Hi All,<br><br>I think Nick is spot on in his discussion re unmet hours. While I'm not saying it's a wrong thing to do, I personally have never used oversizing the system as a way to get rid of unmet hours.<br><br>
As an example, I have been helping someone off the list with his project, a seemingly very simple building with only 5 thermal zones and one PVAVS air handler with dx cooling and hot water heating - system 5. After running my 4 exposures, and having none of them with <b>any</b> hours of unmet loads, I calculated my kW/cfm, heating load, cooling load, boiler kW and all of that, put the calculated results in the baseline, reran the baseline, and for some darn reason I had over 1000 hours of unmet cooling loads.<br>
<br>I checked all my inputs, made a few changes, reran the 4 exposures, and not much changed. So, I put on my thinking cap and read Nick's email - not necessarily in that order. One of the things that occurred to me is that since the building is turned off all weekend my Monday morning pull down loads during the summer might be the cause of the problem, so I put in an optimum start schedule (this might have been required, I haven't double checked) and my unmet hours were reduced by about 300 hours. I had an adequate cfm/sf, something I'm not shy about raising at all since eQUEST defaults it to 0.5 cfm/sf which is usually too small, so I didn't change it. Then I looked at the throttling-range. <br>
<br>For VAV systems the eQUEST/DOE2 manuals say that the throttling range should be <b>at least</b> 4 degrees to insure stable operation and that is what I had it at originally. After thinking about it and doing some simple math in my head I raised it to 6 degrees. My cooling temperature is set at 75 degrees so this means when my room temperature reads 79, set point temp + 1/2 TR + 1 degree, my cooling coils will be activated. Before I did this I had also looked at my SS-F reports and could see that my room temps weren't that far off from the set point temp when I had under cooled hours reported. Using the new throttling range brought me down to less than 500 hours of unmet loads, which may work.<br>
<br>So this is an example of the thinking around what's going on and developing a strategy that makes sense for a specific building. I also looked at my heating/cooling temp schedules, etc., as Nick mentioned. What baffles me is why, after none of my 4 exposures showed any unmet load hours, my baseline did. I, like Nick, have not had that happen before. Perhaps it has something to do with the way the building was zoned, 4 exposures and a core but I don't know for sure.<br>
<br>Any ideas?<br><br><br>Carol<br><br><div class="gmail_quote">On Fri, Nov 19, 2010 at 2:56 PM, Nick Caton <span dir="ltr"><<a href="mailto:ncaton@smithboucher.com">ncaton@smithboucher.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
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<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Hi Michael,</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">I’d like to offer a quick heads up – 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…</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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 – suffice it to say skewed is not always a *good* thing, even if it
does make your performance numbers look good.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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 – 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.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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 – as you’re getting at with consideration to drift points. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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 – 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!</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Anyway, that’s my two cents, for what it’s worth =) – hope it
might help lead others along the path!</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">~Nick</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"><img src="cid:image001.jpg@01CB87F1.CC44F350" alt="cid:489575314@22072009-0ABB" height="37" width="119"></span><b><span style="font-size: 11pt; color: rgb(45, 77, 94);"></span></b></p>
<p class="MsoNormal"><b><span style="font-size: 11pt; color: rgb(45, 77, 94);"> </span></b></p>
<p class="MsoNormal"><b><span style="font-size: 11pt; color: rgb(45, 77, 94);">NICK CATON, E.I.T.</span></b><b><span style="color: rgb(45, 77, 94);"></span></b></p>
<p class="MsoNormal"><span style="font-size: 7.5pt; color: rgb(204, 153, 0);">PROJECT ENGINEER</span><span style="font-size: 7.5pt; color: rgb(204, 153, 0);"></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: rgb(45, 77, 94);">25501 west valley parkway</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: rgb(45, 77, 94);">olathe ks 66061</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: rgb(45, 77, 94);">direct 913 344.0036</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: rgb(45, 77, 94);">fax 913 345.0617</span></p>
