture control capabilities are limited. In cold, heating-dominated climates, the increased ventilation air and the re-introduction of humidity to the indoor environment can help control wintertime window condensation and static electricity. E. Stand-Alone Units Stand-alone units are installed without any duct connections tied into the existing or new air-conditioning or heating system. There will be no common air return or delivery system; the ventilation provided by the ERV will enter and exit the home through dedicated grills, ducts, and openings. Depending on the name brand of the system designed/purchased, there may be factory-provided installation kits with pre-insulated ducts, mated inlet and outlet grills, and sound attenuators to keep air movement and fan noise down. Other units will need field- fabricated/-assembled ducting. All duct systems need to meet the codes of the highest local standard or jurisdiction. Figure 7.6 illustrates the exchange of air in a residential structure. Where the unit is installed has a significant impact on where the inlet and outlet ducts are installed. Additionally, the actual inlet and outlet will need to be located in an appropriate wall, ceiling, soffit, or roof penetration that works with the unitâs location. An HRV system can incorporate small, separately switched booster fans in high moisture or odor-producing rooms to help control moisture or heat generated by activities like showering or cooking. Range hoods will generally be separately ducted. An additional design consideration is whether to install tees in the supply ducting to individually ventilate rooms or choose a central location and allow natural air movement and changes in air density to circulate the outdoor air. Efforts should be made to use short runs of flexible duct to prevent excess restriction of airflow; in long runs, standard stovepipe-style ducting should be used. Units for residential service come in both 120- and 240-volt systems and include standard controls, and some have variable speed fans. F. Integrated Units Integrated units are used in conjunction with existing ducting and systems. Their key benefit is lower cost. It is simply less expensive to integrate with an existing system than it is to install a secondary stand-alone system. Space inlet and outlet air to the ERV can be picked up from the existing air stream, leaving only the outdoor portion to be completely new. Figure 7.6. Residential air exchange.
144 Guidelines for Airport Sound Insulation Programs 7.8 Additional Design Considerations 7.8.1 Code Deficiencies A. Mechanical Typical mechanical code deficiencies involve the following: â¢ Inadequate spacing between outdoor air intakes and combustion vents; â¢ Lack of outdoor air (ventilation) in a building, or inadequate ventilation; â¢ Inadequate anchorage of roof-mounted equipment to the roof structure; â¢ Inadequate seismic bracing for ceiling- or structure-suspended equipment, such as fan coils, furnaces, and ductwork; or â¢ Inadequate strapping of domestic water heaters in seismically active regions. B. Electrical Typical electrical code deficiencies involve the following: â¢ Lack of ground fault interrupter on receptacles near kitchen or bathroom counters; â¢ Lack of adequate clearances around and in front of electrical panels, meter/load centers, sub- panels, and disconnect switches; â¢ Improper electric utility service entrance into the property, weather heads and related con- duits, or feeder sizing; â¢ Undersized electric utility service, resulting from the addition of new air conditioning in properties that previously had none; â¢ Lack of attic lighting in instances where mechanical (HVAC) equipment is installed in the attic; improper location of attic light switch (switch not within proper proximity of the attic access panel); or â¢ Antiquated knob-and-tube electric wiring. Duct runs should be as short and straight as possible. The correct size duct is necessary to min- imize pressure drops in the system and improve performance. Insulate ducts located in uncon- ditioned spaces, and seal all joints with duct mastic. (Never use ordinary duct tape on ducts.) According to the EPA energy website, most energy recovery ventilation systems can recover about 70% to 80% of the energy in the exiting air and deliver that energy to the incoming air. However, they are most cost-effective in climates with extreme winters or summers and where fuel costs are high. In mild climates, the cost of the additional electricity consumed by the system fans may exceed the energy savings from not having to condition the supply air. Energy recovery ventilation systems require more maintenance than other ventilation systems. They need to be cleaned regularly to prevent deterioration of ventilation rates and heat recovery and to prevent mold and bacteria on heat exchanger surfaces. 7.7.3 Best Practice Recommendations: Energy Design 1. Consider ERVs or HRVs when designing ventilation to meet new air quality standards, as opposed to using continuous-operation bath and kitchen fans. 2. Providing adjustable modes of operation can reduce total energy consumption. 3. Install ducting for ventilation according to jurisdictional standards or manufacturerâs instructions.
