[Bldg-sim] Conservative design cooling load calculations vs baseline sizing

Nick Caton ncaton at smithboucher.com
Thu Dec 5 07:23:27 PST 2013


(A couple folks responded before I finished... sorry if this appears to parrot any more current responses!)



HI Patrick,



To play devil's advocate, I'll just put forward none of the practices you're lamenting are unusual or even necessarily a bad idea from a design perspective.



That said, it isn't unusual in my experience for proposed model cooling capacities to sum larger than a baseline model counterpart (and this can quickly become an arbitrary figure when you've got many small systems).  If however you are looking at many magnitudes difference between your models, that in my experience can be a bright red flag to carefully review your model's assumptions of loads & scheduling against the mechanical designer's - you may be missing critical information.



I would also contend LEED & 90.1 together have very little to say regarding equipment sizing methodology - particularly for determing schedules or which loads are to be considered at 0%, 100%, or anything between for determining capacities.  The only related rules that come to mind are the weather items Mike mentions and the basic requirement for the baseline model to match the proposed model generally for all such scheduling inputs.



Your energy modeling software of choice may dictate what degree of control you have in this matter, but I can volunteer that for eQuest/DOE2 a separate set of schedules and weather conditions can be assigned for both heating and cooling design days, independent of normal operation.  These inputs are used on the LOADS side of the simulation and pretty much directly effect the results for system capacity autosizing.  Coming out of the wizards, you'll find by default eQuest assumes "normal" fractional operation schedules are to be used for heating and cooling design days (HDD/CDD).  This at times can be in sharp contrast to the load assumptions used for equipment sizing protocol outside of an annual simulation, and if I were you I'd also consider reviewing such scheduling assumptions with your mechanical designer.

[cid:image001.png at 01CEF197.B330F950]

[cid:image002.png at 01CEF199.83784270]



I'd also reinforce that while energy modeling can inform and provide insight one can't get anywhere else, at the end of the day the burden of such decisions (and the associated liabilities) are in the designer's hands.  I try to convey such information in a way that avoids "butting heads," but there are times someone at the table isn't really there to talk, learn, and consider changing their minds.  You can try your best to make a case, but ultimately you can't make yourself responsible for what other's paychecks are written for.  Done politically, as Mike suggests, you can leverage your expertise to potentially win new design work if that's within your scope of interests, but be careful to avoid burning bridges ;).



Hope that helps a bit!



~Nick



NICK CATON, P.E.

SENIOR ENGINEER



Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com



-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Michael tillou
Sent: Thursday, December 05, 2013 7:19 AM
To: Patrick Bivona
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Conservative design cooling load calculations vs baseline sizing



Hi Patrick,



I just wanted to clarify for you that Appendix G (G3.1.2.2.1) requires the simulation of sizing runs for equipment selection based on either the peak from the weather file or ASHRAE 99.6% heating and 1% cooling design temperatures.  As far as I know this is not something USGBC or GBCI has written a clarifying rule on for LEED.



As far as being frustrated over engineers doing overly conservative load calculations, welcome to life as an energy analyst.  The best you can hope for is to use simulation to show them and the building owner that they are over engineering the system and try to get some concession.  Ultimately at the end of the day it's the engineer who is stamping the work and taking on the liability that has the final say.



Mike.



Sent from my iPad



On Dec 4, 2013, at 11:17 PM, Patrick Bivona <patrick.bivona at gmail.com<mailto:patrick.bivona at gmail.com>> wrote:



> Hi,

>

> When sizing cooling equipment for apartments, the design team on my project used a worst case scenario approach of maxing out all internal loads. For instance, lighting would be on during the day, with full occupancy and all plug equipment running, while the sun is hitting the windows. Adjacent rooms would be considered without cooling.

> For LEED, the sizing for the baseline is based on schedules representing typical operations for occupancy, lighting, plug, etc. That leads the baseline to size equipment that has smaller capacity than what considered for the proposed design.

> There's an extra dimension, in the fact the design team sized equipment for each individual room, reaching their peak load at different times of the day. So the total cooling capacity is the sum of the worst possible scenarios. The model currently uses a single zone per apartment, with a not so worst case scenario.

> How do I solve this conundrum? Am I missing something?

> Thanks,Patrick

> _______________________________________________

> Bldg-sim mailing list

> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org

> To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>

_______________________________________________

Bldg-sim mailing list

http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org

To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20131205/2fdd6d56/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 39094 bytes
Desc: image001.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20131205/2fdd6d56/attachment-0004.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.png
Type: image/png
Size: 49800 bytes
Desc: image002.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20131205/2fdd6d56/attachment-0005.png>


More information about the Bldg-sim mailing list