Someone asked me a number of years ago "Where do you start when someone comes in the door asking you to design a GCHP system for their new building?" I couldn't come up with an immediate answer for him. I felt kind of like my grandmother probably did when someone asked her for the recipe for the muffins you just enjoyed. It didn't come out of a recipe book. She had baked them so often, and in so many different situations, that if she didn't have one ingredient, she knew exactly what she could substitute and how it would work out. So where do you start with a GCHP system?
Once I'd had a chance to think about it, I realized that there was a process that a good designer followed, but I'd never seen it written down anywhere or heard anyone verbalize it. After thinking about it and talking to a number of system designers, a description of the process started taking shape. Start with a solid understanding of the amount of energy that the building will need to extract from or reject to the ground. Once you have a good understanding of the building loads, you realize it's possible to change the building loads by working with the building design team...change the glass, lighting, ventilation air strategy, roof construction...a lot of things that can be changed. You can change the loads to make the GHX work more efficiently with less pipe in the ground.
You also begin to realize that there's not much you can do about the site and the geology. They are what they are. You can't change them. You can test the ground and you can change the configuration of the boreholes or trenches you put in the ground...but you can't change it. You have to deal with it the way it is.
Once you know the loads and understand the ground you have to work with, you can play with the mechanical system that will be connected to the GHX. The design of the system schematic and distribution system will have an impact on the energy loads to and from the ground. As a designer, you make the equipment selections and design the distribution system based on the loads and ground you have to deal with.
After that, you have to communicate the design to the contractors building the system and ensure it's installed the way it was intended. Once it's installed, the building owner or operator needs to understand conceptually how a GCHP system operates. That's it's not simply connected to an infinite energy source in the way a conventional HVAC system is connected to a gas line. They need to realize they are working with what is, in effect, a rechargeable battery that should be monitored to ensure the system is working as intended.
These systems are not complicated, but they are different than a conventional system. The design approach is different and how the building is run after it is built is different than a conventional system, but the payback can be impressive.
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In my blog I'll be expressing my opinions about what I've the learned about ground coupled heat pump (GCHP) systems over the last 30 years. I've been very fortunate to work with many interesting people who are passionate about this technology...engineers, geologists, mechanical contractors, drillers, excavation contractors...in different parts of the world. I've learned a lot from them and will be using this forum to pass on some of the things I've learned and feel are important. Please feel free to use this information if you feel it's worthwhile...hopefully you can avoid some of the same mistakes I've learned from.
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