HVAC and Ventilation Strategies 145 7.8.2 Electrical Upgrades The addition of HVAC to certain buildings may trigger an upgrade to the existing electrical system installed in the building. Electric meters or combination meter/load centers may need to be replaced with new ones. Code-deficient or undersized utility service entrance cable, including the weather heads, may need to be replaced as well if the electric service is being upgraded. The utility company typically covers the cost of running new conductors from its transformer up to the service entrance or weather head. 7.8.3 Electrical Utility Coordination A service upgrade may be required if the required electrical amperage for the new HVAC sys- tem being recommended causes the buildingâs electrical demand to exceed the code-regulated or utility-mandated maximum allowable capacity of the existing service size. Service upgrades must be coordinated with the local utility and building department. Often a cluster of electric service upgrades for multiple buildings concentrated within a specific neigh- borhood triggers a necessary upgrade of the transformers installed within the neighborhood. Although the SIP design team is typically not responsible for utility-owned transformer upgrades, it is important that the design team share with the local utility company the anticipated electric load increases that will result from the addition of air conditioning systems. This will allow the local electric utility to plan for any potential impact to their electric distribution network. This scenario is most relevant in neighborhoods or districts that historically have not had air conditioning systems installed and that thus may experience a significant increase in electricity demand after their installation. 7.8.4 Coordination with Other Parties A. Management of the Architecture and Engineering Interactions As with most construction projects, many disciplines or trades are involved. The architectural design and HVAC design professionals need to coordinate treatment designs to the property. It is important that the design be integrated and communicated to the building owner. B. Accommodating Interior Components of HVAC Systems The addition of HVAC systems occasionally requires changes to the structure of the building being treated. Depending on the attic, crawl, and unconditioned spaces available in a dwelling, there may need to be soffits, chases, drop ceilings, closets, or other structural changes to contain system changes. Soffits and chases are virtually the same sort of construction except that soffits run along horizontal surfaces and chases are mostly vertical structures. As long as the systems are sealed and do not require access for maintenance, these structures are acceptable. If access is required, closets with doors or access panels need to be installed. Replacement equipment located in the interior of the house, such as air handlers, may not be the same size as the old equipment. It is important to verify the maximum and minimum clear- ances needed for new equipment and determine if alterations to closets or other architectural constructions will be necessary. Reducing interior storage space often requires negotiation with the building owner, and locations cannot be assumed until discussed. C. Homeowner Associations, Covenants, Conditions, and Restrictions Many neighborhoods have restrictions to construction and home features. Before construc- tion begins in any homeowner association (HOA), deeds covenant restricted, architectural restriction community, historical district, or other form of neighbor agreement community,
146 Guidelines for Airport Sound Insulation Programs the restrictions of that neighborhood must be determined. Consultation can be in the form of compliance with the written agreements of the association or through cooperation with the compliance body. Working with the association personnel will ensure compliance. The location of new units outside the envelope of the structures may be restricted to a specific type, color, or size. Screens or other constructions may be necessary to meet zoning codes or deed restrictions. It is imperative to determine what restrictions may exist. D. Products, Warranties, and Service Contracts In systems where new equipment is required, the desired warranty on selected equipment needs to be determined as a program policy. Some manufacturers of equipment do not give the desired warranty length with the equipment. Many manufacturers now offer extended war- ranties on specific parts or all of the unit parts but not on the labor. Generally, labor is only included during the first year or the first 5 years, depending on the manufacturer. However, as unit efficiency and features increase, the manufacturers offer longer and more robust warranties. Unit efficiency increase also means a unit cost increase. The design requirements will dictate the equipment choice. The best practice recommendation for the minimum energy standard sought for all SIPs is Energy Star. From the EPA Energy Star website, minimum standards entail air conditioners and heat pumps with SEER ratings of 15, oil furnaces with AFUE of 85% or higher, and gas furnaces of 90% AFUE or higher. It is likely that units this far above the builderâs standard will come with extended warranties. In cases where the factory warranty of a unit is not sufficient to meet the parts and labor stan- dard sought, a purchased warranty may be necessary. All major manufacturers offer extended warranties for a price. These warranties are a complement to the proffered warranty, but some- times they have a requirement for service to remain in compliance with warranty issues. The required service is typically a service contract. Service contracts ensure compliance with the required regular maintenance (i.e., cleaning, filters, and operational checks) to guarantee proper operation and avoid breakdowns resulting from poor or absent maintenance. It is rare for pro- grams to provide these service contracts. Specifically, the ERV and HRV equipment warranties may be limited; at the time of this writ- ing, extended warranties may not be available to fulfill the needs of the sound insulation design team. Due to the emergent nature of these products, the abundance of manufacturers, and the variation in features, market research will be required to find a group of manufacturers suitable for SIPs willing to compete with equivalent quality products. It may be required to negotiate warranties directly with manufacturers or request design considerations to meet requirements suitable for long-term warranties. 7.8.5 Easements and HVAC Unit Placement A. Equipment Placement Design teams need to be aware of the zoning restrictions on location of equipment used in projects. Consideration of noise production and aesthetics are just some of the issues at hand. New, more efficient units are often larger than the units that are being replaced. Programs may need to provide concrete pads and alter some landscape features to place HVAC equipment. Without exception, units cannot infringe on property lines or be placed inside of setbacks. As unit efficiency increases, the equipment size increases, and it should not be assumed that the new units will fit in the old locations.
