About 400 gallons/yr and about $60.00 a month electric bill. (400~500 KWh)
10.7 cents a KWh.
Re-thinking geothermal
- Thread starter Rob-D
- Start date
- Views: 13358
About 400 gallons/yr and about $60.00 a month electric bill. (400~500 KWh)
10.7 cents a KWh.
You can't have a COP over 100% unless you found the magic bullet.
Thanks for the comments everyone!
Well, too my surprise I just worked some numbers to see if I could get a ball park figure.
Here's what I came up with:
During the deep winter I timed my oil furnace to see what the use was. The furnace is about 105 BTU's and it runs from 12 to 15 minutes on the hour when it's sub zero out. So roughly that's 25K BTU's an hour.
With an electric element in the boiler I can get 3,400 BTU's per 1 KWh and that equates to ~7.4KWh x 24 hr/day x 30 days/month = ~ $500.00 a month to run the place with an electric element in winter. The geo is 3.9 times more efficient (from my PE guy) than the heating element so 500/3.9 = ~$130 a month with geo. (not bad, it really surprised me!)
I just got the cost from my excavator and with a geo system I can buy on the net I can be up and running for about $7,000.00 give or take after the gov. gives me back 30%. If I'm saving 500-130 = $370 a month for 3 to 4 months that comes to about $1200-$1500 a year plus I get AC in th summer and if I run hot water an extra benny there too.
Bottom line I'm paying back in 5 to 6 years going with the geo and that's not accounting for the 6.8KW grant for PV that's going in this summer which will take a big chunk out of the geo electric cost. Essentially I'll be heating my house for free or pennies a month after a few years along with getting money back on my intertie in the summer. So the geo looks like it's good so far.
The thing that makes it is the geo's 3.9 to 1 over the element.
Thoughts?
Rob
Well, too my surprise I just worked some numbers to see if I could get a ball park figure.
Here's what I came up with:
During the deep winter I timed my oil furnace to see what the use was. The furnace is about 105 BTU's and it runs from 12 to 15 minutes on the hour when it's sub zero out. So roughly that's 25K BTU's an hour.
With an electric element in the boiler I can get 3,400 BTU's per 1 KWh and that equates to ~7.4KWh x 24 hr/day x 30 days/month = ~ $500.00 a month to run the place with an electric element in winter. The geo is 3.9 times more efficient (from my PE guy) than the heating element so 500/3.9 = ~$130 a month with geo. (not bad, it really surprised me!)
I just got the cost from my excavator and with a geo system I can buy on the net I can be up and running for about $7,000.00 give or take after the gov. gives me back 30%. If I'm saving 500-130 = $370 a month for 3 to 4 months that comes to about $1200-$1500 a year plus I get AC in th summer and if I run hot water an extra benny there too.
Bottom line I'm paying back in 5 to 6 years going with the geo and that's not accounting for the 6.8KW grant for PV that's going in this summer which will take a big chunk out of the geo electric cost. Essentially I'll be heating my house for free or pennies a month after a few years along with getting money back on my intertie in the summer. So the geo looks like it's good so far.
The thing that makes it is the geo's 3.9 to 1 over the element.
Thoughts?
Rob
KennyG
Super Member
COP is always over 100% (1.00). The mistake in the previous post was calling it "efficiency". COP is a measure of how much heat can be moved with a given input of energy, so it isn't limited to 1.00. It depends on the thermodynamic cycle being used. While the "efficiency" of the heat pump (how much energy is being put into the working fluid from the energy of the pump) is less than one, that is not directly related to how much energy is moved to or from the heat source to the heated/cooled space.
Chilly807
Elite Member
Rob,
To be frank, I think you're over thinking the efficiency question. As of today, to the best of my knowledge (we have a geo system) there is no more efficient readily available mechanical way to heat a home than with a geothermal heat pump. Period.
The numbers of 300 to 400 % efficiency are correct. For every kilowatt you put into the system, you get 3 to 4 out in the form of heat. Colder climates drop efficiency based on the ground temperature. We're in Nova Scotia, and as I recall our ground loop temperature is comparable to yours.
The drawbacks are simple. You have a fairly complex heating system, with pumps, heat exchangers, compressors, etc. Those are neither simple nor cheap to repair or replace.
The $25k price tag seems high to me. Our's is a 3 ton turnkey system using radiant heat in the floor (single story, 2100 sq foot slab on grade construction, no basement). No AC. We have three 6 foot deep trenches holding 3500 feet of 3/4 geothermal specific piping laid out in "slinkies".
Our total cost including excavation was 20k CDN three years ago. By total, I mean total, it was new construction so everything is included, even the floor piping.
