[Bldg-sim] ASHRAE 90.1-2007 modeling for a Baseline system with humidity control

Jim Dirkes jim at buildingperformanceteam.com
Tue Apr 24 10:25:04 PDT 2012


From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Tuesday, April 24, 2012 12:32 PM
To: Jim Dirkes; bldg-sim at lists.onebuilding.org;
EnergyPlus_Support at yahoogroups.com
Subject: RE: [Bldg-sim] ASHRAE 90.1-2007 modeling for a Baseline system with
humidity control

 

Hi Jim!  Two separate thoughts:

 

1.       My position is that for Appendix G baselines, mandatory provisions
(#.4) are a given, as spelled out in the first Appendix G passages.
Prescriptive requirements (#.5) do not apply except where specifically
called out, such as with the envelope tables for determining baseline
constructions.  

2.       It seems to me a clearer Appendix G mandate that the baseline's
thermostat/humidity setpoints must match the proposed design.

 

Without cracking open my copy to find citations, my strong hunch is that any
reviewer who does note "excessive reheat quantities" could be refuted on
both above points, emphasizing (and finding citations for) the second.

 

A related/potentially helpful thought outside the framework of Appendix G:
I think there are exceptions permitting dehumidification reheat in 90.1...
I roughly recall this coming up once and finding it a non-issue through some
exception/passage.

 

~Nick

cid:489575314 at 22072009-0ABB

 

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 

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jim Dirkes
Sent: Tuesday, April 24, 2012 9:10 AM
To: bldg-sim at lists.onebuilding.org; EnergyPlus_Support at yahoogroups.com
Subject: [Bldg-sim] ASHRAE 90.1-2007 modeling for a Baseline system with
humidity control

 

Dear Forums,

A recent discussion with a colleague has made me question my understanding
of the proper way to model an HVAC system when humidity control is a project
criteria.  Imagine a building in South Florida that requires the space
humidity not to exceed 55% RH. 

1.       The building might use Baseline system #4 (heat pump with electric
supplemental heating).  I have modeled that in the past simply as a normal
heat pump with sub-cool + electric reheat for humidity control.

2.       Another possibility is a System #5 or #6 (VAV fan with VAV or PFP
boxes and reheat). 

 

The question is this:

90.1 has restrictions on the amount  of air that may be reheated (It's the
greater of 0.4 cfm / sq.ft. or 30% of the peak airflow rate plus a few other
items). These are noted in Section 6.5.

Appendix G, however, does not reference the requirements of Section 6.5
anywhere (that I can see).  Do they apply to a Baseline energy model?

 

Thanks for your input!

 

 

Description: BPT BizCard JVDII Updated

Making me think..

Seek truth while you are young, for if you do not, it will later escape your
grasp

 

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