Moving back to my native New Zealand this year, I had the chance to try a different kind of heating system for our house here. One of the most intriguing technologies I’m hearing about here is something I never heard of – an air heat pump.
I was familiar with the very eco correct “geothermal” or ground heat pump, only because I write about green building. This pumps air through pipes that loop through your house and down about 5 feet underground where the temperature is a relatively constant 55 degrees F, summer and winter, from Maine to Miami, bringing up a moderate temperature, even though above-ground temperatures can veer from below 0 to over 100 through the seasons. Staying at a moderate 55 F year round makes it a lot easier to make up the difference (with heating or cooling) to the comfortable 65 or so that we humans evolved to like best.
So I was surprised to find that here, “air” heat pumps appear to be such a normal and everyday way to heat a home, that flashy advertisements vie for your attention in every hardware store, showing how comfortable and warm your family will be with a heat pump to complete the happy home.
But strangely, no marketing emphasis is put on the incredible energy efficiency of the air heat pump! Yet the only energy it needs is the small amount of electricity needed to drive the fan to squirt the heated air, and an air compressor.
It delivers more energy than a 100% efficient heater, which uses 9 kw of electricity to deliver 9 kw of heat. But heat pumps transfer 3 to 4 times the energy that it takes to operate, so they can deliver the same 9 kw of heating from under 3 kw of power.
They extract heat from ambient air outside, filter out particles, molds and pollens and bring heated, dried air inside, using a process a bit like the refrigerator working in reverse. Air heat pumps are controlled by a thermostat so you can adjust heating levels, just like with an actual heater.
That heat pumps can warm a home with no electricity for heating – even when it is colder outside than inside – makes them seem to work by something akin to magic.
The way it actually works is science. It’s kind of how a fridge works:
1. A refrigerant gas is contained inside a copper tube that runs from the outside to inside, and this gas has the ability to absorb heat from air.
2. The gas is passed through a compressor, which heats it up to over 140 degrees F.
3. The gas carries the heat through copper pipes that enter the house to be stored in the heat exchange unit.
4. Fans blow the heat in.
In the summer, you can simply run them in reverse, to cool the inside of the house, sending the heat out.
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