EcoRenovator - View Single Post

abogart · 02-27-12, 09:10 AM

I just plugged the numbers from a Water Furnace geothermal heat pump in to the mix. Factoring in open loop with a shallow well pump and 50°F entering water temp, the numbers are disappointing. Efficiency does beat out everything else... until I factor in the 1.2kW for the well pump running constantly to supply 11GPM of water to the thing. At that point it is more expensive to run than my current 80% gas furnace. In fact, a 4 ton ASHP at 25°F OAT still beats out the rest by a few cents per hour.

Looks like it might just be a good idea to eventually replace the central AC with a decent HP and set it up to run only when the outside air is at a decent temp. There's really no major benefit to modifying my current system, other than the need to replace the old AC unit, which we don't use much anyway.

Edit: I didn't account for the cost offset of using the discharge water for things like lawn watering in the warmer months. However, we don't use the AC unless ABSOLUTELY necessary in the summer, and I really wouldn't have the need to water the lawn when it's 45°F outside and the unit is not running much for heating anyway.

02-27-12, 09:10 AM	#12
abogart Efficiency Afficionado Join Date: Jan 2012 Location: Michigan, US Posts: 68 Thanks: 21 Thanked 6 Times in 4 Posts	I just plugged the numbers from a Water Furnace geothermal heat pump in to the mix. Factoring in open loop with a shallow well pump and 50°F entering water temp, the numbers are disappointing. Efficiency does beat out everything else... until I factor in the 1.2kW for the well pump running constantly to supply 11GPM of water to the thing. At that point it is more expensive to run than my current 80% gas furnace. In fact, a 4 ton ASHP at 25°F OAT still beats out the rest by a few cents per hour. Looks like it might just be a good idea to eventually replace the central AC with a decent HP and set it up to run only when the outside air is at a decent temp. There's really no major benefit to modifying my current system, other than the need to replace the old AC unit, which we don't use much anyway. Edit: I didn't account for the cost offset of using the discharge water for things like lawn watering in the warmer months. However, we don't use the AC unless ABSOLUTELY necessary in the summer, and I really wouldn't have the need to water the lawn when it's 45°F outside and the unit is not running much for heating anyway. Last edited by abogart; 02-27-12 at 09:15 AM..