There are several heat pumps manufactured that are capable of producing 130°F (55°C) water, and some even produce water as hot as 145°F (63°C). There are projects that require water this hot, but on most projects it's possible to design a distribution system that can heat the building with much lower water temperatures, and to make changes on existing buildings that will allow the use of much lower water temperatures.
The efficiency of a heat pump is directly related to temperature difference between the heat source (where you're getting the heat from) and the heat sink (what you're using the heat for). And the difference in efficiency can be significant. The following graph illustrates the difference in efficiency based on the temperature difference between the heat source and heat sink.
The coefficient of performance (COP) of a water to water heat pump when there's temperature difference of 80°F (44°C), highlighted by the blue bar, is about 2.9. When the temperature difference is 50°F (28°C), highlighted by the orange bar, the COP increases to 4.5...an increase of 69%.
As an example, if you design a distribution system that requires 120°F (49°C) and the GHX temperature to the heat pump is 40°F (4°C), the temperature difference is 80°F (44°C)...and the COP is approximately 2.9. If you design the same system in which the water temperature distributed to the building is 90°F (32°C), the temperature difference is 50°F (28°C) and the COP increases to 4.5. Same heat pump...more appropriate distribution system...greatly increased operating efficiency.
Paying attention to the whole system...the GHX, the mechanical equipment and the distribution system...pays dividends in overall system efficiency. It improves system efficiency and improves the owners return on their investment. There are additional benefits to designing a system with a smaller temperature lift that I'll talk about another day.
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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