Scott Houser is a maintenance foreman with the Fairbanks North Star Borough School District. He was an integral part of Weller heat pump installation and is currently maintaining the system to ensure it works correctly. In this video he briefly discusses how the heat pump at Weller is used to heat ventilation air.
Read on to find out more about how the ground source heat pump at Weller School works…..
What do we use to help store our food and keep it cool? A refrigerator! A refrigerator works by taking heat from its interior (where the food is) and moving it outside. The heat comes off the coils located behind the refrigerator and goes into the room.
A heat pump is like a refrigerator, except instead of moving heat away from the food inside it, a heat pump moves heat into a building. A Ground Source Heat Pump (GSHP) like the one at Weller gets this heat from the ground. The soil outside has a fairly steady temperature all year (for information on the temperature of the soil around Weller, check out the Ground Temperature page).
Pipes buried in the ground are filled with fluid that brings heat to the heat pump. In September 2010, workers buried pipes underground at Weller School. These pipes are arranged in slinky coils and make up the heat pump ground loop.
The ground loop at Weller consists of 6 trenches, which are about 100 feet long. In each trench is nearly 1000 feet of pipe arranged in coils. That’s over a mile of pipe buried underground! Three of the trenches are 8 feet deep, and the other three are 12 feet deep. All of them are buried behind the school on the south-facing hill. After the loop was buried, the pipes were filled with fluid to transfer the ground’s heat to the heat pump. The fluid is a mix of water and ethylene glycol, a chemical that keeps the water from freezing in the winter. A circulating pump located next to the heat pump forces the fluid to go through the pipes in the ground and then brings it back to the heat pump. As the fluid goes through the loops underground, it gets warmer because the temperature underground is higher than the temperature of the fluid when it leaves the heat pump. When the fluid comes back to the heat pump, it brings the warmth with it.
There are pipes that connect the ground loop to the heat pump. They travel through the ceiling of a classroom to a utility room on the second floor, where the heat pump is located. It sits next to fans that bring in fresh air, air filters, and the storage area for Christmas decorations.
The pipes in the classroom ceiling are white because they are covered in insulation. The temperature of the fluid is colder than the classroom, even after it has been warmed by the ground loop. The insulation prevents condensation from occuring on the pipe surface. There are 2 pipes-one takes fluid outside to the ground loop, and the other pipe brings fluid inside to the heat pump.
There is one more really cool feature of the Weller heat pump system: Weller School has solar panels that are used to help warm the soil. Fairbanks doesn’t have very much sun in the winter time, but in the summer, there is lots of sun. The Weller GSHP has extra pipes that can be opened to allow the ground loop fluid to travel through the solar panels on the roof of Weller School to gain additional heat in the summer. When the GSHP is not needed to heat the ventilation air (such as during the summer) the ground loop fluid can transfer the heat it gains in the solar panels to the soil. Engineers are hoping that this extra heat in the summer will help the ground to stay warm year after year as the heat pump operates. Scientists at CCHRC are watching the ground temperatures to see if this will be true!