It cost us 5-6k more than any comparable heating system, which I expect to recover in the first 5 years.
Now, whether it makes sense or not is where different variables come into play. If you're staying in that house for at least 5 years, re-sale value, insurance costs, etc, are all factors. Your pay-off time may vary, but if you're in it for the long run, you'll come out ahead in my opinion.
It's costing me roughly half what I used to pay in heating costs for my old house, which was oil-fired forced air heat. The kicker is, the new house is almost double the size of the old one, and it's heated to the same degree 24/7 instead of morning and evening with the old house.
We burn some wood as well to reduce our cost even more, but the numbers are for pretty much sole use of the heat pump, with recreational use of the wood stove.
Sean
To be frank, I think you're over thinking the efficiency question. As of today, to the best of my knowledge (we have a geo system) there is no more efficient readily available mechanical way to heat a home than with a geothermal heat pump. Period.
The numbers of 300 to 400 % efficiency are correct. For every kilowatt you put into the system, you get 3 to 4 out in the form of heat. Colder climates drop efficiency based on the ground temperature. We're in Nova Scotia, and as I recall our ground loop temperature is comparable to yours.
The drawbacks are simple. You have a fairly complex heating system, with pumps, heat exchangers, compressors, etc. Those are neither simple nor cheap to repair or replace.
The $25k price tag seems high to me. Our's is a 3 ton turnkey system using radiant heat in the floor (single story, 2100 sq foot slab on grade construction, no basement). No AC. We have three 6 foot deep trenches holding 3500 feet of 3/4 geothermal specific piping laid out in "slinkies".
Our total cost including excavation was 20k CDN three years ago. By total, I mean total, it was new construction so everything is included, even the floor piping.
It cost us 5-6k more than any comparable heating system, which I expect to recover in the first 5 years.
Now, whether it makes sense or not is where different variables come into play. If you're staying in that house for at least 5 years, re-sale value, insurance costs, etc, are all factors. Your pay-off time may vary, but if you're in it for the long run, you'll come out ahead in my opinion.
It's costing me roughly half what I used to pay in heating costs for my old house, which was oil-fired forced air heat. The kicker is, the new house is almost double the size of the old one, and it's heated to the same degree 24/7 instead of morning and evening with the old house.
We burn some wood as well to reduce our cost even more, but the numbers are for pretty much sole use of the heat pump, with recreational use of the wood stove.
Sean
piller
Gold Member
A resistive heating element is 1:1, you put in one unit of electrical energy and you get one unit of heat. With a heat pump however you put in one unit of electrical energy and it can provide three or four units of heat. Air source heat pumps lose efficiency at low and high outside air temperatures. Ground source heat pumps (geothermal) take advantage of the relatively constant ground temperature and they operate efficiently regardless of the air temperature.
OK, you also mentioned you micro-hydro system, I want to hear more about that.
OK, you also mentioned you micro-hydro system, I want to hear more about that.
eepete
Platinum Member
Rob, your numbers look to be in the right ball park. As a sanity check, it seems that just about every geo decision has paybacks in the 5 to 10 year range. Mine is high because I did a pond loop, abandoned it, and put in a ground system so I have $7K or so for the pond loop that I have to recover. I might even be at 12 years payback because of that 
.
I suspect that if geo systems had 15 year payback periods, there would not be enough systems sold to make it worth anyones while, and the low volumes would raise the prices even more. So there's a 2nd sanity check on your 5-6 year payback period.
So now that you are in the right ballpark, can you get information on the difference in performance for using 40 degree ground water vs. 50 degree (or whatever the well produce up there?) As you saw in my numbers, for our two stage compressors the 1st stage performance was very different, and that translates into less run time with the warmer input water.
As for the PV-Geo situation: Last September we went on a one week trip. We left the cooling up at 80 degrees during the entire trip. Our 7.7KW of PV provided 85% of the energy the house used. When we came back, that number dropped to 60% because we were cooling the house more. I just ran 7 month of PV data, and the PV is providing right at 50% of our energy for the house, and that reduces our cost by about 65% (we get more money for the electricity we make than we pay for what we use). I expect those numbers to get better as the days get longer, and next September I'll have a year of data. To normalize our net consumption, we are at 2 cents per square foot per month (7 month average).
I think that the geo systems are unnecessarily overpriced in this area. It's not hard to figure out what the installers are making, and it's far more than any of the other trades. But that means more competition in time, and the prices will adjust. Chilly's post makes me think that you analyze as best you can, and then turn that off and go for it. These systems are really good and efficient, and even if you don't hit you numbers exactly all will be good in the fullness of time. And this from a borderline OC geek (Ok, "OC"and "geek" are a bit redundant...) :laughing:.
