I think you have almost answered your own question. Design days are convenient, but you have to also be aware of zone location and orientation. I was involved
with a litigation several years ago for an overheating dormitory suite. Turns out that the highest solar heat gain for southeast facing windows in the Boston area occurs in mid-October, a time when temperature conditions call for heating. The hapless ME
designed a two pipe fan coil heating and cooling system, consequently when heating was required in one area while cooling in another, the system could not work.
General procedure is to use the design days to initially size systems. The initial sizing typically contains a percentage oversizing to account for unusual circumstances,
and it begins to account for diversity in large systems where central plant loads are a combination of fluctuating zone loads. Then an annual simulation is run and you check for unmet hours, a sign that some systems may still be undersized. How involved
you get with this process depends on your systems. Initial sizing without an extra factor can give you base loads you can use for various equipment sizing selections. Checking selected equipment is important. E+ can tell you need a 7/8 Ton DX cooling system,
but when you search equipment you are likely to find that 1 or 1.5 Ton equipment is the smallest made for this application. Once you have selected actual equipment, the annual run check for unmet hours will flag bigger problems for you, but review of performance
details is always helpful.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, February 06, 2018 5:04 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Desing using design day file or weather file
There are four zones and each zone is oriented in different direction and it is obvious that in such kind of situations, one can expect peak cooling load occurs at different time since the zone's orientation is different .
In energy plus I observed if we size as per the design day, we will see the peak cooling load of each and every zone on the same design day and at different times....
at the same, I also observed if we size as per weather file days, then I could see the peak is occuring on different days and at different times.....
which one I should consider for desining? is it design day or weather file days? as the design as per weather file days is more sensible than design day?
Design days are taken from EPW files ,where there will be only one design day. it can be either 7/21, or 5/21 for summer. my question is it can be someother day as well where the peak can be still greater than 5/21. why only 5/21 or 7/21?
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Posted by: "Edward G. Lyon" <EGLyon@xxxxxxx>
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