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BTUH/HDD/SF

Doug_7
Doug_7 Member Posts: 233
I would count all finished heated rooms that are considered to be living space.

I would not count unfinished or unheated space such as a utility room or boiler room. I would not count heated garages.

A more compact living space will save energy. A square two story house will be much more efficient than a single story rectangular house with the same living area.

The Europeans have very detailed and standardized procedures and require standardized training and certification of building assessors. The attached drawing is from a European procedures manual does not entirely answer your question but gives a good indication of the detail they go into - in this case distinguishing between heated and unheated areas.

Doug

Comments

  • Gordy
    Gordy Member Posts: 9,546
    Formula For Dwelling Efficiency

    There was a thread a while back "Any test houses" That talked about the over all efficiency of a dwelling.

    Should the formula BTUH/HDD/SF=BTUSF take into account the lack of heating plant efficiency? I believe it should, to verify the actual btus lost by the dwelling. Not Btus lost by the heating plant.


    Gordy
  • Doug_7
    Doug_7 Member Posts: 233
    BTU/HDD/SF Method for Building Energy Efficiency

    The Btu/HDD/SF method measures the overall energy efficiency of the total building taken as one system.

    The Btus are the total fuel input Btu's. So the method includes both the heating plant efficiency losses and the actual btus lost by the building due to insulation and infiltration.

    If you install a high efficiency boiler or furnace, you will reduce the amount of fuel Btu's required to produce the same amount of useful heat required to heat your building, and reduce your total fuel Btu used / sq ft / HDD / year, improving your building energy rating.

    Anything you do to improve either the efficiency of the heating plant or the efficiency of the building shell will show up in an improved overall building energy efficiency.

    The method as used in Europe determines both the Actual and Potential building energy performance rating. The Potential rating is a theoretical calculation of what the building energy performance could be with reasonable retrofits with a payout of 5 years or less.

    It is a simple and fiendish method, useful for comparing different buildings or tracking one building energy performance over time as improvements are made.

    Doug
  • Gordy
    Gordy Member Posts: 9,546
    Excepted formula

    Not to disregard the excepted overall efficiency formula.

    But to check the envelopes efficiency. One needs to subtract the heating plants inefficiency. So we know what Btus were used by the envelope itself, and not up the stack.

    Gordy
  • Doug_7
    Doug_7 Member Posts: 233
    building envelope's efficiency

    Yes, I agree - You can get to the building envelope's efficiency directly by using the boiler output Btus rather than Boiler input Btus. The trouble is to know the actual boiler efficiency.

    The heat losses from the building envelope are the largest part of the total building heat requirement.

    The other issue is domestic hot water, which would also have to be deducted if fueled from the same fuel source. I clock both the gas meter and the DHW gas use (burner ON time).

    I say that overall method is fiendish because it gives the total heat requirement. After that you can break it down into the fuel use due to the building envelope, the boiler inefficiency and domestic hot water etc.

    I have done all this and it is pretty informative on knowing what to tackle first to reduce fuel use and cost.

    Doug
  • Gordy
    Gordy Member Posts: 9,546
    Cutting through the mustard

    I agree with you Doug. Overall efficiency on a dwelling verses getting down to actual heating/cooling loads does not really tell the whole story.

    We can look at appliances of every kind, and decide if it is going to be the most efficient available with out to much debate..... If it is dialed in like it is suppose to be.

    Gordy

  • metric

    I'd like to confuse things a bit ;~) First, I'd take into account only "imported energy" which shows up on the bill. Next, I'd consider a separate measure which does not figure in degree days. This measure would take into account all imported energies so phantom loads and user habits would weigh more heavily on the btu/square foot/year number. Otherwise one only seems to be concerned about the heating load, which limits what the people living in the house can have an effect on. A solid metric can be a very useful tool.

    Yours, Larry
  • Doug_7
    Doug_7 Member Posts: 233
    I want to reduce utility consumption and cost

    Larry - I agree that it is important to have a metric - If we don't measure performance, how can we improve performance.

    If you called in an Energy Auditor to assess your building energy performance, he would use one-year of actual utility bills to "Benchmark" your actual building heating energy use in btus/ft2/hdd.

    That would typically include the energy use for space heating and domestic hot water. This shows where the building stands compared to many other buildings that have also been "Benchmarked".

    Yes it is "imported energy". The actual energy use as per utility bills and includes the effects of actual weather conditions and occupant behavior.

    For my own building I have a primary breakdown of energy use for space heating and DHW.

    For space heating I have a detailed breakdown that shows how much energy is lost by boiler inefficiency and calculated heat losses through ceiling, walls, windows and basement.

    For DHW heating I have a breakdown that shows how much energy is lost up the flue when firing, standby losses, recirculation piping losses and how little of the heat actually goes into heating the DHW for use.

    The detailed breakdown of heating energy use by cause shows what to work on that will have the most benefit.

    I treat electricity separately. I have a breakdown into lighting and other including motive power. I don't add this into heating energy. I also get the summertime air-conditioning load.

    What you measure depends on what you are trying to accomplish. I want to reduce my utility consumption and cost.

    Google btus/ft2/hdd and you get 3,000 hits. Some are pretty interesting.

    Doug
  • Gordy
    Gordy Member Posts: 9,546
    Square footage

    Doug, When calculating square feet of the dwelling. Do you use all heated space? Example being a radiant heated basement of a ranch style house.

    Gordy
  • Gordy
    Gordy Member Posts: 9,546
    Interesting

    To note that there is a ratio percentage of window/door area to floor area of a room. I like that as a design guide. And it seems like a pretty generous ratio....unless McMantion is on the drawing board.


    Gordy
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