HVAC and Ventilation Strategies 147 B. Flood Zones Flood restrictions on equipment locations exist in coastal plains and low-lying areas of the country. Restrictions may require something as simple as an elevated pad in an area with minimal flood restrictions, or requirements may be a fully supported platform placing the equipment above the base of the first floor. In flood zones of this type, no ductwork is allowed in crawl spaces unless the bottom of the duct is above the maximum flood restriction height. Since SIPs typically deal with existing homes, this may require a significant consideration in the mechanical system location. Coastal flood zones offer additional problems to unit location. In addition to flooding, there is often the problem of erosion. It is recommended that consideration be given to placing equip- ment on platforms attached to the home, on upper decks or landings, or on the roof. C. Roof Versus Ground Pads The difference between a ground-mounted unit and a roof-mounted unit is far more than location. It is common to have condensing units and outdoor sections of heat pumps mounted on the ground in areas where space is sufficient, vandalism is low, and other restrictions do not preclude it. However, some design considerations may necessitate an alternate location. Raised platforms as described in the flood section may be used to put a unit in a safer location when the roof is unavailable, inaccessible, or architecturally unsuitable for various reasons. A concern with roof-mounted equipment is the wind load. Although condensing units and heat pumps have small footprints, they can have significant sail area. Units have flipped, twisted, and relocated during high wind storms, norâeasters, and hurricanes. Consideration of wind access to the equipment may necessitate structural supports and ties to prevent unit movement. Bolt- ing, strapping, or some other means of restricting the movement of units during high winds may affect costs and design criteria. 7.8.6 Best Practice Recommendations: Additional Considerations 1. Deficiencies in existing buildings can create huge cost overages if not addressed in the developmental stages of an SIP. 2. Electrical upgrades and service changes require specific safety practices and need to be coordinated with utility contractors and customers before work begins. 3. Maintainable equipment must be accessible. 4. Install quality equipment and involve customer/owner in final choices for warranty options. 5. Location of outdoor equipment may require consideration of HOA restrictions, flood zones, building geography and structure, and environmental impact. 7.9 Institutional Properties Institutional buildings vary in size and scope, from a one-room church to a community col- lege. Institutional buildings are defined under codes and standards as commercial. Mechanical equipment is divided into two basic categories: light commercial and commercial. Light com- mercial covers equipment up to 50 tons capacity; commercial covers everything else. Industrial is a separate category and outside the scope of this document. ASHRAE 62.1 is the jurisdictional
148 Guidelines for Airport Sound Insulation Programs standard for commercial ventilation in most districts, but local officials need to be consulted before any design considerations are put to paper. Necessarily, the mechanical issues for effective installation of residential systems and their proper protection against infiltration, contamina- tion, and other issues are true for commercial systems. ASHRAE 62.1 divides the commercial sector into many categories, and each category has subdivisions. Some examples of the larger categories are correctional facilities; educational facilities; food and beverage service; hotels, motels, resorts, and dormitories; office buildings; public assembly areas; retail; and sports and entertainment. For one further example, the educational category has 13 subdivisions. Any SIP involving an institutional building will be significantly more complicated than one for the aver- age residence. It may be prudent in certain projects to exceed minimum design standards both within the envelope and when choosing the equipment serving the building. This is inherently clear when considering the impact of west-facing glass or multi-pane, heat-absorbing glass and when consid- ering localities with extreme ambient conditions. In all cases, it is advised that the SIP team con- sider several factors before final decisions are set in concrete: up-front costs, long-term effects for minimizing envelope permeability, maximizing the aesthetic, and gaining maximum efficiency. 7.9.1 Ventilation for Acceptable Indoor Air Quality Many of the IAQ issues and questions covered in Section 7.3 of this document are true for institutional buildings. One significant difference is the volume of air needed not just for occu- pancy comfort, but also for ventilation air. The commercial standard ASHRAE 62.1 does not concern itself with thermal comfort, which is contained in ASHRAE 55-2010. Existing buildings are also not part of the standard unless local jurisdiction makes inclusion mandatory, typically due to renovation, additions, or changes that fall under the standard. Since SIPs normally involve existing buildings, why review ASHRAE 62.1? As with all governing agencies, ASHRAE publica- tions are guides subject to local jurisdiction. One significant method for superseding any local jurisdictional question is engineering a solution. It is important to remember that no standard will cover all possible situations. ASHRAE 184.108.40.206 notes, âAdditional requirements for labora- tory, industrial, health care, and other spaces may be dictated by workplace and other standards, as well as the processes occurring within the space.