From: Nick Caton [mailto:ncaton@xxxxxxxxxxxxxxxx]
Sent: Tuesday, April 24, 2012 12:32 PM
To: Jim Dirkes; bldg-sim@xxxxxxxxxxxxxxxxxxxxx; EnergyPlus_Support@xxxxxxxxxxxxxxx
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
NICK CATON, P.E.
SENIOR ENGINEER
Smith & Boucher Engineers
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From: bldg-sim-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:bldg-sim-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Jim Dirkes
Sent: Tuesday, April 24, 2012 9:10 AM
To: bldg-sim@xxxxxxxxxxxxxxxxxxxxx; EnergyPlus_Support@xxxxxxxxxxxxxxx
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!
Making me think….
Seek truth while you are young, for if you do not, it will later escape your grasp