How do we design a geothermal system to the exact energy needs of the home?

Video transcription follows:

What we’re looking at is identifying the amount of equipment we need, and corresponding earth connection, that will deliver back the heat that is lost per hour on the coldest winter day. We identify that by every material that is the house is built out of how many square feet, is there an exposed foundation outside, how many doors and windows there are, what is the national weather data, and we feed that all into a piece of software that spits out a calculation that says “Ok, the living room needs this much on the coldest day, the main part of the house needs this much on the coldest day, the upstairs needs this much” and that tells us, collectively, what the whole house needs. Then, once I know how much equipment I need to serve X number of BTU’s in the winter and the summer, that dictates how much earth coupling I need.

One of the biggest issues that we find with geothermal applications in new england is that people don’t always put in the ideal amount of earth coupling. They will often try to save money on the install, which is absolutely understandable, and they’ll say “well, you need this much for the equipment to run like it was in the laboratory when it got that rating of X, but gee, that’s really expensive, and I know that you want me to try to save some more money, so I’ll shorten up that line a little bit.” The earth connection, whether it’s a loop or an open system, like it is in this system, is a permanent radiator in the ground and that radiator has to be matched and have the right amount of capacity to serve X amount of heat pump tonnage. So if I undersize that radiator, that system may still run, especially when it’s not really really cold, or really really hot, but as you get closer and closer to that capacity day, that earth connection is going to become less and less thermally effective because it’s smaller than it needs to be.

So, one of the big things that water energy is known for among our contractors is that we’re very square headed about that design. When we provide design support, whether it’s through heat loss calculation, or to size the earth coupling that’s associated with that heat loss, we tend to be like “Look, yeah, we could do it for that, but your not going to get that result that your unit promises because you have departed from the temperatures of exchange that they used in a laboratory when they rated that unit. So that’s really the critical piece for us.