[Equest-users] how to reduce the unmet hours?

[Arpan Bakshi]

Zhiren,

There was an excellent discussion on unmet hours fairly recently. Here it
is provided below --


-----------------------------
Arpan Bakshi
YRG sustainability
Direct 646 704 2880

---------- Forwarded message: UNMET HOURS ----------

From: Michael Collarin <MCollarin at elmengr.com>
Date: Mon, Nov 22, 2010 at 4:11 PM
Subject: Re: [Bldg-sim] Adjusting Capacity for Unmet Cooling
To: Nick Caton <ncaton at smithboucher.com>, Nearedge <near_ej at yahoo.com>,
cjaigath at yahoo.com
Cc: bldg-sim at lists.onebuilding.org


 Nick,



Thank you for the response. My first energy modeling experience was with
eQuest, but have been using Trane¡¯s TRACE 700 more extensively. In addition
to the bldg-sim lists, the TRACE support is an excellent resource for those
using the software, especially when it comes to unmet hours.



As you mention, and as I was alluding to in my third paragraph (starting
with ¡®Before taking this step,¡¯), there are certainly other areas that
should be addressed prior to adjusting the cooling and heating capacities. I
was not trying to cover all of them and did not want to get too in depth, as
there are numerous areas that could be contributing to the unmet load hours
and a review of the model would be necessary to determine what changes must
be made to remedy the model. I¡¯d like to note that I said the model and not
the unmet hours. As you and Carol have illustrated, I fully agree that we
aren¡¯t supposed to be trying to manipulate the model to give us our desired
outcome, but rather provide an accurate model. I do not think anyone should
be taking liberty with the capacities to such extremes just to meet the
requirements for unmet load hours. I even scratched my head the first time I
read through that section and thought, ¡°well what¡¯s the point?¡±



My response wasn¡¯t meant to suggest that modelers wildly vary cooling and
heating capacities to obtain their desired results, but to clarify that
Neeraj¡¯s comment (copied below) was in fact contrary to what ASHRAE requires
in Appendix G. Perhaps a few disclaimers were in order J

Correct me if I am wrong but on the contrary I think that ASHARE baseline
PRM fixes the cooling and heating capacities to 1.15 and 1.25 respectively
and the user is allowed to bump up the supply CFM in increments if
necessary.



In conclusion, I offer these bullet points:

¡¤         Design airflow rates are *set* using a 20-degree delta T between
supply air and room space

o   These shall not be adjusted to ¡°fix¡± unmet hours

¡¤         Baseline cooling and heating capacities are initially set to 115%
and 125% respectively

o   These may be adjusted incrementally, but should not be relied upon to
¡°fix¡± a poorly produced model. In fact, their adjustment should be
considered last, after all other approaches have failed.

¡¤         It is important to understand what an unmet hour is and why they
occur

o   It is of even greater importance to remedy the cause of the unmet hour
rather than ¡°fudging¡± the numbers

o   Refer to your software¡¯s Building Temperature Profile report, if such a
report exists, to help find the source (space, system, etc) of the unmet
hours

o   Thermostat Drift Points and Utilization Schedules have been primary
culprits

¡ì  Other areas affecting unmet hours include but are not limited to the
following: Thermostat placement, fan cycle operation, optimum starts,
building envelope entries, Ventilation (outside air) schedules



Happy modeling!



*Michael M. Collarin, EIT, LEED AP BD+C **|** **Elm Engineering, Inc. | 212
S Tryon St | Suite 1375 | Charlotte, NC 28281***

PHONE 704-335-0396 Ext. 108|* *FAX 704-335-0399* *|* *www.elmengr.com



*From:* Nick Caton [mailto:ncaton at smithboucher.com]
*Sent:* Friday, November 19, 2010 5:57 PM
*To:* Michael Collarin; Nearedge; cjaigath at yahoo.com
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* RE: [Bldg-sim] Adjusting Capacity for Unmet Cooling



