A heat pump uses a combination of low-temperature ground heat and electricity to provide heat to a building. A higher input temperature to the heat pump (from the ground loop) will cause the heat pump to operate more efficiently. A more efficient heat pump uses less electricity to deliver the same amount of heat. The efficiency of a heat pump is called the coefficient of performance, or COP. The COP for heat pumps range from 1, not very efficient, to 5 or 6, very efficient. In Fairbanks an estimated COP would probably be around 3. That means for every unit of electrical energy that the heat pump uses it delivers 3 times the amount of heat to a building. For example, if the heat pump uses 10 kilowatt hours (kWh) of electricity, it will output 30 kWh of heat. The COP is calculated by dividing the heat energy delivered by the heat pump by the electrical energy into the heat pump. For the Weller heat pump the equation look like this:
At Weller, we are trying to make the ground loop temperature hotter by using 6 solar panels to pump solar heat into the ground during the summer. Then in the winter the heat pump will draw heat from the ground into the school’s air handling system. The graphic below shows how the parts of the system are connected together. The connecting pipes are red and blue and the connecting data wires are dashed grey lines.
The heat pump system parts are spread out around the school. The ground loop is buried on the south side of the school, where the ground receives the most heat from the sun. The heat pump itself is in the fan room, which is on the third floor of the school (around the ceiling of the gym). The solar panels are on the south side of the roof. In the video below, Robbin Garber-Slaght explains how the fluid from the ground loop is warmed in the solar panels in the hybrid heat pump system. Robbin is an engineer at the Cold Climate Housing Research Center, and is monitoring the electrical and temperature data from the heat pump at Weller.
We are monitoring the heat pump so we can understand how well it works. What we learn at Weller will help the school district decide how to make schools more efficient in the future. You can see how the heat pump is working by checking some of the data points in the building.