Dear Jerry,
Hoping that you're still around, I'll mention one more
thing.
A "design day" is supposed to reflect a condition which will
only occur, say, less than 1% of the heating or cooling season. The
heating season is easier to discuss, since heating systems are concerned
primarily with temperature loss through the building envelope or infiltration,
both of which are temp-dependent. Moisture is assumed to be close to
zero in the outdoor air for cold climates.
The goal is make darn sure your client does not get cold and
send their attorney over to ask why they're cold after spending all that money
to have you design or build their facility!
That said, MOST heating (and cooling) systems are
over-designed for a variety of reasons. You always have the option of
making a more careful load calculation and one possible way to do this is to run
E+ and see where the actual peak load occurs for the weather pattern you're
using. Keep in mind, though, that TMY data is NOT a real weather year for
any particular year.
Early in my career, I designed a heating system with NO safety
factor and it turned out to be a bit too small. I and others in my firm
spent many hours trying to figure out where the error was (calcs or
construction), but ended up supplementing the heating system at our
expense. Not a happy situation! Since then, my philosophy for
heating system design has been something like "Make it plenty big, with great
part-load efficiency".
p.s., Rather than "harsh", think "concise". Most folk on
this forum are trying to contribute insights while in the midst of many other
responsibilities. As a newbie myself, I have been very grateful for the answers
I've received from the rest of the forum, even though some of my questions could
have been answered with much less patience due to myself making dumb
errors.
The Building Performance
Team
James V. Dirkes II,
P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616
450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jerry McManus
Sent: Wednesday, June 24, 2009 6:08 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: winter design day
I could say something about "tone", but I'll refrain.Yes, it is clear to me now that in the winter the outside temps are far enough below any realistic heating set point that a daily range is unneccessary.I was quite interested in this topic, and I had already started work on a wikibook for EnergyPlus, but now I'm so put off by the harsh treatment towards my very first newbie question that I probably won't bother wasting anymore time here. Thanks!----- Original Message -----From: Linda LawrieSent: Wednesday, June 24, 2009 12:58 PMSubject: Re: [EnergyPlus_Support] Re: winter design day It's the tone...
Thanks for the quick reply, but to be honest I'm still not convinced. If a
design day is intended to be worst case scenario (as opposed to realistic
weather simulation) then why wouldn't summer design days also have a 0 daily
temperature range?
Winter days are not just one temperature -- there is no solar (so there is no possibility that winter sun will help warm the space) They are designated as "Winter Design Day" in our definitions that are supplied. Usually there won't be people, etc. Yes, Winter is usually when heating happens and equipment or people or sun into the space will help.
Summer days have range due to different diurnal climates and summer more often is about humidity. Here it is "Summer Design Day" and the people, equipment etc are supplying extra load to the space.
The Design Days are intended to be used for "sizing" equipment giving one an idea of potential extremes of their buildings.
Read about Loads Calculations in the ASHRAE Handbook of Fundamentals (Chap 14-19 in 2009 HOF) for more information. That will give you some background on philosophy.
EnergyPlus Development Team
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