Every person, theoretically, is in favor of the idea of a greener planet. Eco-friendly, sustainable, and net zero are all buzz words seen throughout environmentally conscious markets. It makes sense, right? Use a reusable bag at the grocery store, turn off the water when you’re brushing your teeth, recycle. But what does green living mean in terms of building or the actual construction of a building?
This is where geothermal energy comes in. Geothermal energy is thermal energy generated and stored in the Earth. Using the concept of geothermal energy in a building allows for greener heating and cooling opportunities in a home or workspace.
How does a Geothermal System work?
The best way to explain this is with an example courtesy of Craig Fishbach, of Daikin Applied, during his time on the How Great Buildings Work podcast. Craig explained his take on geothermal systems, “I can kind of relate it to a refrigerator. So, a refrigerator keeps the goods inside cold. But it also, on the back of the refrigerator, has to get rid of heat. That is what we call the heat of rejection. So, we’re just lucky enough to find the reversing valve where we can operate this water-cooled air conditioner in the cooling mode, generating the cold air, and we have to reject the heat to the water loop in that cooling mode. Then the reversing valve just switches it. Instead of rejecting the heat to the water loop, now we’re going to reverse the evaporator and the condenser and we’re going to take this heat rejection and move it over to the indoor evaporator coil. Now we can heat the air. Then at the same time, while we’re heating that air, the waterside is getting colder. It’s kind of one of those thermal dynamic rules. We have the ability to reverse the heating and cooling direction of the unit based on space demand. When we’re cooling, we’re rejecting heat and when we’re heating, we’re absorbing heat from the water loop.”
Now that we have an understanding of how a geothermal system works, it’s important to understand that these systems often rely on a loop system so as not to lose valuable water or air. In his interview with JM Engineering founder, John Melvin, Craig mentioned that there are basically three loop systems:
- The first is an open loop, often referred to as a pump and dump. Craig gave a great Florida type application example, “Way back in the 80s they had a need for air conditioning. So, someone took one of these water to air heat pumps and hooked it up to some groundwater and pumped that water out of the ground and ran it through the heat pump unit in the heat rejection mode. So, they pulled 75-degree water out of the ground and dumped it at 10 degrees higher. We rejected heat out of the heat pump and now we’re at 85 degrees. That gave us the ability to cool the air.”
- The second loop is a closed loop. This loop was designed by figuring out how to configure plastic pipe to the Earth, and how to get the right amount of heat rejection out of that plastic piping. The goal was to build it into a loop and not have that environmental danger of dumping the water into the ground or into a pond. This closed loop system is more environmentally safe than an open loop.
- The last system is referred to as a hybrid loop. This loop is designed to have a closed loop geothermal system, but cooling dominance. So, a little bit less loop is used and supplemented with heat rejection with a closed circuit of APP cooler or a cooling tower. Craig Fishbach suggested that this hybrid is the most common of the three loop systems used today.
The next important question is one of Efficiency.
We asked Craig how much more efficient a geothermal system is than a traditional HVAC system. He told us, “Somewhere in the area of 25% more efficient. We typically see 25% to 35% energy savings with a closed loop geothermal system. A simple payback depending on the building size, etc., I would say anywhere from 5 to 10 years on a payback. However, the bigger buildings would actually do like a 20-year life cycle cost. So, 20 years would be an approximate life expectancy of a water source heat pump unit itself.”
What’s the moral of this story?
Geothermal systems allow for greener, more sustainable buildings.
The best part is that JM Engineering specializes in these geothermal systems and has helped multiple architects utilize this system in new construction.
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