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<P><FONT SIZE=2 FACE="Arial">Ok - here's a question, maybe stimulate a little controversy but as many of you know - that's the way I like it. </FONT>
<BR><FONT SIZE=2 FACE="Arial">-10 F freezer, 100,000+ square feet. Reasonably steady product loading 24 hours a day (say 90 tons +/- 25 tons in a given hour).</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Two envelope systems: 5" metal skin panel with expanded polyurethane vs. thermal mass panel of 8" HW concrete interior, 6" extruded polystyrene, 2-1/2 HW concrete exterior.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Polyu conductivity .0142 btu/h-ft-F (LTTR basis). Metal skin wall U without external skin resistance (DOE2) = ..033. Polystyrene .0167, thermal mass wall U = .030. </FONT></P>
<P><FONT SIZE=2 FACE="Arial">Question - which one is better? That's a loaded question but from a strictly thermal performance measure - kWh per year to cool - is there more difference than the .030 vs. .033 U-value would imply?.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">We are using eQuest (Doe2.2) and it show the thermal mass as `slightly' better. The manufacturer, based largely on testimonial evidence, insists it is MUCH better. </FONT></P>
<P><FONT SIZE=2 FACE="Arial">One issue that they raise is infiltration through the metal skin panels and the impact on in-situ R value. They site ORNL test results that apparently show this but I've not seen them. I know ORNL did some testing on apparent R of mass walls but it didn't seem conclusive to me that it would apply in this situation.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Anyone out there that can cite well documented research about the differences? Anyone have comments about DOE2's strengths and weaknesses in capturing the effects of the large wall thermal mass?</FONT></P>
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<P><FONT SIZE=2 FACE="Arial">Mark E. Case, President</FONT>
<BR><FONT SIZE=2 FACE="Arial">etc Group, Inc.</FONT>
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