Hi Michael,



I¡¯d like to offer a quick heads up ¨C your interpretation of what 90.1 has to
say regarding addressing unmet hours is spot on and well-stated, no
disagreements here.  Neeraj however is indirectly making a pretty valid
point that I¡¯d hate for anyone to miss¡­



If you only ever approach addressing unmet hours by bumping the oversizing
factors, you may well be missing something critical.  I for one was in this
train of thought when I started out.  To the letter of the standard, indeed
this is all we¡¯re *prescribed* to do to remedy the situation, but this
approach will not always work, and may result in baseline models with a very
skewed performance ¨C suffice it to say skewed is not always a *good* thing,
even if it does make your performance numbers look good.



Whenever I have unmet hours, I¡¯ve learned through others on these lists to
investigate the ¡°why¡± and ¡°when¡± of those unmet hours as a first step.  More
often than not, unmet hours in my models, when they do occur, have nothing
to do with lacking heating or cooling capacity ¨C fan (airflow) scheduling
conflicts, thermostat setpoints and unrealistic deadbands are the primary
culprits.  The systems effectively aren¡¯t running as frequently or for a
duration as they should be.



When this is the case, and I can assure Neeraj is not alone in this
experience, fluffing the oversizing factor may appear to ¡°remedy¡± the issue,
but often as not may *not*  be enough to pull your baseline/proposed models
into the prescribed requirements for unmet hours.  In some cases, you might
even make the situation worse.  I¡¯m pretty sure the spirit of the standard,
by specifying a maximum number of unmet hours, is to allow both the proposed
and baseline systems to run when they need to satisfy the loads



For whatever combination of reasons, and luck may be a part of it, it has
been a long while since I¡¯ve created an autosizing 90.1 baseline model whose
unmet hours did not ring in at either zero or the single digits, and as such
did not require any adjustments.  I personally feel this has had a lot to do
with understanding the mechanics behind what defines and can cause an unmet
hour ¨C as you¡¯re getting at with consideration to drift points.



As you say, future versions of 90.1 may be more nuanced, but I personally
feel the manner in which unmet hours are currently addressed does a
disservice to those aspiring to be quality energy modelers ¨C one can easily
be misled to believe an unmet load hour is a problem in and of itself with
an easy ¡°fix,¡± without recognizing it¡¯s really a symptom of a problem...
bumping capacities without first addressing the cause of unmet hours is
something like a doctor only giving you a band-aid for a cut when what you
need is a tetanus shot!



It may be worth mentioning that my experience is dominantly within the world
of  eQuest/DOE2.  I would not be surprised to find other engines/software
have varying ¡°typical¡± causes of unmet hours.



Anyway, that¡¯s my two cents, for what it¡¯s worth =) ¨C hope it might help
lead others along the path!



~Nick



[image: cid:489575314 at 22072009-0ABB]**

* *

*NICK CATON, E.I.T.***

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

*Check out our new web-site @ *www.smithboucher.com* *



*From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Michael Collarin
*Sent:* Friday, November 19, 2010 1:46 PM
*To:* Nearedge; cjaigath at yahoo.com
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Adjusting Capacity for Unmet Cooling



Neeraj, it is in fact the contrary.



ASHRAE 90.1-2007 Appendix G requires you to model Baseline Airflow Rate
using a 20-degree F temperature difference between the supply air and room
air temperatures. Therefore, if your room set point is 75F for cooling, set
your cooling leaving air temperature to 55F and vice versa for heating; 72F
heating set point requires a 92F leaving air temperature. This establishes
your CFM airflow within the model. Do not vary these to adjust unmet hours.



If you have unmet heating or cooling hours (over 300 or greater than 50
between baseline and proposed), you may incrementally adjust the baseline
cooling and heating capacities (originally oversized 15% and 25%
respectively) accordingly to reduce the overall unmet hours (below 300) or
the difference between baseline and proposed (within 50).



Before taking this step, be sure to look at your thermostat drift points. If
the cooling set point is 75, but the cooling drift point is 84, when the
space is unoccupied this would allow the space to move toward 84 degrees.
When the space becomes occupied and the simulation tries to cool to 75, the
system will not be able to achieve this within the allotted time (1 hour)
and you will have an unmet cooling hour.



