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The building envelope serves as a barrier preventing heat transfer from inside to outside (during winter) and from outside to inside (during summer). But if you have substantial internal gains in your zone, increasing R-value of the building envelope will increase the amount of cooling required, because the heat produced in the zone can no longer exit through the envelope as easy. I was surprised when I first heard this, but it is entirely logical.
To check out if this is really the case:
- Save a copy of your file as something else,
- Remove all but the 1st scenario.
- Remove all lighting, motors, pools, processes and miscellaneous equipment and occupants from the zone. That should eliminate all internal gains.
- Make 2 scenarios: one with a lower R-value on windows (walls or whatever) and one with a higher R-value.
- Simulate and look at results.
Since you no longer have internal gains, cooling energy usage should decrease with increased envelope R-value. The increased R-value is keeping heat out of the zone.
Whereas, when you had substantial internal gains, cooling energy usage increased with increased envelope R-value. The increased R-value was keeping heat in the zone.
(A possible exception to this is a building with huge glass facades. If you think of the solar gains as internal gains, you can see why this could be an exception.)
Otherwise feel free to contact our Tech Support staff at (805) 329-6565, or via email at firstname.lastname@example.org.