by Shane Henson — October 26, 2011—Building owners seeking an innovative way to reduce energy costs may benefit from using hybrid ground-source heat pumps (GSHP). According to a recent report from the U.S. Department of Energy (DOE), Hybrid Ground-Source Heat Pump Installations: Experiences, Improvements and Tools, compared to ground-source heat pump systems, new hybrid systems offer more financial and environmental benefits.
DOE, Alliant Energy, and Madison Gas & Electric co-funded the study, which analyzed operating data from three working hybrid GSHP systems. The Energy Center of Wisconsin, with assistance from the University of Wisconsin Solar Energy Laboratory, observed two hybrid systems in Las Vegas, Nevada and one in Madison, Wisconsin for one year to examine hybrid GSHP in climates with different heating and cooling needs. In all three cases, the hybrid design was effective in comparison to other HVAC system designs. The study validated hybrid systems as a cost-effective alternative to traditional ground-source heat pump systems.
According to the report, all GSHP systems have benefits such as saving money and reducing fossil fuel usage. In standard GSHP systems, also known as geothermal heat pumps, a large underground heat exchanger made from a loop of plastic pipes is buried or drilled into the ground. A fluid circulates through the pipes, to move heat between the in-ground heat exchanger and a heat pump, which regulates building temperature. The upfront installation cost for this underground loop is significant, up to half the cost of the entire system, but necessary to achieve the desired temperature levels.
With the hybrid system, the size of the underground loop is drastically smaller, making drilling less expensive and less invasive. To compensate for the smaller loop system, conventional technology (such as cooling towers or boilers) is used to meet a portion of the peak heating or cooling needs. Balancing the load of the GSHP with traditional HVAC equipment lowers up-front costs, while still providing the energy efficiency of a GSHP. This study showed that due to typical building load fluctuations, the standard equipment runs so infrequently it doesn’t substantially reduce the energy savings.
