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

[Kevin Kyte]

Check this out..








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
________________________________________________________________________
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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 Xiaobing Liu
Sent: Tuesday, July 10, 2007 12:33 PM
To: BLDG-SIM at gard.com
Cc: fieldkm at yahoo.com
Subject: [BLDG-SIM] Loads not met interpretation in ASHRAE 90.1-2004

Kristin:

Thanks for your reply. I will forward your response to the list.

If the standards only address sensible load, I'm wondering whether the Unmet
Load Hours is sufficient to evaluate the performance of a HVAC system,
especially in humid climate where indoor humidity control is an essential
part of the HVAC system. Since indoor humidity control may consume
significant energy depending on the equipment/system used, I think the unmet
latent load or the indoor humidity level should also be accounted for in the
building energy performance evaluation to get fair comparison between
proposed and baseline building designs.

Xiaobing

-----Original Message-----
From: Kristin Field [mailto:fieldkm at yahoo.com]
Sent: Tuesday, July 10, 2007 11:10 AM
To: Xiaobing Liu
Subject: Re: [BLDG-SIM] Loads not met interpretation in ASHRAE 90.1-2004


Xiaobing,

I tried to send this email to the list, but there's a
glitch that doesn't allow my messages to get through. 
Anyway, here's my response for you at least:

My interpretation is that the standard is addressing
sensible load only and that it is for building-wide
hours of load unmet, not by zone.  Anyone disagree?

For eQUEST/DOE-2.2, this would mean that I'd say to
use the number on the BEPS report instead of from the
SS-R reports (although those are very helpful to look
at for other reasons).

Kristin Field

--- Xiaobing Liu <XLiu at climatemaster.com> wrote:

> All:
> 
> Regarding the Unmet load, is it for sensible load
> only or total load (sensible and latent)?
> 
> Xiaobing
> 
> -----Original Message-----
> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com]On
> Behalf Of Perron,
> Brett
> Sent: Tuesday, July 10, 2007 9:47 AM
> To: BLDG-SIM at gard.com
> Subject: [BLDG-SIM] Loads not met interpretation in
> ASHRAE 90.1-2004
> 
> 
> John,
> The few LEED projects I've modeled for (3), we've
> used unmet load for
> hours for the whole building.  I like to use the
> Summary Tab under the
> Air-Side HVAC screen to view details about my
> systems including unmet
> load hours.  The only thing is that it's only
> available for the baseline
> design and can't compare with any parametric runs.
> Hope this helps, 
> Brett
> 
> -----Original Message-----
> From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com]
> On Behalf Of Rohini
> Brahme
> Sent: Tuesday, July 10, 2007 10:12 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?
>  
> John R. Aulbach, PE, CEM
> Project Manager
> Nexant, Inc.
> 100 North Barranca, Suite 820
> West Covina, CA 91791 USA
> Phone: 626-430-9054
> Fax: 626-430-9060
> email: jaulbach at nexant.com
>  
>  
>  
> 
> 
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