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Leave that heat pump thermostat alone in winter...

... but you can turn the AC off in the summer


REGION —If a heat pump is operated in the most efficient way possible, and as intended, the cost per month in one apartment of about 800 square feet in Livingston Manor is about $80 per month in the winter months. If the heat pump is operated in the least efficient way, the cost during those months jumps to about $300 or more.

So what’s the most efficient way to operate the heat pump? Pick a comfortable temperature and leave the thermostat alone. Turning the unit off and on, or turning the thermostat up or down by more than two degrees Fahrenheit, or letting the temperature drop by more than two degrees then reengaging the unit, automatically starts the backup unit, typically an electric strip—and that’s expensive.

So, for instance, if the thermostat is set at 70 degrees Fahrenheit and you are going to work and turn the thermostat off, in the cold months the temperature in the house or apartment will drop. Let’s say the temperature in the living area drops to 55 degrees Fahrenheit, and when you get home, you turn the thermostat back up to 70. That will automatically turn on the back-up or electric heating strip as well as the compressor, and these electric units will continue to produce expensive heat along with the less expensive heat produced by the main heat-producing element.  And that expensive back-up heat will remain on until the temperature in the living area reaches 68 degrees Fahrenheit. So, any savings you may have achieved by turning the unit off will be more than eaten up by the cost of running the electric strip for a couple of hours.  

Here is another way to understand it. Most heat pumps produce heat in two ways; one way is very efficient and the other is not. The efficient way works like an air conditioner that has been turned around. The coolant picks up heat outside and comes through a pipe to the inside of the building, where it is compressed. The compression heats up the coolant, and a fan blows the heat across the coiled tube and the heat is dispersed into the house or apartment through ducts and vents. The coolant then goes through an expansion joint, which has the opposite effect from compression: it becomes very cold, and goes outside and picks up more heat.

And yes, believe it or not, there is heat to be picked up even when the weather is very cold outside. If you’ve ever stepped behind the exhaust fan from a freezer in a fast food joint in the summer, you can feel that hot air is coming out of that freezer. That is true even though the freezer is already at zero degrees.

Still, heat pumps become less efficient when operating in cold temperatures, so whether or not you change the thermostat, when the outside temperature drops below about five degrees Fahrenheit, the second, inefficient method of producing heat kicks in. It’s the equivalent of turning on a large electric heater.

Naturally, people who purchase heat pumps are price and energy conscious, and they don’t want to waste either. Once again, the way to do that is to set a comfortable temperature and leave the thermostat be. That way, the heat strip is only engaged when the temperatures outside drop very low and the heat pump really needs the assistance of the electric strip. This also means that in most homes in this region, in the winter, the heat pump will be running nearly constantly on many days and nights in the winter.

But the summer is a different story. In the summer, just about all heat pumps can be used as air conditioners, which effectively reverses the operation of the heat pump to pick up heat inside the home or apartment and dump it outside. In the air conditioning mode, there is only one way to cool the air, and that is by using the compressor in the air conditioner; there is no back-up method of cooling, so you don’t have to worry about a more expensive energy source kicking in and can turn the units on and off, or the thermostat up and down, without incurring extra costs.

Multiple sources say it is a myth that consumers will save money the leaving the air conditioner on all day while the residents are away at work. This from a site the specializes on heating and cooling (tinyurl.com/y9jb2dab): “Does Turning the System ‘OFF’ While You’re at Work Save Money? Jennifer Thorne Amann, building programs director of the American Council for an Energy-Efficient Economy says yes—turn off your AC!”


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