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Energy Assessment: Boiler sizing from Sap software help please

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    • CommentAuthorkebabman
    • CommentTimeApr 3rd 2012 edited
     
    I have downloaded the cSAP software from http://www.2013ncm.bre.co.uk/
    that was kindly mentioned recently and hopefully I have made an acceptably accurate inputting of data for my house.
    I am now wanting to know how I size a boiler from the results. I guess I should be looking at the "energy consumed by build kWh" in the SAP section? For the worst month I get a total figure of 6200 kWh, so do I divide this by say 30 days. I am then wondering how many hours I then divide by. If I divide by say 15 hours I get a figure of 13.77kWh.
    The house is listed, about 250m2 floor area, rubble stone walls with no wall insulation but I have put in that we hopefully will be able to put d/g into most windows and can insulate the roof pretty well and will draughtproof as well as possible. The EPC says F which seems about right.
    I used some other boiler calculators a while ago and got a figure of around 28kW for boiler size. But obviously this software should be far more accurate if I have entered the data correctly.
    Does anyone live in a house of similar construction and so could let me know their boiler size/heating requirements and their floor area please?
    Any comments regarding the kWh figure as it sound too low to me.
    Cheers
    Andrew

    PS I guess that I am really after the hourly heating requirement so that I can see how often a thermal store will need to be charged up by a biomass boiler that would obviously have a far higher kw output than the hourly heat requirement.
  2.  
    SAP is completely inappropriate for boiler sizing. You need to calculate the worst-case heatloss (in kW, not kWh) of your house and use that for the sizing.

    I've used hot2000 on an old house and it has turned out to be pretty accurate - you can download it free here: http://canmetenergy.nrcan.gc.ca/eng/software_tools/hot2000.html

    Paul in Montreal.
    • CommentAuthorkebabman
    • CommentTimeApr 3rd 2012 edited
     
    Paul, thanks for the link I will give it a go, the reason that I tried out the SAP software was that an ASHP installer guy I visited said that I had to have a SAP done to to size the heat pump.
    • CommentAuthorkebabman
    • CommentTimeApr 3rd 2012
     
    Done some searching and found my question answered.
    I see that I multiply the heat loss coefficient by my delta T and deduct internal heat gains which gives a figure of 33kw . Closeish to the 28-30kw I got from the simple online boiler calculators.
    • CommentAuthordelboy
    • CommentTimeApr 3rd 2012
     
    Kebabman I fear you are not an expert in specifying heating appliances. I would seriously advise you to have a pro spec your system. You will presumably need a pro to install it anyway?

    As Paul says, definitely do not rely on SAP for the design of anything - its own creators stress that it is not a design tool.

    I wouldn't touch your ASHP installer with a bargepole if he's advising you to use SAP to size his product. He sounds like he hath not a clue what he's talking about. Unless you misunderstood each other, and he thought you were building a new house, in which case you would need to get a SAP done to pass building regs.
    • CommentAuthorkebabman
    • CommentTimeApr 3rd 2012 edited
     
    @Delboy I was just trying to get a more accurate figure of energy useage for a fairly large old house rather than the back of fag packet calculators online.
    When the ASHP guy initially said one unit of around 11kw was going to be sufficient it just didn't seem to be in the right ball park at all. I expected someone who installed ASHP's to know roughly the correct sizing, I told him about the house.
    Sure I will get a MCS pro to install it, we are forced to in the hope of the never arriving RHI!

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