When Passive Strategies Aren't Enough

More Efficient Active Systems
Beginner

Inside this Article

The minisplit interior unit
Small and fairly unobtrusive minisplit indoor units require no ducts.
The minisplit exterior unit
The minisplit exterior unit dumps the heat pulled out of the interior. In winter, the unit can run in reverse to produce heat.
A whole-house fan
A whole-house fan exhausts hot air out through the attic space, or directly to the outside. Cooler air is drawn into the home through open windows.
Evaporative cooler
Evaporative coolers work well in hot, dry climates.
The minisplit interior unit
The minisplit exterior unit
A whole-house fan
Evaporative cooler

Passive strategies may not always be enough to beat the heat, depending on your home’s age, construction, and location. And even though newer central air units are more efficient than their older counterparts, overall, central air conditioning systems use a lot of energy.

In 2005, the Energy Information Administration reported that air conditioning accounted for 8% of residential energy use, consuming 0.88 quadrillion Btu per year. Air conditioner use in the United States results in an average of about 100 million tons of carbon dioxide emissions from power plants every year. Here are some ways you may be able to avoid central air entirely.

Minisplit Systems

Although minisplit systems are often chosen by homeowners who have no existing ducts in their homes, their high energy efficiency makes them an excellent candidate for any home. Minisplits got their name because they have two components: an exterior compressor/condenser, and one or more interior units installed on a wall or ceiling.

Minisplit systems use air-source heat pump technology to provide cooling or heating. Refrigerant is pumped through tubing from the outdoor condenser and compressor to the indoor unit(s). In cooling mode, indoor air to be cooled is drawn across the unit’s interior evaporator coil and distributed via a fan. Humidity is removed from the room’s interior via a drain in the indoor unit.

Compressors of various sizes are available; the most powerful systems can support up to four indoor units and are capable of cooling an entire house (depending on size). Minisplit systems are energy efficient because they take advantage of zone cooling. Each interior unit is individually controlled to turn off cooling to a room or rooms when unneeded. Most, if not all, minisplit systems have a built-in timer so you can program when they turn on and off without being at the control.

Central air conditioning ducts may leak conditioned air—an efficiency problem not possible with minisplits. The U.S. Department of Energy reports that duct losses can account for more than 30% of energy consumption for central A/C, especially if the ducts run through an unconditioned space such as an attic.

Solar Attic & Whole-House Fans

Many people confuse attic fans with whole-house fans, primarily because both are usually installed in the attic. Attic fans are designed to cool and ventilate the attic only. They help regulate the temperature of your roof, thereby extending the life of your roofing. They also reduce the amount of heat that radiates from the attic to the living space. If you already have central air, a solar attic fan is an excellent option for reducing your energy costs and your carbon footprint.

Whole-house fans are oversized exhaust fans that pull in cool air (from open windows) while expelling hot air. As the name implies, they’re used to cool the entire house when the outside air temperature is lower than inside.

For houses with air conditioning, a strategy is to use whole-house fans to eliminate air conditioning use at night. On average, a whole-house fan uses 90% less energy than an air conditioner. Depending on your climate and your home’s thermal mass, it may be possible to precool the entire house sufficiently overnight to avoid air conditioning entirely.

Comments (5)

tyme2par4's picture

I can attest to the value of a mini-split. My parents have had a Daikin unit for a few years now, and I just installed a new Mitsubishi Hyper-Heat unit in my house. The 18 kBTU unit can cool the whole first floor and is almost completely silent. Even the outdoor unit is very quiet.

ewoodhouse's picture

Generally a good article, but I'm dismayed that the author recommends attic fans. Even a casual scan of the building science literature makes it pretty clear that attic fans depressurize an attic and draw conditioned air into it, in most cases increasing energy use. I'm surprised that Home Power would let something like this slip through.

zap101's picture

Attic fans work without hvac, if one opens a lower window can cool down a home in 15 minutes.

Another issue that seems to be passed over is attic fans installed without any additional soffit vents or gable vents ...

zap101's picture

Attic fans used to cool down the home not while using ac is very effective. Think a giant boost to the chimney effect. opening windows in the lower level or basement can make ac not needed.

s premena's picture

Good brief article - I'd like to mention a 'swamp cooler' that does NOT put the humid air into the house - has additional heat exchanger humid air to house air. www.coolerado.com - somewhat more expensive and complicated but keeps humidity and legionarie's bugs out of the house... I like my cool air dry. [I have no financial interest in or experience with the the Coolerado product it just looked like a good idea when I saw it years ago].

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