Energy Insight: How do electric heat pumps work?

What if you owned a sophisticated machine, which could utilize the principles of fluid dynamics and the phase change properties of modern refrigerants to both heat and cool your home? If your home uses an electric heat pump, which most homes in Clarksville do, then you already own such a machine.

Would you want us to explain to you, in great detail, how your heat pump works and how you can operate it most efficiently? Of course you would.

One of the most amazing things about a heat pump is that it does not actually produce any heat, unless it’s very cold in the winter and your ’emergency’ of ‘auxiliary’ heat runs. A heat pump, as its name would imply, only ‘pumps’ heat from one place to another. This is possible because the properties of the refrigerants used in heat pumps allow them to change from liquids to superheated vapors and back again in what heating, ventilation and air-conditioning (HVAC) professionals call the refrigeration cycle.

Figure 1

Figure 1 is a simplified diagram of the refrigeration cycle. At step one, the refrigerant in your HVAC system is distributed by a compressor. In cooling mode, refrigerant is sent to the exterior heat exchange coil from the compressor as a superheated vapor.

The super-heated vapor passes through the exterior heat exchange coil at step two. Because the vapor is extremely hot, the outside ambient air temperature is sufficiently cold to lower the temperature of the super-heated vapor, which converts the vapor into a liquid. This is effective even if outside ambient air temperatures exceed 100°F.

So now, the super-heated vapor has lost some of its heat and it’s become liquid. The liquid refrigerant travels on to an expansion valve at step three. The expansion valve lowers the pressure of the liquid, which, in turn, converts it into a liquid and gas mixture. (Think of the mist exiting the nozzle of a spray bottle as a half-accurate analogy.) Under lower pressure, the liquid and gas mixture is now significantly colder.

Now we’re close to having the refreshingly cold air that comes out of your vents in the summer. This very cold, liquid and gas mixture travels through the interior coil of your heat pump. Air is passed over the cold interior coil by a fan, and then this cold air is distributed to the rooms of your home through a network of supply ducts.

Now, thanks to science, you’re watching Netflix swaddled in a blanket even though it’s 98° outside.

The cycle continues as the cold air in the interior coil heats up and travels back through the compressor. A reversing valve is used to reverse the flow of the coolant in the system in order to heat your home in the winter. Whether heating in summer or cooling in winter, the principles at work are essentially the same. One important difference to note is that, in winter, a heat pump becomes much less efficient and most systems have built in ’emergency’ or ‘auxiliary’ heat back up. These backup heating systems run automatically when outside temperatures are low enough and generate heat by pushing electrons through resistive materials, causing those materials to heat up. Auxiliary heat is a much more energy intensive heating mechanism and causes significantly increased electric use during the coldest periods of the year.

Safe to say, this is an over simplification of the process, but with this basic understanding we can efficiently operate these systems. Plus, if you want to know more about this you can call us. We can talk about this stuff for hours, and who doesn’t enjoy talking about the physics of HVAC systems?

Want to learn how to use the principles described here to operate your HVAC equipment efficiently and save money on your electric bills? Read Energy Insight: How can you efficiently operate your heat and air-conditioning.

For more energy-saving tactics check out our other articles and sign up as a CDE Lightband Power Partner to get access to our latest Energy Insight articles and energy efficiency offerings.

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