wsexton1,
Welcome to the conversation!
A GSHP, consists of three systems:
- a ground-coupled system
- a heat pump system
- a heat exchanger (HX) system
All heat will come from the ground-coupled system.
The heat pump facilitates the extraction of the heat.
The HX system will make the heat available in the house.
The proper way to begin is to assess the maximum heating needs of your house. This need will be expressed in various ways, in the US, it is expressed as BTU/hour. This will usually be on the coldest night of the year. It is actually a bit more complex, but this is a good place to begin.
From that starting place, the next step is to design a ground-coupled system that is capable of supplying heat at that maximum rate. The design will be based on well-understood principles, and will include some testing to assure that the design is actually correct.
The next step is to design (or select) a proper heat pump. The compressors are rated in BTU/hour (in the US), so the compressor is selected based on the maximum heating need of the house. The heat pump will have two HXs in it, so the HXs will be selected to match the compressor's input & output. Again there is a bit more to it, but this is a good starting point.
The last step is to design the system that will bring the heat into the house. In your case, you mentioned that there was some radiant system already installed. The radiant system will be designed to match the output from the heat pump. It is very important to understand that most previously designed radiant underfloor heating systems use fossil fuel, are designed for supply temperatures in the 140F to 160F range. GSHP systems will supply heat in the 100F to 120F range, so a fossil fuel system will not provide the heat rate you seek.
Quote:
Originally Posted by wsexton1
...I currently have an 85m closed loop borehole in my property...
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There are very many factors involved here, that need to be known before an educated guess is possible. But, knowing absolutely nothing about your closed loop bore hole, other than "85m", I will take a guess that has almost no basis in fact, and estimate that it could be capable of around 12,000 BTU/hr, maybe a bit more, possibly less.
Quote:
Originally Posted by wsexton1
...and some underfloor heating circuit laid.
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Again, is the underfloor circuit built for fossil fuel temperatures or for GSHP temperatures? It may or may not be very useful to you.
Quote:
Originally Posted by wsexton1
I was basically wondering how you went about determining the size of your ... other circuit pumps?
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These would be based on the heat needs, which would dictate flow rates, and also pipe length, diameter, etc.
So, these decisions are based on many interdependent considerations, and a proper design would proceed approximately as I indicated, and then final results would be carried back to the beginning, and rechecked for feasibility, and changes made until a final design emerges.
Please understand that my outline is highly simplified to give you the overall idea, and that many other important considerations enter in to a realistic design.
I don't know if you read the entire
Homemade Heat Pump Manifesto, but much of the information you seek is there.
Also there are some excellent threads on
DIY radiant floors on the EcoRenovator site.
I hope this has been useful to you.
Best,
-AC_Hacker