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

[Taylor, Russell D UTRC]

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
________________________________________________________________________
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-----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?


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