<p class="MsoNormal"><i><span style="font-size: 10pt; color: rgb(45, 77, 94);">Check out our new web-site @ </span></i><span style="font-size: 11pt; color: rgb(31, 73, 125);"><a href="http://www.smithboucher.com" title="blocked::www.smithboucher.com" target="_blank"><span style="font-size: 10pt;">www.smithboucher.com</span></a></span><u><span style="font-size: 10pt; color: blue;"> </span></u><span style="font-size: 11pt; color: rgb(31, 73, 125);"></span></p>
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<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<div style="border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span style="font-size: 10pt; color: windowtext;">From:</span></b><span style="font-size: 10pt; color: windowtext;"> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a>
[mailto:<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of </b>Michael
Collarin<br>
<b>Sent:</b> Friday, November 19, 2010 1:46 PM<br>
<b>To:</b> Nearedge; <a href="mailto:cjaigath@yahoo.com" target="_blank">cjaigath@yahoo.com</a><div><div></div><div class="h5"><br>
<b>Cc:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] Adjusting Capacity for Unmet Cooling</div></div></span></p>
</div>
</div><div><div></div><div class="h5">
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Neeraj, it is in fact the contrary. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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).</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">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.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Regards,</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<p class="MsoNormal"><b><span style="font-size: 8pt;">Michael
M. Collarin, EIT, LEED AP BD+C </span></b><b><span style="font-size: 7pt; color: green;">|</span></b><b><span style="font-size: 7pt; color: green;"> </span></b><b><span style="font-size: 7pt; color: green;">Elm
Engineering, Inc. | 212 S Tryon St | Suite 1375 | Charlotte, NC 28281</span></b><b><span style="font-size: 7pt; color: green;"></span></b></p>
<p class="MsoNormal"><span style="font-size: 8pt; color: green; letter-spacing: 0.9pt;">PHONE 704-335-0396 Ext. 108</span><span style="font-size: 8pt; color: green;">|<b> </b>FAX
704-335-0399<b> </b>|</span><b><span style="font-size: 8pt; color: gray;"> </span></b><span style="font-size: 8pt; color: gray;"><a href="http://www.elmengr.com/" title="blocked::http://www.elmengr.com/" target="_blank"><span>www.elmengr.com</span></a></span><span style="color: rgb(31, 73, 125);"></span></p>
</div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div>
<div style="border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span style="font-size: 10pt; color: windowtext;">From:</span></b><span style="font-size: 10pt; color: windowtext;"> Nearedge [mailto:<a href="mailto:near_ej@yahoo.com" target="_blank">near_ej@yahoo.com</a>] <br>
<b>Sent:</b> Friday, November 12, 2010 12:51 AM<br>
<b>To:</b> <a href="mailto:cjaigath@yahoo.com" target="_blank">cjaigath@yahoo.com</a><br>
<b>Cc:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] Adjusting Capacity for Unmet Cooling</span></p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal" style="margin-bottom: 12pt;"><span style="font-size: 10pt;">Hello Jaigath,<br>
Using the performance rating method (PRM), in my experience it is usually an
issue of low supply CFM.<br>
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.<br>
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.<br>
Best,<br>
Neeraj</span></p>
<div>
<p class="MsoNormal"><span><span style="font-size: 10pt;">Neeraj</span></span><span style="font-size: 10pt;"> <span>Kapoor</span><br>
t: +91.99581.70018</span></p>
<p class="MsoNormal" style="margin-bottom: 12pt;"><span><span style="font-size: 10pt;">e</span></span><span style="font-size: 10pt;">: <span>neeraj</span>[at]<span>kalpakrit</span>[dot]com<br>
<span>Kalpakrit</span> Sustainable Environments Pvt. Ltd.<br>
<a href="http://www.kalpakrit.com" target="_blank">www.kalpakrit.com</a></span></p>
<table style="width: 303.75pt;" border="0" cellpadding="0" width="405">
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Address</span></u><span style="font-size: 10pt;">:<br>
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t: +91.124.430.9490/ 1/ 2<br>
f: +91.124.430.9493</span></p>
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<p class="MsoNormal"> </p>
</div>
<p class="MsoNormal">On 11-11-2010 10:30, Jaigath Chandraprakash wrote: </p>
<div>
<div>
<p class="MsoNormal">Hello All,</p>
</div>
<div>
<p class="MsoNormal">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?</p>
</div>
<div>
<p class="MsoNormal">Thanks,</p>
</div>
<div>
<p class="MsoNormal">Jaigath</p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal"> </p>
</div></div></div>
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