Fuel Savings from Solar DHW
Question:
How does one go about calculating the potential fuel savings from installation of a solar DHW system? At present, we have a propane-fired furnace, hydronic heat, and a separate storage tank for DHW heated off the same furnace. Maine has recently implemented a credit for solar DHW, even when off grid, but I don’t have any idea how to figure my fuel savings. Thanks. — ron (off the grid in Downeast Maine)
Response:
Ron, first of all, you should know how much propane you need during a summer month. Multiply this times 12, and you know a good estimation what you need to heat your water up in a year. This estimation is a bit too high, as during the cold month, your furnace will be hot from the house heating anyway, so you don’t need any energy to heat up the furnace itself – what you do during summer. Then it depends on the solar system, you can get 60-80% savings by it, depending on the size of the system, isolation, amount of warm water needed, … Is that good enough for a rough draft? Christian PS: If you have a modern furnace, you might be able to save a lot of energy by reducing the times when you heat up the water – I saved about 60% just by reducing the times when the water was heated up to once in the morning and once in the evening (it stayed warm enough for about 4-6 hours, we rarely need warm water in the afternoon). Thus if you give up the idea of 24 hours of hot water, this will save you a large amount. But this depends on your personal situation and possibilites (and the isolation of the storage tank).
– Hide quoted text — Show quoted text -> How does one go about calculating the potential fuel savings from > installation of a solar DHW system? > At present, we have a propane-fired furnace, hydronic heat, and a separate > storage tank for DHW heated off the same furnace. > Maine has recently implemented a credit for solar DHW, even when off grid, > but I don’t have any idea how to figure my fuel savings. > Thanks. > — ron (off the grid in Downeast Maine)
Response:
> How does one go about calculating the potential fuel savings from > installation of a solar DHW system? > At present, we have a propane-fired furnace, hydronic heat, and a separate > storage tank for DHW heated off the same furnace. > Maine has recently implemented a credit for solar DHW, even when off grid, > but I don’t have any idea how to figure my fuel savings. > Thanks. > — ron (off the grid in Downeast Maine)
A google of "solar thermal"+"cost savings" yielded among other links: http://www.solardepot.com/r_solar_hot_water.htm They have a PDF at the bottom. http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf
Response:
A further search of "solar water heating"+savings yeilded: http://www.solarroofs.com/economics/ That is a commercial site, but they list Maine.
– Hide quoted text — Show quoted text -> How does one go about calculating the potential fuel savings from > installation of a solar DHW system? > At present, we have a propane-fired furnace, hydronic heat, and a > separate > storage tank for DHW heated off the same furnace. > Maine has recently implemented a credit for solar DHW, even when off > grid, > but I don’t have any idea how to figure my fuel savings. > Thanks. > — ron (off the grid in Downeast Maine) > A google of "solar thermal"+"cost savings" > yielded among other links: > http://www.solardepot.com/r_solar_hot_water.htm > They have a PDF at the bottom. > http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf
Response:
>Ron, >first of all, you should know how much propane you need during a summer >month. Multiply this times 12, and you know a good estimation what you need >to heat your water up in a year.
