Upgrading Out of Date Heat Pump Terminology

If you’re anything like me, you are probably hearing a lot about beneficial electrification these days. Beneficial electrification is a win-win for consumers and the environment-- it reduces carbon emissions while also reducing energy costs-- so it’s not surprising it’s a hot topic. And it’s hard to have a conversation about beneficial electrification in the home without turning to heat pumps. But you may be asking yourself, what’s so special about a heat pump?

A heat pump is a fantastic piece of technology. Many in the home performance industry, myself included, recognize that heat pumps are the heating technology of the future and, increasingly, the present. They are low cost, efficient, safe, and don't require fossil fuels. 

In 2019, almost 30% of the 130,000 homes rated using Ekotrope’s HERS rating software had an air source heat pump as their primary heating system (Check out this post to learn more about how builders achieve lower HERS scores). In many regions, heat pumps have been the most cost-effective and efficient option for heating a home without natural gas for years. As heat pump technology continues to improve, and the need to reduce fossil fuel consumption becomes more urgent, more and more people are choosing heat pumps even when natural gas is available.

However, the terminology we use to describe how a heat pump works has not evolved as much as the technology has. In the past, heat pumps were used exclusively for cooling (you might ask: ‘then why are they called heat pumps?’; the reason is they move heat, which can be used to cool or to heat). Much of the heat pump terminology we still use is a holdover from those earlier days. Because the heat pump can be used for multiple purposes, the technology is complex and often confusing to those who do not have an understanding of thermodynamics. Outdated terminology simply compounds that problem.

With use of heat pumps on the rise, it seems beneficial to demystify how the system works, and a good place to start is updating the nomenclature we use to describe the mechanics of heat pumps.

Background: How a Heat Pump Works

A heat pump moves (pumps) heat from one place to another. Heat energy naturally wants to move to areas with lower temperature and less pressure. A heat pump utilizes this principle by pumping a fluid (known as a refrigerant) at low temperature and pressure where it absorbs heat and at high temperature and pressure to another location where it releases heat. In this way, a heat pump can be used both for heating and cooling, and it uses opposite processes to do so.

The outdoor unit of a heat pump, often called a Condenser.

Moving from Condenser to Compressor

The outdoor unit of a heat pump is commonly called a condenser. This name makes sense when the heat pump is running in cooling mode; the refrigerant will condense in the outdoor unit. But when the heat pump is running in heating mode, the refrigerant does the opposite; it evaporates. I propose we do away with the name Condenser. A more accurate term would be outdoor unit or compressor, which is one of the principal components of the outdoor unit.

Moving from Evaporator to Indoor Coil

The indoor coil of a heat pump is often called an evaporator. Similar to condenser, this is a legacy term that only makes sense when the heat pump is in cooling mode; the refrigerant evaporates in the indoor coil. But, in heating mode it condenses in the indoor coil. A better reflection of how the system actually works would be to call this component the indoor coil.

Why Change the Nomenclature?

Changing the nomenclature is not simply about semantics. It’s about bridging the gap between people in the industry who have a theoretical understanding of thermodynamics and those who have a more practical understanding of how the equipment works. We should strive for a simpler, more accurate set of terms that provides a common language and understanding, and we shouldn’t be afraid of revising outdated terms that no longer serve the profession.

At Ekotrope we are always looking for ways to update our knowledge, and as a result, the product we offer. This is just one of the recent ways we have challenged our own thinking around home energy efficiency. We would love to see the industry adapt in ways both big and small to help more people understand how systems and equipment work.