Lower your summer electricity bills by supercooling your home

A smart Ecobee thermostat set at sixty degrees to supercool a house.
eco bee

Energy prices are rising and summers are not getting any cooler. If you’re saving money and getting comfortable this summer, consider using a trick called hypothermia to keep your house cooler for less.

What is hypothermia?

When you hear the term hypothermia, you might be reminded of a science class long gone, but don’t worry: you don’t need to brush up on high school physics or wear safety glasses to benefit.

In the HVAC industry, subcooling — also called “subcooling” or “precooling” — is the practice of running air conditioning at optimal times to significantly cool an environment. Then the AC system is operated less or not at all during the period without subcooling.

This results in a reduced financial and energy burden while maintaining the same (or even better) level of comfort achieved by more traditional air conditioning operation.

In practice, for most people this looks like running your air conditioner at night to lower the temperature of your home below what you would normally set with your thermostat.

If you typically set the thermostat at 72°F during the day, set the thermostat back down to a much lower temperature like 65°F or even 60°F at night. The colder the better – within reason.

During the day, you then set the thermostat to a higher temperature and continue with the hypothermia you were doing.

What are the benefits of hypothermia?

While we just mentioned the financial and energy benefits, let’s take a closer look at what they are and who they apply to.

Virtually anyone can benefit from hypothermia, but depending on variables like your local climate and the type of energy pricing system your local utility uses, you may only see some of the benefits, such as cost.

Your air conditioner works harder at optimal times

The first benefit of hypothermia applies to everyone: if you run the air conditioner at night, the system doesn’t fight the sun.

When the sun shines on your home and daytime temperatures are higher, the AC system doesn’t just work to remove the existing heat from your home – and you, your pets, your appliances, and just everyday activities like cooking or running your computer around playing a game all generate heat – but to dissipate the heat brought in by the sun.

At night, your home radiates heat to the surroundings and the sun doesn’t stream through the windows, adding more heat. This allows the air conditioner to run more efficiently and extract more heat from your home.

And dissipating heat isn’t just about making the air around you feel cool. Removing heat also cools the structure of your home and all the things in it.

Significantly cooling your home at night is essentially “sucking” heat out of all your furniture and even the walls and floors. When you arrive the next day, your well-cooled home will act as a heat sink, making you feel more comfortable and putting less strain on the air conditioner.

It’s no exaggeration to say that your goal when using subcooling as an HVAC strategy is to cool your home down to the ‘bones’ of the building.

You benefit from electricity prices outside of peak traffic times

A Nebraska electric utility pricing chart showing peak and off-peak pricing.
Nebraska Public Energy District

The additional demand that increased AC usage in hot weather places on a power grid is significant. Some utilities simply increase the cost of electric power in the summer to meet demand, but most of them either have general peak and off-peak rates – or they have a program you can opt into to further incentivize their customers to use off-peak electricity.

The chart above is from the Nebraska Public Power District and is a good guide to the type of peak and off-peak fares you can expect in the United States. Not only does the utility have a morning and late evening off-peak rate and a traditional peak window during the 2-7pm block that coincides with high AC demand, but it also has a super off-peak rate at night.

Every hour you run your AC at night, which helps you avoid running your AC during that peak tariff window, is a 300% saving since you’re spending ~5 cents per kilowatt hour instead of ~20 cents.

Even if your local utility doesn’t offer anything like a heavily discounted “super off-peak rate,” you should expect to easily save about 50-150% off nightly off-peak rates.

You will put less wear and tear on your HVAC system

Labor and materials are becoming increasingly expensive, and anything you can do to extend the life of your costly HVAC system is ideal to delay service calls or even a full system replacement. With replacement costs in the “I should have bought a used car instead” range, every extra year you squeeze out of a system is welcome.

Subcooling is a great way to minimize wear and tear on your HVAC system in hot weather because it allows your air conditioner and associated hardware like your furnace fan to run continuously throughout the night when the temperature is lower, rather than cycling on and off throughout the day when the temperature is higher .

You will sleep better

It’s great to use your air conditioning more efficiently and save money with off-peak tariffs, but here’s a totally comfort-oriented reason to use subcooling to cool your house at night: You’ll sleep better.

While people often enjoy sleeping comfortably snuggled in lots of blankets, no one really likes to sleep hot. According to experts, the optimal sleeping temperature for humans is between 60°F and 27°F.

Sleeping in a room above this temperature can lead to sweating, trouble sleeping, and general malaise. It’s such a problem for some people that there are entire product lines like ChiliSleep and BedJet dedicated solely to optimizing sleep temperature.

The best thing about using a system like hypothermia is that it allows you to cool your homes nice and low for that restorative cool sleeping in a cave. Anything else, like saving money, might be icing on the cake for us.

How to supercool more effectively

An air conditioner standing in front of a house next to flowering bushes.
Christian Delbert/Shutterstock.com

Obviously, the heart of hypothermia is turning the thermostat all the way down before bed and cranking it back up when you’re awake to ride that deep chill you did overnight.

But there are always ways to tweak an optimization, right? So if you’re considering hypothermia, consider some of these tips to make it go smoother and more effectively.

Use a smart thermostat for easy scheduling

Fumbling with the thermostat by hand is so last century. While you can use a standard programmable thermostat to program a schedule, it’s much more convenient to use a smart thermostat.

Best Smart Thermostat

ecobee smart thermostat

The ecobee SmartThermostat makes it easy to schedule off-peak times and automatically adjust your thermostat for comfort.

In addition, some smart thermostats have additional sensors that you can place in critical areas, such as: B. the ecobee SmartThermostat. If you’re worried that your hypothermia plan might cause, for example, the room you keep your dog in while you’re at work getting too hot, you can use the smart sensor to monitor that room.

Schedule the fan during the day

You may be used to your HVAC fan only running when heating and cooling are active, but we recommend using the fan during downtime, especially when using subcooling, to just circulate the air.

By setting the fan to blow during the day, you move air through your home and keep the temperature stable, so individual rooms don’t get stuffy or hot while other rooms stay much cooler.

Settings vary between thermostats and systems, but it’s common to find a setting like “Run fans for X minutes every hour” or something similar. If you have a newer system with a variable speed fan, you can usually enable a comfort mode where the fan will blow at a low and slow speed throughout the day to maintain an even air temperature.

Minimize heat gain during the day

In addition to your nightly hypothermia routine, you should also use proven techniques to keep the heat out. Every bit of heat your air conditioning system doesn’t need to remove is an all-round win and will make your subcooling efforts more effective.

Close the blinds and draw the curtains on all windows exposed to direct sunlight. If appropriate for your location, consider installing heat-reducing film on the windows and/or installing awnings to keep the heat out before it burns out the inside of your home.

Minimize air gaps and leakage points

Again, this is just a good general practice whether you’re hypothermic or not, but look for places where air is entering or exiting your home, or where the insulation is poor.

Most utility companies have free or very inexpensive programs where someone will come to your home and do a fan test and give you tips on where to caulk or better insulate your home. Not only are such visits usually free, but they’ll also usually give you free LED bulbs, help you insulate exposed pipes, and otherwise provide you with additional cost savings.

Replacing weatherstrip on a door or using caulk or spray foam to seal gaps around windows or vents is a great way to keep all that cool and conditioned air in your home.

The subtleties of buttoning up your home to keep the cool air inside out, the heart of hypothermia is keeping things as cold as possible each night. The colder you make the house at night, the longer you can survive the heat of the day without the air conditioner turning on. So remember, if you feel the need to grab a throw blanket during your late-night Netflix binge, do it right.

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