Evaporative cooling is the same mechanism that humans use to maintain a healthy internal temperature. Perspiration on the skin surface evaporates as air flows over it, making you feel cool. The evaporation process uses up heat. In a house, the evaporative cooler uses water flowing over a pad instead of perspiration to remove heat from the air through evaporation. There are several types of evaporative coolers available. Each type has its advantages, i.e., cooling ability, cost, ease of maintenance.

The Desert House uses a fairly new evaporative cooler design generically called the single pad draft evaporative cooler. As the name implies, this cooler uses a single paper cellulose pad that is constantly wetted by a recirculating water pump and water distribution line. An electric motor creates air movement by sucking warm dry outside air across the moist cooler pad and pushing the resultant cool moist air into the house via a network of ducts. The cellulose pad contains thousand of small holes and surfaces, significantly expanding the surface area where evaporation can take place.

Evaporative cooling works extremely well when outside relative humidity levels are below 35% or when the dew point is 55 degrees or less. The cooler continues to provide some cooling above these levels, but not as effectively.

Decreased cooling ability as a result of increased outside humidity is a limiting factor for this type of cooling. Most Phoenix residents who have the option of choosing between the two systems, tend to use the evaporative air conditioner during the hot dry months of May, June, September and October and switch to refrigerated air during July and August, the two hot humid months. Another serious limitation is the large amount of water used by evaporative coolers. Recent estimates of the average water consumption in the Phoenix area ranges from 100-240 gallons per day. In regions where water supplies are limited, evaporative cooling may be an unreasonable luxury.

Evaporative coolers have many advantages over refrigerated air conditioning systems. Energy usage is roughly one third that of refrigerated systems. Evaporative coolers are cheaper to install and maintain. Most of the time the home owner can perform routine maintenance and if maintained properly the unit brings fresh moist air into the home, providing a healthy environment for plants and animals.

The refrigeration cooling at the Desert House is a heat pump air conditioning system. Unlike the evaporative system described above, the heat pump provides cool dry air during the cooling season and warm dry air during the heating season.

Heat naturally flows from warm areas to cool areas until a temperature equilibrium is reached. During hot weather, freon, a refrigerant, is kept quite cold in an interior coil. The freon absorbs heat from warm air passing through the coil, the cool air is circulated through the house by the fan. The heated refrigerant is pumped to the outdoor coil and heat is dissipated into the atmosphere. To heat the interior, during the cold season, the process is reversed. Refrigerant absorbs heat from the outside at the outdoor coil, and is pumped into the building interior where cool air is heated at the indoor fan coil.

Heat pumps are cost effective compared to other types of cooling and heating systems. First, heat pumps accomplish two functions, heating and cooling, thus eliminating the need for two different heating and cooling systems. Second, moving or pumping available heat into or out of buildings is much more energy efficient than creating new heat by burning fuel. Electrical power is only used to run the blower motor and the compressor. Third, since fuel is not used at the site there is no need for a ventilation system and the risk of carbon monoxide poisoning is nil.

Estimates of energy and money savings vary depending upon the type of heat pump and demand imposed upon it, but usually heat pumps are from 20-50% more efficient than separate cooling and heating units.