A geothermal system connects buildings and pumps hot and cold water to heat and cool them.
A condenser water system operating at relatively low temperatures presents an attractive opportunity for air-to-water heat pump (AWHP) integration because of the reduced temperature lift required for efficient operation.
The Eversource Networked Geothermal Pilot Project in Framingham, Massachusetts, is a first-of-its-kind, utility-scale demonstration that tests using a shared geothermal energy network to provide low-carbon heating and cooling to multiple residential, commercial and municipal buildings. The system connects the buildings through a common ambient temperature hydronic loop.
Three borefields are positioned throughout the loop to exchange heat between the ambient loop and the ground. Multiple water source heat pumps, including both water-to-water and water-to-air, are installed at each connected building to exchange heat with the ambient loop and provide heating and cooling to each building. Condenser water is delivered to each heat pump between 30° and 90°F.
The ambient loop main distribution pumps and associated hydronic equipment are housed in the main pump house. The pumps control the flow through the ambient loop to maintain the temperature of the loop. For added resiliency, Eversource decided to include an electric boiler in the design to provide emergency heating capacity. Future taps for air-source heat pump chillers were also included in the design to provide emergency cooling capacity along with additional heating capacity (see Figure 4).
As a pilot project, it is important for Eversource to be able to respond to an emergency and maintain heating and cooling services to their customers. By using an AWHP, the system can provide redundant heating and cooling capacity and the reliability of the entire system is increased.
This project demonstrates how integrating AWHP technology with an ambient temperature loop can enhance system resilience while supporting long-term electrification and decarbonization goals.