There are some changes to ASHRAE 90.1-2010 that will effect unmet hours, but
for the time being, if you are modeling a project using 2007 or 2004, this
method should help you eliminate the unmet hours.



Regards,



*Michael M. Collarin, EIT, LEED AP BD+C **|** **Elm Engineering, Inc. | 212
S Tryon St | Suite 1375 | Charlotte, NC 28281***

PHONE 704-335-0396 Ext. 108|* *FAX 704-335-0399* *|* *www.elmengr.com



*From:* Nearedge [mailto:near_ej at yahoo.com]
*Sent:* Friday, November 12, 2010 12:51 AM
*To:* cjaigath at yahoo.com
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Adjusting Capacity for Unmet Cooling



Hello Jaigath,
Using the performance rating method (PRM), in my experience it is usually an
issue of low supply CFM.
Correct me if I am wrong but on the contrary I think that ASHARE baseline
PRM fixes the cooling and heating capacities to 1.15 and 1.25 respectively
and the user is allowed to bump up the supply CFM in increments if
necessary.
I have a feeling that the issue of unmet load hours has been discussed many
times before -- so, the archives will be a good resource as well.
Best,
Neeraj

Neeraj Kapoor
t: +91.99581.70018

e: neeraj[at]kalpakrit[dot]com
Kalpakrit Sustainable Environments Pvt. Ltd.
www.kalpakrit.com

*Office Address*:
610-A Udyog Vihar, Phase-5,
Gurgaon, Haryana - 122016
t: +91.124.430.9490/ 1/ 2
f: +91.124.430.9493

*Registered Address*:
101 Anupam Apartments,
Mehrauli-Badarpur Road,
New Delhi - 110068



On 11-11-2010 10:30, Jaigath Chandraprakash wrote:

Hello All,

I would like to know how other increase their baseline capacity when they
have unmet load. I have a PSZHP system and in one system, I got more than
400 hrs unmet load. I usually just increase the TR cooling capacity until I
get a lower unmet load but in this case, I think the unmet load is due to
low supply cfm. Is it ok to adjust also the supply fan cfm? I am thinking
that G3.1.2.2 only requires me to adjust only the cooling capacity. Do
others adjust both cfm and cooling load?

Thanks,

Jaigath





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2011/1/4 zhiren zhou <zhouzr at cabr-sh.com>

>  Dear Charles Land
>
>     I¡¯ve found the results in the BEPU as below
>
>
>
>                    PERCENT OF HOURS ANY SYSTEM ZONE OUTSIDE OF THROTTLING
> RANGE = 14.7
>
>                    PERCENT OF HOURS ANY PLANT LOAD NOT
> SATISFIED                =  0.0
>
>
>
>     So how can I reduce the PERCENT OF HOURS ANY SYSTEM ZONE OUTSIDE OF
> THROTTLING RANGE?
>
>
>
>
>
>
>
> *·¢¼þÈË:* Charles Land [mailto:cland at geo-marine.com]
> *·¢ËÍʱ¼ä:* 2011Äê1ÔÂ4ÈÕ 22:46
> *ÊÕ¼þÈË:* zhiren zhou; equest-users at lists.onebuilding.org
> *Ö÷Ìâ:* RE: [Equest-users] where to find unmet hours in eQUEST
>
>
>
> You can look either under your summary tab for your unit or in your BEPS or
> BEPU in your simulation output.  You can also look at your SS_O to see what
> time of the day you zones aren¡¯t being conditioned properly or set up a
> hourly report for a specific zone.
>
>
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *zhiren zhou
> *Sent:* Tuesday, January 04, 2011 9:43 AM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] where to find unmet hours in eQUEST
>
>
>
> Dear all
>
>          Could anyone tell me how or where to find unmet hours in eQUEST?
> Thanks a lot
>
>
>
>                                      arron
>
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to
> EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
>
>
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