[esp-r] a problem about revealing the thermal mass effect on energy consumption by Esp-r

[Gulsu Ulukavak Harputlugil]

Hi All,

I have a very simple problem. You know that for energy efficiency issues,
the thermophysical properties of the materials that composed the envelope of
building is very essential. In order to evaluate the amount of heat transfer
from one side of the wall to other, the most common reference is "R-value,"
or *resistance* to heat flow. The higher the R-value of a material, the
better it is at resisting heat loss (or heat gain). the arithmathically
reverse of R-value is U-factor (or "U-value," as it is often called) which
is a measure of the flow of heat—thermal transmittance—through a material,
given a difference in temperature on either side. In short, for simple
energy calculations we can guess that the lower u-value, the lower energy
consumption. However the mass of the materials have very essential role
during heat transfer even the u-value is constant. High mass materials (the
specific heat and density of the materials show us the heat capacity of the
materials, the high mass materials have high heat capacity) have special
characteristics which are called time lag and degrement factor. Simply
degrement factor reduces the peak loads and time lag delays the peak loads
from one side of the wall to other. (for further information:
http://www.buildinggreen.com/auth/article.cfm?fileName=070401a.xml )
Anyhow, I have a research on sensitivity analysis of the energy performance
and one of the parameters that I evaluate is the effect of thermal mass. I
have wall construction -from outside to inside-composed of plaster (2cm),
insulation (PUR)(2cm), aerated concrete (20cm), plaster (2cm) and the
u-value is 0.48 W/m2K. The specific heat of aerated concrete that I used is
840 J/kgK and the density is 500 kg/m3. I replaced aerated concrete with
heavy mix concrete which has specific heat of 1000J/kgK and density of 2400
kg/m3. In order to make u-value constant (it should be constant otherwise I
can not see the effect of thermal mass alone) I changed the dimension of
concrete from 20cm to 30cm and insulation from 2cm to 6cm. Thus the
u-value stays constant (0.48W/m2K) Now, I made the simulations (rest of
the input parameters for both of the model is completely same). However
heating energy calculated for aerated concrete is 3792.65 kWh, heavy mix
concrete is 3781.27kWh. It is very interesting for me and I go one step
further and use water as a wall construction. Water has a specific heat of
4180 J/kgK. Esp-r warned me that this value is too high but made the
calculations. However the result is very close to the others, 3791.02 kWh. I
checked the surface temperatures and heat storage as well but these are the
same or very very close to each other.
Probably I miss a step which is necessary to activate the effect of thermal
mass. I also tried to use "define uncertanities" option of esp-r but I need
a password to activate it....
Is there anyone to help me?

Thanks in advance...

Gulsu
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.strath.ac.uk/archives/esp-r/attachments/20061002/d013bde1/attachment.html