Re-thinking geothermal

[SpringHollow]

For most of the winter, the temperature will be warmer as you go deeper. I am not sure about the accuracy of your numbers. Maybe it has not warmed up yet that deep in the Spring. You might need to go deeper than 6'.

Ken

 

[Rob-D]

For most of the winter, the temperature will be warmer as you go deeper. I am not sure about the accuracy of your numbers. Maybe it has not warmed up yet that deep in the Spring. You might need to go deeper than 6'.

Ken

Ken,
Things start to get messy once you get below 6' and the expense goes up logarithmically.
The two estimates I got both came in over $6k per ton, both with me doing the excavating.
I measured the (NTC) thermistors resistance and they are matched. I taped them to a stick with markings so that I could maintain exact depth and distance between the sensors.
One more note, I went out after about 24 hours and the temp had stabilized at below my original readings but did not go below 42F.

It's simple math, 1 KWh will give you 3412.12 BTU's. You can get it from a heat pump or an electric element in your boiler but the efficiency difference isn't much.

If I had a ground temp of 56F that would change things drastically but we don't and I've seen 30 below here.

The other thing is the electric to run the compressor, it's not cheap.

The numbers don't look good for geo but I'll wait until the PE gets back to me with his figures and answers my inquires.

Thanks for your ideas and responses.
Rob

 

[oldnslo]

Living on the Illinois, Wisconsin I knowof two families that went geothermal on their new homes. They both buried their lines 13 to 15 ft deep to purposely stay in warmer soil. Frost level around here is figured at 42". Both of these homes where built on 40 acre parcel of land so space was not an issue.

This family had their own excavators so I do not know what the cost was for them to install. The one home is approximately 3500 square feet so I suspect on a home that large the pay off would happen sooner than on an average sized home of 1200 - 1500 square feet.

The oldest one has been is service for 4-years and the owner has been very pleased with how it is working. he was looking at doing a complete system flush and refill so will see what his cost is for that.

Roy

 

[tommu56]

How did you measure the temp in the tench?

I would have drilled back from the face about 2 -3 ft under undisturbed soil to remove the variable of radiation of the temp in the tench.

The other way I would have checked it was to drive a ground rod in the ground 6-8' and take the measurement at the bottom.

Have you looked at having a "dry" well drilled and put the pipes in the well(s) that is how a friend did his with 3 well's about 100' deep in series and back to the unit in the basement.

 

[Rob-D]

Thanks for your comments but I think you're both missing the point. Geothermal is a closed loop system with the ground temperature being higher than the ambient outside temperature in winter and lower in summer.
That's all well and good but we still have to convert that temperature difference to heat regardless of how we do it. The greater the difference the greater the energy expended to reach the final temperature.

With two systems both being closed loop, one running off geothermal and the other off a heating element in the boiler, the one with the lowest temperature differential will use the least amount of energy.

The first question I'm asking is how can a system that costs anywhere from 15 to 30k compete with a system that uses a 15 dollar heating element from Home Depot? The payback is tremendous.

Secondly, even if my measurement system is incorrect by 5F, which it isn't, I will still be better off with the heating element because the temperature differential is lower than the geo ground temp regardless what source or method I use to capture it.

Rob

 

[flyingcow]

This has been a good thread. Geo thermal, or just a straight heat pump have a cost. If you live in the west, where KWH costs are usually lower, it makes it more attractive. We run about 15cents a KWH. Now, throw in the option for A/C in the summer, which isn't such a necessity up north. Not sure what your costs would be for electricity in NY. But if you were off grid, can you generate enough juice to run the system?

Kind of a ramble, but it's what i do best.

 

[Redneck in training]

I have 4.8 kW (5 ton ?) geothermal unit in my house. The heat exchanger are five "fluffed coils" in the pond. The thermostat on heat accumulator is set to 90F for heating and 34F for cooling. The unit is supposed to produce 18.5 kW of heat. I measured the temperature of inlet liquid to the heat exchanger to be at extreme winter about 34 F. The reason I have the thermostat set to only is that at extreme low winter temperature the unit can maintain only about 90 F but our house is still nice and warm. So my conclusion was that there is no need for higher temperature set point.

The guy who installed the pond loop for me has a drill for installation of the ground loops with only very limited trenching. The trajectory of the drill is set such a way that it emerges above ground in desired location. The drill head is removed and two parallel hoses connected at the far end by a U joint are hooked up to the drill and pulled back underground. Since the drill follows circular path the big part of the tube is much deeper than 6ft. The drill head is powered by a hydraulic motor fed by drilling polymer. The polymer lubricates the tubes when they are pulled back and also provides thermal contact to the surrounding material.

 

[Kyle241]

The first question I'm asking is how can a system that costs anywhere from 15 to 30k compete with a system that uses a 15 dollar heating element from Home Depot? The payback is tremendous.

Secondly, even if my measurement system is incorrect by 5F, which it isn't, I will still be better off with the heating element because the temperature differential is lower than the geo ground temp regardless what source or method I use to capture it.

Rob

Agreed. Looked at Geothermal prior to starting my build two years ago and the numbers did not jive for me. The cost I received from three quotes was $32-35k turnkey and I just could not swallow that at the time. While I like the idea, that cost on top of all the other 'green' building methods I was using ended up too high so GT was dropped.

Good luck, I hope you get your answers as I am always interested in other people's successes with energy efficient solutions.

 

[fowllife]

With two systems both being closed loop, one running off geothermal and the other off a heating element in the boiler, the one with the lowest temperature differential will use the least amount of energy.

The first question I'm asking is how can a system that costs anywhere from 15 to 30k compete with a system that uses a 15 dollar heating element from Home Depot? The payback is tremendous.

Secondly, even if my measurement system is incorrect by 5F, which it isn't, I will still be better off with the heating element because the temperature differential is lower than the geo ground temp regardless what source or method I use to capture it.

Rob

You are on the right track. Maybe my first post wasn't very clear, but in my opinion you will probably be better off with an electric boiler ($115 dollar H.D. heating element) then with geothermal. Your 42* ground temp at your limiting depth of 6' is too low to really pay off. The electric boiler seem to be your only real option since you are already locked into radient floor heat. You would still need a chiller for A/C though, or a heat pump set up for water. If you power company charges more for peak demand, or you want to limit your power usage a hybrid system may also work, electric/wood/gas/oil. The electric demand will be high on a cold windy night if you are 100% electric. A decent PE or HVAC guy should be able to tell you your options & run an energy calc on your house and give you an approx. power usage.

 

[Rob-D]

You are on the right track. Maybe my first post wasn't very clear, but in my opinion you will probably be better off with an electric boiler ($115 dollar H.D. heating element) then with geothermal. Your 42* ground temp at your limiting depth of 6' is too low to really pay off. The electric boiler seem to be your only real option since you are already locked into radient floor heat. You would still need a chiller for A/C though, or a heat pump set up for water. If you power company charges more for peak demand, or you want to limit your power usage a hybrid system may also work, electric/wood/gas/oil. The electric demand will be high on a cold windy night if you are 100% electric. A decent PE or HVAC guy should be able to tell you your options & run an energy calc on your house and give you an approx. power usage.

Thanks for the advice.
I think you see where I 'm going.
I understand the benefits of a heat pump and that extracting the heat from the pipes through expansion of gas is very efficient. My question is that, with the temperature of my ground being so low whats the break point where the efficiency of the heat pump is cancelled buy a heating element in the boiler?