Re: [EnergyPlus_Support] Re: winter design day

[Derek Kite <dkite@xxxxxxx>]

In our climate, we see the design day temperatures rarely. There is a large 
difference however. A building without enough heat for the extremes may 
freeze. One tries not to have your name on the lawsuit in such a situation.

Summer extremes end up with a warmer building. Uncomfortable, in some 
situations critical, but not usually. And what constitutes comfort is 
different.

An anecdote. The local hospital did some hvac upgrades a number of years ago. 
Some sloppy engineering was shown when the winter after the work was done we 
actually hit design temperature along with high winds. I happened to be in the 
building that day and it felt like the windows were open. There was some 
damage caused by freezing steam coils and the like.

Hence engineers typically give themselves a margin on the heating side. On the 
cooling side, there are downsides from oversizing; reliability, costs of the 
complexity of control to maintain a stable system over the operation ranges, 
etc.

Of course with the more sophisticated systems, being close on both ends 
matters.

Derek Kite



On Wednesday 24 June 2009 14:36:10 Jerry McManus wrote:
> 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?
>
> You seem to be saying that there is an unspoken assumption in HVAC that
> heat is always on in the winter, but cooling is only when you actually need
> it in the summer.  Is it the experience of building designers that once you
> get below a certain outside temperature then a few degrees either way makes
> no difference in heating loads?
>
>
> ----- Original Message -----
> From: "JV Dirkes II" <jvd2pe@xxxxxxx>
> To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Sent: Wednesday, June 24, 2009 10:44 AM
> Subject: [EnergyPlus_Support] Re: winter design day
>
> > Jerry,
> >
> > Without checking E+ docs, but using my experience......
> > A "design day" is a "worst case" condition.  For winter, that means a
> > sustained cold period with no sun and no internal heat (e.g., lights or
> > PCs).  Using a zero degree daily range is a fairly normal approach to
> > those criteria.
> > A practical example in Michigan, where I'm from, would be an extended
> > weekend (say, Christmas) when the temps drop very low and stay there for
> > hours on end.  The sun, as is usual in MI, doesn't shine.  (Of course it
> > could also be night time.  We're why light therapy got popular.
> > In that instance, the heating system is all you've got; it better be big
> > enough!
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jerry McManus" <jerrymcm@...>
> >
> > wrote:
> >> Hi Folks,
> >>
> >> I'm new to EnergyPlus, and a total noob when it comes to HVAC, so please
> >> be gentle!  Here's my first newbie question:
> >>
> >> While learning about design days I was confused by the fact that all of
> >> the winter design days in the example weather data have a 0 daily
> >> temperature range modifier.  Searching the input\output reference
> >> yielded this note:
> >>
> >> "Note that usual Winter design conditions are for very cloudy days
> >> (clearness = 0), and low temperatures (temperature range=0)."
> >>
> >> Unfortunately no explanation is given why low temperatures should have 0
> >> for the daily temperature range...?  This is one of those things that is
> >> probably obvious to an HVAC pro, but it's not at all clear to me why a
> >> winter design day should not bother with highs and lows in the
> >> temperature range.
> >>
> >> Any help will be greatly appreciated.  Thanks!
> >
> > ------------------------------------
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> >
> > Attachments are not allowed -- please post any files to the appropriate
> > folder in the Files area of the Support Web Site.
> >
> > EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> > Documentation link and press the "search" button.
> > Yahoo! Groups Links
>
> ------------------------------------
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
>
> Attachments are not allowed -- please post any files to the appropriate
> folder in the Files area of the Support Web Site.
>
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button. Yahoo! Groups Links
>
>
>


------------------------------------

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/join
    (Yahoo! ID required)

<*> To change settings via email:
    mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx 
    mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx

<*> To unsubscribe from this group, send an email to:
    EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/