Heating & Cooling
Our ability to control the indoor climate is a great modern convenience that makes it possible for people to live comfortably in regions as frigid as Alaska and as hot and dry as the U.S. desert Southwest. Yet the technologies that allow us to pursue our daily activities at a comfortable temperature and humidity are also some of the largest consumers of energy. In 2006, more than 40% of the energy delivered to residential buildings was used for space heating and cooling, accounting for more energy consumption than any other household use.
The chief source of energy for space cooling is electricity. During the past 30 years, attention has been focused on improving the efficiency of air conditioners, particularly with respect to their heat exchangers, compressors, and controls and motors, as well as better integrated design. Further improvements are likely to come from modified designs that incorporate new refrigerants as well as new thermodynamic cycles.
In 2006, more than 40% of the energy delivered to residential buildings was used for space heating and cooling, accounting for more energy consumption than any other household use.
Despite such impressive strides in equipment efficiency and the improved weatherization of homes, the amount of electricity used for space cooling has actually increased over the past three decades, due to several factors. Many Americans have migrated to warmer areas in the South and West that require more energy to maintain an optimal indoor temperature. Consumer preference for larger homes has grown, increasing the volume of space that requires climate-control, and older homes are frequently being converted from room air conditioning to central air conditioning. Even the climate itself has been a factor; average temperatures have been rising in recent years, resulting in ever more energy needed to cool our homes, especially during the summer season.
To warm us during the cold months, fuel for residential space heating comes from a variety of sources, such as electricity or oil, but natural gas is the most common. Energy demand for space heating is expected to decline over the next two decades as people continue to move to warmer areas and as the climate warms. The adoption of more efficient heating technologies is also expected to contribute to this decrease. For instance, the most efficient new gas furnaces can condense and utilize much of the exhaust heat from combustion, making them 90–97% efficient.
The adoption of other technological improvements is contributing to an increase in efficiency for residential space heating and cooling. Programmable thermostats allow homeowners to adjust the temperature of their home while they are away. Setting back the thermostat 10°F-15°F for 8 hours a day can lead to significant reductions in energy use. Pumps that extract heat from underground, making use of geothermal energy, are currently an expensive but efficient method to provide energy for space heating and cooling. About 35,000 ground-source heat pumps were installed in 2007. However with new government incentives, the market share of this new technology is expected to increase fivefold by 2030, with an average of 90,264 units installed per year.