[Equest-users] Baseline CFM

David Griffin dgriffin at etcgrp.com
Thu Dec 6 13:12:40 PST 2012


I agree with Mike. When I have run into the issue in the past, I have solved it by reviewing my schedules and internal loads to make sure they are realistic.


David Griffin
Energy Analyst
ETC Group, LLC
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From: Busman, Michael R [mailto:MBusman at chevron.com]
Sent: Thursday, December 06, 2012 12:34 PM
To: Gastón Michaud F.; equest-users at lists.onebuilding.org
Cc: Eric Fischel J.
Subject: Re: [Equest-users] Baseline CFM


I don't know if this will help you or not.  I don't claim to be an expert in eQUEST, however, I started doing hourly simulations about 1983 and in another life, spent 17 years with Hilton Hotels Corp., so I do know a little about how hotels operate.

I have found that simulations aren't the greatest for sizing systems versus a load design program, except maybe in the case of a central plant where load diversity can be accounted for.  In a hotel, you need to design for worst case or almost worse case conditions in the individual spaces even though they may not operate that way.  A couple of examples.  For the guest room PTAC units, you probably need to size for the draperies open, guests in the room, and maybe the TV or a couple of lights on.  In reality, the guest is out of the room most of the day and the maid probably closes the draperies and turns off the TV and lights.  So, you might simulate how the room is occupied and used versus sizing the PTAC capacity.  As another example, if the guest is out of the room, he/she is probably out of the hotel, in the restaurant, or perhaps, in a meeting in the ballroom.  Since the guest cannot be in two places at once, you need to look at the sizing versus the operation of the public spaces.  Generally a ballroom area will have a large prefunction/registration/coffee break area outside the ballroom.  If you decide you want 2 systems, one for the ballroom and one for the prefunction area, you'll size the systems for the peak load of those spaces.  If you decide to design a single VAV system for both the ballroom and prefunction area, you will have a smaller system than the total capacity of the two separate systems as it will track the load as guests move back and forth between the ballroom and prefunction area.

It sounds like the VRF systems for the first 3 floors were designed/sized on the airside for the peak load of the separate spaces, but the cooling capacity took diversity into account, similar to a central chiller plant.

You might want to look at how you defined the separate spaces and the amount of internal load diversity from the hourly schedules.

I hope John Aulbach will chime in.  He's been using DOE-2 since you had to chisel the calcs on a stone tablet and was a consultant to Hilton for many years, so he also knows how hotels operate.

My best,

Mike Busman

Michael R. Busman, CEM
Lead Project Engineer II

Chevron Energy Solutions
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From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Gastón Michaud F.
Sent: Thursday, December 06, 2012 10:11 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Cc: Eric Fischel J.
Subject: [Equest-users] Baseline CFM

Good morning everyone,

We are having an issue with the calculated total fan flow of the baseline case and was wondering if someone could help me out.  We are modeling a 12 floor hotel, with a VRF system in the first three floors and PTAC's in the remaining 9 (rooms); for a total conditioned area of about 92325 sf.  The baseline case is modeled with a system 2 per ASHRAE appendix G.
The following table summarizes our issue:

Baseline case

Proposed case

Total cooling capacity

281.5 tons

247 tons

Design airflow rate

39700 cfm

80500 cfm

We used the automatic calculation from eQuest (leaving both capacity and fan flow blank) for the baseline case, and the actual mechanical design for the proposed case.  For some reason, the baseline calculation for the fan flow seems to be very low, and was wondering if anyone has had a similar issue regarding the automatic calculations from eQuest.  If so, has anyone found a solution?

If we analyze other estimates, eQuest is calculating about 0.43 cfm/sf for the baseline, which also seems very low compared to other projects we have worked with.  We are also thinking of using the following formula to estimate the baseline fan flow: Sensible btu=1.09*cfm*dT; but with this approach we get a fan flow about 50% more that the proposed, which also seems unlikely.  Any suggestions for estimating the baseline fan flow which LEED reviewers accept?

Thanks you very much, hope someone can help us out.

  Ing. Gastón Michaud F.
  Tel.: (506) 2222-7529
  Fax: (506) 2256-5608
  From USA: 1-305-433-3668
  Calle 30, Avenida 0 y 2. San José, Costa Rica

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