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OCR for page 7
1
Introduction
District heating and cooling systems are thermal energy networks that
distribute hot water, chilled water, or steam through insulated pipes
to serve commercial, residential, institutional, and industrial energy
needs for space heating, space cooling, and industrial purposes.
District heating and cooling systems permit energy, as distinguished
from fuel, to be bought and sold as a commodity.
While district heating has been used for more than a century and is
a well-understood technology, it remains relatively unknown to the
general public. Many people live or work in buildings served by
district heating and cooling systems without knowing it. In part,
this stems from the var. iety of names the technology is known by.
In the United States, district heating and cooling systems have
been known as central plant heating, cooling, and steam; municipal
heat, power, and steam; campus or areawide heating; total energy
systems; municipal integrated utility systems; integrated central
energy systems; and total integrated or community energy systems. In
Europe, the terms for such systems generally translate as distance
heating or urban heating. In some cases, European district heating is
called block central systems, referring to systems that supply heat to
more than one building from a central heating source.
In part, the different U.S. and European terms reflect differing
energy needs. For example, district cooling is found mainly in the
United States; most European systems supply hot water or steam for
heating and domestic hot water only. Most major U.S. cities are
located farther south than their European counterparts with district
heating, and many high-rise buildings require air conditioning on
their southern and western sides most of the year. In addition,
Americans have become accustomed to air conditioning.
Further, European district heating systems are defined as only
those that sell heat to many different customers. In the Netherlands,
systems are further limited to those that use waste heat* or municipal
.
*Waste heat refers to thermal energy recaptured from either industrial
processes or electrical generation that would otherwise be lost to the
environment.
7
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8
solid wastes as a fuel source. For these reasons, many Europeans view
district heating's contribution to the U.S. energy supply as minimal
(IEA, 1983~.
In the United States, however, most district heating and cooling
systems now serve high-density unitary developments such as college
and university campuses, industrial and commercial complexes, military
bases, and similar institutions. These applications are not like
European systems in that they do not strictly involve the buying and
selling of energy. Nevertheless, they are characterized by the same
increased energy efficiency* (compared with multiple smaller heating
plants) and low-cost energy services achieved by supplying thermal
energy from a central source.
This report will not address the issue of buying and
selling energy in determining the extent of district heating and
cooling in the United States, nor in discussing the technological
features, prospects, and impediments of various systems.
District heating and cooling have had two basic development
patterns in the United States (see Chapter 2 for a discussion of their
history and current status). In the first, steam systems were
developed to serve a variety of users and types of buildings located
in an urban area, typically in the central business district. Such
urban systems are typically run by private, for-profit corporations
subject to regulation and taxes. Most have been operated by
investor-owned electric utilities.
The second type of system was developed to serve institutional
needs. These systems serve a single user, a single or a few related
buildings, or a complex of buildings. They are typically found on
college and university campuses, military installations, industrial
parks, multifamily housing developments, and office, commercial, and
medical complexes. These systems are frequently referred to simply as
Central heating."
Institutional systems are generally run by nonprofit groups, such
as governments, hospitals, and universities, which are generally not
regulated or subject to taxes. Nevertheless, there are some
institutional systems that are owned by private enterprises to serve
their industrial, commercial, or residential uses. The Caterpillar
Tractor Corporation, for example, operates a district heating and
cooling system for its administrative offices and manufacturing
facilities in Peoria, Illinois (Figure 1-1~.
More recently, a third type of district heating and cooling system
has emerged. Most new urban systems have been developed and owned by
nonprofit corporations or municipal governments. At the same time,
several older investor-owned systems have been turned over to
nonprofit corporations or cooperatives. These urban systems are
growing in number and amount of energy provided (see Chapter 2~.
*As used in this report, energy efficiency refers to the total usable
energy obtained relative to the energy content of the fuel burned.
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..... its 1' 2 ~
:
l :~
FIGURE 1-1 Caterpillar tractor plant, Peoria, Illinois (courtesy North
American District Heating and Cooling Institute).
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10
This report will concentrate on urban district heating and cooling
systems. Nevertheless, it will also discuss the institutional
systems, particularly as they relate to urban systems. In the United
States, the former outnumber the latter, are growing in number, and
represent a base for expanding urban systems in the future. The
technology for urban systems is also essentially the same as that for
institutional ones.
