A new technology to replace the air-cooled condenser technology is the Water-Source Heat Pump (WSHP). Instead of rejecting heat to the atmosphere via an air-cooled condensing unit, the WSHP rejects heat to water in a tube-in-shell type of heat exchanger. The fluid-to-fluid heat- exchange process is more efficient than air-to-fluid, and the water is usually at a much lower temperature than the air. Consequently, the heat sink is at a lower temperature, and the higher temperature difference causes an even more efficient heat-transfer process.
Another advantage of the WSHP system is a lower maximum operating temperature of the refrigerant circuit, so the head pressure is lower on the average. This means the entire compressor circuit is longer-lasting and more trouble-free. Also, the system has a very short refrigerant circuit, requiring a small quantity of refrigerant as compared to a split DDX system with a remote condensing unit.
The WSHP operates like a two-pipe fan coil unit, except the system is linked to a cooling tower and boiler, instead of a chiller and boiler. Also, it is possible to have both heating and cooling in the same fluid loop. In fact, for an extensive system sharing a common fluid loop, the net effect of the system is to transfer heat between zones within the facility as (in the winter) interior zones will warm the water and exterior ones will cool the same volume.
The entire system will still have to be changed over to a boiler or cooling tower in season, but small daily fluctuations don’t cause the control problems as in a conventional two-pipe system. Localized heat gains (losses) in the loop will not only be averaged out through the balance of the loop when the discharge from all the units that are heating mixes with water from those in the cooling mode, but also actually increase the overall efficiency of the system because artificial means aren’t be needed to aid the heat-transfer process.
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Excerpt from Energy Conservation Projects.