Before the foundations were cast or the first piece of structural steel was laid for the new teaching and research building on the campus of UMass Medical School in Worcester, work began on a system of geothermal heating and cooling that will reduce the building’s greenhouse gas emissions by 55 percent compared to meeting its HVAC needs exclusively with the campus power plant.
Geothermal systems work by circulating water through loops of pipes buried deep in the ground. The heart of the new building’s geothermal system is a network of 75 boreholes, each six inches in diameter and 500 feet deep, drilled into the bedrock beneath the campus lawn. Water flowing through a closed loop pipe system through these holes will help heat and cool the new building. Drilling began on July 1 and is expected to continue throughout the summer. Once completed, the entire system of boreholes and pipe loops will be buried deep under the grass.
âThis is an important sustainability milestone for the Worcester campus,â said John Baker, associate vice chancellor for facilities management. âThis is a big step towards achieving our long-term decarbonization goals. “
The campus power station will supply electricity to the new building. The plant will also help meet peak heating and cooling demands during the winter and summer months. Over the course of one year, the geothermal system will provide 88% of the heat for offices, laboratories, and educational and public spaces, and 50% of the building’s cooling needs.
If the new building were served exclusively by the campus power plant, it would generate around 3,000 tonnes of greenhouse gas emissions per year. The geothermal system will reduce this carbon footprint by 1,660 tonnes per year, according to an energy analysis of the building carried out by engineering consultants BR + A.
The new building’s geothermal system will surpass the latest building codes ‘stretch’ for energy efficiency and is aligned with the goals for new public buildings expressed in State Executive Decree 594 âLeader by Example: Decarbonize and minimizing the environmental impacts of state government âreleased by Governor Charlie Baker on April 22.
Technically referred to as a hybrid ground source heat pump system, the technology works on the same principle as a window mounted air conditioner that blows air through tubes filled with pressurized refrigerant to cool the air in a room and send hot air outside. Now imagine if this window air conditioner sat on a turntable and could be turned on demand, so that the cold air blows outside and the warm air blows into the house. This is essentially how ground source heat pumps will heat and cool the new building.
A window air conditioner transfers heat from the ambient air in your home. A geothermal system transfers thermal energy stored in the ground. Once you reach a depth of a few meters, the soil remains at a constant temperature, around 50 degrees in our region, all year round. This is one of the reasons why a home’s basement is cooler than the upper floors, even on the hottest days of summer.
The constant level of heat underground – 50-degree soil, rock, or even the air holds a lot of heat – is picked up by water flowing through U-shaped pipes cast in each of the 75 boreholes. Hot water flows through the building and then returns to be cooled in the ground.
The holes are 500 feet deep to give the water enough time in the soil to exchange heat. Seventy-five boreholes are required to provide sufficient water for the system.
A drilling rig will use an impact head to move rock and soil. The hole will be lined with steel casing and water pumped through while drilling to bring soil and rock to the surface. The U-shaped pipe will be lowered and secured in place with a special grout designed to efficiently conduct heat energy.
A network of horizontal pipes will connect the boreholes to a series of heat pumps in the building. Water from the boreholes will flow through one side of the heat pumps, while a second closed loop water system will flow through the other side of the heat pumps, to carry chilled or heated water upwards.
Nestled between each of the closed water loops is a compressor coil filled with a refrigerant that exchanges heat. Higher pressure in the coil increases the temperature. Lower pressure in the coil cools the water.
Each heat pump will have reversing valves, capable of changing the heat exchange flow back and forth. Almost every day, some areas of the building will need heat and others for cooling to maintain proper temperatures. The flexibility of the system allows some heat pumps to be in heating mode, while others operate in cooling mode, at the same time.
âThe constant temperature of the ground is like having a head start to heat the building and a cooler to cool it,â said Suzanne Wood, Associate Director, Sustainability and Campus Services. âWith relatively little electricity input to power pumps and compressors, it keeps the building in good balance and dramatically reduces the need to burn fossil fuels. “
Related article on UMassMed News:
Beginning of excavations for a new teaching and research building