Heat pumps take a back seat in the public consciousness compared to air conditioners and furnaces, but perhaps they shouldn’t. They can provide efficient comfort, and are also capable of both cooling and heating!
This article takes a closer look at what a heat pump is, how it works, and what variables (efficiency, type, brand, etc.) you might want to consider when purchasing or upgrading your heat pump.
What is a Heat Pump?
A heat pump is a piece of HVAC equipment that heats and cools a home. It’s often installed in homes instead of an air conditioner. It runs on electric power, and is often paired with an electric furnace.
Heat pumps don’t generate heat on their own. This is a common misconception. Instead, they absorb heat from one area (a source) and move it to another.
We’ll talk in more depth below about the heating and cooling processes, but the basics of how heat is transferred are similar to that of an air conditioner. A few mechanical differences apply, though, which we’ll discuss.
Air-Source vs. Ground Source
Air-source heat pumps draw heat from the air in a specific area, either inside your home or from the outdoor air.
A ground source heat pump draws or conducts heat into the ground. These are sometimes called geothermal heat pumps.
Geothermal heat pumps are far less common in the US, and they can also be extremely expensive to install.
This article will focus on air-source heat pumps, but know that many of the same parts, processes and details are the same for a ground source model as well.
Dual Fuel and Hybrid Heating Systems
We mentioned above that heat pumps operate on electric power and are generally one aspect of an electric HVAC system.
This is true, but it’s also possible to have different energy or fuel sources for your HVAC.
The most common “dual fuel” system is when a heat pump is paired with a natural gas furnace. I say most common, but even this is comparatively rare.
More often when you have a heat pump, your indoor HVAC unit will have an air handler with heating coils installed inside of it. This is sometimes referred to as an electric furnace. These coils provide supplemental heat in the winter.
When and why this happens is something we’ll get into below, because it deals with when your heat pump will and won’t operate efficiently and will be sufficient for your home comfort.
A Heat Pump’s Cooling Process
The key to the cooling process is the system’s refrigerant, which changes states from gas to liquid. In these different states, it can either absorb or expel heat. It’s the continual exchange of this heat that removes it from your home and gradually cools it.
Inside your home, refrigerant is in liquid form and can absorb ambient heat, which it does when warm air passes over it from the home’s ductwork.
From there, it travels to the outdoor unit where the system’s compressor compresses the refrigerant until it enters its gaseous state. The hot air is emitted and blown out of your system’s outdoor unit via the blower fan.
It then travels back into the home and re enters its liquid state.
That is a very basic rundown of a heat pump’s cooling process. A lot of finely-tuned processes occur to manage the refrigerant and other moving parts during this process. But in general terms, this is what’s happening.
Cycle through this enough times and the heat pump will remove enough heat from your home for it to feel noticeably cooler.
Heat Pumps and Home Heating
Now that we’ve explained heat pump cooling, explaining the heating process will be much easier.
The reason is that the process is exactly the same, but in reverse. So a heat pump is transferring heat from outside into your home.
Do Heat Pumps Work When It’s Cold?
Yes, heat pumps can work when it’s very cold outside, but not always as well as when it’s only a little bit chilly.
The reason for this is simple: there’s less heat in the outside air to transfer into your home. There is still some heat, for clarity, and many heat pumps can continue to keep your house warm even when the outdoor air reaches freezing temperatures.
But the system will be less efficient at this point and will need to cycle more often to maintain heat levels.
At extreme cold temperatures, you might even experience what’s sometimes called “cool heat.”
Think of it this way: maybe your home’s indoor air is at 60 degrees, which is too cold for most people. The outdoor air is 30 degrees, but the heat pump can still absorb some ambient heat from the air.
However, this air might not feel particularly warm to you, especially compared to furnace heat that is often at 90 degrees or higher as it’s blowing out of your vents. If the “cool” air is between 70-80 degrees, it will still warm your home compared to its original 60 degrees, but not as quickly or as efficiently.
Usually in these cases, supplemental heat is used from an electric furnace to add to a heat pump’s heat generation. This keeps your home more consistently warm.
Heat Pump Efficiency Ratings
Heat pumps have two different efficiency ratings, one for cooling and one for heating.
SEER (Seasonal Energy Efficiency Ratio) is used for cooling, just as it is for air conditioners. In recent years, a more sophisticated SEER2 calculation has been introduced that’s often used. Both measure average cooling efficiency over a variety of typical conditions.
Whether your system is measured in SEER or SEER2, just make sure you’re comparing apples to apples with other systems for cost-efficiency purposes.
On the heating side, HSPF (Heating Seasonal Performance Factor) is the metric used. It’s similar to SEER, in that it measures average performance over a typical heating season. Also like SEER, there’s an HSPF2 that is a bit more detailed in the variables and conditions that it measures.
Higher ratings are better. That may seem obvious, but the more important part of the ratings is what you can expect to save when you increase the efficiency of your equipment. For this, it’s usually best to consult with an HVAC professional, who can provide a more details estimate of savings based on your existing equipment and potential upgrade.
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Parts in a Heat Pump
Here are some of the major parts in a heat pump system. This list is non-exhaustive:
- Outdoor fan – collects or emits air.
- Condenser – condenses refrigerant when the heat pump is in its cooling mode.
- Evaporator – changes refrigerant state when heating.
- Refrigerant – liquid or gas, depending on state, that facilitates the transfer of heat.
- Reversing valve – component that reverses your heat pump system from cooling to heating or the reverse.
- Expansion valve – controls the refrigerant flow by limiting it within your system or allowing more depending on the heating and cooling needs of the heat pump.
- Blower motor – pushes air through your home’s ductwork once it’s been heated or cooled (depending on season) by the heat pump.
Your Home Heat Pump
Whether you’re looking to install a brand new heat pump to replace your old one, or considering switching to an electrical system to save on energy costs or make your home more eco-friendly, it’s worth understanding heat pumps and how they can benefit your home.
Efficiency ratings and mechanical processes aren’t everything, though, and the finer points of outlining all of your HVAC upgrade options can only be handled by a trained heating and cooling specialist.
CABS Heating and Air Conditioning has helped thousands of homeowners to do exactly that. Whether it’s a heat pump installation, repair, tune-up, or other home service, we’re here to ensure your home stays comfortable in any season. Give us a call today!
