Alternative cooling systems

Editor's note: This story is adapted from the U.S. Department of Housing and Urban Development's Residential Rehabilitation Inspection Guide, 2000. Click here for other stories in this series.

Geothermal systems are relatively new and operate similarly to air-to-air heat pump systems, but differ in design and installation. What might be considered the condenser are pipes buried in the ground in dry wells or other in-ground systems suitable for transferring or displacing heat. The system is closed and its piping is PVC so corrosion is not a potential problem.

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

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

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

Electric heat pumps are refrigerant-type air conditioning systems that can be reversed to extract heat from outside air and transfer it indoors. Heat pumps are normally sized for their air conditioning load, which in most parts of the country is smaller than the heating load. Auxiliary electric heaters are used to provide the extra heating capacity the system requires in the heating season.

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

Inspect a heat pump like you would a central air conditioning system. Testing in one mode is usually sufficient. However, do not operate air-to-air heat pumps in temperatures below 65 F (18 C) on the cooling cycle and above 55 F (13 C) on the heating cycle. In both conditions the amount of work the heat pump has to do to achieve interior comfort temperatures 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 simple and economical devices. They pass air through wetted pads or screens and cooling takes place by evaporation. Such systems can only be used in dry climates where evaporation 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 water supply valve.

These components are contained in a single housing, usually located on the roof, and connected to an interior air distribution system. In wetted-pad coolers, evaporator pads are wetted by a circulating pump that continually trickles water over them; in slinger coolers, evaporator pads are wetted by a spray; and in rotary coolers, evaporator screens are wetted by passing through a reservoir on a rotating drum. The water in evaporative coolers often contains algae and bacteria that emit a characteristic "swampy" odor. These can be removed easily with bleach. Some systems counteract this pattern by treating the water or by continually adding a small amount of fresh water.

Inspect evaporative cooling systems by examining the condition of each component. Note whether evaporative pads need cleaning or replacement. Look for signs 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 ability to cool the building. If the building is in seismic zones 3 or 4 (California and portions of Alaska, Arkansas, Hawaii, Idaho, Missouri, Montana, Nevada, Oregon, Utah, Wyoming, and Washington), check the evaporative cooler for the presence of seismic bracing to the structure.

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