Supercool Your Home to Save Money on Air Conditioning

Supercooling is having a moment.

Recent stories in Lifehacker and How-To Geek have both touted this counterintuitive strategy for reducing your electric bill.

So what is supercooling, and how can it help you save on your electric bill this summer?

Supercooling, also known as pre-cooling or subcooling, takes advantage of Time of Use (TOU) rates by shifting your energy usage to off-peak periods when electricity is cheaper.

Here’s how it works:

1. During the “pre-cooling” period (before peak hours), you run your air conditioner to a temperature that is far cooler than your normal setpoints, say 66°F.
2. Then during peak TOU rates from 4-9PM, you bump up the thermostat to your usual setpoint, such as 74°F, so that the A/C doesn’t kick on.
3. Because your house is already pre-cooled, it will take a lot longer to warm up, so you’ll stay comfortable without the A/C running.

Two strategies for supercooling to save money on air conditioning

‍Overnight supercooling: One way to do it is to run your air conditioner overnight, when rates are cheapest and the temperature outside drops to its lowest level, so your A/C doesn’t have to work as hard or use as much energy to fight the humidity. You’ll just have to make sure you maintain that cooler temperature until 4PM when on-peak TOU starts.

‍Midday supercooling: The other strategy is to do your supercooling from 12-4PM. These are the last off-peak hours for TOU, so you are getting your home to its coolest level right before the rates jack up for on-peak hours. The disadvantage here is that this is among the hottest parts of the day, so your A/C will be fighting the afternoon sun.

How much can you save on your electricity bill with supercooling?

It’s anecdotal, but one person who used this strategy in Phoenix, Ariz., reported that he cut his monthly bill by $81. (He adopted the supercooling strategy after seeing his monthly bill hit $340 in July.)

One study found that California residential air conditioning represents about 15% of the state’s peak energy load, but only 2% of its total annual electrical consumption. The research found that an annual pre-cooling and nighttime ventilation cooling strategy could save 24% for a typical new construction home in Sacramento.

But wait - won’t I use MORE energy by supercooling? 

In some cases, supercooling actually used more total electricity. But that increased energy consumption happens during off-peak hours, and saves you from on-peak pricing. So even though it uses more energy, you pay less out of pocket (and the extra energy comes when renewable resources are abundant, so it’s better for the environment too).

We recently did an in-house study of supercooling with five OhmConnect employees in various climates and found that it took on average about a half hour to reduce the home’s temperature by 1°F. From this we deduced that it’s best to start pre-cooling at 2PM to bring the temperature down by 4°F before on-peak TOU rates start at 4PM.

Ready to give supercooling a try?

Here are some tips to attain optimum chill:

• Dress warmly: It may seem weird to wear a sweater in the summer, but this will help you stay comfortable when your home plunges into the low 60s during the pre-cooling phase.

• Close windows and blinds: This strategy is all about trapping the cool in your house, so you don’t want cold air leaking out windows or getting warmed by the blazing sun.
• Reduce heat sources: Avoid using your stove, which will heat up the house. You’ll also want to skip the clothes dryer and dishwasher, which both throw off heat.
• Take advantage of TOU: Make sure you understand which TOU rate plan you are on so you know when energy is cheap to start your supercooling.
• Use a smart thermostat: The hardest part of supercooling is remembering to adjust the thermostat at odd hours, so automate it with a smart thermostat that you can set and forget.

Your mileage may vary based on your home. Supercooling works best in well-insulated houses with a heat-reflecting roof. You’re also better off in hot, dry areas -- high humidity can put a real damper on supercooling and make it difficult to achieve results.

Ready to try supercooling? We’d love to hear how it works out. Let us know on Twitter or Facebook.

(Header photo of A/C sign by Tim Mossholder on Unsplash)