I am the President of the New England Geothermal Professional Association, and Director of Achieve Renewable Energy, LLC. (Achieve), which is a Geoexchange/Geothermal design and installation firm located in Salem, MA. In writing this blog post, I hope to broaden people’s understanding of heat pumps in general and Geoexchange in particular. Geoexchange systems offer significant advantages for both homeowners and businesses. In our northern climate, where weather conditions can be extreme in both winter and summer, Geoexchange systems provide distinct benefits over air-source heat pumps (ASHPs). There are multiple reasons for this, and I touch on five of them below. In the interest of brevity, I am presenting summary information, but for each of the five reasons to consider Geoexchange, I provide a link to a more detailed post on Achieve’s website. This way, you, as the Reader, can get a taste of the information and then go deeper if you want.
1. Efficiency and Peak Load Advantages of Geoexchange vs. Air-Source Heat Pumps
Massachusetts experiences wide temperature fluctuations throughout the year, with cold winters and warm, humid summers. Geoexchange systems leverage the stable temperatures found underground, which remain around 50-55°F year-round. This provides a consistent and reliable source for energy transfer during heating in the winter and cooling in the summer.
Heat pump efficiency is important because it drives heating and cooling costs. Geoexchange systems achieve efficiency levels of 300-500%, meaning they can provide 3-5 units of heat for every unit of electricity consumed. In contrast, air-source heat pumps (ASHPs) have up to 300% efficiency at moderate outdoor temperatures but are impacted by lower outdoor air temperatures, with efficiency dropping to as low as 175-250% during Massachusetts’ cold winters. In addition, ASHPs develop frost or ice on their outdoor condenser coils during colder periods. To resolve this, the ASHPs automatically stop operation and use the electric coil on the condenser to melt the ice. After this ‘defrost cycle’, the ASHP will return to heating the building. Geoexchange systems do not require defrost cycles. During peak demand periods, Geoexchange systems help reduce strain on the electrical grid by maintaining high efficiency levels, whereas ASHPs may struggle.
So what does this mean for your bills? Compared to heating with fossil fuels and traditional air conditioning, Geoexchange can typically reduce your heating and cooling cost by 60-70% if you use oil, propane or electric baseboard and 15-30% if you use gas. For example, if you use oil, this would mean that you would completely eliminate fossil fuels use and increase your electric bill by about 30-40% of your current fuel and air conditioning bill. For each Geoexchange installation, these calculations can be made specific to the building. ASHPs use over twice the electricity of GSHPs in a typical year so the ASHP savings, are less than half as good as GSHPs.
For a more detailed discussion of efficiency, Click Here
2. Aesthetic Advantages of Geoexchange in Historic Districts
Historic districts, like many found in Massachusetts, have strict guidelines to preserve the aesthetic integrity of buildings. Air-source heat pumps often require bulky, visible exterior units that can detract from the appearance of historic homes and buildings.
Geoexchange systems, by contrast, have no visible outdoor components. The system’s heat exchange takes place underground, preserving the architectural integrity of historic properties. This can make Geoexchange systems a preferred solution for property owners in historic districts who want modern heating and cooling technology without compromising aesthetics.
Geoexchange requires some space for installation of the underground components. For most houses, an area of 20’ by 20’ can be sufficient. The equipment used in the installation will extend outside of this installation area when working. The area used for the ground heat exchanger is impacted by drilling and excavation during installation but can be returned to use for plantings or driveways after the installation with no visible indication that there is a geothermal system below. Many but not all buildings in historic districts have enough space for installation of a ground heat exchanger. For those that do not, a Networked Geothermal system might be a solution. I discuss networked systems below.
For a more detailed discussion of Historic Districts, Click Here
3. Longer Service Life of Ground-Source Heat Pumps
Geoexchange systems are known for their longevity. The underground piping system, which is the core of the Geoexchange system, can last for 50-100+ years. The heat pump itself is located indoors and typically lasts 25 years with proper maintenance. In contrast, air-source heat pumps are exposed to harsh outdoor weather conditions in Massachusetts and often have a lifespan of 10-15 years.
The longer service life and higher efficiency of Geoexchange systems means fewer replacements and lower long-term costs for property owners, respectively, further enhancing their value over time. In selecting a heat pump type for your building, a calculation of lifecycle cost that considers installation cost, financial incentives, operation cost, and equipment replacement cost is important. Geoexchange, while typically having a higher upfront cost, has a substantial advantage in financial incentives, operation costs, and equipment replacement costs. As a result, Geoexchange is an attractive option for heating and cooling of buildings in our climate.
For a more detailed discussion of Service Life and Lifecycle Cost, Click Here
4. Increased Risk of Refrigerant Loss from Air-Source Heat Pumps
Air-source heat pumps are more prone to refrigerant leaks due to their outdoor components, which are exposed to varying weather conditions. Options such as the popular mini-split ASHPs use much more refrigerant than other heat pump options. ASHPs also use field installed fittings and piping that do not have the same quality control as factory installed fittings. Refrigerants used in these systems, such as R-410A, have high Global Warming Potential (GWP), contributing significantly to climate change when leaked. The GWP of R-410A is 2,088 times greater than CO2. This means that one pound of refrigerant lost has the same impact as discharging over a ton (imperial) of CO2. Refrigerant leaks can cancel out years of CO2 reductions from any type of heat pump and is especially problematic for mini-split or commercial VRF systems because they use much more refrigerant than other types of heat pumps.
Geoexchange systems, which house most components indoors and have fewer refrigerant connections exposed to the elements, are less prone to refrigerant loss. Typical GSHPs have all or nearly all refrigerant fittings installed at the factory. By reducing the likelihood of refrigerant leaks, Geoexchange systems contribute to a lower overall environmental footprint. As of this writing (September 2024), the GSHPs sold by my company have nearly all been converted to refrigerant R-454B. Currently, all mini-split ASHPs continue to use R-410A. R-454B has a lower Global Warming Potential of 465. This is a notable improvement. Achieve looks forward to even lower Global Warming Potential refrigerants being used at some point in the future.
For a more detailed discussion of Refrigerants and Associated Risks, Click Here
5. Potential for Networked Geothermal Systems
Networked Geothermal/Geoexchange Systems use a centralized ground heat exchanger and distribution piping to connect multiple buildings. The networked configuration has two notable advantages: First, buildings without space for a ground heat exchanger can take advantage of Geoexchange by connecting to a network. Second, if there is diversity in the types of buildings and heating and cooling requirements connected, there can be greater efficiency or a need for a smaller ground heat exchanger. An additional advantage is that this ‘geothermal utility’ can be operated by the Community or a municipal utility, reducing reliance on large regional utilities.
Networked Geoexchange is growing in Massachusetts. Achieve Renewable Energy designed and installed the ground heat exchanger for Plummer Youth Promise on Winter Island in Salem. This Networked Geoexchange system is the largest on the North Shore and will service all the buildings on Plummer’s expanded campus, providing all the heating, cooling, and domestic hot water. Achieve is also conducting a feasibility study for St. Peter’s Episcopal Church in Salem under a grant funded by the Massachusetts Clean Energy Center and administered by HEET. The study is evaluating the connection of a variety of buildings in the vicinity of Church, St. Peter’s, Federal and Charter Streets in Salem. The study is expected to be completed in late 2024. Both of these projects may help foster further discussion of Networked Geothermal in Massachusetts.
For a more detailed discussion of Networked Geoexchange Systems, Click Here
