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Help! Underfloor v radiator case study

  1. Nov 9, 2012 #1
    1. The problem statement, all variables and given/known data

    4. ANALYSIS

    The Excel Data File will allow the following analysis to be conducted for both emitter types:

    a) Calculate the variation in both the temperature drop across the emitter ( T) and total heat emitted (Q) over the entire test period for each of the 3 radiator and 4 floor types

    b) Use plots of the variation in the flow/return temperature, temperature drop, and heat emitted over the entire test period to compare the performance of the 3 radiator types

    c) Use plots of the variation in the flow/return temperature, temperature drop, and heat emitted over the entire test period to compare the performance of the 4 floor segments

    d) Use plots of the variation in the heat flux at the heated floor/sub floor and heated floor/external wall interfaces to compare the performance of the 4 floor segment by conducting a heat balance on each floor segment. Assume only 3 heat flow paths (+Y up, -Y down, and +Z out)

    Basically comparing 3 radiators and 4 underfloor systems.





    3. The attempt at a solution

    I have done mc delta t for the rads, but how do I calculate the heat flux for the underfloor. Is it the delta t between the inlet and outlet or inlet and floor temp?

    Also what is a heat balance and how do I calculate the time constant?

    Any other tips or sites to get info? :) Thanks :)
     
  2. jcsd
  3. Nov 11, 2012 #2

    CWatters

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    Homework Helper

    Not really my field but I have UFH in my house!

    As I understand it the power flowing into the floor slab is given by the difference between flow and return temperatures (Oh and the flow rate, and SHC of water). The power leaving the slab depends on the temperature difference between the slab and it's surroundings (and the thermal resistance etc).

    Regarding part d and heat balance. I suspect they are asking you to write an equation showing how under steady state conditions the power going into the slab equals the power leaving the slab. Perhaps something like..

    Power in = Power lost to room (eg +Y direction) + power lost to sub floor (eg -Y) + power lost at perimeter (Z).

    For that I think you need the dimensions of the slab and figures for the thermal resistance. For example you need the thermal resistance between the slab and the sub floor and the temperature of the sub floor. Ditto for the perimeter. If that info isn't available then I'm probably wrong.
     
  4. Nov 11, 2012 #3
    thanks for the reply.

    I'm not sure if I have the thermal resistance figs, they may be given.

    But, the study is comparing different types of floor.
    -timber floor
    concrete floor - no insulation
    concrete - 80mm insulation
    concrete - 250mm insulation

    :)
     
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