Unfortunately for your suggestion, we also use propane for cooking; clothes dryer, and our backup generator. Thanks for your suggestion, though. — ron (off the grid in Downeast Maine)
Response:
- Hide quoted text — Show quoted text -> How does one go about calculating the potential fuel savings from > installation of a solar DHW system? > At present, we have a propane-fired furnace, hydronic heat, and a separate > storage tank for DHW heated off the same furnace. > Maine has recently implemented a credit for solar DHW, even when off grid, > but I don’t have any idea how to figure my fuel savings. > Thanks. > — ron (off the grid in Downeast Maine) >A google of "solar thermal"+"cost savings" >yielded among other links: >http://www.solardepot.com/r_solar_hot_water.htm >They have a PDF at the bottom. >http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf
Thank you for those links. Unfortunately, neither of them seem to allow me to calculate the information I’d like. What I’d like to figure out is, given a certain amount of hot water usage, how much propane will I save with a solar DHW system over the course of a year. If I know that, I can "plug in" various propane costs and figure the money savings. — ron (off the grid in Downeast Maine)
Response:
– Hide quoted text — Show quoted text ->> How does one go about calculating the potential fuel savings from >> installation of a solar DHW system? >> At present, we have a propane-fired furnace, hydronic heat, and a >> separate >> storage tank for DHW heated off the same furnace. >> Maine has recently implemented a credit for solar DHW, even when off >> grid, >> but I don’t have any idea how to figure my fuel savings. >> Thanks. >> — ron (off the grid in Downeast Maine) >A google of "solar thermal"+"cost savings" >yielded among other links: >http://www.solardepot.com/r_solar_hot_water.htm >They have a PDF at the bottom. >http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf > Thank you for those links. Unfortunately, neither of them seem to allow > me > to calculate the information I’d like. > What I’d like to figure out is, given a certain amount of hot water usage, > how much propane will I save with a solar DHW system over the course of a > year. > If I know that, I can "plug in" various propane costs and figure the money > savings. > — ron (off the grid in Downeast Maine)
www.google.com "solar water heating"+calculator gave: http://www.infinitepower.org/calc_waterheating.htm
Response:
- Hide quoted text — Show quoted text ->>> How does one go about calculating the potential fuel savings from >>> installation of a solar DHW system? >>> At present, we have a propane-fired furnace, hydronic heat, and a >>> separate >>> storage tank for DHW heated off the same furnace. >>> Maine has recently implemented a credit for solar DHW, even when off >>> grid, >>> but I don’t have any idea how to figure my fuel savings. >>> Thanks. >>> — ron (off the grid in Downeast Maine) >>A google of "solar thermal"+"cost savings" >>yielded among other links: >>http://www.solardepot.com/r_solar_hot_water.htm >>They have a PDF at the bottom. >>http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf > Thank you for those links. Unfortunately, neither of them seem to allow > me > to calculate the information I’d like. > What I’d like to figure out is, given a certain amount of hot water usage, > how much propane will I save with a solar DHW system over the course of a > year. > If I know that, I can "plug in" various propane costs and figure the money > savings. > — ron (off the grid in Downeast Maine) >www.google.com >"solar water heating"+calculator gave: >http://www.infinitepower.org/calc_waterheating.htm
Paul, Thank you very much for locating that site. It looks like exactly what I want. Now I will go collect the data, and find a conversion for therms to gallons of propane. Both of those tasks should be simple. Best wishes, — ron (off the grid in Downeast Maine)
Response:
– Hide quoted text — Show quoted text ->>>> How does one go about calculating the potential fuel savings from >>>> installation of a solar DHW system? >>>> At present, we have a propane-fired furnace, hydronic heat, and a >>>> separate >>>> storage tank for DHW heated off the same furnace. >>>> Maine has recently implemented a credit for solar DHW, even when off >>>> grid, >>>> but I don’t have any idea how to figure my fuel savings. >>>> Thanks. >>>> — ron (off the grid in Downeast Maine) >>>A google of "solar thermal"+"cost savings" >>>yielded among other links: >>>http://www.solardepot.com/r_solar_hot_water.htm >>>They have a PDF at the bottom. >>>http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf >> Thank you for those links. Unfortunately, neither of them seem to allow >> me >> to calculate the information I’d like. >> What I’d like to figure out is, given a certain amount of hot water >> usage, >> how much propane will I save with a solar DHW system over the course of >> a >> year. >> If I know that, I can "plug in" various propane costs and figure the >> money >> savings. >> — ron (off the grid in Downeast Maine) >www.google.com >"solar water heating"+calculator gave: >http://www.infinitepower.org/calc_waterheating.htm > Paul, > Thank you very much for locating that site. It looks like exactly what I > want. Now I will go collect the data, and find a conversion for therms to > gallons of propane. Both of those tasks should be simple. > Best wishes, > — ron (off the grid in Downeast Maine)
You are welcome. You will notice a bug in the gas payback. You will have to shift a few decimal places to get the right answer.
Response:
- Hide quoted text — Show quoted text ->>>>> How does one go about calculating the potential fuel savings from >>>>> installation of a solar DHW system? >>>>> At present, we have a propane-fired furnace, hydronic heat, and a >>>>> separate >>>>> storage tank for DHW heated off the same furnace. >>>>> Maine has recently implemented a credit for solar DHW, even when off >>>>> grid, >>>>> but I don’t have any idea how to figure my fuel savings. >>>>> Thanks. >>>>> — ron (off the grid in Downeast Maine) >>>>A google of "solar thermal"+"cost savings" >>>>yielded among other links: >>>>http://www.solardepot.com/r_solar_hot_water.htm >>>>They have a PDF at the bottom. >>>>http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf >>> Thank you for those links. Unfortunately, neither of them seem to allow >>> me >>> to calculate the information I’d like. >>> What I’d like to figure out is, given a certain amount of hot water >>> usage, >>> how much propane will I save with a solar DHW system over the course of >>> a >>> year. >>> If I know that, I can "plug in" various propane costs and figure the >>> money >>> savings. >>> — ron (off the grid in Downeast Maine) >>www.google.com >>"solar water heating"+calculator gave: >>http://www.infinitepower.org/calc_waterheating.htm > Paul, > Thank you very much for locating that site. It looks like exactly what I > want. Now I will go collect the data, and find a conversion for therms to > gallons of propane. Both of those tasks should be simple. > Best wishes, > — ron (off the grid in Downeast Maine) >You are welcome. You will notice a bug in the gas payback. >You will have to shift a few decimal places to get the right answer.
Tried it, and got results that seem to pass the "logic" test. That means the numbers are close to an off-the-cuff guesstimate from a local contractor. Thanks again. — ron (off the grid in Downeast Maine)
Response:
Interested to see what your what your #’s actually were Ron. I know my bank of solar thermal now gives me about $700 worht of heat…Paul
– Hide quoted text — Show quoted text ->>>>>> How does one go about calculating the potential fuel savings from >>>>>> installation of a solar DHW system? >>>>>> At present, we have a propane-fired furnace, hydronic heat, and a >>>>>> separate >>>>>> storage tank for DHW heated off the same furnace. >>>>>> Maine has recently implemented a credit for solar DHW, even when off >>>>>> grid, >>>>>> but I don’t have any idea how to figure my fuel savings. >>>>>> Thanks. >>>>>> — ron (off the grid in Downeast Maine) >>>>>A google of "solar thermal"+"cost savings" >>>>>yielded among other links: >>>>>http://www.solardepot.com/r_solar_hot_water.htm >>>>>They have a PDF at the bottom. >>>>>http://www.solardepot.com/pdf/2005/thermal_broch_insert_6-2005.pdf >>>> Thank you for those links. Unfortunately, neither of them seem to allow >>>> me >>>> to calculate the information I’d like. >>>> What I’d like to figure out is, given a certain amount of hot water >>>> usage, >>>> how much propane will I save with a solar DHW system over the course of >>>> a >>>> year. >>>> If I know that, I can "plug in" various propane costs and figure the >>>> money >>>> savings. >>>> — ron (off the grid in Downeast Maine) >>>www.google.com >>>"solar water heating"+calculator gave: >>>http://www.infinitepower.org/calc_waterheating.htm >> Paul, >> Thank you very much for locating that site. It looks like exactly what I >> want. Now I will go collect the data, and find a conversion for therms to >> gallons of propane. Both of those tasks should be simple. >> Best wishes, >> — ron (off the grid in Downeast Maine) >You are welcome. You will notice a bug in the gas payback. >You will have to shift a few decimal places to get the right answer. > Tried it, and got results that seem to pass the "logic" test. That means > the numbers are close to an off-the-cuff guesstimate from a local > contractor. > Thanks again. > — ron (off the grid in Downeast Maine)
Response:
Sounds like you got your stuff figured out Ron, but here are some generally useful figures for this sort of thing…generally correct, though I have seen slightly (not hugely) different numbers for some of them from other sources. Mostly in english (now US,as the olde country went metric and we did not) units, but that’s what I mostly work in, as to most suppliers near me). 1 BTU heats 1 pound of water 1 degree F About 8 pounds of water per gallon 1 gallon of LPG = 91500 BTU (multiply by efficiency of appliance) 1 gallon of #2 fuel oil or diesel – 138000 BTU (multiply by efficiency of appliance) 1 cord of "average" wood – about 12,000,000 BTU (multiply by efficiency of appliance) 1 KWH electric = 3413 BTU 1 LB of air = 13.9 cubic feet Specific heat of air = 0.24 (1 BTU will heat one pound of air up about 4.16 degrees F). — Cats, coffee, chocolate…vices to live by
Response:
>Interested to see what your what your #’s actually were Ron. I know my bank >of solar thermal now gives me about $700 worht of heat…Paul
It’ll be a bit as the R-Value of the water heater; and the efficiencies are not numbers I can easily lay may hands on. However, with propane now at $1.99/gal, it looks like my hot water cost is probably around $450/year. — ron (off the grid in Downeast Maine)
Response:
– Hide quoted text — Show quoted text – >Sounds like you got your stuff figured out Ron, but here are some >generally useful figures for this sort of thing…generally correct, >though I have seen slightly (not hugely) different numbers for some of >them from other sources. >Mostly in english (now US,as the olde country went metric and we did >not) units, but that’s what I mostly work in, as to most suppliers near >me). >1 BTU heats 1 pound of water 1 degree F >About 8 pounds of water per gallon >1 gallon of LPG = 91500 BTU >(multiply by efficiency of appliance) >1 gallon of #2 fuel oil or diesel – 138000 BTU >(multiply by efficiency of appliance) >1 cord of "average" wood – about 12,000,000 BTU >(multiply by efficiency of appliance) >1 KWH electric = 3413 BTU >1 LB of air = 13.9 cubic feet >Specific heat of air = 0.24 (1 BTU will heat one pound of air up about >4.16 degrees F).
Thank you for that information. It will be useful when I develop more specific measurements. — ron (off the grid in Downeast Maine)
Response:
ARE you running a tank or a tankless water heater?????
– Hide quoted text — Show quoted text ->Interested to see what your what your #’s actually were Ron. I know my bank >of solar thermal now gives me about $700 worht of heat…Paul > It’ll be a bit as the R-Value of the water heater; and the efficiencies are > not numbers I can easily lay may hands on. > However, with propane now at $1.99/gal, it looks like my hot water cost is > probably around $450/year. > — ron (off the grid in Downeast Maine)
Response:
>ARE you running a tank or a tankless water heater?????
I have an Amtrol BoilerMate (runs on a zone from my furnace/boiler). — ron (off the grid in Downeast Maine)
Response:
> I have an Amtrol BoilerMate (runs on a zone from my furnace/boiler).
A good setup with an efficient furnace, except that there’s no insulation on it as it comes (at least the several I’ve seen, including one I grabbed (intending to use as a "scrap starting point for something else, since it leaked) that appears to only need a gasket (what some people will not do to fix a simple leak – or, I haven’t seen the "real problem" with it yet). Quite easy to remedy the lack of insulation, to whatever level you desire…but I’ve seen installed setups where that has not been done – why not, I can’t imagine. — Cats, coffee, chocolate…vices to live by
Response:
>> I have an Amtrol BoilerMate (runs on a zone from my furnace/boiler). >A good setup with an efficient furnace,
It’s a Weil-McLane furnace — supposed to be efficient. >except that there’s no >insulation on it as it comes (at least the several I’ve seen, including >one I grabbed (intending to use as a "scrap starting point for something >else, since it leaked) that appears to only need a gasket (what some >people will not do to fix a simple leak – or, I haven’t seen the "real >problem" with it yet). Quite easy to remedy the lack of insulation, to >whatever level you desire…but I’ve seen installed setups where that >has not been done – why not, I can’t imagine.
I think there’s got to be some insulation, as the outer wall is quite a bit cooler than the water temperature ??? Ambient Temp: 71
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