Eric Swartz
9th June 2017, 13:18
Hi,
I'm considering implementing a geothermal-type heat pump system for a non-geothermal application in my home. Instead of a vertical or horizontal loop system, using a thermal water tank as a thermal battery. The engineering is sound on paper but I wanted to see if anyone else out there has heard of this.
Problem:
1. my home has an out-dated electric forced air furnace supplemented with an under-sided woodstove which is rated for 1250 sq feet. Electricity costs about $250/month for the coldest 3 months of the year, plus another $250 worth of firewood (one cord).
2. its in Western Washington with 1600 sq feet surrounded by 10 acres of forest.
3. The small house heats up pretty quick with a woodstove but nursing the fire more than once a day is too much time. Takes a good hour to start getting the house warm and we have toddlers running around and its one more thing to monitor.
Proposed Solution:
Install a new over-sized woodstove, a thermal water reservoir and split geothermal heat pump/electric system. When the house is above 70 degrees the air conditioner kicks on and cools the home while transferring the extra heat into the thermal water reservoir (which is basically a large hot water tank with no heating coils).
The whole system gets its energy from the woodstove while the thermal water reservoir is warm and then automatically switches over the electricity (as a normal split-system).
1. 6pm make dinner and start the woodstove. Burns for 3 hours.
2. When the air temp surpasses 70 the AC kicks-in transferring extra heat from the air into the water tank. This continues for a couple hours til 9 or 10pm.
3. at 10pm the fire dies down and the house temp actively cools to 55 packing that additional 15 degrees into the thermal water tank, making sleeping nice and cool.
4. At 7am the thermostat turns back on the heat pump and it pulls energy out of the thermal reservoir and preheats the house without having to make any fires.. allowing me to be on-time for work but waking up to a pre-warmed house.
Why not a wood furnace or boiler?
Because monitoring and dealing with loading wood in the back of the utility room isnt nice. Also, the direct warmth of a woodstove in the livingroom in winter is very nice and the forced air system intake is 6 feet from the woodstove, thus circulating the hot air right into the heat pump system.
Why not real geothermal?
Because I dont have $40,000 to pay for drilling or installing a loop field and if I did I'd use it elsewhere. The cost doesn't justify cost savings for my smallish home.
Size of thermal reservoir?
Water's thermal energy density is about 800 times more than air. The 13,000 cu. ft. house would require about 20 cu. ft. of water to heat it to the same temperature once. Largish hot water tanks can hold about 80 gallons so that would be enough to bring the entire home up to temp from 50F to 70F four times (as the water in the tank drops from 70F, 5 degrees each time down to 50F).
Has anybody heard of others doing this? Math checks out and it should be all standard equipment. Why aren't others doing this yet?
Less time tending wood fire
Wood heating for me is free
Automatically heats up the home in the AM and maintains with standard thermostat
Automatically cools home in summer or when woodfire over heats home
Electric split system kicks in whenever needed
Wood backup if power goes out (just cant utilize heat pump)
Expandable to heat pump water heater later on
Expandable thermal reservoir tanks if needed
Expandable to solar thermal roof system if desired
Cost is only standard split heatpump/electric system plus thermal water tank.
-Eric
I'm considering implementing a geothermal-type heat pump system for a non-geothermal application in my home. Instead of a vertical or horizontal loop system, using a thermal water tank as a thermal battery. The engineering is sound on paper but I wanted to see if anyone else out there has heard of this.
Problem:
1. my home has an out-dated electric forced air furnace supplemented with an under-sided woodstove which is rated for 1250 sq feet. Electricity costs about $250/month for the coldest 3 months of the year, plus another $250 worth of firewood (one cord).
2. its in Western Washington with 1600 sq feet surrounded by 10 acres of forest.
3. The small house heats up pretty quick with a woodstove but nursing the fire more than once a day is too much time. Takes a good hour to start getting the house warm and we have toddlers running around and its one more thing to monitor.
Proposed Solution:
Install a new over-sized woodstove, a thermal water reservoir and split geothermal heat pump/electric system. When the house is above 70 degrees the air conditioner kicks on and cools the home while transferring the extra heat into the thermal water reservoir (which is basically a large hot water tank with no heating coils).
The whole system gets its energy from the woodstove while the thermal water reservoir is warm and then automatically switches over the electricity (as a normal split-system).
1. 6pm make dinner and start the woodstove. Burns for 3 hours.
2. When the air temp surpasses 70 the AC kicks-in transferring extra heat from the air into the water tank. This continues for a couple hours til 9 or 10pm.
3. at 10pm the fire dies down and the house temp actively cools to 55 packing that additional 15 degrees into the thermal water tank, making sleeping nice and cool.
4. At 7am the thermostat turns back on the heat pump and it pulls energy out of the thermal reservoir and preheats the house without having to make any fires.. allowing me to be on-time for work but waking up to a pre-warmed house.
Why not a wood furnace or boiler?
Because monitoring and dealing with loading wood in the back of the utility room isnt nice. Also, the direct warmth of a woodstove in the livingroom in winter is very nice and the forced air system intake is 6 feet from the woodstove, thus circulating the hot air right into the heat pump system.
Why not real geothermal?
Because I dont have $40,000 to pay for drilling or installing a loop field and if I did I'd use it elsewhere. The cost doesn't justify cost savings for my smallish home.
Size of thermal reservoir?
Water's thermal energy density is about 800 times more than air. The 13,000 cu. ft. house would require about 20 cu. ft. of water to heat it to the same temperature once. Largish hot water tanks can hold about 80 gallons so that would be enough to bring the entire home up to temp from 50F to 70F four times (as the water in the tank drops from 70F, 5 degrees each time down to 50F).
Has anybody heard of others doing this? Math checks out and it should be all standard equipment. Why aren't others doing this yet?
Less time tending wood fire
Wood heating for me is free
Automatically heats up the home in the AM and maintains with standard thermostat
Automatically cools home in summer or when woodfire over heats home
Electric split system kicks in whenever needed
Wood backup if power goes out (just cant utilize heat pump)
Expandable to heat pump water heater later on
Expandable thermal reservoir tanks if needed
Expandable to solar thermal roof system if desired
Cost is only standard split heatpump/electric system plus thermal water tank.
-Eric