The earth absorbs 50% of the sun’s energy, making the earth itself the best solar collector!  Rather than trying to harness geothermal energy radiating out of the center of the Earth, a Ground Source Heat Pump (GSHP) draws on the solar energy banked in the first ten feet underground.  Just below ground, temperatures remain constant, regardless of air temperatures above. We use this constant temperature to supplement the heat a building requires.  

A ground source heat pump moves heat stored in the ground or a lake into a building. Just like it sounds, a heat pump pumps heat from one place to another. 

In 2010, ACES’ installed a heat pump at Hallam Lake. Instead of using heat banked in the ground, we use heat banked in our lake. We pump hundreds of gallons of water from the lake at 48ºF through our heat pump. We take a little bit of heat out each gallon of this water.  The water that returns to the lake is only a few degrees cooler at 45ºF.   So we’ve taken a little heat from many gallons, which adds up to plenty of heat.  Water flows through a network of pipes in our radiant floor at 110º, heating the interior of the building.  The 3º of heat from the lake supplements the 110º water in the pipes.  

How does the heat pump actually work? It’s like your refrigerator. In the fridge, the goal is to move heat away from your food to keep it cool. Heat is transferred outside the refrigerator.  Food stays cold in the fridge because of a chemical called refrigerant. Refrigerant allows matter to change state: from a liquid to a gas or vice versa. The phase change between liquid to gas is the magic behind how we move heat. As a liquid, refrigerant absorbs heat from inside the fridge. Then it vaporizes into a gas and the refrigerator cools. This is the same as when your sweat cools you as it evaporates from your forehead. The refrigerant flows to the back of the refrigerator, carrying the heat it absorbed, and then expels it outside. So a heat pump is the opposite of a refrigerator: a refrigerator moves heat out while a heat pump moves heat in.  

Since GSHPs are four times more efficient than a traditional forced air heating system,  the heat pump reduces Hallam Lake’s energy demand by 67% annually. 

Many thanks to Resource Engineering Group for providing the expertise to set up our system, as well as the generosity of CORE, the Environment Foundation, The Ruth Brown Foundation, and an anonymous donor.