As 90-degree temperatures lingered and the heat index flirted with 110, we decided to the put heat pump in cooling mode this week. In other words, we turned on our version of AC.
Up to now we have been stayed comfortable without mechanical cooling thanks to the home’s insulation and tight construction. In addition, our architect designed overhangs to shade the windows during the summer, blocking heat from the sun. Ceiling fans cool the bedrooms. In the basement, the heat pump water heater actually chills the house a bit by removing heat from surrounding air to warm the water.
I should add that we’re relatively heat-tolerant people, so our definition of comfort might not match everyone’s. But this week’s heat wave was too much even for us. What’s neat is the same heat pump that warms the house in winter by drawing heat from outside can cool the house in summer by acting in reverse, pushing heat outside. Heat pumps are more efficient at extracting humidity than standard air conditioners, according to the U.S. Department of Energy web site. However, they move air slowly rather than blasting it, which means it can take longer to cool a space.
The upshot is, our heat pump is performing extremely well in the heat wave. Twenty-four hours after we switched it on, the second-floor temperature dropped from 89 degrees to 77 degrees, stabilizing around 75 degrees at night. The humidity fell from 64% to 45%. Alas, everyone is getting a good night’s sleep.
The cost to cool seems reasonable. At its maximum cooling capacity of 24,000 BTUs, the heat pump uses about 1.4 kilowatts per hour. That costs $3.73 per day, or about the price of a large iced coffee. That compares with about $2.50 per day for heating in March, according to our rough calculations. We figure cooling might cost more for us because we use it only during extreme conditions like a heat wave, when we need to run it constantly. Also, the heating operation is assisted by numerous supplemental sources such as appliances, computers, cooking, sunlight and the pellet stove.
What’s more, the heat pump is REALLY QUIET. In fact, you can hardly hear it, making it a big improvement over the rumbling din of a standard AC. I love that!
On the downside, there is one temporary glitch in the system. The thermostat isn’t working correctly so the heat pump does not shut off when the temperature reaches the set temperature. In other words, we have to shut the system off and on manually. Our HVAC contractor believes there is a sensor problem. In practical terms it’s not a huge deal right now, since we are only cooling the house in extreme temperatures when we’d want the system running pretty much constantly anyway. Still, we hope to get this resolved by the fall, when we will really need a thermostat.