Table 1-1 covers the relative advantages and disadvantages of steam
and hot water systems. The table covers aspects of hot water systems
in the low-temperature (250°F; 120°C), medium-temperature
(350°F; 175°C), and high-temperature (450°F; 230°C) ranges,
with their respective required pressurizations. Not all elements of
the table apply to each temperature or pressure level. Plastic pipes,
for example, are not suitable for high-temperature use.
HOW DI STRICT HEATING AND COOLING SYSTEMS WORK
All district heating or cooling systems have four basic components:
the fuel or resource, thermal production, transmission and
distribution systems, and an end user or customer (RDA, 1981~. Urban
district heating and cooling systems take many different specific
forms. A factory may sell waste heat to surrounding properties, a
cogenerating electric utility may sell hot and chilled water or steam,
or a municipal solid waste incinerator may sell heat to a thermal
production plant. Systems also vary from single production facilities
with a single distribution system to networks of independent producers
and distributors (Figures 1-2 and 1-3~.
The technologies and fuels used to produce thermal energy likewise
vary. Simple boilers can be used to distribute hot water in a single
loop to a variety of buildings. Boilers and chillers can provide hot
and chilled water to users, with supplemental systems for specialized
large users. The system may consist of a large number of independent
production sites using direct combustion, recovered heat,
cogeneration, and direct electricity to provide heat, cooling, and
domestic hot water.
The end user is usually the owner or operator of a single building
or group of buildings. A heat exchanger is used to convert the
thermal energy that the system provides into heating or cooling for
the end user. Demand for energy, measured in British thermal units
(Btu) per hour or its equivalent, is influenced by climate, building
size and characteristics, and the needs of end users. Consumption or
sales reflect the total energy supplied to end users.
Fuels
The resource is the fuel or fuels used. District heating and cooling
works best when abundant and renewable low-cost fuels are used, taking
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11
TABLE 1-1 Comparison of Steam District Heating and Hot Water District
Heating
System Advantages
Disadvantages
_
Steam
district
heating
Pumps not required
Can be a one pipe
system with no return
Retrof it of old urban
steam buildings may
be easier
Piping range of 1 to 2
miles (1.6 to 3.2 km),
3 miles (4.8 km) maximum,
for older systems; newer
ones can achieve longer
ranges with improved
insulation.
If steam is extracted from
a cogenerator, a great
deal of electricity is
sacrificed.
Steel pipes are required--
they are expensive and
they corrode.
Water must be conditioned
to prevent mineralization.
If condensate is not
returned (it usually is
not), water, water
conditioning, and low-
grade energy are wasted.
Use of high-temperature
steam for space
heat/service water
heating is a poor energy
and use match.
High heat loss during
distribution (15-45
percent).
Piping, boiler, personnel
codes are stringent;
steam is not as safe as
hot water.
Installation is
difficult--pitched
piping, steam traps, pipe
expansion, manholes.
Maintenance costs are
higher than for hot water
systems.
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12
TABLE 1-1 Comparison of Steam District Heating and Hot Water District
Heating (continued)
System Advantages
Hot water
district
heating
Piping range of 15
miles (25 km),
possibly up to
70 miles (110 km).
Less cogenerator
electricity
sacrifice than for
steam.
Plastic pipes can be
used--less expensive,
no corrosion.
Water need not be
conditioned; if it is,
closed loop anyway.
Closed loop, so water is
not wasted; nor is low-
grade energy.
Good energy end use match.
Low heat loss during
transmission and
distribution (5-15
percent).
Construction and operation
codes easier to meet;
relatively safe.
Installation, retrofit
to buildings generally
easier than for steam.
Lower maintenance costs
than steam systems.
Metering energy use is
relatively easy.
Disadvantages
-
Metering energy use is
difficult.
Very susceptible to
missizing or loss of
large customer.
Difficult to operate under
conditions of varying
loads.
Pumps are required--system
balancing is important.
System needs two pipes.
Cannot provide high pressure
steam if a customer on the
circuit requires it--can
act only as preheat.
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13
TABLE 1-1 Comparison of Steam District Heating to Hot Water District
Heating (continued)
System Advantages Disadvantages
Not as susceptible to
missizing as steam
systems are.
Easy to operate under
conditions of varying
thermal load.
Hot water can be stored.
