on the laboratory ventilation system, with the goal of managing airflow and temperature control to eliminate waste and reduce overall energy use. In “Laboratories for the 21st Century” the U.S. Environmental Protection Agency (EPA/DOE, 2006), reports that in most studied cases, retro-commissioning, when planned and executed well, resulted in reductions of at least 30% of overall facility energy use with a payback period of less than 3 years.
The typical retro-commissioning process proceeds in five major steps:
1. Planning. Bring facility and EHS staff, design engineers, and users together to discuss goals. Gather information about the current system, including the original plans, as-built plans, major alterations, and current function, including ventilation rates. Develop the retro-commissioning plan.
2. Preinvestigation. Verify all systems including the direct digital control or building automation systems, evaluate all components that affect energy use, and verify monitoring systems.
3. Investigation. Benchmark utility and energy use data, analyze trends, and test all equipment. Testing should include functional testing of chemical hoods and related components, including face velocity tests, containment tests, etc.
4. Implementation. Select which improvements will be made and prioritize them. Implement the improvements and test performance.
5. Handoff. Clearly document information and provide training to laboratory personnel and maintenance personnel.
Common conditions that lead to energy waste include
• overabundance of laboratory chemical hoods,
• laboratory chemical hoods with large bypass openings,
• dampers in fixed positions,
• overventilated laboratory spaces,
• excessive duct pressure,
• fans set to override position,
• fans that are no longer operating efficiently,
• constant volume systems with no setback for temperature or airflow when unoccupied, and
• high face velocities.
Whether retro-commissioning for energy efficiency or for safety, ensure that all stakeholders are involved in the process. Once the work is complete, continue to monitor efficiency and safety. It is important to include trained laboratory personnel in the feedback process. If systems are not used correctly or if they are bypassed, the retro-commissioning efficiency may deteriorate.
The laboratory ventilation system, whether it is the general ventilation, a chemical hood, or a specialized exhaust system, is a critical means to control airborne chemicals in the laboratory.
At a minimum, a well-designed laboratory ventilation system should include the following:
• Heating and cooling should be adequate for the comfort of laboratory occupants and operation of laboratory equipment.
• A differential should exist between the amount of air exhausted from the laboratory and the amount supplied to the laboratory to maintain a negative pressure between the laboratory and adjacent nonlaboratory spaces. This pressure differential prevents uncontrolled chemical vapors from leaving the laboratory. Clean rooms may require a slightly positive pressure differential. There should be separation between common spaces and the clean room to prevent migration of airborne contaminants.
• Exhaust ventilation devices should be appropriate to materials and operations in the laboratory.
Many devices are used to control emissions of hazardous materials in the laboratory. A risk assessment helps to determine the best choice for a particular operation or material (Table 9.3).
NOTE: Clean benches are not designed for use with hazardous materials. These are appropriate for use in work with materials that necessitate clean work conditions and should only be used for materials or chemicals that one could safety use on a benchtop.
9.C.1 Risk Assessment
For all materials, the objective is to keep airborne concentrations below established exposure limits (see Chapter 4, section 4.C.2.1). Where there is no established exposure limit, where mixtures are present, or where reactions may result in products that are not completely characterized, prudent practice keeps exposures ALARA (as low as reasonably achievable).
For chemicals, determine whether the material is flammable or reactive or if it poses a health hazard from inhalation. If no significant risk exists, the work does not likely require any special ventilation. If potential risk does exist, look at the physical properties of the chemical, specifically its vapor pressure and vapor density.