LEED NC Submittal Template, Heating/Cooling Hours Loads Not Met

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"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

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

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....

Brandon Nichols's picture
Joined: 2011-10-01
Reputation: 0

Brandon and All,

I believe that they mean from G3.1.2.2 that each hour (of the 8760) for
which there is at least one zone where the load is not met should be
accounted for (meaning that in eQuest for example, your PERCENT OF HOURS
not exceed 3.4). And that truly penalizes buildings with many zones as
you write.

Personally, I think that it is more realistic to just consider the
"worst case zone".

Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

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:


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

Certainly larger project simulations with multiple zones will suffer
from this added definition.


Dan Russell, EIT

Dan Russell's picture
Joined: 2011-09-30
Reputation: 0

Comments from a recent USGBC review used the BEPS report to confirm
hours load not met.

Best, Linda

Linda Morrison

Linda Morrison's picture
Joined: 2011-10-02
Reputation: 0

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

Jay Keazer's picture
Joined: 2011-09-30
Reputation: 0

I have noted that the number of hours as per the % shown in the BEPS report is always slightly high than the actual. In a situation where you are close to 300 hours or 50 hours as applicable, it is best to check the SS-F reports and calculate the highest number of hours under-cooled or under-heated in any zone?for each month.?Adding the highest number for undercooled?in each month for each?zone and the highest number for underheated in each month for each zone will give the total number of unmet hours.
Consider only the highest number. Do not add all hours. That?could be even higher than 8760.
Ruju Rathod.

ruju rathod's picture
Joined: 2011-09-30
Reputation: 0

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.

Michael Tillou's picture
Joined: 2011-10-02
Reputation: 0

I have always looked at the SS-F report. Does any one else use it?

Carol Gardner's picture
Joined: 2011-09-30
Reputation: 0

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 Xu's picture
Joined: 2011-10-02
Reputation: 0

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

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

Gaurav Mehta2's picture
Joined: 2011-09-30
Reputation: 0

I think the "Percent of Hours Any System Zone Outside of Throttling
Range" is rather the number of hours for which there is at least one
under-cooled or under-heated zone divided by 8760 (the eQuest commented
reports I have indicate that "The denominator used for this %
calculation is always 8760.")


Demba Ndiaye

Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

This may make the SS-F report the most useful one.

Carol Gardner's picture
Joined: 2011-09-30
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