Electricity bills can go up on hot summer days. People want to remain comfortable. It's possible that your household fought over the best way to cool your space. Running the air conditioning all summer long without break is more efficient than turning it off during the day when you don't want to use it.
We are a team of architectural and building systems engineers who used energy models that simulating heat transfer and A/C system performance to tackle this perennial question: will you need to remove more heat from your home by continuously removing heat throughout the day or removing excess heat only at the end of the day
The answer depends on how energy intensive it is. How well your house is insulated, the size of your air conditioner, and outdoor temperature and humidity are some of the factors that influence it.
It depends on whether you let your home heat up while you're out of work or cooling it when you get home.
Think about how heat is created. The building has less stored heat than outside, which causes it to flow into your home. Your A/C will always have 1 unit of heat to remove every hour if the amount of heat is given by a rate of 1 unit per hour. You can have up to eight hours of heat at the end of the day if you turn off your A/C.
AdvertisementHome owners have a limit to how much heat they can store. The amount of heat that enters your home depends on the temperature of the building. If you only have to remove five units of heat at the end of the day if your home can only store five units of thermal energy, then you won't have to do much else.
The process of heat transfer slows down when the temperature inside is the same as the temperature outside. Keeping your A/C off during the hottest parts of the day increases the efficiency of the system. There is no single answer to whether you should blast the A/C all day or wait until the evening.
A test case of a small home with typical insulation in two warm climates is needed. We used energy modeling software created by the US National Renewable Energy Laboratory to look at multiple test cases for energy use in a 1,200 square foot home.
Three temperature strategies were considered. A person has an indoor temperature of 76 Fahrenheit. The temperature can go up to 89 F (31.6 C) during an eight-hour workday. For a short time, the last uses a temperature setback of 89 F.
We looked at three different A/C technologies, including a single stage central A/C, a central air source heat pump, and minisplit heat pump units. The typical residential buildings have central A/C units and heat pumps. In one-to-one replacements of central A/C units, central A/C units are more efficient than minisplits, but they are more expensive to set up.
AdvertisementWe wanted to see how the A/C was used. The A/C system would surge when the thermostat setpoint returned to 76 F (24.4 C) and also for all three cases when outdoor air temperatures are usually the highest. In the setbacks, we programmed the A/C to start cooling the space before the resident returns to ensure thermal comfort when they return.
Even when the A/C temporarily spikes to recover from the higher indoor temperatures, the overall energy consumption in the setbacks is still less than when the temperature is constant. This could result in energy savings of up to 11 percent.
If the home is better insulated, the A/C is more efficient, and the climate is less dramatic, the energy savings may go down.
The central air source heat pump and minisplit heat pump are not as efficient as they could be. The benefits of a four-hour setback are more complicated than an eight-hour one.
Three people are associated with the University of Colorado Boulder, including a PhD student in architectural engineering, an assistant teaching professor of Building Systems Engineering, and an assistant professor of Building Systems Engineering.
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