[Bldg-sim] LEED Energy Modeling with eQUEST

[Seth P. Spangler]

Bill and Janne,

 

Below is an email which I believe best describes the intent of unmet load hours and how to figure out how many there are in a given project. I have always used the same practice with positive results.

 

Seth Spangler, LEED® AP 

Design Engineer

 

RMF Engineering, Inc 

Ph: (843) 971-9639 ext:1497

Fax: (843) 971-9641 

sspangle at rmf.com

 

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of gaurav mehta
Sent: Friday, August 22, 2008 4:19 PM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Spam:Re: LEED NC Submittal Template,Heating/Cooling Hours Loads Not Met

 

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

 

________________________________

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Monday, January 12, 2009 10:00 AM
To: Kairento, Janne; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] LEED Energy Modeling with eQUEST

 

Hi Janne,

 

For figuring out the unmet load hours, the 300 hours per year is out of the 8,760 hours simulated. If every zone in the building simultaneously experiences an unmet load (such as when heating is first turned on after the building is allowed to get very cold), that only counts as one hour (or maybe two or three for a heat pump). The BEPS and BEPU DOE 2.2 reports show the percent of hours outside of throttling range. My understanding is that if this value is 3.4% or less (300/8760) than the condition is met.

 

Bill

 

William Bishop, EIT, LEED® AP | Pathfinder Engineers LLP

Mechanical Engineer

 

3300 Monroe Ave., Suite 306 
Rochester, NY  14618

TEL (585) 218-0730 Ext. 114
FAX (585) 218-0737 

bbishop at pathfinderengineers.com

 

www.pathfinderengineers.com

P Please consider the environment before printing this email

________________________________

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Kairento, Janne
Sent: Monday, January 12, 2009 9:36 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] LEED Energy Modeling with eQUEST

 

Hey All, 

 

I am curious as to how to break up the thermal blocks in eQUEST. eQUEST allows each zone to be broken down into different space types by percentage. According to Appendix G, Table G3.1, Section 7, three conditions have to be met in order to clump thermal blocks together: the space use classification has to be the same, they have to have exposure to one façade (or a façade with a <45 deg bend), and they have to be served by the same type of HVAC equipment. When a large zone is created based on the area being conditioned by a HVAC system, breaking down the spaces by the percentage doesn't meet the three conditions required. If spaces are broken down according to the ASHRAE requirements, it often leads to a large amount of zones. If all zones have at least 1 hr. of unmet heating or cooling, and there are greater then 300 zones, the model will exceed the amount of hours allowed. Any suggestions on an approach on zoning to simplify the model that meets ASHRAE requirements?

 

Thanks, 

Janne

 

Janne Kairento, E.I.T., LEED AP  
Cosentini Associates 
One Broadway 
Cambridge, MA 02142 
Phone: 617.494.9090 
Fax:  617.494.9292 

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