SOURCE: Office of Technology Assessment (1982).
respective capital cost comparison into account. The fuel may be heat
recovered from an industrial process, municipal solid waste
incineration (Figure 1-4), or electric power generation.
Technological integration makes it economically feasible to convert
geothermal and solar energy, coal, and other underused energy sources
into thermal energy.
Thermal Production System
Depending on community needs, the thermal production system can be
either a centrally located facility or several interconnected plants.
Numerous technologies are used to meet the thermal and electrical
loads of a community, including coal- and solid waste-fired boilers,
chillers, internal combustion engines, heat exchangers, and central
heat pumps.
District heating and cooling systems can also rely on cogeneration,
the simultaneous production of electricity and thermal energy.
Cogeneration recaptures much of the heat usually lost during
electrical generation and uses it directly or converts it into thermal
OCR for page 14
14
a uc
F ~Cogenerellon)
:/ ~ Resource Recovery
I .~Thermal Loodi .. .~ ' ~
Geotl`-r~nal~ ~
::~\
nstu a' 9a A)
oil Co nal
Bollere
~---\
Industrial Waste
Heat Recovery
Increases
Energy
it'\ ~
Low Temp Industrial
Process Heat
~_~
Institutlonal Heating
Air Conditioning
A\ '..4
\ .4V
Reeldentlel Heating
Water Heating
Supply \ ~
Options ~
V Hest Pump
Comme clef Fleeting
Conditioning
FIGURE 1-2 Possible elements of district heating and cooling systems
(Argonne National Laboratory).
OCR for page 15
15
~3
Thermal
production
plant
Transmission line
/
Distribution line~ / ~ ~ b
Consumer building containing
in~building equipment
FIGURE 1-3 Schematic diagram of simplif fed district heating and cooling
system (Santini and Bernow, 1979~.
OCR for page 16
16
U]
a)
o
-
'4 ~
OCR for page 17
17
energy. Cogeneration plants (Figures 1-5 and 1-6) have an overall
energy efficiency rate of about 70 to 80 percent in the United States,
whereas facilities that generate only electricity operate at about 30
to 35 percent efficiency (RDA, 1981~.* European cogenerating
facilities reportedly show efficiencies of up to 90 percent (Lars
Astrand, personal communication, 1983~. This increased efficiency
benefits both thermal and electrical customers.
Transmission and Distribution
The transmission and distributior~ system (Figures 1-7 and 1-8)
transports thermal energy to end users through a network of insulated
pipes. The pipe loop carries energy in the form of steam or hot or
chilled water to the end users. A separate pipe returns water with
most of the energy removed (or added in the case of cooling) to the
production plant for reprocessing. The pipes-can be buried directly
in the ground, placed in tunnels or concrete culverts, or located
above ground. Communities with high space cooling requirements and
high densities may choose to distribute both hot and chilled water,
depending on the season.
In hot water systems, piping is typically effective for a distance
of up to about 15 miles (25 km). Booster pumps can be used to extend
the range up to 70 miles (110 km). Steam systems (Table 1-1), on the
other hand, have ranges of only up to 3 miles (5 km) although newer
steam systems can have longer ranges. Long-distance thermal
transmission systems (without thermal loss) are not yet economically
feasible, although the technical capability exists.
Storage capacity may be incorporated into the distribution system
if demand does not always coincide with supply. Storage systems can
be built both above and below ground.
The economics of the distribution system is important in
determining service areas for new and expanding systems (OTA, 1982~.
The relationship between load density and piping costs influences
which areas within a community can be profitably served. Because of
the high capital costs of district heating and cooling systems, they
are typically planned to serve high-load, high-density areas, such as
central business districts, first, with expansion later to lower-
density areas (see Chapter 41.
-
*This comparison of the efficiency rates of cogeneration and
electrical generation does not address the question of quality of
energy, which is beyond the scope of this report.
OCR for page 18
18
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OCR for page 19
PURCHASES
1.7 %
COAL
66.2 %
3.14 x 10
NATURAl
GAS
PURCHASES
COAL
85.8 %
1 2
5.48 x 10
OIL
=,~_ _
FED _ _
=19_ _ _
3 ~ 2~:#'-~1' ~.
