[Bldg-sim] Spam:Re: LEED NC Submittal Template, Heating/Cooling Hours Loads Not Met

[gaurav mehta]

There are two things that need to be separated.

   1. What are the Appendix G requirements for "unmet load hours"
   2. Where does one find the information from the output report of the
   software?



1. Appendix G requirements



The main purpose of this requirement is to ensure that the equipment is not
undersized and does not result in too high unmet load hours. Undersized
equipment consumes less energy along with resulting in large unmet load
hours (depending upon the location). Moreover, if the difference between the
baseline and proposed unmet load hours is high, it can either penalize or
benefit the savings (hence the requirement that the difference shall not
exceed 50 hours between the baseline and proposed case).



When one sizes equipment, it is done for the worse case scenario, meaning if
it can meet the loads of the worst zone then it would be able to meet the
loads of other zones. Therefore, looking at the worst zone would make sense.



Having said that, one also needs to keep in mind, there are various building
types using a variety of HVAC systems that use Appendix G. Some are 24/7
facilities and some are schools or offices, etc. Some use zonal systems and
some have an AHU per floor or one AHU for the whole building. I am not an
authority on Appendix G, however, to me it seems appropriate that the
Appendix G requirement is for the whole project and not for the worse zone.



For a large project, with large number of zones, the total unmet
cooling/heating hours can well exceed 8760. If this is what the simulation
results show then it is an indication-either the system is highly undersized
or there is something wrong with how the system has been modeled or both!



As a practice, I always look at the SS-R reports and add the unmet cooling
hours for the whole project and I maintain them well below 300 and similarly
I add all the unmet heating hours and maintain the total well below 300 for
the whole project. And I also make sure that the difference between both the
proposed and baseline is below 50 fro both heating and cooling. I formed
this habit when I was single and I didn't have a life. Although I am married
now, but I still maintain this habit (till my wife threatens to abandon me!)






2. Output from the simulation software (eQuest)



The BEPS/ BEPU reports show the worst zone scenario. Please look at SS-R
report; identify the worse zone- (the zone which has the largest unmet load
hours, determined by adding the unmet cooling and heating hours). Add unmet
cooling hours and unmet heating hours of this zone, divide this number by
the Total Run Hours also shown on the SS-R report and calculate the
percentage. The same percentage is reported on the BEPS/ BEPU reports as
"Percent of Hours Any System Zone Outside of Throttling Range".



The total run hours in the SS-R report equal the hours the fan operate (for
a typical office building the fans run 11 hours each day from 7am to 6pm).
Typically it would be ~2761 hours and not 8760 hours based upon the
following formula:

11hrs * 5 days/week * 52 weeks a year – 11hrs * # of holidays + # of hours
during the unoccupied hrs when fans turn on to maintain setback temperature.


Thanks and Happy Friday!