Pete
.I suspect that if geo systems had 15 year payback periods, there would not be enough systems sold to make it worth anyones while, and the low volumes would raise the prices even more. So there's a 2nd sanity check on your 5-6 year payback period.
So now that you are in the right ballpark, can you get information on the difference in performance for using 40 degree ground water vs. 50 degree (or whatever the well produce up there?) As you saw in my numbers, for our two stage compressors the 1st stage performance was very different, and that translates into less run time with the warmer input water.
As for the PV-Geo situation: Last September we went on a one week trip. We left the cooling up at 80 degrees during the entire trip. Our 7.7KW of PV provided 85% of the energy the house used. When we came back, that number dropped to 60% because we were cooling the house more. I just ran 7 month of PV data, and the PV is providing right at 50% of our energy for the house, and that reduces our cost by about 65% (we get more money for the electricity we make than we pay for what we use). I expect those numbers to get better as the days get longer, and next September I'll have a year of data. To normalize our net consumption, we are at 2 cents per square foot per month (7 month average).
I think that the geo systems are unnecessarily overpriced in this area. It's not hard to figure out what the installers are making, and it's far more than any of the other trades. But that means more competition in time, and the prices will adjust. Chilly's post makes me think that you analyze as best you can, and then turn that off and go for it. These systems are really good and efficient, and even if you don't hit you numbers exactly all will be good in the fullness of time. And this from a borderline OC geek (Ok, "OC"and "geek" are a bit redundant...) :laughing:.
Pete
Rob, your numbers look to be in the right ball park. As a sanity check, it seems that just about every geo decision has paybacks in the 5 to 10 year range. Mine is high because I did a pond loop, abandoned it, and put in a ground system so I have $7K or so for the pond loop that I have to recover. I might even be at 12 years payback because of that
I suspect that if geo systems had 15 year payback periods, there would not be enough systems sold to make it worth anyones while, and the low volumes would raise the prices even more. So there's a 2nd sanity check on your 5-6 year payback period.
So now that you are in the right ballpark, can you get information on the difference in performance for using 40 degree ground water vs. 50 degree (or whatever the well produce up there?) As you saw in my numbers, for our two stage compressors the 1st stage performance was very different, and that translates into less run time with the warmer input water.
As for the PV-Geo situation: Last September we went on a one week trip. We left the cooling up at 80 degrees during the entire trip. Our 7.7KW of PV provided 85% of the energy the house used. When we came back, that number dropped to 60% because we were cooling the house more. I just ran 7 month of PV data, and the PV is providing right at 50% of our energy for the house, and that reduces our cost by about 65% (we get more money for the electricity we make than we pay for what we use). I expect those numbers to get better as the days get longer, and next September I'll have a year of data. To normalize our net consumption, we are at 2 cents per square foot per month (7 month average).
I think that the geo systems are unnecessarily overpriced in this area. It's not hard to figure out what the installers are making, and it's far more than any of the other trades. But that means more competition in time, and the prices will adjust. Chilly's post makes me think that you analyze as best you can, and then turn that off and go for it. These systems are really good and efficient, and even if you don't hit you numbers exactly all will be good in the fullness of time. And this from a borderline OC geek (Ok, "OC"and "geek" are a bit redundant...) :laughing:.
Pete
Thanks Pete,
I'm strongly biasing to geo at this point. (one geek to another!)
It's interesting that you abandoned your pond. I was thinking of sinking some sensors to see what my temp is compared to the ground. I have about a 1/3 acre pond (12 feet deep at center) with six or seven springs running in it.
The other thing i was thinking of was using my radiant floor aluminum fins on the geo ground tubes just to get a 'what if' measurement. Perhaps a shorter slinky run because the aluminum would warm the tubes faster. I'm thinking of digging a short run to do a comparison of aluminum finned tubes and non-finned tubes. Has anyone done anything like this?
My well will work as it has 20+ flow rate but I don't like the idea of tapping into it.
Rob
Right now my stream is running well enough to provide about 300 to 500 watts. I'm thinking of a modified Mitchell/Banki. The Banki is an old design but it has great potential for low head apps like mine. I'm working on a direct drive NdFeB magnet alternator for it that's pretty close to the ones I use in my windmills.
The turgo is a nicer application of the basic pelton design if you have decent head but a low flow rate.
The Stream Enigine is supposed to be relatively good for a small commercial microhydro product although I have no experience with it personally, Google it if you need to see some pics. I think they give you some idea of what kind of power to expect with specific flows and heads.
