[Bldg-sim] Perimeter Slab Insulation

[David Bradley]

Keith,
 If you have a cooling dominated application and a relatively cool 
average annual ground temperature, insulating underneath the slab is 
going to disrupt some amount of free cooling that you are getting. 
Adding insulation would drive cooling energy up a bit and heating energy 
down. Depending on the magnitude of the heating and cooling changes, you 
could see a net increase in HVAC energy over the year. An increase in 
heating energy and no change in cooling energy is a bit suspicious. You 
might look into how the software you are using models the ground heat 
transfer. There has been a good bit of work done and recently wrapped up 
under IEA Task 34/45 on evaluating the ground coupling models used by 
various simulation tools.
Kind regards,
 David


Keith Swartz wrote:
>
> Do any of you know the reasoning behind why the 2006 edition of the 
> International Energy Conservation Code (IECC) removed the requirement 
> for insulation for unheated slabs for some climate zones? I have done 
> a few energy models recently with slab insulation as a potential 
> energy saving measure. The numbers were very small, which was 
> expected, but what surprised me was that the savings were negative. 
> Adding insulation to the slab actually _increased_ annual energy usage 
> (very slightly). Cooling was unaffected, but fan energy was slightly 
> higher during the heating season. My quick search for research reports 
> or other insights to explain this came up empty. Do any of you have 
> any thoughts? Are the results so insignificant that the differences I 
> am seeing in the calculations could just be considered "noise"?
>
>  
>
> _____________________
>
> Keith Swartz, P.E., LEED AP
> Energy Engineer / Senior Project Manager
> Energy Center of Wisconsin
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