When discussing the environmental benefits of heat pumps, refrigerant leakage is often cited as an area of significant concern, and rightly so. As discussed in an earlier edition of our newsletter, most of the refrigerants used in residential heat pumps have a very high global warming potential (GWP), which means that they contribute significantly to climate change if they escape into the atmosphere. This means that relatively small amounts of refrigerant leakage can negate the environmental benefits associated with the energy efficiency of heat pumps. In this article, we will discuss the true environmental impact of residential heat pumps by considering refrigerant leakage.
A recent study conducted by mechanical engineers at Steven Winter Associates compared the carbon dioxide output of two different residential heating systems: a single-room mini-split air-source heat pump (R-410a refrigerant) and an efficient gas hydronic baseboard system. They found that the heat pump generated 1 lb/ft2 of carbon emissions annually, assuming no refrigerant leakage. Alternatively, the gas hydronic system produced 2 lb/ft2 of annual carbon emissions. These results make sense, as the efficiency benefits of heat pumps over gas heating are well-documented. However, when accounting for refrigerant leakage, these results change significantly as shown in the table below.
This table shows that as the refrigerant leakage approaches 10%, heat pumps generate an amount of carbon emissions equivalent to that of the efficient gas hydronic system. As leakage rates increase above 10%, the environmental benefits of heat pumps become increasingly devalued. While refrigerant leakage clearly poses a problem, it is important to consider the actual rates of refrigerant leakage from residential heat pump systems.
A study conducted by the Department of Energy & Climate Change (DECC) in the United Kingdom attempted to quantify the leakage frequency and rates of heat pumps by looking at data collected from over 500 installations. The report found that only 10% of all domestic heat pump systems were found to leak refrigerant, with equivalent annual leakage rates ranging from 1.82-10%. This amount of refrigerant leakage is relatively trivial, and still ensures that heat pumps are more environmentally friendly than any other fossil fuel heating technologies. This study also arrived at the conclusion that by 2050/51, the negative impacts associated with refrigerant leakage are projected to be just 0.62% of the calculated benefits, indicating that the deployment of heat pumps will be essential to the efforts against climate change. While refrigerant leakage is still a significant problem that needs to be prevented, it should not deter people from installing heat pumps, especially when it comes to replacing existing fossil fuel heating systems.