The term Heat Pump may seem a little deceptive when considering using a Heat Pump for AC (cooling). In reality, if you already have a conventional air conditioner in your home, you are already using a Heat Pump for cooling. That’s right; an air conditioner uses the same principles of refrigeration to cool the air in your home. You see, cooling (or air conditioning) is simply the process of removing heat. We use a refrigeration system to move heat out of the indoor air in your home and discharge it outside the home. In this article, we’ve already answered the first question – can you use a heat pump for AC? Yes! Let us continue to look at some of the heat pump options you have as a homeowner looking for a Heat Pump for AC. We’ll also take a look at some of the considerations when deciding on a heat pump for AC (or heating). If you’d prefer to watch a video on this subject, we posted a recent video on our YouTube channel: Heat Pumps for AC.
Heat Pump Options for AC
There are many types of Heat Pumps available to homeowners today. The heat pump must be carefully selected for your home cooling (and heating) needs. Otherwise, you could be left with a system that either doesn’t perform as advertised, if at all. In some cases, an incorrectly selected system can lead to longer-term reliability issues and a system that is more expensive than it should be. An air source heat pump system today should last for 15 years. Alternatively, a ground source heat pump system should last 25 years or more. What’s the difference, and which is suitable for your home? Glad you asked!
Air Source Heat Pump (Air-to-Air)
An Air Source Heat Pump is quite literally just that – a heat pump that uses the air as its thermal energy source. A heat pump doesn’t create heat like a fossil fuel furnace does (by fuel combustion). Instead, it simply moves heat from one place to another. In technical terms, we call those two places heat is transferred between the source and sink. The significant difference between a heat pump and a conventional air conditioner is that the heat pump can REVERSE or switch the Source and Sink locations. For example, with a conventional air conditioner, the heat source is the warm indoor air (as this is where the heat needs to be moved from to provide a cooling effect). The “sink” is, therefore, the outdoor air. Using a heat pump, we can reverse that process and use the outdoor air as the “source” and the indoor air as the “sink.” You might ask how it can extract usable heat from the outdoor air. Without getting too technical, I would suggest that there is a lot of heat in outdoor air (in terms of how refrigeration systems move heat). Consider this; if you’ve ever heard of the term “absolute zero,” the temperature at which no further cooling effect can be applied. Essentially, no more heat can be extracted to go below that temperature, no heat. This temperature is -273C. There is technically extractable heat in every degree above -273C. Now, in practical terms, most “cold climate” Air Source Heat Pumps today will extract heat down to about -25C. However, these systems may not do this all that efficiently, and other constraints like system capacity factor into the application and design of these systems. So back to cooling, now we know that an Air Source heat pump is essentially the same as that old air conditioner we’ve always been using; it’s just reversible. There are performance advantages of new heat pumps for cooling. In recent years new compressor technologies have come online that allow Air Source Heat Pumps to perform better in cooling than that old air conditioner. However, just like in heating mode, as it gets warmer outside (the sink), it gets harder to dump heat from your indoor air outdoors. Therefore, power consumption goes up, and efficiency drops. I’ve always said – the day you need your air conditioner, the most is the day it’s the least efficient.
Ground Source Heat Pump (Water-to-Air)
Okay, so how do we solve the problem of efficiency decline in “peak” conditions (cooling or heating)? Enter Ground Source Heat Pumps (Geothermal). You guessed it! Using a ground source heat pump, we harness the ground as our “source” for heating and reverse the heat pump for cooling; we use the ground again as our “sink.” To do this, we need to design and build a “ground heat exchanger,” a network of pipes built to absorb and reject heat through an intermediate heat transfer fluid that interacts with the earth’s temperature around the pipes. You see, just below the frost line (speaking in Ontario/Eastern Canada), the temperature of the soil is somewhere between 8C and 10C. This is a fantastic source of low-grade heat for our heat pump in winter and an extremely cool SINK for heat in the warm summer when outdoor air conditions break 30 or 40C. This moderate temperature provides the highly efficient operating conditions that a heat pump loves, which creates efficiencies upwards of 400% or greater in many cases. This also plays into the reliability and longevity of ground-source heat pumps. If heat pumps are not struggling at their limits when they operate, that refrigeration system can be assured a long life. Of course, making all this outstanding performance happen requires the installation of a piping network. Now don’t get me wrong, a ground heat exchanger can be installed almost anywhere. Ideally, the heat exchanger can be installed horizontally by trenching equipment. This is ideal because it is the least costly method of installation. This is typically applied in rural areas with a land area of at least 2 or 3 acres. In urban areas, systems can be drilled vertically into the ground, so they don’t require a large footprint. However, specialized drilling costs can be considerably higher, negatively impacting these systems’ economic payback.
Air Source (Air-to-Water)
Okay, by now, you have to think there has to be an option in-between. Correct, there is a technology that exists in between Air Source (Air-to-Air) and Ground Source (Water-to-Air), and it’s Air-to-Water. Now, I say it exists in between as Air-to-Water provides “Ground Source-like” efficiencies without the cost or burden of the ground heat exchanger. This certainly doesn’t mean an Air-to-Water system will cost similar to a basic Air-to-Air system, as there is more involved, but on the spectrum looking broadly at these systems, air-to-water would fall somewhere in between. The challenge here is that most contractors today have not yet learned about the significant opportunity that Air-to-Water can provide homeowners with. The common perception is that air-to-water is for application in hydronic heating systems (conventional hydronic heating systems use a fossil boiler for thermal energy). The opportunity being missed is that an air-to-water is a fantastic system to couple with a hydronic air handler. Water is a very efficient and comfortable way to transfer heat. Using it within a hydronic air handler makes the water act as an intermediary between the refrigeration circuit of the heat pump and the house’s indoor air. This allows for flexibility in design and increased ability to deliver higher comfort and higher efficiency compared to an Air-to-Air system. The added benefit should the homeowner choose is the addition of highly efficient heating of domestic hot water (DHW). This is all built-in to the same system.
Application and Design of Heat Pump For Your Home
We’ve discussed a few very technical things in this article, and we expect homeowners will have questions! Evolved Thermal Energy is here to answer those questions and help you determine the suitable system for your home. Once we’ve determined your options, we’ll connect you with one of our contractors for installation. Switching to a heat pump and electrifying your home HVAC systems requires much more upfront consideration, knowledge of building science, and house-as-a-system principles. When adding in complexities of geothermal or air-to-water systems, many HVAC contractors may not be comfortable designing these systems; this is where we help both the contractor and the homeowner. Our job is to help homeowners determine which system is right for them, what fits their application and budget, and then support the contractor through the design and installation process.
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