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Introduction The design and construction of central plants for heating and cooling is one of the most challenging and interesting aspects of the HVAC design profession. Central plants range in size from small to very large, from residential to industrial utility scale. There are many ar-eas of inpidual expertise and many levels of competence among de-signers. In this chapter we discuss several fundamental types of plants and aspects of plant design, still leaving much detail to literature and experience beyond the scope of this book. See Ref. 1 for additional
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discussion of the topics treated here.20917
7.2 General Plant Design Concepts
Independent of the service being produced, some concerns are common
to central plants.
1. Siting. Central plants preferably are located in the middle of or
adjacent to the loads they serve. Distribution piping costs may loom
large if primary piping runs long distances to get to the service point.
On the other hand, the combining of multiple service units into one
plant is the act which achieves the economy of scale and the conven-
ience of operation, so distance is a tradeoff, but the central location is
still a favored point to start. For large plants serving congested cam-
puses, a remote or peripheral location may be preferred. This allows
better access to the plant and removes plant, traffic, noise, and emis-
sions from the more densely populated areas.For high-rise buildings, there is the question of the basement, roof,
or in between. On-grade locations have the best access. Sometimes
buildings are occupied from the ground up during extended construc-
tion, suggesting a low-level site. Where water systems are involved,
pressures may become very high at lower building levels. This is less
of a problem with chillers than with boilers. Systems with boilers often
take the equipment to the roof, partly for pressure considerations,
partly to eliminate the problem of taking the flue up through the
building, partly for emission dispersion. Cooling towers need to be
near the chiller served if possible, to reduce the cost of piping, but the
cooling-tower vapor plume can be a problem in cool weather if it im-
pacts the building (window cleaning, condensation on structure, etc.).
A vapor plume is a cold-weather visual problem in year-round opera-
tion and may cause a local ‘‘snow’’ effect in cold climates.
2. Structure. The enclosure and support for major plant equip-
ment should be strong enough to withstand vibration, to support
equipment and piping, to contain yet accept expansion and contrac-
tion, to enclose and subdue noise, and to support maintenance through
access and hoist points.
In some environments, plant structures are fully enclosed by heavy
masonry. In the industrial environment, in mild climates, plant struc-
tures may be open, offering only a roof and access, possibly a sound
enclosure. Some well-designed plants may take on an aesthetic aspect
including large expanses of glass and careful lighting. It is a fun ex-
perience to sculpt in pipe and equipment for all to see. This can be
accomplished with little premium construction cost, but it takes more
design time and an artist’s inclination. Some feel that a plant that
looks good may work better, since more time is given to function and
layout than in the ‘‘quick and dirty’’ arrangements so often encoun-
tered. Well-arranged plants usually are more easily maintained, given
the space associated with form and symmetry.
As a general note, reinforced-concrete floors and below-grade walls
have proved to be durable. Steel-frame superstructures with inter-
mediate floors of concrete and steel work very well. Steel members
with grating for walkways are very popular.