Closed Loop Heat Pumps

Individual heat pumps (ยง10.4.4) have a number of drawbacks in nonresidential buildings. However, closed-loop heat pumps, more accurately called water-to-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 dehumidifica-tion 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 all-water, 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.

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