flyingcow
Veteran Member
Rob,
How much oil you use a year to heat your house? And how much$$$'s is your electric bill?
How much oil you use a year to heat your house? And how much$$$'s is your electric bill?
Re-thinking geothermal
- Thread starter Rob-D
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AHNC
Gold Member
I would suggest that you look at minisplit heat pumps. You will not get the same COP as a water source but you will be very close. As well, with your radiant heating you will find the mshp the ideal compliment. No matter how you try to control it radiant is best when you have a substantial load against it. The lead/lag issue on slabs is a problem in the shoulder seasons, the mshp will do better than the radiant in that condition. Go to miniheat.com and run a few numbers. Pay particular attention to the table showing the hrs/yr at a temp. Buy it for the heating efficiency as, in the north, itis there that you get your return on investment. As well, you get very high effiency cooling/dehu. I must include this disclaimer. I represent Fujitsu in New England, but I use them as suggested in the home I just sold in Feb and the home I'm moving into.
leonz
Super Member
Hey Rob,
Another option is building a deep pond and lining it to hold water and then running loops of black PVC and securing the loops down with cinder blocks to hold them down in the deep water for you.
The deep pond will take up less time digging but you need to buy a good pond liner.
Another option is building a deep pond and lining it to hold water and then running loops of black PVC and securing the loops down with cinder blocks to hold them down in the deep water for you.
The deep pond will take up less time digging but you need to buy a good pond liner.
KennyG
Elite Member
I think the original poster has the correct take on the issue. If the ground is only 42 deg, it's not going to be too efficient on heating. However, I'm really surprised that it would be that cold at 6 ft down. To get a good measurement, you have to excavate, bury a probe, fill and compact and then wait for it to stabilize. If you measure the exposed earth after you excavate, I would doubt that it's a good reading.
It would defeat your advantage in doing your own work, but vertical shafts seem to be the preferred way to go these days. Drilling costs are way down in a lot of areas and a few 100 ft. deep boreholes will provide the heat sink.
It would defeat your advantage in doing your own work, but vertical shafts seem to be the preferred way to go these days. Drilling costs are way down in a lot of areas and a few 100 ft. deep boreholes will provide the heat sink.
buckeyefarmer
Epic Contributor
In my area, 5' deep trench is adequate. You can make up for depth with more loop. The difference for me from 6' to 5' deep was about 20' more of pipe per loop, which is probably cheaper than digging the extra foot.
GHP are also 4-5 to 1 as efficient as straight electric coil heat.
Search some of the other threads on Geothermal that have been posted here.
GHP are also 4-5 to 1 as efficient as straight electric coil heat.
Search some of the other threads on Geothermal that have been posted here.
Brad_Blazer
Veteran Member
You have it pretty mixed up in this post. Electricity is high quality energy. You can convert it directly into heat at 100% effficiency at as high a temperature as your materials can withstand. The temperature difference from a resistance element in the duct to the air in the duct will self regulate to transfer all of the energy to the air as long as there is enough air flow to prevent the elements from burning up.
Electricity can also be converted into work with high efficiency. The work can run a heat pump which pulls ADDITIONAL energy from a low temperature heat source into your home. Any efficency losses convert work into heat which is still utilized as output. The WORST result you can get from a geothermal heat pump is a COP of 1 which is the same as resistance heat at 100% efficiency. ( A conventional air source heat pump could possibly get less since the compressor is outside where it may lose some heat to ambient) The temperatures you listed should yield a COP of at least 4 which means for every KW of electrical power you get 13,650 BTU/hr of heat ransfer (4x3413).
That still doesn't mean it makes economic sense but I just wanted make sure you understand that a geothermal heat pump will always outperform resistance heat.
schmism
Super Member
your not understand the geothermal system correctly
you dont take the 45 deg fluid in the ground loop and move the temp of that fluid all the way to 110 deg which you then blow air over to make heat.
you use electrical compressor to move the energy from one "side" to the other.
just like you dont try to cool 95 deg summer hot outside air into 65 deg cold air for inside the house.
its the differential between the 2 temps that you need to move.
so say your house is at 65 and you want to move it to 70... you need to "find" 5 deg of energy.
you could "find" 100% of that energy in pure electricity (in the form of resistive heat)
you could "find" a 100% of that energy in burning a fuel (like coal, wood, natural gas or fuel oil)
or you could "find" that energy in another fluid and simply move it from fluid A to fluid B (were A is the ground loop fluid, and fluid B is the air in your house)
it is the compressor that does the work to move the energy from fluid A to B.
