[BLDG-SIM] Loads not met interpretation in ASHRAE 90.1-2004

[Graham Carter & Megan Lyall]

I would have thought the 300 of 8,760 would be on a zone by zone  
basis and then system by system basis so number of zones shouldn't  
impact it.  But I practice in Australia and I haven't looked through  
90.1 since the 1989 revision when I was in Canada ... so just an  
opinion.

Also the SS-R report is very useful, particularly for VAV systems.   
It will show you how the zone air volumes are distributed as a % of  
design and reports loads under-cooled and under-heated by zone.   
However a few years back I came across a lot of hours under-heated or  
under-cooled and couldn't work out why.  Turns out it includes any  
hours the fans run which could be for night purge when setpoints are  
not being held.  To my knowledge this hasn't been changed.  I am  
unsure whether loads not met works the same way (i.e. includes night  
purge hours) ...

G

On 11/07/2007, at 6:08 AM, Taylor, Russell D UTRC wrote:

> In DOE2.1E and in DOE2.2/eQuest, you can view the number of unmet  
> loads
> hours on a zone-by-zone basis in the SS-F report. This reports the
> number of hours that the zone loads were not met broken down by month
> and by category (i.e. heating or cooling).
>
> In addition, the BEPU report gives you the total of unmet loads  
> hours as
> a percentage for the system simulation and the central plant  
> simulation.
> Be aware that the system unmet loads fraction can be misleading as  
> it is
> the number of zone loads not met by the system summed over all the
> zones. Therefore, if one zone has unmet loads for 8760 hours then the
> fraction will be reported as 100% even if all the other zones have  
> zero
> unmet loads.
>
> With regard to the loads not met by the plant in the BEPU report, if
> these occur at the same time as an unmet system load there will be
> double counting of loads not met by the simulation.
>
> My own view is that the Appendix G definition of unmet loads unfairly
> penalises simulations with large numbers of zones. For example, in  
> a 10
> zone simulation, each zone would need to have 30 hours with unmet  
> loads
> to reach the 300 hour limit. But in a simulation with 100 zones each
> zone would only need 3 hours of unmet loads to reach 300 unmet loads
> hours.
>
> If I were to rewrite the relevant section of Appendix G to correct  
> this
> problem I would multiply the number of hours of unmet load for each  
> zone
> by that zone's fraction of building floor area. This would  
> normalise the
> measurement of unmet loads to the size of the building and the  
> number of
> zones in the simulation so that the maximum possible percentage of  
> unmet
> loads would be 100%.
>
>
> ______________________________________________________________________ 
> __
> _______
>
> Russell D Taylor, Ph.D.
> UTRC | 411 Silver Lane, MS 129-85 | East Hartford, CT 06108 | Ph:  
> (860)
> 610-7485
> ______________________________________________________________________ 
> __
> _______
>
>
> -----Original Message-----
> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of  
> David S
> Eldridge
> Sent: Tuesday, July 10, 2007 3:41 PM
> To: BLDG-SIM at gard.com
> Subject: [BLDG-SIM] Loads not met interpretation in ASHRAE 90.1-2004
>
> You can click on the building level in the left-hand panel explorer  
> when
> you are in the air-side module of eQuest, and then go to the summary
> tab.  It will summarize the zones and systems that have unmet loads.
>
> (If you have selected a particular air system in the explorer you will
> get the summary for only that system rather than all of the systems.)
>
> I haven't experimented enough to know how it calculates the "building
> total" unmet hours...if simultaneous unmet zones/systems count  
> double or
> not.  It does provide an overall project system unmet hours for you to
> use.
>
> The temperature and humidity reports are also useful in the full  
> output
> -- in the sim viewer program you can scroll through the zones with the
> down arrow once you've selected the desired report to spot any  
> irregular
> temperatures.  This might be hard to spot that one spurious hour,  
> but it
> will help you see if you are getting a lot of unmet hours at a time  
> you
> thought the system was supposed to off for example, or if the unmet
> hours are at start-up.  Or perhaps there is a zone that has high
> temperatures in winter due to a west facing window and the cooling is
> off.
>
> Last idea, make sure you have consistent zone setpoint schedules and
> zone design heating and cooling temperatures.  Maybe you have changed
> the setpoint schedules during the project and not gone back to the
> design setpoint to make the corresponding change.
>
> David
>
>
>
>> -----Original Message-----
>> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of  
>> Rohini
>> Brahme
>> Sent: Tuesday, July 10, 2007 9:12 AM
>> To: BLDG-SIM at gard.com
>> Subject: [BLDG-SIM] Loads not met interpretation in ASHRAE 90.1-2004
>>
>> I usually look through the zone report (SS-H? - the one which shows
> the
>> undercooled or underheated hours for each zone) to see if any zone  
>> has
>> unreasonably high numbers. Fixing these zones usually gets me a very
>> low number for unmet hours for the total of all zones. I would be
>> curious to see what others have to suggest. In your case, going
> through
>> 76 zones would be quite tedious.
>> - Rohini
>>
>> All:
>>
>> ASHRAE 90.1-2004 has design criteria for Equipment capacities on Page
>> 176 of the Standard (G3.1.2.2). It talks about Unmet load hours on  
>> the
>> proposed design AND the baseline design not exceeding 300 hrs (of
> 8,760
>> Hrs), and the delta between base and proposed not differing more than
>> 50 hours.
>>
>> Is this WHOLE BUILDING, or BY ZONE? I have 76 zones in my building,
> and
>> to play the Unmet loads game between these two models is harder than
>> trying to hold water in my hands.
>>
>> Any thoughts, interpretations, or suggestions?
>
>
> ==================
> You received this e-mail because you are subscribed
> to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe
> from this mailing list send a blank message to
> BLDG-SIM-UNSUBSCRIBE at GARD.COM
>
>
> ======================================================
> You received this e-mail because you are subscribed
> to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe
> from this mailing list send a blank message to
> BLDG-SIM-UNSUBSCRIBE at GARD.COM

======================================================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM