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  1. #1
    Join Date
    Mar 2013
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    112

    Heat Loss based on utility bills.

    I am trying to caculate my heat load based on electric and propane usage.Name:  Electric usage 2011 2012.jpg
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    From my electric bill I have used 15132 Kwh in the period from March 2012 to March 2013. If I take away 450 kwh /month for non heat usage I get 9732kwh/year.
    For the period from April 2011 to April 2012 I used 15182Kwh or 9782 for heat , so it is consistant in usage the 2 time periods. I used April because for March 2011. It was an estimated number. HDD for the periods were March 2011 to March 2012 4397degC 65F = 18.3C and 0F = -17.7C so dT of 36 used in caculations.

    using the formula (heatloss/hr / dT) * HDDS for total loss /year in BTU's

    Using a loss of 24000btus/hr of heat loss of ((24000btu's hr x24) / 36 ) * 4397= 70.35 Million BTU's You would need 70.35 million BTU's of heat.

    From my utility bill i have used 9782kwh's x 3412 btu's/kwh = 33.37million for the year from electric baseboard heaters.
    I also use propane and have used 750 liters per the time period. 750 x24603 btu's/l gives me 18.45 Million. a total of 51.8 Million.

    Therefore my heat loss should be less than 24000btu's per hour.

    Working backward's I have ((51.8million / 4397hdds) * dT 36C)/24 =17600 BTU's/hr. Is this the correct way to do this.

    If I am missing something or doing it incorrectly please let me know.

    Thanks.

  2. #2
    Join Date
    Jan 2012
    Location
    Broomall, PA
    Posts
    397
    That's alot of math.....my head hurts. You're not actually calculating heat loss/load, you're just figuring out how many btu's you used for the year. If you used your information combined with some degree day forcasting, you stil wouldnt get to where you're trying to go.
    You should do a heat loss based on a room by room calculation. Then you can determine the btu's. needed, and the right size equipment. Combine that with your degree days will give you total btu's for the season, which then can use your data/with electric rates to determine how much it will cost you to heat your home.
    Why are you asking? Curiosity, or just for your own information?

  3. #3
    Join Date
    Mar 2013
    Posts
    112
    Thanks Steve

    I did a load caculation using the HVAC Calc software and I came up with ~ 21000 BTU's/hr. I have been told by two contractors that I need a 3 ton HP or 36000 BTU's. I dont think I do need one that large.

    Shouldn't the electric used be able to correrspond to the heat load of the house.

    Right now I only have the propane and 5 Kw of baseboard heater and it heats fine.



    I re-did my BTU's used for this past winter from Dec 1 when the propane was delivered( we only get it delivered 2 times a year and I am not out of Propane yet.(the other delivery is in July)

    I used 6216Kwh of electric for 21M btu's and in the caculation I said all propane was used and my fireplace is 68% efficient. for another 12.9 Million. I used the HDDS for that period and I came up with 21500 btu's /hr.



    Jimmy

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by JimmyP View Post
    Shouldn't the electric used be able to correrspond to the heat load of the house.
    No, load calculations for sizing equipment are based on peak design day loads.

    Your electric and fuel bills won't show you how much electricity or fuel was used during the few hours the outdoor temperature was at the design temperature on the days it reached it.

    Your bills also reflect usage by other items in the home that consume energy/fuel.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    Mar 2013
    Posts
    112
    Quote Originally Posted by mark beiser View Post
    No, load calculations for sizing equipment are based on peak design day loads.

    Your electric and fuel bills won't show you how much electricity or fuel was used during the few hours the outdoor temperature was at the design temperature on the days it reached it.

    Your bills also reflect usage by other items in the home that consume energy/fuel.
    I removed 450kwh's per month for the other items.

    Ok so you design for 36000 BTU's /hr heat loss ( which is what thay told me I needed), and you get that output from the heat pump @ 47F. If you are loosing that much heat @ 47F, wouldn't it be groosely oversized If I am only loosing ~ 8000btu's per hr @ that temp. What you reaaly need then is a heat pump that will supply 36000 Btu's at 0 when you will more than likely be loosing 36000 BTU's and not the 18000 or so that the heat pump puts out.

    From the load caculation I have a heat gain of 21000 sensible so I need a 2 ton for cooling. which is what they are supposed to be designed for cooling not heating.

