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Heat Pumps
A heat pump extracts heat from a source and transfers it to a
sink
at a higher temperature. According to this definition, all pieces
of
refrigeration equipment, including air conditioners and chillers
with
refrigeration cycles, are heat pumps. In engineering, however,
the
term heat pump is generally reserved for equipment that heats
for
beneficial purposes, rather than that which removes heat for cooling
only. Dual-mode heat pumps alternately provide heating or cooling.
The preparation of this chapter is assigned to TC 9.4, Applied
Heat Pump/
Heat Recovery Systems.
Heat reclaim heat pumps provide heating only, or simultaneous
heating and cooling. An applied heat pump requires competent field
engineering for the specific application, in contrast to the use
of a
manufacturer-designed unitary product. Applied heat pumps
include built-up heat pumps (field- or custom-assembled from components)
and industrial process heat pumps. Most modern heat
pumps use a vapor compression (modified Rankine) cycle or an
absorption cycle. Any of the other refrigeration cycles discussed
in
Chapter 1 of the 1997 ASHRAE Handbook—Fundamentals are also
suitable. Although most heat pump compressors are powered by
electric motors, limited use is also made of engine and turbine
drives. Applied heat pump systems are most commonly used for
heating and cooling buildings, but they are gaining popularity
for
efficient domestic and service water heating, pool heating, and
industrial process heating.
Applied heat pumps having capacities ranging from 24,000 to
150,000,000 Btu/h operate in many facilities. Some of these
machines are capable of output water temperatures up to 220°F
and
steam pressures up to 60 psig.
Compressors in large systems vary from one or more reciprocating
or screw types to staged centrifugal types. A single or central
system is often used, but in some instances, multiple heat pump
systems are used to facilitate zoning. Heat sources include the
ground,
well water, surface water, gray water, solar energy, the air,
and internal building heat. Compression can be single-stage or
multistage.
Frequently, heating and cooling are supplied simultaneously to
separate zones.
Decentralized systems with water loop heat pumps are common,
using multiple water-source heat pumps connected to a common
circulating water loop. They can also include ground coupling,
heat
rejectors (cooling towers and dry coolers), supplementary heaters
(boilers and steam heat exchangers), loop reclaim heat pumps,
solar
collection devices, and thermal storage. The initial cost is relatively
low, and building reconfiguration is easily accommodated.
Community and district heating and cooling systems based on both
centralized and distributed heat pump systems are feasible.
Heat Resources
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