Best regards,


Gaurav Mehta



On 8/22/08, May Xu <may.xu at hok.com> wrote:
>
> The definition of "unmet load hours" in Edition 3 of LEED-NC 2.2 (page
> 187) is "occupied periods where any zone is outside its temperature
> setpoint". I noticed the words "occupied period". Does it mean the unmet
> hours in "non-occupied periods" (e.g. at mid-night when no people in the
> building) can be excluded? If I am right, the % in BEPS report counts
> both occupied period and non-occupied period.
>
> May
>
> -----Original Message-----
> From: bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Carol
> Gardner
> Sent: Friday, August 22, 2008 2:44 PM
> To: Michael Tillou
> Cc: bldg-sim at lists.onebuilding.org; 'Brandon Nichols'
> Subject: Re: [Bldg-sim] Spam:Re: LEED NC Submittal Template,
> Heating/Cooling Hours Loads Not Met
>
> I have always looked at the SS-F report. Does any one else use it?
>
>
> Michael Tillou wrote:
> > If you're using eQuest the Air Side Summary report in the eQuest
> interface
> > has all that info.  It is also reported in SS-R Zone Performance
> Summary in
> > the .SIM file.
> >
> > -----Original Message-----
> > From: bldg-sim-bounces at lists.onebuilding.org
> > [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jay
> Keazer
> > Sent: Thursday, August 21, 2008 5:16 PM
> > To: Dan Russell; Brandon Nichols; bldg-sim at lists.onebuilding.org
> > Subject: Re: [Bldg-sim] Spam:Re: LEED NC Submittal
> Template,Heating/Cooling
> > Hours Loads Not Met
> >
> > I am not certain, but I think the unmet load hours on the BEPS report
> is
> > consistent with the definition in Addendum a.  The BEPS report says
> "Percent
> > of hours any system zone outside of throttling range."  To me this is
> the
> > same as "one or more zones" being out of range for a particular hour.
>
> >
> > Adding up the unmet load hours of every zone would count a lot of
> coincident
> > unmet hours and could get large with a lot of systems (note this is
> what
> > SS-R does for multiple zone systems).  It could be greater than 8760,
> and I
> > don't think this is what appendix G is looking for.  If a lot of zones
> are
> > out of range during an hour (say an exceptionally cold night) that
> should
> > only count as 1 hour.
> >
> > I don't think that the number on the BEPS is for the "worst case
> zone."  I
> > just checked a SIM file I had open and the BEPS report listed 3.3%
> unmet
> > load hours, so 289 hours (actually anywhere from 285-293).  Looking
> through
> > SS-R for each zone, the worst case had 177 hours under heated + 24
> hours
> > under cooled, so 201 total unmet hours.
> >
> > I have always gone by the BEPS (i.e. 3.4% or less is good), but have
> never
> > known how to find more detailed output regarding how many are cooling
> vs.
> > how many are heating.  Theoretically I think you could do this with an
> > hourly report for every zone and some postprocessing, but I don't
> really
> > want to go there.  Anybody have a more practical approach?
> >
> >
> > Jay Keazer,  EI
> > Energy Engineer
> > TME, Inc.
> > 2039 N Green Acres Road
> > Fayetteville, AR  72703
> >
> > ph   479.521.8634
> > fax  479.521.1014
> > jkeazer at tmecorp.com
> > www.tmecorp.com
> >
> >
> >
> > -----Original Message-----
> > From: bldg-sim-bounces at lists.onebuilding.org
> > [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Dan
> Russell
> > Sent: Thursday, August 21, 2008 1:12 PM
> > To: Brandon Nichols; bldg-sim at lists.onebuilding.org
> > Subject: Spam:Re: [Bldg-sim] LEED NC Submittal
> Template,Heating/Cooling
> > Hours Loads Not Met
> >
> > Brandon, I have been on the same page regarding this issue, and have
> > submitted for successful LEED certifications using those assumptions
> ..
> > until I read Addendum a to 90.1-2004, which adds the definition of
> "unmet
> > load hour" to Section 3.2.  The definition is:
> >
> > unmet load hour: an hour in which one or more zones is outside of the
> > thermostat setpoint range.
> >
> > Unfortunately this seems to clearly indicate the unmet load hour value
> asked
> > for refers to all zones at once.
> >
> > My previous assumptions to only consider the worst-case zone were
> based on
> > the example set forth by the USGBC's document titled "Example LEED-NC
> > v2.1 Energy & Atmosphere Credit 1 Submittal", which I referenced back
> when I
> > did my first LEED submittal in 2005.  This document is still available
> from
> > their server at the following address:
> >
> > http://www.usgbc.org/ShowFile.aspx?DocumentID=2423
> >
> > This document uses the following paragraph to demonstrate compliance
> with
> > the unmet load hour requirement:
> >
> > "The worst-case zone in the budget case is a North classroom. This
> zone is
> > under-heated 40 hours out of the year in the Energy Cost Budget case
> and 0
> > hours per year in the Design Energy Cost case. This is within the 50
> hour
> > per year limit required by ASHRAE 90.1-1999."
> >
> > Now, if Addendum a were not used in any part as basis for LEED
> submittal one
> > could possibly argue using the quoted precedent above.  Granted, the
> above
> > precedent applied to the 1999 version of 90.1 and the 2.1 version of
> LEED,
> > but it seems to reasonable that the implications made there should
> carry
> > over until otherwise directed (as in Addendum a).
> > Furthermore, it is my opinion that 90.1-2004 (not including addendums)
> does
> > not clearly resolve the issue.  The ASHRAE technical committee must
> have
> > agreed, hence the inclusion of the new definition for "unmet load
> hour" in
> > Addendum a.
> >
> > So, if Addendum a is not used, there may be a possibility to consider
> unmet
> > load hour only on a worst-zone basis.  However, if Addendum a is used
> it
> > seems clear that the unmet load hour applies to all zones at once.
> >
> > Certainly larger project simulations with multiple zones will suffer
> from
> > this added definition.
> >
> > Thanks,
> >
> >  Dan Russell, EIT
> >
> >
> >
> >
> > -----Original Message-----
> > From: bldg-sim-bounces at lists.onebuilding.org
> > [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Brandon
> Nichols
> > Sent: Thursday, August 21, 2008 11:22 AM
> > To: bldg-sim at lists.onebuilding.org
> > Subject: [Bldg-sim] LEED NC Submittal Template,Heating/Cooling Hours
> Loads
> > Not Met
> >
> >
> > All,
> >
> > "Table 1.3 -- Advisory Messages" of the LEED NC Submittal Template
> requests
> > "number of hours heating loads not met" and "number of hours cooling
> loads
> > not met".  We've taken a vote here in the office, and its 2-0 in favor
> of
> > reporting the worst case zone as shown on the BEPS report.
> >
> > But we have some lingering doubts... can anyone say definitively what
> > numbers are being asked to for here?  our runner-up in the voting was
> the
> > total of all zone hours out of throttling range -- however this could
> easily
> > exceed the limit of 300 hours on a large project with many zones.
> >
> > As 300 hours is less than 5% (3.4% actually) of 8760, we think that
> the 300
> > hours is "per zone", not a total limit for the entire project.
> >
> > Comments appreciated....
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