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Thumbs up KEEP IT SIMPLE

    Quote Originally Posted by JimmyP View Post
    Thanks Steve

    I did a load caculation using the HVAC Calc software and I came up with ~ 21000 BTU's/hr.

    Right now I only have the propane and 5 Kw of baseboard heater and it heats fine.

    Jimmy {POST # 3}
    IT'S AN ABSOLUTE _ NO BRAINER _ TO ADD A 2-TON GREENSPEED.
    _______ ___________ __________ __________________
    vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv vvvvvvvvvvvvvvvv

    It will handle > 99% of the heat loss.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by dan sw fl View Post
    IT'S AN ABSOLUTE _ NO BRAINER _ TO ADD A 2-TON GREENSPEED.
    _______ ___________ __________ __________________
    vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv vvvvvvvvvvvvvvvv

    It will handle > 99% of the heat loss.
    I haven't heard very good things about the Nordyne controller. Infinity control is still one of the best out there. Especially with zoning. Their logic for airflow to help control humidity is pretty impressive. A properly sized unit in an average home can maintain humidity level very precisely even in low load conditions, unless it's a cloudy day or early morning with cooler temps.

  8. #8
    Join Date
    Mar 2013
    Posts
    112
    Quote Originally Posted by motoguy128 View Post
    I haven't heard very good things about the Nordyne controller. Infinity control is still one of the best out there. Especially with zoning. Their logic for airflow to help control humidity is pretty impressive. A properly sized unit in an average home can maintain humidity level very precisely even in low load conditions, unless it's a cloudy day or early morning with cooler temps.
    Thanks

    I have read the lower 19SEER FT4BG can use a 2 stage controller( honeywell or others) and I was recommended Azrel zoning with it. It says can have 5 stages in heating and cooling.


    The IQ drive controller is needed for theFT4BI.

    They both have the modulating inverter compressor. I think the FT4BI is double the cost.


    Jimmy

  9. #9
    Join Date
    Mar 2013
    Posts
    112
    Quote Originally Posted by dan sw fl View Post
    IT'S AN ABSOLUTE _ NO BRAINER _ TO ADD A 2-TON GREENSPEED.
    _______ ___________ __________ __________________
    vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv vvvvvvvvvvvvvvvv

    It will handle > 99% of the heat loss.
    Ok Great.


    Thanks!

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Then guess what, you bills and load calculation match (imagine that). Sounds like you only need a 2 or 2.5 ton heat pump depending on climate and equipment models selected. 3 ton would be too large and you'd have dehumidificaiton problems in summer.

  11. #11
    Join Date
    Mar 2013
    Posts
    112
    Quote Originally Posted by motoguy128 View Post
    Then guess what, you bills and load calculation match (imagine that). Sounds like you only need a 2 or 2.5 ton heat pump depending on climate and equipment models selected. 3 ton would be too large and you'd have dehumidificaiton problems in summer.
    Thanks Motoguy.

    That was the point of the exercise, I was thinking I was on the right path. I believed the number I came up with using the HVAC Calc but when the professionals came in and came up with ~ 38000 BTU's/ hr heat load I doubted thier numbers and needed some clarification. That is if I have done it correctly.

    Jimmy

  12. #12
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,064
    Quote Originally Posted by JimmyP View Post
    Thanks Motoguy.

    That was the point of the exercise, I was thinking I was on the right path. I believed the number I came up with using the HVAC Calc but when the professionals came in and came up with ~ 38000 BTU's/ hr heat load I doubted thier numbers and needed some clarification. That is if I have done it correctly.

    Jimmy
    It's very common for contractors to fudge their inputs (or not even do a calc) to get ~500sqft per ton, most everyone is so scared to undersize that most grossly oversize.

  13. #13
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    The heat pump doesn't need to supply 100% capacity at design temepratures. Normally you size for AC load, unless you live realy far north. IF you size for heating you have humidity problems in summer when cooling even with a 2 stage system. A well insulated house will have a better balance of heating load to cooling load, since a large part of of heat loss and gain are internal loads. Thsoe loads offset each other, since it gets added to cooling in summer and subtracted in winter. A well done spray foam house with enough thermal mass might not even need a significant heating systems (passively heated) and might have just a cooling system and dehumidifier.

    I forget, are you using a dehumidifer for latent loads? If so, then yes, you could oversize a little for heating and go with a 3 ton 2 stage heat pump and use the whle house dehumidifer to manage latent loads. That's a very good setup.

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