Alternative cooling systems

Editor's note: This story is adapted from theU.S. Department of Housing and Urban Development's Residential RehabilitationInspection Guide, 2000. Clickhere for other stories in this series.

Geothermal systems arerelatively new and operate similarly to air-to-air heat pump systems, but differin design and installation. What might be considered the condenser are pipesburied in the ground in dry wells or other in-ground systems suitable fortransferring or displacing heat. The system is closed and its piping is PVC socorrosion is not a potential problem.

Geothermal systems are normally installed without a back up or emergencyheating system and all their components except the buried coils are usuallyinside the house. For more information, consult the Geothermal Heat Pumps:Introductory Guide published by the International Ground Source Heat PumpAssociation.

A geothermal heating and cooling system can be operated in a heating orcooling mode under any outside temperature. Although expensive to install, theynormally are efficient and economical to operate.

Gas-absorption cooling systemsoccasionally may be found in older residential buildings. Such systems use theevaporation of a liquid, such as ammonia, as the cooling agent and, like a gasrefrigerator, are powered by a natural gas or propane flame.

Electric heat pumps are refrigerant-type air conditioningsystems that can be reversed to extract heat from outside air and transfer itindoors. Heat pumps are normally sized for their air conditioning load, which inmost parts of the country is smaller than the heating load. Auxiliary electricheaters are used to provide the extra heating capacity the system requires inthe heating season.

Like air conditioning systems, heat pumps can be either split or integral.Integral systems located outside the building should have well-insulated airducts between the unit and the building. If located on or within the building,they should be mounted on vibration isolators, be thermally protected, and havean adequate condensate drainage system.

Inspect a heat pump like you would a central airconditioning system. Testing in one mode is usually sufficient. However, donot operate air-to-air heat pumps in temperatures below 65 F (18 C) on thecooling cycle and above 55 F (13 C) on the heating cycle. In both conditionsthe amount of work the heat pump has to do to achieve interior comforttemperatures is not enough to really test the heat pump's ability to perform.

Check also for the following problems:

• Auxiliary heater failure. Electric resistance auxiliary heaters are designed to activate (usually in stages) below about 30 F (-1 C) outdoor temperature when the heat pump cannot produce enough heat to satisfy the thermostat. If possible, activate the auxiliary heaters to observe their operation. Operating failures may be caused by a faulty heater element, faulty relays, a faulty thermostat, or a faulty reversing valve.
• Improper defrosting. During cold, damp weather, frost or ice may form on the metal fins of the coil in an outdoor unit. Heat pumps are designed to defrost this build up by reversing modes either at preset intervals or upon activation by a pressure sensing device.

• Faulty reversing valve. In most heat pumps, a reversing valve changes modes from heating to cooling (some heat pumps use a series of dampers instead) when the thermostat is changed.

A roof-mounted evaporative cooler.This type of cooling unit is relatively simple to inspect, repair, and maintain.

Evaporative cooling systems are simpleand economical devices. They pass air through wetted pads or screens and coolingtakes place by evaporation. Such systems can only be used in dry climates whereevaporation readily takes place and where dehumidification is not required.Evaporative coolers consist of evaporator pads or screens, a means to wet them,an air blower, and a water reservoir with a drain and float-operated watersupply valve.

These components are contained in a single housing, usually located on theroof, and connected to an interior air distribution system. In wetted-padcoolers, evaporator pads are wetted by a circulating pump that continuallytrickles water over them; in slinger coolers, evaporator pads are wetted by aspray; and in rotary coolers, evaporator screens are wetted by passing through areservoir on a rotating drum. The water in evaporative coolers often containsalgae and bacteria that emit a characteristic "swampy" odor. These can beremoved easily with bleach. Some systems counteract this pattern by treating thewater or by continually adding a small amount of fresh water.

Inspect evaporative cooling systems by examining the condition of eachcomponent. Note whether evaporative pads need cleaning or replacement. Look forsigns of leakage and check the cleanliness and operation of the water reservoir,float-operated supply valve, and drain.

Inspect all distribution ductwork and evaluate the system's overall abilityto cool the building. If the building is in seismic zones 3 or 4 (California andportions of Alaska, Arkansas, Hawaii, Idaho, Missouri, Montana, Nevada, Oregon,Utah, Wyoming, and Washington), check the evaporative cooler for the presence ofseismic bracing to the structure.

Check the location and condition of the whole house or attic fan, if one ispresent. Inspect fan motors for signs of overheating and examine fan belts forsigns of wear. Check all operating controls and associated electrical wiring andcheck to see that the attic fan thermostat is set at about 95 F (35 C).