The result is a function of which way you run the circuit. in the winter you make fluid A colder and fluid B warmer... exactly opposite in the summer
while there is an efficiency to worry about when you consider the min/max fluid temps (of either side of the system) i dont think its that significant between 55 and 45 deg ground temps. I may be a mechanical engineer but im not one that designs geothermal systems.
While its great to think you save half or more on the cost of project (which i dont deny is a real possibility especially if doing the ground loop labor yourself)
your obvious lack of understand on how the system works gives me serious concerns that you would know enough of what your doing to have a successful install. at which point you've botched a 10-15K install.
My advise is to talk with a few more contractors and find one to properly explain how the system works and work a deal to allow you to do some of the install work to save on the install price.
you dont take the 45 deg fluid in the ground loop and move the temp of that fluid all the way to 110 deg which you then blow air over to make heat.
you use electrical compressor to move the energy from one "side" to the other.
just like you dont try to cool 95 deg summer hot outside air into 65 deg cold air for inside the house.
its the differential between the 2 temps that you need to move.
so say your house is at 65 and you want to move it to 70... you need to "find" 5 deg of energy.
you could "find" 100% of that energy in pure electricity (in the form of resistive heat)
you could "find" a 100% of that energy in burning a fuel (like coal, wood, natural gas or fuel oil)
or you could "find" that energy in another fluid and simply move it from fluid A to fluid B (were A is the ground loop fluid, and fluid B is the air in your house)
it is the compressor that does the work to move the energy from fluid A to B.
The result is a function of which way you run the circuit. in the winter you make fluid A colder and fluid B warmer... exactly opposite in the summer
while there is an efficiency to worry about when you consider the min/max fluid temps (of either side of the system) i dont think its that significant between 55 and 45 deg ground temps. I may be a mechanical engineer but im not one that designs geothermal systems.
While its great to think you save half or more on the cost of project (which i dont deny is a real possibility especially if doing the ground loop labor yourself)
your obvious lack of understand on how the system works gives me serious concerns that you would know enough of what your doing to have a successful install. at which point you've botched a 10-15K install.
My advise is to talk with a few more contractors and find one to properly explain how the system works and work a deal to allow you to do some of the install work to save on the install price.
Redneck in training
Elite Member
Heat pump (the key word is pump) doesn't generate heat. It "pumps" large amount of low level heat to smaller amount of high level heat. The smaler is the temperature rise the higher is the efficiency. Typical geothermal heat pump has efficiency about 400% to 450%. In other words every kW os electric power will pump about 4 kW of heat. Some large units (MW size) have much greater efficiencies.
Another thing to consider is selection of the HP for your climate. There is a difference between heating a swimming pool in Florida and heating house in Canada.
Another thing to consider is selection of the HP for your climate. There is a difference between heating a swimming pool in Florida and heating house in Canada.
sawduster98
Silver Member
FWIW...when I built my place here in western NY and it came down to installing a heat system I chose geo. I overbuilt the house in terms of insulation and windows and was able to use a 2 ton forced-air system with 2 285' loops. Since an excavator was already on-site it only cost me an additional $480 to dig the trenches. The geo system cost $15k and the ductwork an additional $2k. I also use the system to preheat my hot water. The whole house is electric only. I didn't look at this project in terms of a pay-off period as I'd have to install some kind of heat regardless and quotes I got for high-end propane furnaces were around $10k + $2.5k for A/C. With geo, A/C comes 'free'.
First year results: took a little getting used to and getting everything tweaked in but the worst month total elec bill was $258 in Jan keeping the house at 71 degrees.
What I never counted on was the decrease in my homeowners insurance. Since I have no "ignition sources" in the house, my rate decreased dramatically ($200/yr).
First year results: took a little getting used to and getting everything tweaked in but the worst month total elec bill was $258 in Jan keeping the house at 71 degrees.
What I never counted on was the decrease in my homeowners insurance. Since I have no "ignition sources" in the house, my rate decreased dramatically ($200/yr).
eepete
Platinum Member
Great comments here!
An interesting aspect of geo is that the numbers are more constant. The outside temperature just affects heat loss of your house, and very little the temperatures the heat pump has to work with. As such, one should be able to figure out the:
1) Cost to install a system (be it simple resistive electric or geo)
2) Cost to operate the system.
Since you know the desired output temperature, and have the ground temperature (input temp), the manufacturer of any geo system should be able to get you a power consumption number. It's a little harder to turn that into a "dollars per month in the heating season". I suspect that as long as you are consistent in these approximations you'll have an apples to apples comparison.
The one piece of data you're missing is what is the temperature of the water with a well based system. Perhaps there is someone local to your area has this answer. You can then get power consumption for both the ground loop and well loop systems and see what 10 to 15 degrees warmer water would really mean for you.
