Geothermal energy?

[NeilBlanchard]

Greetings,

If you drill a well, you can use the water with a heat pump to both heat and cool your house. Example: 3600sq ft house in Nova Scotia (well insulated, but not "super insulated") cost just $68 to heat for the whole winter!

You can realize similar savings if you need to use it for A/C as well. The 54-55F ground and ground water are the perfect heat source and heat sink. The heat pump only has to do a little bit of work, because of this.

MIT has developed a way of "drilling" very deep holes (7-8 miles!) so the Earth's heat can be used to make steam, which can be used to generate electricity. So, you can have Iceland's (or New Zealand's, or Yosemite's) type of geothermal power (just about) anywhere on Earth.

Both of these are "true" geothermal energy.

[IndyIan]

diesel_john,
Do you heat with your pond system as well in the winter? How's the efficiency then?

I've lots of horror stories with heat pumps and geothermal but as other people have said here its all in the installation. We have 130' well and then a 100' run into the house and the variation of water temperature is huge from winter to summer. The 100' run is well below the frost line but its definitely colder in the winter and warmer in the summer so I'm always doubtful about trench installations. All these systems work on temperature difference so the closer the air temp and your input temp get the less efficient it gets.

The other stories I've heard is people just pumping water out of a well and running it through a heat exchanger and then dumping it! Ground water is not an unlimited resource and unless you have some fancy system to get it back into the ground(which is probably illegal anyways) most of it will be evaporated. In many areas the groundwater takes 100's or 1000's of years to recharge.

Also I call B.S. on this.

Example: 3600sq ft house in Nova Scotia (well insulated, but not "super insulated") cost just $68 to heat for the whole winter!

Is it a summer home with passive solar and someone kept it a 3 Celcius all winter? That is like me selling woodstoves as free heat*

*If you have free wood...
Ian

[NeilBlanchard]

Hello,

You would either pump the water back down the well (above the intake), or you can have a second well to do this, or you could have a leeching field.

The example I gave was from my brother, who stayed in that very house (they run it as a B&B). So, it is a real number. To corroborate it, I used to work in an office condo (back in the late 80's) that had this type of system, and the heating bill was ~$100 a winter.

I'm going to be doing more research on this -- my mother needs a new heating system, and she is very interested. We could even put a small PV solar panel on her house to offset the electricity use.

This works on the same principle as a refrigerator: the heat pump is able to move/concentrate heat very easily with the temperature of ground water.

[Otto]

Keep in mind that water is ~800 times denser than air, so the latent heat in 1 cubic foot of ground water at ~50 degrees F has vastly more energy than 1 cubic foot of ambient air at 25 degrees F. So, much less water is needed to supply a given amount of heat.

My lot has a very fortunate location, at the foot of a hill and on a lake. The natural subsurface flow of the ground water is downhill to the lake, so the groundwater comes for free, courtesy of gravity. No need for a pump or well, although immersing a heat exchanger in the lake would work almost as well, although the lake water is colder in winter than the groundwater.

Regardless of the source of heat or air conditioning, it is vital to have a well insulated house, which will then need less heat from any source than a drafty house.

[diesel_john]

[QUOTE=IndyIan;28580]diesel_john,
Do you heat with your pond system as well in the winter? How's the efficiency then?

The COP (heat) is about 4. You get 4 kw of heat for every 1 kw the pumps use. Plus the household water heating is off the desuperheater which is much more efficient than an electric water heater. A bigger hot water tank for storage is helpful.
Mine is in the ordering parts stage. I won't be complete till end of summer.
I just went to a meeting last week.

General rules of thumb (but your mileage could vary greatly) on the loops. I only considered close loops because of scaling problems in open loop. (water quality?)

vertical wells: 200'-300' per ton, 150' deep. 10' apart. $1000-3000 per well.

horizontal trench: 300'-600' per ton, 8' deep. up to $4000 per ton

pond minimum 1/2 acre, 8' deep. 300'+ per ton. If your going to let the tubes get covered with silt then more tubing is required. Slinky lay out more tubing. Wholesale on the tubing is about a $1/ft. for 3/4". Fittings are special heat fuseable plastic. No metal parts in the ground.

300' generally max. loop length.

What i am curious about is how much heat will the pond store into Fall and how much cooler will the pond be next spring into the AC season?

[IndyIan]

Diesel_John
I am impressed on your energy return from a pond, does the surface not freeze in the winter? Water is least dense at 4C and so the colder denser water goes to the bottom. I have to admit I don't fully understand how these things work but I thought 1 or 2C water and -5C air temps wouldn't be very good for pumping heat around. But what do I know? I'm just a neandertal wood burner

Neil,
I would love to see the specifics of how they are heating for $68 a winter, spread over 5 months, thats $13.60 a month, I don't think a forced air furnace fan for a large house can be run for that much. Plus how can they even see that on their electric bill? especially for a variable usage business.
Maybe if they went from an old crappy forced air system with the fan on all the time, to a new hydronic system with on demand circulator pumps, I might believe there bill only went up $68, but thats different than $68 outright.

