
A year after doing my DHW heating efficiency test, I've had the opportunity
to replumb my radiant heat system to get the most efficiency possible from my
Ground Source Heat Pump (GSHP). Since
a GSHP efficiency depends on the temperature of the water it's delivering, this
page just documents the Radiant Heat side, and attempts to calculate the actual
efficiency of the system.
Test Procedure.
Here are the results: Electrical Load:
Water Temperatures:
Water Pressure:
Analysis: First I'll determine the actual GSHP efficiency, then I'll calculate the overall Radiant Heat system efficiency. Heat Extracted: This is an allimportant number, it indicates how much
heat is being extracted from the ground loop. This can be calculated based
on the water flow rate and temperature drop across the Source Heat
Exchanger. Flow rate can be determined by measuring the pressure drop
across the heat exchanger and then using lookup tables. My measured
pressure drop was 5.2 psi, which extrapolates to about 7.5 GPM based on the
chart above. Heat extraction can be calculated as GMP * Temp Diff. *
500. Electrical Load. This is now easy to determine with the new
watt meter. However, some numbers do need to be subtracted from the
indicated power load. There are two sourceside circulator pumps which
each draw 420W (1.75A @ 240V), and two load side circulator which each 84W (0.7A @ 120V). This is also a minimal housekeeping load of
48W from other devices. Heat Capacity: Water Furnace assumes that in addition to the heat
extracted from the source water loop, the electrical energy consumed by the heat
pump is also converted into heat and fed into the load fluid, so the total Heat
Generated is HE + (KW * 3.413). Coefficient Of Performance: COP is defined as: Heat Energy
Generated divided by Electrical Energy Consumed. Expressed in BTUH this
would be HC / (KW * 3.413). So in the final analysis my system seems to be performing at about par with
what should be expected.
This site is all about building a cool, energy efficient house, that makes maximum use of earth sheltered design, passive solar heating and cooling, geothermal exchange energy management, and right sizing of the house for it's designated use. The home's placement is on a southfacing hillside in Deep Creek Lake, Maryland. This site describes the design process, the technologies used and the expected results. We also have a comprehensive Links Page for anyone who is also interested in designing a similar project. 