[Equest-users] Unusual Result

Bobby Sy rsg4999 at gmail.com
Tue Feb 28 19:28:46 PST 2012


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
________________________________________________________________________________________________


Jaigath,

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

Energy Engineer / Senior Project Manager
Energy Center of Wisconsin
455 Science Drive, Suite 200, Madison, WI 53711
Phone: 608.238.8276 x123
Fax: 608.238.0523

The Buildings Team
Design decisions through energy, economics and emissions analysis.
www.ecw.org/Buildings<http://www.ecw.org/Buildings>

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www.ecw.org/university/<http://www.ecw.org/university/>
From: Karen Walkerman [mailto:kwalkerman at
gmail.com<http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org>
]
Sent: Friday, September 24, 2010 6:15 AM
To: Jaigath Chandraprakash
Cc: bldg-sim at
lists.onebuilding.org<http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org>
Subject: Re: [Bldg-sim] Unusual Result

If most of your cooling loads come from internal loads as you said, then
having windows with a higher U-value allows the building to lose heat to
the outside any time it is cooler outside than inside.  If you look at
ASHRAE 90.1, the requirements for windows changes dramatically as you move
from colder to warmer zones.  In warmer zones, the allowed U-value is
higher, but the SHGC is lower.

Also, it is usually good to verify that this is actually the case, often
installed equipment runs only a fraction of the day, or at a fraction of
the peak energy use.  If your internal loads are not actually as high as
you are modeling, this could change things.

Lastly, does the building have an economizer?  This may make sense for this
particular project.

--
Karen
On Fri, Sep 24, 2010 at 5:59 AM, Jaigath Chandraprakash <cjaigath at
yahoo.com<http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org>
<mailto:cjaigath at
yahoo.com<http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org>>>
wrote:
The project I am working on is an office building that operates 20 hrs per
day with most of the loads occuring at night and low occupancy on daytime.
It is a cooled by a DX roof unit and has a very high internal load. No
heating equipment is required because the building is in Climate 1. I was
surprised that when I changed my window U-value from 0.3 to 0.7 I got less
cooling consumption. I always thought that getting low u-value will give me
less coling consumption. Can somebody tell me why I am getting less cooling
when I use a higher window U-value?

Thanks,

Jaigath
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