Redneck in training's comments about the low cost of simple resistive electric vs. the high cost of geo really draws a focus on the payback period (or if you like, "pay me now vs. pay me later").
Sawduster's comments points out the importance of the cost difference of the systems being looked at in addition/in stead of just the "big cost of geo". Of course, one has to have the up front funds in the first place. It's all about the increase in installed cost of the system vs. the decrease cost of operation. The devil's in the deltas.
Like many financial decisions, wouldn't it be nice to know how much longer you had to live to help with this choice.... After all, some people define a perfect financial life as one where the check to the mortician bounces :laughing:.
When there is just too much information, you have to simplify. I think you can get the installed costs OK. As for the operating costs, I'd try to come up with a BTUs you need, perhaps your current oil consumption will get you close. Now you have your system installation costs, and your operating costs. I'd ignore the possibility (certainty?) of increased electricity costs. In your case, it's much less of an issue and even for the grid dependent, rising cost just work in your favor but should not be counted on.
I'm making a subjective post here, but one last comment. When people get granite counter tops or a bonus room added to their house, they don't go through this "payback period" calculation like they do with HVAC systems. The reason is it adds to the value of the house. If you go the resistive electric with payback period of some number of years, when you go to sell your house it has less value than if it has an efficient heating system. Yes, this is a "Do I fly first class or do my heirs fly first class" problem. None the less, the house that has all of it's decisions based on "pay me later" (a.k.a the "typical" builder spec house) has less value 20 years down the road than one with more insulation and a more efficient HVAC system. My parents 4000 sq ft house that was built in 1960 was just torn down. It was too expensive to heat and cool, and it had a lot of "Deferred maintenance issues" with it. When the house sold 40 years after it was built, it was sold for $50K. It had little value. I fly coach a lot...
I know this doesn't solve your technical evaluations, but I hope it can help you focus on a few numbers, and focus on your personal long term goals and that will help you decide. Yep, I drone on like an inefficient heat pump...
Pete
An interesting aspect of geo is that the numbers are more constant. The outside temperature just affects heat loss of your house, and very little the temperatures the heat pump has to work with. As such, one should be able to figure out the:
1) Cost to install a system (be it simple resistive electric or geo)
2) Cost to operate the system.
Since you know the desired output temperature, and have the ground temperature (input temp), the manufacturer of any geo system should be able to get you a power consumption number. It's a little harder to turn that into a "dollars per month in the heating season". I suspect that as long as you are consistent in these approximations you'll have an apples to apples comparison.
The one piece of data you're missing is what is the temperature of the water with a well based system. Perhaps there is someone local to your area has this answer. You can then get power consumption for both the ground loop and well loop systems and see what 10 to 15 degrees warmer water would really mean for you.
Redneck in training's comments about the low cost of simple resistive electric vs. the high cost of geo really draws a focus on the payback period (or if you like, "pay me now vs. pay me later").
Sawduster's comments points out the importance of the cost difference of the systems being looked at in addition/in stead of just the "big cost of geo". Of course, one has to have the up front funds in the first place. It's all about the increase in installed cost of the system vs. the decrease cost of operation. The devil's in the deltas.
Like many financial decisions, wouldn't it be nice to know how much longer you had to live to help with this choice.... After all, some people define a perfect financial life as one where the check to the mortician bounces :laughing:.
When there is just too much information, you have to simplify. I think you can get the installed costs OK. As for the operating costs, I'd try to come up with a BTUs you need, perhaps your current oil consumption will get you close. Now you have your system installation costs, and your operating costs. I'd ignore the possibility (certainty?) of increased electricity costs. In your case, it's much less of an issue and even for the grid dependent, rising cost just work in your favor but should not be counted on.
I'm making a subjective post here, but one last comment. When people get granite counter tops or a bonus room added to their house, they don't go through this "payback period" calculation like they do with HVAC systems. The reason is it adds to the value of the house. If you go the resistive electric with payback period of some number of years, when you go to sell your house it has less value than if it has an efficient heating system. Yes, this is a "Do I fly first class or do my heirs fly first class" problem. None the less, the house that has all of it's decisions based on "pay me later" (a.k.a the "typical" builder spec house) has less value 20 years down the road than one with more insulation and a more efficient HVAC system. My parents 4000 sq ft house that was built in 1960 was just torn down. It was too expensive to heat and cool, and it had a lot of "Deferred maintenance issues" with it. When the house sold 40 years after it was built, it was sold for $50K. It had little value. I fly coach a lot...
I know this doesn't solve your technical evaluations, but I hope it can help you focus on a few numbers, and focus on your personal long term goals and that will help you decide. Yep, I drone on like an inefficient heat pump...
Pete