Individual heat pumps (ß10.4.4) have a number of
drawbacks in nonresidential buildings. However,
closed-loop heat pumps, more accurately called waterto-
air heat pumps, offer an efficient option for heating
and cooling large buildings. Each room or zone contains
a water-source heat pump which can provide heating or
cooling, along with air filtration and the dehumidification
associated with forced-air air-conditioning.
The water source for all of the heat pumps in the
building circulates in a closed piping loop, connected to
a cooling tower for summer cooling and a boiler for
winter heating. Control valves allow the water to bypass
either or both of these elements when they are not
needed (Figure 10.10). The primary energy benefit of
closed-loop heat pumps is that heat removed from overheated
interior spaces is used to provide heat for
underheated perimeter spaces during cold weather.
Since the closed-loop heat pump system is an allwater,
piped system, distribution energy is low, and
since direct, local control is used in each zone, control
energy is also minimized, making this system one of the
most efficient. Although the typical lack of a fresh-air
supply eliminates the potential for an economizer cycle,
the heat recovery potential discussed above more than
makes up for this drawback.
Heat pump systems are expensive to install and
maintenance costs are also high. Careful economic
analysis is necessary to be sure that the energy savings
will be great enough to offset the added installation and
maintenance costs. Closed-loop heat pumps are most
applicable to buildings such as hotels which exhibit a
wide variety of thermal requirements along with simultaneous
heating requirements in perimeter zones and
large internal loads or chronically overheated areas such
as kitchens and assembly spaces.