[esp-r] Re: pcm

[Achim Geissler]

Hi Arianna,

according to the info in mscomp.db2 (good place to look for further information) if you assume latent heat is constant in the temperature range Tsolid-Tmelt, then a=0 and b=latent heat (however in the unit kJ/(kg K) and not as you give kJ/kg … likely use a temperature span of 1 K and you will have the same number with a correct unit - but no idea if this would be correct for your specific PCM - more data on the material would be helpful).

You may try (assume PCM melts is from 25.5 to 26.5 °C)

     0 = a (25.5+273) + b
100 = a (26.5+273) + b

b= -a (25.5+273)

100 = a (26.5+273) - a (25.5+273) => a = 100/1 = 100 kJ/(kg K^2)

=> b = -29850 kJ/(kg K)

This would give the function latent(T)=100 kJ/(kg K^2)*T K - 29850 kJ/(kg K).

This should cover the second case described in mscomp.db2, the general idea being that you integrate from start of melting to end of melting (you need a temperature span) and when melting is done, you should end up with your given overall latent heat. Mind, though, that I have not tested above procedure for the simple PCM model.

The value of the conductivity could be chosen as or close to the embedding material value (provided the PCM is embedded e.g. in plasterboard). Otherwise, you would need to know approximately what type of material the PCM is and look for some literature values for conductivity (solid and molten).

Best
Achim


On Mar 5, 2015, at 4:15 PM, Arianna Sdei <A.Sdei2 at brighton.ac.uk> wrote:

> Dear All,
>  
> I would like to modify an old model that uses PCM. I know the melting point of the material 26C and the latent heat 100kJ/kg. All other parameters are unknown to me at the moment. How can I set up parameters for conductivity and a and b in the equation y=ax+b in a way that the indoor temperature reduction is maximized?
>  
> please let me know,
>  
> kind regards.
>  
> Arianna 
> 
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achim.geissler at intergga.ch




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