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Over half of the energy used in residential and commercial buildings goes to heating and cooling the air to keep occupants comfortable.

Most of the time, cooling is achieved by using electricity to run a vapor-compression “air-source” heat pump that transfers heat into or from the outside air. Heating is achieved by running the heat pump in the opposite direction, or by using a resistance heater. Alternatively, burning fuel, whether in a fireplace, or via a propane or gas-fueled furnace, provides heat.

Taking advantage of natural outdoor temperatures will produce a heating or cooling effect with even less energy than you’d use with a brand new air-source heat pump.

Some of the systems described below can be installed during a heating, ventilation and air conditioning system retrofit, but it is generally easiest and least expensive to consider them during initial building design and to install them during construction. A supplemental conventional fueled or electric system may still be required for extreme temperatures, but such a system would be smaller and used less frequently than it would if a conventional system was the only source of heating or cooling.

Improve the heat transfer efficiency of a heat pump by submerging the heat transfer coils in outdoor water (a “water-source” heat pump), or by burying them underground (a “ground-source” heat pump). In the northwest, surface water, and the ground a few feet below the surface, are each usually about 55 degrees year-round. Deep water can be notably cooler, and if a water-source heat pump could be placed in deep water economically, it would perform even better. When indoor air temperatures are cold, heat can be extracted from the (warmer) ground or water source. When temperatures are warm, heat can be transferred from the building, into the (cooler) source.

An inexpensive “swamp cooler” can be used to bring air into a hot building by running it through a water-soaked pad. As the water evaporates, it absorbs heat energy, so the air entering the building is cool. In dry climates like central Washington, this is energy-efficient. It also contributes to building humidification.

Another inexpensive option is to simply use cool outside air, available free and in large amounts, to replace indoor air that’s too warm. The device used to do this is, appropriately, called an “economizer.” You don’t want to save money on cooling just to wind up with problems caused by too much moisture, so an economizer should be designed as part of a larger system that accounts for ventilation and humidity requirements.

If you’re close enough to a source of cool water, or a hot spring, you can set up pipes to run some of the water through coils in your building. As it travels, the cool/warm water will absorb/release heat from/into the building. The water can then be returned directly to its source. This requires building design with the appropriate hydronic piping and controls. This is a very effective mechanism to reduce the use of fuel or electricity for thermal control. However, it requires proximity to the source water, and, when used on a large scale, it can affect the temperature of the source water. The concept is not suitable for every situation.