ANALYSIS OF UNDERGROUND THERMAL ENERGY STORAGE FOR GREENHOUSE HEATING: CASE STUDY OF AN ORGANIC DAIRY FARM IN NEW HAMPSHIRE, USA

One strategy for reducing the reliance on fossil fuels is to utilize waste heat for other useful purposes, such as space heating. The strategy of underground thermal energy storage (UTES) has been widely adopted in Europe and has been getting increased attention in the US in recent years. Industrial, agricultural, and co-generation facilities often have waste heat that has the potential to be stored and used, offsetting the need for fossil fuels.

This study investigates the feasibility of using waste heat generated from an aerobic compost facility at the University of New Hampshire’s Organic Dairy Research Farm as an economical means to extend the growing season of a greenhouse. Smith (2016 UNH PhD dissertation) reports that the compost facility has the potential to produce 80,000 BTUs per hour throughout the year, a thermal equivalent of approximately 5,000 gallons of fuel oil.

We investigate the feasibility of storing the waste heat in the bedrock via a set of vertical boreholes, each with a double u-tube ground loop heat exchanger, and extracting the stored heat via a connected geothermal heat pump. The heating load is modeled using hourly outdoor air temperature and solar insolation data obtained from the National Renewable Energy Laboratory. Heat storage and flow in the subsurface is simulated using the solute transport model MT3DMS, which has been shown to efficiently model subsurface heat flow due to the mathematical similarities between solute and heat transport. Preliminary results suggest that UTES can be an effective strategy to utilize waste heat and extend the growing season of a greenhouse.

Implementation of UTES to use waste heat from other sources could potentially further increase the availability of locally grown produce without increasing the use of fossil fuels.