Unusual Result

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Hi everyone,

I found this thread from the bldg.sim archive and I tabulated the figures
in tables 5.5-1 through 5.5-8 for glass assembly U-value for metal framing
for every climate zone.
*Climate Zone* *Definition* *Metal Framing* U-Value SHGC 1 Very Hot
and Humid 1.20 0.25 2 Hot and Humid 0.70 0.25 3 Warm-Humid 0.60 0.25 4
Warm 0.50 0.40 5 Mixed Humid 0.45 0.40 6 Mixed 0.45 0.40 7 Very Cold 0.40
0.45 8 Sub-arctic 0.40 0.45

I understand that SC usually has greater effect than the U-value, I used
to be under the impression that the lower the U-value the better. It turned
out that it depends on the climate zone.

I also have this unusual result. They did explain it well but I am eager to
hear from other fellow simulators regarding this matter. Or does anyone
have any related articles that explain this in detail? thanks in advance.

- Bob


Karen is right on. Lower window U-values and additional insulation in walls
and roofs can cause a net energy increase in buildings with high internal
heat gains. If you look at the month-by-month consumption, you may see that
the "better" envelope helps out in winter and summer, but hurts in spring
and fall. The overall net effect over the year is sometimes negative.

When the air outside is cooler than inside, then some of the internal heat
can get out of the building through the envelope. A more insulated envelope
slows the heat escaping through the envelope, so more of the heat has to
get out of the building through the HVAC system, resulting in more cooling
energy. If there is an economizer ("free cooling"), the effect is not as
severe the net effect of more insulation could be positive.

Keith Swartz, P.E., LEED AP

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