. ~ ~:~ 5= ~
0 ~ ~ r9
. ~ ~ INDUSTRIAL
'.: ' ~ 2.~ 1 ~ xl
F~,~-=~--~X x _
it__ c ~
6,15 X 108 .
~ =1 1 ~
~ ~ V.
5.77X.01° _
LOST ENERGY
70.4%
1 3.31 X 10 2
USEFUL ENERGY
~ 2 9.6%
_ 1.39 x loll
_~= ~
CONVENTIONAL ENERGY FLOW - 1980
P I O U A .
POWER
PLANT
By_
_ _ _ .
ELECTRICAL
ENERGY
GENERATED
~ o_
_~ 1,47 X~C
~ ~2.96'X i6~' _~ _~
_ _~ , ~**+? ~#:::'# 1
~ ~ ~2 ~ 3 x lo ~COMMERCIAL ~ ~ ~
6.2 %-~ ~ ~ =.= ~ ~ ~ ~
3.96 x 10 ~ ~ 4.414 X 101° _' _~ ~ [ '
~ ~ ~ 5.711X109 [~-l.1 ~ jU:.?',.
NATURAL ~ ~9 ~ ~ j ~
6.5%1 ~ g . _ 2.19x107 l.] ~
4.17 X 1ol1 ~\ ~3 ~· ~D ~_ ! 4.e7 ~ lO~ ~ ~
\\. ~ I--~
\\ ~GOVERNMENT |
\\~
TRANSPORTATION |
3.50 x 10' 1 ~
DISTRICT HEATING ENERGY FLOW |
- 2000
.. ¢~.. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
| LOST ENERGY
45.9%
t:: :::::::::: ~2,93 ~ ~ o 2
:...'.,:!
i~i
''1
~USEFUL ENERGY
54.1%
_ 12
_J.45 x 10
FIGURE 1-6 Energy flow analysis, 1980-2000, for the Piqua, Ohio,
district heating and cooling system (Resource Development Associates).
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20
FIGURE 1-7 District heating transmission line in New England connects a
downtown heat distribution grid to the thermal production plant several
miles away (North American District Heating and Cooling Institute).
OCR for page 21
21
~ ~7
~ ~'!~:~'t~
:: ~ I: : 'I: ~ .', I:
. I, ~ ~ : ~ ..,. .,, ..,.. ~,.~" ~ ~.
" ' ' ~ ~ ~ ~ : ~ ~ ~ ~ ' ~ " ~ ~ ' ~ ' ~ . ~ , . ~ ~ ~ , ~ , . , ~ , ~ ~ , ~ , ~ ~ ' ~ ~ . ~ . .
:~:~:~::~:~::'~:~:~::~.: ~
:: ~'~,''~.~,~L',:~.~',~ :~..:.,', ''"... ::'.~) ~
~,.~:~t,.,....~,,,.~,., ~ i: .:.::'
- , . ~.~ ,,~,
...'.2'2'.."" '."'.'.
*a
a::::
::
if
~ .
~ .
~ .
:
it', ~"~:t
FIGURE 1-8 Welding 10-inch steel for 320°F hot water distribution pipe
to the state capitol, Trenton, New Jersey (North American District
Heating and Cooling Institute).
OCR for page 22
22
Customers
End-use buildings require either heat exchangers or heat pumps to
convert the steam or hot or chilled water into heating, cooling, or
industrial energy for residential, commercial, medical, or industrial
users. Planning for a system should consider how much energy users
will require, when they will need it, and the temperature at which
they will use it. The system should provide thermal energy at rates
that are economically attractive and stable.
To be competitive, operators have to recognize that customers
expect their energy costs to represent a relatively constant share of
their total budgets. The determining factor, however, will be the
costs of district heating and cooling compared to those of competing
fuels. Whether particular systems are developed may depend on the
costs to end users for equipment and its installation, as well as the
cost of the energy delivered. The cost of converting an existing
building to district heating and cooling will range from less than
$0.70 per square foot ($7.50/m2) (Table 1-2) to more than $2.70 per
square foot ($29/m2), depending on building type and mechanical
system (Santini and Bernow, 19791.
ATTRIBUTES OF DISTRICT HEATING AND COOLING SYSTEMS
District heating and cooling has several attributes that make it
advantageous to end users. All are subject to variables such as
finance costs, costs of competing fuels, and type of use. Still,
these attributes are what make district heating and cooling attractive.
0 Low cost. District heating and cooling systems can be designed
and operated competitively. Because they can use coal, municipal
solid wastes, and cogenerated thermal energy, their fuel costs are
typically lower than competing systems that use oil or natural gas.
O Reduced capital costs. These systems reduce users' capital
investment by eliminating the need to buy and install furnaces,
boilers, and air-conditioning systems. Such costs are, in effect,
shifted to other investors.
o Increased building space use. Such systems permit more
profitable and efficient use of building and housing space. The area
they require is substantially less than that required for conventional
heating and cooling equipment. One central plant can replace
individual boilers in each building. The space saved can be used for
other purposes, for example, more rental units, office space, or
hospital rooms.
o Reduced operating and maintenance costs. By eliminating the
need for onsite boilers, district heating and cooling also reduces
operating, maintenance, and insurance costs in that it transfers some
or all of these costs and responsibilities from the building owner or
operator to the district heating and cooling system.
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23
TABLE 1-2 Costs of Retrofitting Buildings to Use Cogenerated Hot
Water (1979 $/ft2)
Gross
Building
Area
(ft2) Heating
Office building, 10 floors
Absorption chilling
Steam/hot water heat
Office building 10 f loors
Compression chiller
Steam/hot water heat
Apartment building
Window air conditioning
Hot water heat
Retail store, rooftop
direct-expansion
air conditioning
Steam heat
Hot water heat
Retail store, rooftop
direct-expansion
air conditioning
Gas/air heat
SOURCE: Santini and Bernow (1979~.
200,000
400,000
200,000
400,000
200,000
400,000
1,500
1,500
0.76 0.37
0.41
0.21
0.76
0.41
0.32
0.24
0.88
0.74
2.45
2.29
12.20 18.67
7.67 18.67
30,000 2.78 4.19
Cost ($/ft2)
-
Air
Conditioning Total
1.13
0.62
1.64
1.15
2.77
2.53
30.87
26.34
6.97
0 Improved air quality. There is evidence that replacing many
individual, untreated boilers with one treated central pi ant generally
reduces emissions and thus contributes to reduced air pollution (see
Chapter 4~.
O Increased profits. Both electrical utilities and some
manufacturers can sell the heat they generate from their industrial
processes as thermal energy to other users, thereby gaining a new
source of revenue.
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24
o Renewed commercial development. District heating and cooling
can also help stimulate economic development and the revitalization of
downtown areas in older cities (Latimer, 19841. Reliable,
cost-effective systems attract industry and business. Stable,
affordable energy supplies can help revitalize downtowns and
surrounding residential neighborhoods, particularly for moderate and
low-income citizens, by retaining dollars in local economies.
District heating and cooling production and delivery systems
represent an investment in a city's infrastructure that uses initial
capital investment to achieve long-term cost savings from a reduction
in the amount of energy used (Hanselman, personal communication,
1984~. The ability to use several fuels can be engineered for each
system to take advantage of local energy sources while, on a national
level, reducing the need to import oil, thereby minimizing reliance on
unstable supplies and taking advantage of world price fluctuations.
Based on a model developed by Argonne National Laboratory (for more
detailed information on the Argonne model, see Chapter 3), the
Department of Energy (DOE) estimates that each quadrillion Btu* of
energy supplied through district heating** will create a demand for
$19 billion worth of construction and manufacturing employment. The
DOE figures show that this represents a $27 billion market for piping
and other equipment and a $1 billion market for domestic fuel sales
annually. DOE also estimates a net national fuel savings of more than
$11 billion annually after 20 years from reduced fuel imports if
district heating were to grow to account for 3.5 quads of energy
delivered (Teotia et al., 1981~.
In part, the employment figures represent the value of the new jobs
that any large-scale public works project, such as installing new
sewer or water pipes, would entail. But this further illustrates how
a district heating and cooling system would help revitalize a city
and, in particular, its downtown area.
*One quadrillion Btu or "quad" equals 1015 Btu of energy. It is
equivalent of about 500,000 barrels of oil per day for a year, or
about 50 million tons of coal, or the output of 18 1,000-MW power
plants at average use (OTA, 19821.
**The model looked at district heating only, not district cooling.
Thus, these figures may be conservative when considering systems that
supply both heating and cooling.
Representative terms from entire chapter:
hot water
