[Equest-users] Unmet Load Hours Calc

[Dakota Kelley]

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.

 

 

 

  
                                

DAKOTA KELLEY 

Project Designer | Energy Analyst

                          

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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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