[Bldg-sim] Unusual Result

Karen Walkerman kwalkerman at gmail.com
Fri Sep 24 04:14:47 PDT 2010


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>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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