Quote:
Originally Posted by doug30293
Based on ARI ratings for several heat pumps I looked at it appears that 1/2 ton up on the evap coil is good for one point on the SEER scale. This seems to be the standard approach between 14 and 15 SEER.
I could not find any evidence that one ton (two sizes) up on the evap coil results in further improvement. Perhaps 1/2 ton is the edge of diminishing returns.
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This is in reference to the indoor coil in an air handler. With a heat pump, oversizing the indoor coil too much will kill your supply air temperature. Instead of 120 degF air coming out of registers, you will have 110 degF air, which feels "not so hot". Efficiency may rise a smidgen, but the overall "warmth" provided may be seen as diminished by the average user. Not a good thing to most.
What we are talking about here is the outdoor unit heat exchanger being oversized. With the correct refrigerant metering scheme, heat transfer will be increased. This will lead to increased mass flow through the compressor, and higher discharge temperature and pressure. Indoors, this leads to increased condenser temperature and pressure in the air handler, and increased supply air temperature at the registers. Perceived "warmth" effect will be increased regardless of whether you change the indoor coil or not.