OP
Rob-D
Veteran Member
About 400 gallons/yr and about $60.00 a month electric bill. (400~500 KWh)
10.7 cents a KWh.
Re-thinking geothermal
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About 400 gallons/yr and about $60.00 a month electric bill. (400~500 KWh)
10.7 cents a KWh.
OP
Rob-D
Veteran Member
You can't have a COP over 100% unless you found the magic bullet.
OP
Rob-D
Veteran Member
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
Elite 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
OP
Rob-D
Veteran Member
OP
Rob-D
Veteran Member
OP
Rob-D
Veteran 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
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
