Air-cooled chillers are popular with smaller commercial facilities that aren’t quite big enough to justify a chiller and cooling tower. Air-cooling is an energy-intensive process that requires many fans operating to cool the refrigerant. The more efficient chillers stage the fans to match the cooling load. Others have staged scroll-type compressors for an even more efficient operation. These options are usually factory-installed, although it’s possible to implement the controls as a retrofit project to optimize the existing system.
Another add-on option is called a desuperheater. This is a simple shell-and-tube heat exchanger, with the refrigerant of the air-cooled chiller circulating through the desuperheater tubes before entering the cooling coils. The shell side of the desuperheater is used to heat domestic water. Even with a facility that has a hot-water demand that doesn’t coincide with the cooling load—such as a county prison that cools all day, but where hot showers are needed only at the end of the day—a storage tank can retain the water at setpoint until it is required. This tank can double as a water heater, for backup and winter use.
The desuperheater is an inexpensive appliance that is easily installed, with the necessary valves, thermostats, and other controls. The energy savings are more than free heating of domestic water but also result from the reduced use of electricity to operate the air-cooled chiller’s fans. This usually takes place during regular business hours, when a demand charge is levied by the utilities on commercial users, so the electricity savings can be significant.
Some major manufacturers offer desuperheaters as an option on new air-cooled chillers. If the chiller is to be used at a facility with a substantial daily hot-water use, such as a school, hospital, or correctional facility, it is an option that is worth serious consideration—even more so if the facility has electric heat.
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Excerpt from Energy Conservation Projects.