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Roof insulation ↑ cooling loads ↑ why ? OpenStudio

asked 2017-02-13 07:12:40 -0500

shahin1992's avatar

updated 2017-08-20 14:46:58 -0500

i'm doing a school assignment to study the impact of roof insulation on Cooling loads and i'm getting more loads when i apply higher R insulation layer and i don't understand why !! Roof Insulation Vs Energy consumption Chart Here is the OpenStudio Osm please share your thoughts with me on this. Best Regards

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Somewhat of a duplicate question, someone else can be the judge though.

Adam Hilton's avatar Adam Hilton  ( 2017-02-13 08:28:11 -0500 )edit

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answered 2017-02-13 08:25:28 -0500

Adam Hilton's avatar

updated 2017-02-13 14:34:54 -0500

It's a matter of a space being able to 'breathe'. While increasing insulation will reduce heat gain to a space it will also reduce heat loss to a space.

Say your system is a space with exterior ceiling, floors, and walls, and typical office internal loads. During unoccupied hours when the sun is down $Q_{in}$ is probably pretty small and less than $Q_{out}$ with a roof insulation of say R-30, so your space will cool. Now when that's increased to R-34 we'll assume that both $Q_{in}$ and $Q_{out}$ are reduced by 5%, and since $Q_{in}$ was smaller than $Q_{out}$ $\Delta Q_{in}$ < $\Delta Q_{out}$, so the space will cool less than the previous situation. Where this becomes tricky is when you've increased your insulation to a point where you're now trapping all the heat from your internal loads inside the space such that it can't escape at night when it was previously able to.

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thank you , i do understand that concept and i wanted to test that by two different steps, the first one was to increase the level of insulation for the wall and that actually reduced the cooling load not increased it " i expected both would have a similar pattern". the second step was to increase the area of the skylight on the roof to check if also that will decrease the cooling load but it didn't, in fact it did only for 1% skylight roof ratio but increasing the skylight to 2% or 3% increased cooling loads. also the range used for R5.6 " no insulation" - R16 is not very high level.

shahin1992's avatar shahin1992  ( 2017-02-13 09:30:29 -0500 )edit

It's a balancing act. It can't be said that increasing insulation will always decrease cooling energy and likewise that decreasing insulation will always increase cooling energy. There are many variables at play here. In your first test you changed the exterior wall insulation which only affects exterior zones. These are spaces that generally require heating in the winter and cooling in the summer. Your second test changed exterior roof insulation which will affect both interior and exterior zones. The interior zones likely require cooling in both summer and winter.

Adam Hilton's avatar Adam Hilton  ( 2017-02-13 09:50:00 -0500 )edit

It's the interior zones that are generally more reflective of the increased cooling loads when increasing insulation because of the fact that they generally still need cooling during low OAT times.

Adam Hilton's avatar Adam Hilton  ( 2017-02-13 09:53:55 -0500 )edit

@adhilton we just fixed MathJAX. Sorry for the trouble.

Neal Kruis's avatar Neal Kruis  ( 2017-02-13 14:13:23 -0500 )edit

Not a problem, thanks!

Adam Hilton's avatar Adam Hilton  ( 2017-02-13 14:29:38 -0500 )edit

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Asked: 2017-02-13 07:12:40 -0500

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Last updated: Feb 13 '17