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U values help needed

  • 20-12-2010 12:26am
    #1
    TengoKbailar
    Closed Accounts Posts: 2 ✭


    Hi,
    I have an old mid terraced house 1900ish in Liverpool and I am trying to work out what size central heating system to install.
    I have spent a couple of days on Google and got most of the U values except for the floors/ceilings.
    The ground floor is a suspended wood floor with an air gap of 30 - 40 cm underneath constructed of 150mm joists & 25mm floorboards
    The ground floor ceiling is lath & plaster on the 150mm joists with 25mm floorboards of the first floor
    The first floor ceiling is lath & plaster on 150mm joists with 100mm of insulation in between them and above this is a slate pitched roof.

    I am trying to find the U values for the respective floors/ceilings and how to adjust them for the air space under the ground floor and the heat rise to the first floor and the top ceiling.

    I would be very grateful for any information and advice :)

    Thanks
    Michael


Comments

  • #2
    Lantus
    Registered Users, Registered Users 2 Posts: 3,027 ✭✭✭Lantus


    An uninsulated suspended floor can have a U value of anything from tyically 0.5 to 1.1 and is dependant on the area to perimeter ratio of the ground floor and the material of the ground. (rock, sand, clay etc.)

    The FF ceiling would be around .35 or .4 at a guess.

    Unless your planning on heating the downstairs at a radically different temp to upstairs you dont need to consider internal heat transfer.

    Remeber to include air infiltration in your calcs. By far the biggest load.

    0.33.N.V.(tIN-tOUT)

    N is the air change rate. For an old building with rubbish windows you may want to use a figure of 2. Typically .5 to 1.0 for a more modern house. If some rooms are better sealed than others then use different values for different rooms. As you can see inputting 2 into this equation and 0.5 will get you very different heat loss values (answer in Watts.)


  • #3
    TengoKbailar
    Closed Accounts Posts: 2 ✭TengoKbailar


    Hi lantus,
    Thanks very much for your help
    I have used
    area m2 X temp difference X Uvalue = W/m2 0C
    do I need to include the perimeter for the floors & walls too?
    Could you give me a value for the first floor ceiling?
    The ground under the first floor is earth

    Thanks again
    Michael


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