How Does a Heat Pump work?

The basic function of a heat pump is to move heat from one location to another. It sounds simple enough and really, the process is rather simple. The technology involved moves the heat from a low temperature heat source to a higher temperature heat sink. A heat sink is something that absorbs and disperses heat from something else using thermal contact.

A heat pump pulls heat from the air or the ground. Thus, you have air-source heat pumps and ground source heat pumps. It should be pointed out that as the temperature drops during the winter, so does the efficiency. This is because there is less warmth in the exterior air so the unit has to work harder to squeeze out what’s available.

Let’s say you live in a fairly moderate climate. During the winter, your ground source heat pump will pull the hot air from the ground into your home to heat it. During the summer, the ground source heat pump will pull the heat out of your home in disperse it under the ground; this is how it functions as an air cooler. So, during the winter, the ground is the heat source. During the summer, the ground is the heat sink. Another name for the ground source type of pump is a geothermal heat pump.

Like air conditioners, they de-humidify the interior air, but they do a better job of it. This has two beneficial effects – they consume less energy and provide more cooling relief on those hot days of summer when the mercury starts to rise.

The prime difference between this type of climate control technology and conventional A/C units is that it moves heat rather than generating heat. Because of this, pumps can provide up to four times the amount of energy they conserve. Simplistic, but therein lies the magic.

There are several varieties of pumps, the air-source (also called reverse cycle chiller), the ductless mini-split, the geothermal, and the absorption heat pump (the newest kind). For homes that heat and cool using electricity, the air-source model will reap energy savings of thirty to forty percent!

Anatomy of a Typical Heat Pump

These pumps use a refrigeration system consisting of a compressor (advanced ones are scroll compressors), one copper tube coil outdoors and one indoors, both using aluminum fins to help in heat transfer (like a heat sink).

These typical units are called split systems because of this indoor/outdoor coil configuration. They use a central fan to circulate the air.

When in the heating mode, the refrigerant in the outside coil absorbs available heat which causes it to evaporate into a gas state. Then, the indoor coil does just the opposite, releasing the heat, and changing the refrigerant back to liquid.

As stated above, pumps are best for moderate climes. When the mercury drops below 40 degrees, electric resistance coils must kick in to help (think bread toaster), decreasing efficiency.

Developments over the past 30 years in air-source heat pumps have delivered 1 ½ to 2 times more in energy savings. A few of these tweaked units are the reverse cycle chiller, the cold climate heat pump, and the all-climate heat pump.

Reverse Cycle Chiller (RCC)

Best for homes that use electricity rather than gas, these units allow homeowners the flexibility to choose between air distribution systems. Want a radiant floor system? No problem. How about a forced air system pumped into multiple zones? Ditto.

A large, insulated water tank is integral to the RCC. The pump cools or heats the water, depending on the season. In the winter, coils can deliver hot water to a radiant floor system.

Some employ a Refrigeration Heat Reclaimer (RHR). It operates in a similar fashion to a desuperheater coil.

Cold Climate Heat Pump

Because it uses a backup booster compressor, this unit can operate efficiently down to 15 degrees Fahrenheit (-9.44 degrees Celsius). Additionally, it uses a heat plate exchanger (economizer), if included, to bring efficient operation to conditions below 0 degrees (-17.77 Celsius).

Preliminary studies show an impressive 60% improvement over standard air-source pumps! The downside? They’re not yet available to the general public on a large scale. Look for that to change.

The All-Climate Heat Pump

The interesting thing about this variation is that it is specifically targeted to very cold climates, rather than a mix of warm/cool environments. This really opens up the market for consumers in the upper reaches of both North America and Europe.

It’s downside? The initial cost of the unit. But if the savings predicted by Wenatchee Valley College in Washington, (up to 60%!), prove comparable to residential savings, this unit will pay for itself in short order.

Ground Source Heat Pump or Air Source Heat Pump – Which is More Energy Efficient?

Which type of heat pump do you think is more energy efficient? Is it the ground source or the air source unit? The ground source or geothermal unit is more energy efficient because temperatures under the ground are more stable throughout the year than the air temperature.

Not all heat pumps are designed to operate as both heating and cooling devices. The installation and setup of these heating and cooling devices are more than your standard home heating and cooling equipment. However, the return in energy savings will be a benefit after three to ten years. The average heat pump should last up to twenty-five years if properly maintained.

Some scientists feel that if there were more of these devices in use, we could help lower the earth’s energy costs and help alleviate global warming.

Heat Pump Features to Look For When Shopping

Who should consider a pump rather than an air conditioner? First, as mentioned above, a moderate, rather than extreme climate, is a good match. Second, is the existing system on its last legs? If the SEER rating on the old unit is low, a pump will pay for itself rather quickly (A rating of thirteen to sixteen is the average today; older units are as low as six!).

Also, new construction is a great time to install one, along with all the Energy Star rated appliances.

Here are some of the prime considerations to choose from:

  • Two-speed compressors – Unlike single speed compressors, two-speed models can deliver only the capacity needed. When operating in the low-speed mode, much less electricity is consumed.
  • Compatibility with zone control systems – Two-speed compressors play well with zone control systems, which keep different rooms at different temperatures using automatic dampers.
  • Dual-speed or variable speed blower motors – These move air at the needed velocity, as opposed to single speed which blow at full speed at all times.
  • High-efficiency desuperheaters – Pumps integrated with a desuperheater use waste heat to heat water; it accomplishes this three to four times more efficiently than an electric water heater. Adding a tankless water heater as back-up subdues one more home energy hog.
  • Scroll compressors – These use two spiral-shaped scrolls to compress the unit’s refrigerant. They can produce up to fifteen percent more warm air than piston compressors.

Installation of Heat Pumps Can be Costly

These devices are not cheap but in the end can save you money on your energy costs, although the upfront cost can be a deterrent for many people. The decision is up to you though. If you happen to know anyone who has one of these devices installed, contact them to get some first-hand knowledge of the pros and cons before making a purchase. Contact a local heating and cooling contractor to see if they have any more information on the installation and maintenance of heat pumps, including air source and ground source heat pumps.