â Section 4 of the standard outlines requirements that must occur prior to ventilation system design. The first discussed is regional air quality and whether the building area is in compliance with the National Ambient Air Quality Standards for each pollutant in Table 4.1 of the standard. The second is local air quality, which is an observational survey of the building site and sur- roundings during normal occupancy to check for local contaminants that may be a concern if allowed to enter the building. The final step is to document the observations and discuss them with the building owners. A list of observation points is given in ASHRAE 220.127.116.11.2. 7.9.2 Systems and Equipment Intake inlets, exhaust outlets, penetrations, and routes are important considerations during the design phase of commercial buildings to stay in compliance with Table 5-1 and Section 5.3 of ASHRAE 62.1. There are also some exceptions and appendices that discuss intake and exhaust locations. Mechanical ventilation equipment is commonly obtained as designâbuild from one of the major high-quality air-conditioning equipment manufacturers. The advantage of designed sys- tems is the ability of the products to be packaged together. It is customary to have complete, self-contained units with intake fans, exhaust fans, heat exchangers, filtration, and any specialty
HVAC and Ventilation Strategies 149 items all on one skid ready to install. If heating and cooling are part of the package, the units can usually be designed to fit together or even be factory-attached. The most common ventilation practice in commercial equipment is to add an economizer or minimum outdoor air intake to packaged heating and cooling equipment. Typically, build- ing pressurization is relieved by barometric dampers in roof vents or hoods. Economizers work similarly to intakes except that they are automatically adjustable based on building pressure. Economizers are often linked with mechanical exhausting of building pressure and tracked by operational controls. Additional methods for addressing outdoor ventilation use heat exchangers of various types to recover building energy before exhausting. Common types of energy recovery products are des- iccant wheels, heat tubes, air-to-air heat exchangers, and water-cooled heat exchangers. What- ever the system type, the goal is to remove energy from the building exhaust air and condition the ventilation air. Desiccant wheels use building air to dehumidify a membrane that rotates between the intake and exhaust sections of an air handler. When the incoming air comes into contact with the dehydrated membrane, it gives up moisture and some heat before entering the building. Heat tubes filled with refrigerant easily migrate under differing temperature condi- tions. The refrigerant moves between the intake and exhaust sections, alternately recovering and rejecting energy as it moves. Air-to-air heat exchangers are self-explanatory. Water-cooled heat exchangers have local reservoirs and pumps that move water over the inlet section of a typically plastic heat exchanger, cooling the ventilation air. This is not an exhaustive list, and new products are continually entering the market. 7.9.3 Indoor Air Quality As mentioned in the residential section, IAQ is an emerging issue that has far-reaching impact. The design procedure for treatment of outdoor air and the subsequent conditioning of indoor air requires examination of air intake rates. In addition, a survey of possible local contaminant sources, contaminant concentration targets, and perceived acceptability targets should precede design decisions. ASHRAE 62.1 sets the design standard for IAQ systems as performance-based, intending to maintain concentrations of specific contaminants at or below limits specified during the design process. ASHRAE 62.1.6 details filtration procedures, product specifications, contami- nant standards, and distribution zone standards. Table 6-2 of the standard outlines measurements for air-zone distribution effectiveness. Section 7 of the standard covers construction issues, and Section 8 looks at humidification and some general operational and maintenance issues. 7.9.4 Best Practice Recommendations: Institutional Properties 1. Commercial buildings require professional engineering to meet the demands of properly designed sound insulation treatments in conformance with local code compliance. 2. Do not overlook intakes and exhaust locations for or around new equipment. New code requirements often necessitate revising exhaust piping of an existing building. 3. Maintaining indoor air quality in commercial buildings varies largely by use; there- fore, detailed information regarding building operation and purpose will be consid- ered when choosing a ventilation strategy.