Using Diesel_john's figures of 4 to 1 return on input, assuming electric heat costs $200/month(this is dreaming in my area, realistically $400-600 or more) for a house, that still gets us down to $50/month, which is a fantastic deal for sure.

Really, to compare systems we need to see cost per btu at specific temperatures. Even my woodstove becomes less efficient in cold temps as I'm drawing in air from somewhere to make up what's going out the chimney.
Ian

[dremd]

Originally Posted by IndyIan

diesel_john,


The other stories I've heard is people just pumping water out of a well and running it through a heat exchanger and then dumping it! Ground water is not an unlimited resource and unless you have some fancy system to get it back into the ground(which is probably illegal anyways) most of it will be evaporated. In many areas the groundwater takes 100's or 1000's of years to recharge.

That is the method used around me, I've had more than one business try and sell it to me, when I mentioned loops (which they would imply I dreamed up) they had no clue what I was talking about. <- Probably my reason for confusion on this thread. . . .

[diesel_john]

Originally Posted by IndyIan

Diesel_John
I am impressed on your energy return from a pond, does the surface not freeze in the winter? Ian

(heating)The COP of 3.7 to 4.2 assumes 32 degree entering fluid.
(cooling)The EER of 17 to 24 assumes 77 degree entering fluid.
My pond did not freeze over last winter for more than a few hours, because i have a wind powered air pump which pumps air under the ice. The column of bubbles coming up lifts/melts the ice. It tends to make the whole pond the same temperature, i don't know if it adds energy to the water or just brings up warm water from 20 feet down. But during the day which absorbs more heat from the sun water or ice? So maybe the sunlight adds more heat than the cold air takes away. I have read that air pumps should be turned off in the winter in geothermal applications. Because the bottom of the pond could freeze around the tubing reducing the heat transfer. I think moving water might prevent that. I am thinking it would be tough to get 0.9 million gallons of moving water down close to 32 degrees F. This pond has twice as much surface area in common with the ground as it does with the air.

[diesel_john]

Energy Feasibility
Cost of 1 million Btu's from different energy sources in my area.
elect. 293kw @ $0.10= $29.30
" " " $0.06=$17.58
natural gas 90%eff. 11.1 therms @ $1.378Ccf=$15.69
LPG 90% 12.1 Gals. @ $2.25=$33.97
#2 oil 80% 8.929 Gals. @ $4.00=$35.71
air to air heat pump COP of 1.7, 172.4kw @ $.10=$17.23
geothermal heat pump COP of 4, 73.25kw @ $.10=$7.32

3413 BTU/kw
NG 100,000 BTU/Therm
LPG 91,800 BTU/Gal
#2 140,000 BTU/Gal

[IndyIan]

Originally Posted by diesel_john

Energy Feasibility
Cost of 1 million Btu's from different energy sources in my area.
elect. 293kw @ $0.10= $29.30
" " " $0.06=$17.58
natural gas 90%eff. 11.1 therms @ $1.378Ccf=$15.69
LPG 90% 12.1 Gals. @ $2.25=$33.97
#2 oil 80% 8.929 Gals. @ $4.00=$35.71
air to air heat pump COP of 1.7, 172.4kw @ $.10=$17.23
geothermal heat pump COP of 4, 73.25kw @ $.10=$7.32

3413 BTU/kw
NG 100,000 BTU/Therm
LPG 91,800 BTU/Gal
#2 140,000 BTU/Gal

You forgot wood.
White Oak 28.2 Million BTU per cord, $200/cord cut and split
Mixed hardwood 22 Million BTU per cord, $80/cord in logs

Assuming a 66% efficiency woodstove gives a cost of;
$10.75 per million BTU for white oak
$5.50 per million BTU for mixed hardwoods requiring your labour.

I am impressed that the geothermal heat pump beats processed firewood, someday when I get tired of, or unable to do firewood we will have to look into it.

I have never dropped a thermometer down the ice fishing hole but its my understanding that the whole lake is basically at the same temperature, if any water is significantly warmer it rises to the surface, gets cooled and drops again. But your system assumes this and still get the 4 to 1 return which is fantastic. I suspect a woodstove is a little bit cheaper to install but they are definitley not for everyone or all houses.

The way I figure is that I have 100 acres of natural solar collectors so I might as well use the free energy and its fun playing lumberjack once in a while too.
Ian