In addition to climate, several characteristics of a home and its cooling system influence how much energy is required to maintain comfortable indoor conditions during hot weather. These characteristics include the home's building envelope, sun exposure and shade, cooling system efficiency, thermostat settings, and heat generated inside the home.
A home's building envelope is the physical barrier separating the conditioned interior from the outdoors. It includes the roof, walls, floors, windows, and doors.
Heat naturally moves from warmer areas toward cooler areas. During hot weather, heat therefore moves through the building envelope from the warmer outdoors toward the cooler interior. Insulation slows this heat transfer, reducing the amount of heat the cooling system must remove.Air leakage can also allow warm, humid outdoor air to enter the home through gaps and cracks around windows, doors, walls, ceilings, and other openings.
A well-insulated and air-sealed home generally requires less energy to maintain a comfortable indoor temperature than a poorly insulated or leaky home.
Sunlight can significantly increase the amount of heat entering a home. Solar energy heats roofs and exterior walls and can enter directly through windows, increasing indoor temperatures and cooling demand.
The amount of solar heat a home receives depends on factors such as its orientation to the sun, window placement, surrounding trees and buildings, and exterior shading. Shading the home and its windows can reduce solar heat gain and decrease the amount of heat the cooling system must remove.
Different cooling systems require different amounts of energy to provide the same amount of cooling. More efficient systems can remove the same amount of heat from a home while consuming less energy, resulting in lower operating costs.
System performance can decline when equipment is poorly maintained or when airflow is restricted. Dirty filters, obstructed equipment, and other maintenance issues can make it more difficult for a cooling system to maintain comfortable indoor conditions efficiently.
For central cooling systems, ductwork also affects efficiency. Cooled air can escape through leaky ducts, while poorly insulated ducts can gain heat as they pass through hot attics, garages, crawl spaces, or other unconditioned areas. As a result, some of the energy used to cool the air can be lost before that air reaches the living space.
The thermostat setpoint determines the indoor temperature that the cooling system attempts to maintain. During hot weather, lower thermostat settings generally require the cooling system to operate more frequently and for longer periods of time.
The greater the difference between the outdoor temperature and the desired indoor temperature, the more heat tends to enter the home. Raising the thermostat setpoint while maintaining a comfortable indoor environment can therefore reduce cooling demand and energy costs.
Heat can also be generated inside the home. For example, people release body heat, meaning homes with more occupants generally have greater cooling loads.
Light bulbs, cooking equipment, appliances, and electronics also release heat into the home when in use. Activities that release water vapor, such as showering, boiling water, and steaming food, can also increase indoor humidity, adding to the amount of moisture that an air-conditioning system may need to remove.
Individually, these heat sources may be relatively small compared with outdoor heat gain, but together they can increase the amount of energy required to maintain comfortable indoor conditions.