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What size heat pump?

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  • 27-10-2005 3:18pm
    #1
    smadger
    Closed Accounts Posts: 80 ✭✭


    Hi,

    I'm getting quotes for underfloor heating and a ground source heat pump from various companies. They've all been given the same plans (dormer with UFH on both floors and area of 270 sq m, or 2900 sq ft).

    What's worrying me is that each quote is coming in with a different power output from the heat pump, varying from 11kW up to 18kW.

    I'd be worried about underspec'ing the heat requirements and being left freezing in the depths of winter. At the same time, no-one want's to pay over the odds for a system that's too big.

    Have any of you had a similar problem and what conclusion did you come to?


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    #2
    RedLady
    Closed Accounts Posts: 66 ✭✭RedLady


    Hi,

    I have had the same problem. Our house will be 2500 sq ft and what I asked all these companys for is a system that will heat water for the UFH and for the domestic hot water. Most of them who gave me quote for the 11kw pumps, quoted me for Solar Panels to seperatly heat the domestic Hot Water. Dunstar quoted me for a 15 kw pump to heat water for both. Althernative Heating Company in Cork told me that 11 kw should be plenty big enough for both domestic and UFH as the weather compensator should allow for changing between both. Climate Master in Galway also gave me a quote for a 12 kw pump to heat water for the UFH and the Domestic hot water - this is for a DX system.

    It is quite confusing as when they all give different specs. I think because of the fact the we are going to be putting in a Heat Recovery System, tripple glazing windows and as much insulation as we can and that the site is south facing with most of the living accomodation facing that way, that a 11-12 kw pump should be sufficient. If the bank manager allows me to spend anymore, I might try and get a self install Vacum Solar Panel for the domestic hot water which should give hot water for most of the year as they rely on light and not direct Sunlight to work.

    I too would be interested in what other peoples thoughts on the different specs are.

    Regards,


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    #3
    patrido
    Closed Accounts Posts: 299 ✭✭patrido


    my quotes even had different floor areas from exactly the same plans :)

    the differences can be due to lots of things and mistakes in the calculations could be one, but let's rule that out for the moment.

    firstly, different assumptions about u-values, heat loss, etc. noone asked me what type of insulation or windows i was putting in so i don't know what assumptions they made there. did they take the average house, the average new house, the latest regulations? who knows.

    they also have to make a guess about the lowest external temperature. some will pick zero degrees, some will be degree higher or lower. one company may have taken regional temp variations into account.

    some companies will assume that your internal temperature will be 20 degrees in every room, while others assume that hallways will be 17ish, kitchens 18, bathrooms 22. all of these will make the calculations vary.

    also, many quotes add in an estimate for DHW. no company asked me how many people were in the household, or whether we liked baths or showers. they had to have made more assumptions, so expect quite a lot of variation in what they estimated.

    whatever heat requirement they calculate, they then have to round up to their next biggest pump. the one that quoted 18kw might have calculated 14kw, but had nothing smaller than 18kw.

    the best bet might be to get your engineer to do a detailed heat loss calculation for your whole house based on your actual specs and not assumptions.


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