[Equest-users] LEED Review Comment Help

Travis Miller tmiller at dcengineering.net
Tue Jan 18 15:58:01 PST 2011


I have used the advice below to bring cooling into the base case design, which was fairly straightforward since the system was a packaged single zone using a furnace for a heat source per table G3.1.1A.

Trying to integrate cooling into the proposed design is giving me fits. The proposed design is a radiant slab. Per the LEED reviewer and appendix G, I have to model an identical cooling system for each case. I created the same cooling system but when I go to assign cooling to any of the zones, it subsequently un-assigns the heating system. I am assuming that this is the case because you can’t have (2) systems tempering one space.

My outside the box solution is to run two models - one with the correct cooling system and one with the correct heating system and combine the required components to for one complete report – I’m sure the LEED guy will love that.

Am I missing something? Any ideas/suggestions regarding my approach would be greatly appreciated. Thanks again

Travis

From: Jeremy Poling [mailto:Jeremy.Poling at transwestern.net]
Sent: Wednesday, December 29, 2010 2:55 PM
To: Karen Walkerman; Travis Miller
Cc: equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] LEED Review Comment Help

Note – the upper limit of the semi-heated definition varies by climate zone.  It appears the reviewer cited the wrong value, but pointed you in the right direction to look.  Table 3.1 in ASHRAE 90.1-2004 lists the upper limit for semi-heated conditions by climate zone.  For Zone 6B a semi-heated space would be one that has a system with a maximum heating output between 3.4 btuh/sf and 20 btuh/sf.  The italics are my emphasis – I’m sure there is a difference of opinion on the email lists here, but in my experience the reviewers interpret the values to be the maximum rated capacity of the system, not the design output.  They don’t want to reward a system that can be operated as if the space were conditioned by considering the system to be serving a semi-heated space, only to have the occupants later jack the thermostats back up and result in real energy use exceeding the 20 btuh/sf (in your specific case).

In your response you need to show you’ve done the analysis for the spaces you consider semi-heated and that the space calculates out as a semi-heated space and not a conditioned space.  Otherwise, you need to design in a cooling system that meets the requirements of Appendix G, but you are allowed to set the thermostat to 100F so that the system never turns on in either the baseline or design model.

Jeremy R. Poling, PE, LEED AP+BDC
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Karen Walkerman
Sent: Wednesday, December 29, 2010 3:42 PM
To: Travis Miller
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] LEED Review Comment Help

Basically, if the space is provided with heating, of a capacity greater than 15 btu/h-sq ft, then it is a conditioned space.  Appendix G requires that all conditioned spaces be provided with heating and cooling for modeling purposes.

In the past, when I have a building that is not occupied during the summer, I have done the following:

In the proposed design model:

1.  model the heating plant as designed
2.  model a cooling system equal to the baseline cooling system

In the baseline model:

model the building with heating and cooling, determining the baseline system following the usual method

IN BOTH MODELS:

create a thermostat schedule where, the cooling setpoint is set-back during unoccupied hours.  Usually, I set the thermostat back to 90F +/-.  If your building truly doesn't need cooling, the cooling plant will never come on.

--
Karen

2010/12/29 Travis Miller <tmiller at dcengineering.net<mailto:tmiller at dcengineering.net>>
I have put together an eQuest model for a LEED project where there is no cooling installed for the proposed design. This spurred the following GBCI reviewer comment:

According to the primary HVAC system input and Table 1.4, no cooling has been provided for in the Baseline or Proposed buildings; However, cooling equipment should be modeled in both cases if the spaces are considered conditioned per the definition in Section 3 (page 13) of ASHRAE 90.1‐2004. Please refer to the definition of conditioned space, semi‐heated space, and unconditioned space in Section 3. If the heating output capacity is greater than or equal to 15 Btu/h‐sq. ft. then the space is considered conditioned so cooling should be included in the Baseline and Proposed Case models. The cooling should be modeled using the Baseline cooling system type (system type # 3)in both the Baseline and Proposed Case models, using identical cooling capacity ratios and efficiencies in the Baseline and Proposed Case. If the heating output capacity is less than 15 Btu/h*sq. ft., then the space is considered semi‐heated or unconditioned, so only heating equipment should be included in the Proposed and Baseline models; the heating type, capacity ratios, fan volume, and fan power for these spaces should be modeled identically between the Baseline and Proposed Case. Please revise the Proposed model and Baseline model as needed so the correct system type is modeled in all spaces. Please also indicate the total heating capacity and building area for semi-conditioned spaces to verify that they qualify as semi-conditioned spaces. In addition, please update Table 1.2 and Table 1.4 as needed reflecting the changes.

I have read and re-read the ASHRAE section referenced with regards to the definitions of a space and what would make a building required to be modeled with cooling but I am not seeing what the reviewer is seeing. Any help or insight would be appreciated.

A little background of the building: non-traditional school building with no summer use. Proposed design uses radiant floor heating. Climate zone 6B. Heating output for the different zones within the building is between 15-20 Btu/h*sq.ft.

I do not get into modeling very often, but I have found this forum to be an extremely valuable resource. Hopefully I will be able to contribute something for someone else in the future.

Thanks

Travis Miller

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