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abogart · 02-13-12, 09:34 AM

I might have messed up the numbers in the HP calculations. Since the specs on the given HP didn't include electricity usage at each temp, I divided the kW heat output at each outdoor temp by the COP to find the kWh power usage. I was looking at the specs on a Goodman 4 ton HP (found here) today. They give the amp draw at various outdoor temps. Using this to determine kWh energy usage, I found this unit to be a few cents cheaper per hour on the high stage than my gas furnace is at outdoor temps down to 10°F. Either this unit is more efficient for heating, or I just didn't use the right numbers on the first one. The payback period would be something like 17 years (rough estimate) at this rate, but at least I'd feel better about using a greener and more efficient source of heat. This doesn't account for varying daily and seasonal temperatures either. I'm sure that on the warm winter days when the outside temp does creep up around 35-40, I'd see much cheaper heating with the HP. Not to mention that replacing the outdated, undersized AC unit with a higher efficiency unit will save a good chunk of change on summer cooling.

02-13-12, 09:34 AM	#5
abogart Efficiency Afficionado Join Date: Jan 2012 Location: Michigan, US Posts: 68 Thanks: 21 Thanked 6 Times in 4 Posts	I might have messed up the numbers in the HP calculations. Since the specs on the given HP didn't include electricity usage at each temp, I divided the kW heat output at each outdoor temp by the COP to find the kWh power usage. I was looking at the specs on a Goodman 4 ton HP (found here) today. They give the amp draw at various outdoor temps. Using this to determine kWh energy usage, I found this unit to be a few cents cheaper per hour on the high stage than my gas furnace is at outdoor temps down to 10°F. Either this unit is more efficient for heating, or I just didn't use the right numbers on the first one. The payback period would be something like 17 years (rough estimate) at this rate, but at least I'd feel better about using a greener and more efficient source of heat. This doesn't account for varying daily and seasonal temperatures either. I'm sure that on the warm winter days when the outside temp does creep up around 35-40, I'd see much cheaper heating with the HP. Not to mention that replacing the outdated, undersized AC unit with a higher efficiency unit will save a good chunk of change on summer cooling.