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Old 12-30-20, 01:55 PM   #3
jeff5may
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So with an understanding of the overall heat pump refrigeration cycle, I will focus on the geothermal/ground source end of the system.

With a ground loop based system, the two main things that contribute to heat flow are surface area and temperature difference. With a conventional (glycol, alcohol, water, etc.) based system, the refrigerant exchanges heat through a refrigerant to water hx. The liquid is then pumped through the ground loop. This leads to a reduction in system efficiency due to the reduction of delta temperature between both the refrigerant to fluid and the fluid to ground loop. Also, a circulation pump must be employed to move the heat transfer fluid.

With a DX system, the refrigerant flows through the plumbing directly through the ground loop. Much like a passive solar system, the heat is radiated directly through the plumbing and into or out of the ground. In this heat transfer method, the main limit to heat flow is the immediate temperature of the ground. Since dirt or rock has a relatively low ability to absorb or release heat compared to the pipe, we have localized gradients forming in the ground and this heat travels slowly.

Historically, in general, the HVAC industry seeks to minimize the system that contains pressurized refrigerant. Copper, bronze, aluminium and other metals cost more than a circulation pump, so the vast majority of manufacturers build a refrigeration loop that's "inside the box". This also leads to a smaller mass of refrigerant in the loop, which both simplifies troubleshooting and reduces cost. With a water to water system, the pump controls for both sides, and sometimes one or both pumps are in the same box as the heat exchangers and compressor.

Last edited by jeff5may; 12-30-20 at 02:35 PM.. Reason: Information
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