The first thing you need to do is build a weir and measure your flow rate and then figure your head. I used a laser level over about a 400 to 600 foot run for head but you can do it with pressure.
Rob
Chilly807
Elite Member
Ours were between 80 and 95 feet long, plus a connector trench to get us out away from the house to where we wanted to run the actual trenches. Looks a lot like a chicken's foot, with a 50 foot tail running under the frost wall and up through the floor into the utility room.
We spent about $1500 on the materials (geo specific pipe and electro-fusion couplings) for the ground loops, plus $1200 for excavation. I think we got off easy on the excavation price, it took longer than he expected, but he stuck by his quote.
Sean
eepete
Platinum Member
My geo installer was a little embarrassed at the difference in performance of the pond vs. ground. My pond is about a half an acre, 8 feet deep. It was 40 degrees. My geo installer measured a 10 acre pond that was 14 feet deep, it was 42 degrees. So at least at this latitude, the size and depth of the pond didn't make much difference.
Also there are very few ponds around here that are more than 15 feet deep because all the rules for pond building, maintenance, and liability change if the pond is deeper than 15 feet. I suspect that the size of the pond is a very small factor (once you're over an acre or so) and that depth might be more, but only at really big depths. I remember scuba diving in rock quarries in the summer and spring and hitting a thermocline at around 35 feet or so- not a typical pond depth.
And Rob, abandoning the pond was a very expensive maneuver that moves the payback way out. I'll let you know how that worked for me in 2022, and it will come down to how much electricity cost by then.
Pete
Also there are very few ponds around here that are more than 15 feet deep because all the rules for pond building, maintenance, and liability change if the pond is deeper than 15 feet. I suspect that the size of the pond is a very small factor (once you're over an acre or so) and that depth might be more, but only at really big depths. I remember scuba diving in rock quarries in the summer and spring and hitting a thermocline at around 35 feet or so- not a typical pond depth.
And Rob, abandoning the pond was a very expensive maneuver that moves the payback way out. I'll let you know how that worked for me in 2022, and it will come down to how much electricity cost by then.
Pete
My excavator came in at $1250 which I think is a fair price but he knows me and we have worked together before. He did my fuondation when I built the house.
I'll bet it was!
I'm curious about how the springs will effect my pond but I'm leary about using it as a heat source. I'm going to throw a thermistor in the deep end just to see what's there.
You know that story, you almost wish oil would go through the roof once you have everything in and running!
Rob
Chilly807
Elite Member
If it wasn't for everything else being affected by the oil price, I'd agree with the sentiment.
Sean
Redneck in training
Elite Member
When we build our house there was not water in the pond to speak off. The coils were about half above the ice. I measured the water temperature in the inlet of the HP to be about 26F. Nevertheless the heat was working fine whole winter. The pond water temperature is not the whole story. The pipes between the pond and the house will also extract some heat from the ground.
MacLawn
Veteran Member
- Joined
- Aug 1, 2007
- Messages
- 1,418
- Tractor
- JD 2210
I've read this entire thread, and am more confused than ever on geothermal! Whew, y'all boys must be engineers...
I did read somewhere online about geothermal about algae growing on the pipes in the pond based systems, and that can reduce the efficiency. Also, I read that the ground based pipes must be encased in some kind of conductor material - kind of a mortar, etc. stuff. Can't remember, but I did read about those issues. Anybody know?
I did read somewhere online about geothermal about algae growing on the pipes in the pond based systems, and that can reduce the efficiency. Also, I read that the ground based pipes must be encased in some kind of conductor material - kind of a mortar, etc. stuff. Can't remember, but I did read about those issues. Anybody know?
Redneck in training
Elite Member
Algae growth might have some effect I suppose but it is easy and cheap to somewhat oversize the heat exchanger (fluffed coils) in the pond. As far as grout. It depends on the soil and the way the pipes are installed. When installing horizontal loops grout is seldom if at all used. It is used usually when vertical or horizontal drilling is used.
I couldn't justify the cost to go geo-therm either. I looked at the excavation cost and it didn't make sense to me. We put in a air source heat pump. Looks about like a large AC unit, and has a reverse for making heat in the winter. During the dead of winter we burn corn/wood pellets.
Spend some time with this: www.eia.doe.gov/neic/experts/heatcalc.xls
It was going to take me a long time to recover the added costs of the geo unit vs. the heat pump, and I think in the end, the heat pump cost me less than a AC unit + LP furnace.
Spend some time with this: www.eia.doe.gov/neic/experts/heatcalc.xls
It was going to take me a long time to recover the added costs of the geo unit vs. the heat pump, and I think in the end, the heat pump cost me less than a AC unit + LP furnace.
Here are some similar links:
