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KW Conversion to Nat Gas

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AL_29
AL_29 Member Posts: 44
in THE MAIN WALL
Can anyone tell me a simple formula to convert KW usage to what Natural gas usage would be.

Thanks

AL

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  • Ironman
    Ironman Member Posts: 7,376
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    KW & BTU Simple Answer

    1 Watt = 3.413btu's. 1 KW = 3,413btu's.  One cubic foot of natural gas produces about 1,000 - 1050btu's. You would have to multiply this times the efficiency of the appliance to get the actual output. Example: 100k btu's x 95% = 95k btu's.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Tom Blackwell_2
    Tom Blackwell_2 Member Posts: 126
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    BTU's

    Electricity produces 3413 btu's per kilowatt hour.

    Natural gas produces 1,000 btu/cu ft  x efficiency (.8) = 800 btu/cu ft useable energy.

    In terms of therms- 100,000 btu

    electricity = 29.3 kwh/therm

    Gas = 125 cu ft/therm at 80% efficiency ( one therm = 100 cu ft)
  • AL_29
    AL_29 Member Posts: 44
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    Calculations

    My geo customer used

    6669 KW to heat and light his house.

    Was not happy about his 800 bill because a kw costs us around 12cents

    Nat gas from our supplier was 48 cents a therm

    Having trouble calculating what his gas bill would have been if he had 95% eff furnaces heating his house and boiler for radiant?
  • Ironman
    Ironman Member Posts: 7,376
    edited February 2011
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    Geo vs. Nat.

    This is going to be a rough estimate because the heating is not separated from the rest of his bill. But 70% for heating is a fair guess without more details. So here goes:

    6669 x .7 = 4668kw x .12 = $560.20.  4668kw = 15,931,884btu's. This would be for electric resistance heating, but a good geo should be operating at a 3.0 C.O.P(coefficient of performance).  Therefore,  15,931,884 x 3(cop) = 47,795,652btu's.

    47,795,884 / 100,000 = 477.95 therms (100,000btu per therm). 477.95 @ 95% = 503.11 therms x .48c = $241.49.



    I have assumed a properly functioning geo under average heating conditions. Obviously, there could be alot of variables not factored in.



    Maybe Brad White or someone else could come closer with the info provided.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Multiply or divide??

    I would divide by the efficiency.



    If the load is 100,000 btuH, and the boiler is 95 % efficient, then 100,000 divided by .95 = 105,263. So, you would have to put IN 105, 263 to get 100,000 btuH out.



    105,263 divided by 1050 = 100 CFH.



    I think the original poster was trying to determine the cost per unit difference between electricity and natural gas, and if so, then the formula would be based on a THERM cost, which is 100,000 btu's.



    With electricity, it would take 29.29 KWH's to meet 100,000 btuH. The efficiency of an direct resistance appliance would be essentially 100 %,



    At Denvers cost of $0.10 per KWH, then the electrical per therm cost would be $2.93 per therm.



    Using the above calculation for the 95% efficient appliance, and Denvers natural gas cost of $0.50 per CCF, then the NET cost per therm to deliver 100,000 btu's with a 95% efficient appliance would be $0.50.



    So, here in Denver, the cost of electricity is 5.86 times more expensive than natural gas.



    (Denvers energy content is actually only 830 btu/cf, as opposed to the normal well head value of 1050)



    HTH





    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Ironman
    Ironman Member Posts: 7,376
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    Guess it depends...

    If you're starting from the top or bottom?



    Mark, do my numbers on the last post down look reasonable or did I miss something?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • AL_29
    AL_29 Member Posts: 44
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    Accurate

    Bob, 

       I came up with a number around 275.00 earlier today adding in delivery cost and taxes from my house bill. You came up with the same numbers I did but I did it in an entirely different way. Thats why I came here for an answer. What factors could we consider to making this system that much more to operate. I have 3000 ft of basement 600 ft of garage radiant tons of windows with floor warming all the way around the windows out four feet.

    I am going to have a look at my loop temps and amp draws to try and figure this out. But due to deregulation in IL we are able to purchase electricity from suppliers rather than Com Ed. Com ed was the only supplier available for years and years.

    Thanks for all the info

    AL
  • Brad White
    Brad White Member Posts: 2,398
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    Nothing I would add

    to Ironman's analysis!  All of the right questions have been asked, especially about the COP. This has to be one large house and the electric rate is 2/3rds of what we pay in Boston.



    What is the location and local degree-days?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • AL_29
    AL_29 Member Posts: 44
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    Factors

    My gas bill was 161.00 for the same period as your telling me his gas bill would have been 240.00

    The house in question is 3 times the size of my house with 3600 ft radiant and another 1200 of floor warming. Doesnt seem right but that is what I came up with. I will try contacting Brad White.

    AL
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Another way to look at it...

    If the house were heated with electric baseboard, his bill would be 3 times as much as it is. Probably not much solace, but it would be true.



    Achieving a COP of 3 to 1 is a dream at best with the current BANG BANG controls used by the majority of GSHP manufacturers. I'm guessing, under ideal conditions it is possible, but in reality, you are probably closer to a 2 or 2.5 to 1. It can be calculated, but you are going to need a number of data loggers to determine it for a long period of time, versus looking at it for just a few minutes.



    Over promising and under delivering are common traits of GSHP systems. What does your ground source consist of? Horizontal loop, VBH, pond/lake loop? It DOES make a difference.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • AL_29
    AL_29 Member Posts: 44
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    house

    It is a large house. Around 5500 sq' of conditioned space. We may be using the geo radiant to deice the roof and roof drains. I don't remember if we added that or not on this one. We are in Chicago and I am not sure what the degree days were.
  • Ironman
    Ironman Member Posts: 7,376
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    Other Factors

    The most obvious question to me is to ask if the geo is performing as it should? There could be alot of back up heat coming into the usage
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • AL_29
    AL_29 Member Posts: 44
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    Performance

    This is the only system that we had high bill on. The back up is 95% gas furnaces because the homeowner wanted a generator to produce emergency heat. High outage area. We will have to figure out performances and loop temps. I can make the gas furnaces kick on at any outdoor temp if I desire. I am going to dig into it!
  • AL_29
    AL_29 Member Posts: 44
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    Data Loggers

    I have been looking for data loggers to test some of the systems I have in. I have three pond loop installs and that homeowner is estatic at his savings. He is also on real time pricing. This peticular install is a Verticle bore 300'. I also have lots of horizontal installs. I want to data log all of them for my own knowledge because I just don't trust the engineers and there specs. If you have any names of data loggers you could give me that would be great.

    AL
  • Ironman
    Ironman Member Posts: 7,376
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    High Bill

    Could there also be something besides the heat that's spinning the meter like a helicopter? Excessive hot water usage? Pool pumps? Enough Christmas lights that they can spot them from the space station? (my wife almost achieved this).
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Another thing to consider...

    I had a GSHP customer who decided to go with the Demand Rate, which means they get their KWH at a fairly inexpensive rate, BUT, they are charged for the DEMAND imparted by the system, and it is on a ratchet charge. In other words, if you hit 80 KW of demand for electrical use during the peak heating season, and you actual KW demand was less for the balance of the year, the ratchet charge keeps your demand charges at the higher rate until a higher demand is recorded or 6 months passes, which ever occurs first.



    We had calculated his operating expenses at the conventional hourly KW charge. With NO demand charge. He changed the rules of operating costs himself.



    Look at his bills and make sure he is not getting dinged for demand.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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