[Equest-users] Unmet Load Hours Calc

[Matthew Dubrovich]

I recently received a similar response from a reviewer (same person?).  Unfortunately my initial response was not enough so now the team must appeal the denial.  See below.  Per the attached screenshot from the eQuest detailed reports help file, my understanding of the hours outside of the throttling range is the same as Dakota’s: BEPS % Hours Outside * SS-E hours fans on = Total # of Hours Outside Throttling Range.  Correct?  If it is, then I guess I just need a better way to explain it to the reviewer…

Initial comment:
1. Section 1.3 of the Template provides the total unmet load hours for the Proposed (74 hours) and Baseline models (65 hours); however, the BEPS report for the Baseline and Proposed model indicates that the total number of unmet load hours is 70 (0.8% * 8,760 hours) and 140 (1.6% * 8,760 hours), respectively. The total unmet load hours for each model is determined by multiplying the number of hours in a year (8,760) by the ‘Percent of hours any system zone outside of the throttling range’ in the BEPS report or the BEPU report. With the revision, the total unmet load hours for the Proposed model exceeds the total unmet load hours for the Baseline model by more than 50; however, Section G3.1.2.2 requires that the Proposed model does not exceed the total unmet load hours for the Baseline model by more than 50. Please revise the baseline model per the prescriptions of Section G3.1.2.2 so the total unmet load hours for the proposed model does not exceed the total unmet load hours for the baseline model by more than 50. Please note that the total unmet load hours for the Proposed and Baseline models cannot exceed 300 as required by Section G3.1.2.2.

My initial response:
Per eQuest help documentation, the “percent hours any system zone outside of the throttling range” should be multiplied by the hours the fans are operating in order to calculate total underheated/undercooled hours. Per the SS-L [same as SS-E since this building only has one system] report, the fans are operating on average
7388 hours per year in the Baseline and 4706 hours per year in the Proposed. That means the Baseline and Proposed models indicate that the total number of unmet
load hours is 59.1 (0.8% * 7388 hours) and 70.6 (1.5% * 4706 hours), respectively. The different fan runtimes are due to the time the fans must run during unoccupied hours to maintain setback temperatures.

Denied!
1. The response narrative to preliminary comment 1 states that the hours outside throttling range apply only to hours in which the interior fans operate however the eQUEST Help states that the “percent of hours any system zone outside of throttling range is the percentage of hours when the temperature in any conditioned zone is outside of the thermostat’s throttling range”. If appealing this credit please revise the Baseline case per the prescriptions of Section G3.1.2.2 so that the difference in the number of unmet load hours is less than 50.


Matt Dubrovich, PE, CEM, BEMP

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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Dakota Kelley
Sent: Thursday, July 22, 2010 5:34 PM
To: Brett M. West; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Unmet Load Hours Calc

Brett,

Let me state a few things, and then I’ll offer my interpretation of the comment:


·         The numbers in the SS-R report are the same numbers shown in the Air-Side Summary report.  These reports will yield inflated system totals, and therefore simulation totals, for multi-zone systems due to simultaneous counting of separate zones which belong to the same system.  Use them to determine the ratio of unmet heating and cooling hours relative to the two combined, but the sum of hours in these reports is not necessarily the same as multiplying the BEPS percentage by “hours fans on”.

·         Multiplying the BEPS percentage by the “hours fans on” in the SS-E report yields the correct sum of unmet heating and cooling hours, regardless of whether you are modeling multi- or single-zone systems.  Use the ratio obtained above to allocate this total between heating and cooling hours (I have posted previously<http://lists.onebuilding.org/htdig.cgi/equest-users-onebuilding.org/2010-July/005293.html> that there may be a more accurate method of allocating heating/cooling hours, but no one has corrected me).

·         The “hours fans on” includes hours the fans are scheduled on and the hours they are scheduled off but cycle on.  Refer to DOE2.2 Volume 4 (build 47), page 138 (SS-C report description), for the “hours fans on” definition.  This definition is echoed on page 142 (SS-E report description).  Therefore, for any system that cycles during off hours, all 8,760 hours have the potential to be counted as an unmet hour.

Now for the review comment.  The “hours each zone exists” phrase doesn’t make sense on the first pass.  However, due to the last bullet point above and baseline requirement G3.1.2.4, “hours each zone exists” is practically the same thing as “hours the systems are on”.  All 8,760 hours have the potential to be counted as an unmet hour if the hourly T-stat setting & throttling range are not satisfied.  What if the proposed model doesn’t cycle over night?  I say that’s a bad idea; I would never design a system that way unless an owner wants mold, frozen pipes, etc.  Define a reasonable set back temperature, allow fans to cycle, and they will stay off if cycling is unnecessary.

Where the comment is confusing/wrong is: “SS-R reports have been used…does not take into account coincident hours”.  Yes, it does.  It double-counts coincident hours on a multi-zone system, and because it is a system-level report, each system’s zones are counted separately.  It is as “coincident” as it gets.  I’m not sure how the reviewer rejects the SS-R report but then arrives at totals which are apparently greater than what was reported.  I have no .SIM file to review, but the smell of nonsense is strong.


[cid:image003.jpg at 01CB29C8.FD9F3AA0]



DAKOTA KELLEY
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From: Brett M. West [mailto:bwest at rmf.com]
Sent: Thursday, July 22, 2010 8:01 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Unmet Load Hours Calc

I have a question regarding the way unmet load hours are calculated in eQuest. I have received the following comments from the USGBC reviewer after submitting my energy model.

1. The response narrative to preliminary comment 1 states that the SS-R reports have been used to determine the number of unmet load hours for each case however this method does not take into account coincident hours. Additionally, the number of hours any system outside of throttling range is not the number of hours the HVAC system is in operation but rather it is the number of hours each zone exists during the building simulation, or 8,760 hours. Therefore the number of unmet load hours is 333 in the Baseline case and 508 in the Proposed case and the simulation does not meet the requirements of Section G3.1.2.2. If appealing this credit please revise both cases using the prescriptions of Section G3.1.2.2 until the number of unmet load hours is less than 300 for both cases and the number in the Proposed case does not exceed the number in the Baseline case by more than 50.

I thought the unmet load hours were calculated only during times when the fans are actually running in the simulation. This is why I always pull my unmet hours from the SS-R report, adding up the unmet hours for both cooling and heating for each individual unit. I can also go into the SS-E report and calculate the number of hours my fans are actually running and then calculate the total number of hours by using the percentage of hours outside the throttling range given in the BEPS report.

If you calculate the hours in the manner the reviewer has outlined then there is no way to show which hours are heating and which are cooling and you have to provide that breakdown in the EAc1 template.

Any input on this topic would be greatly appreciated.

Thanks in advance.


BRETT M. WEST

RMF ENGINEERING
T: 843.971.9639 ext. 1499
F: 843.971.9641
bwest at rmf.com<mailto:bwest at rmf.com>

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