[Equest-users] 2007 90.1 Appendix G3.1.2.4

[Brad L. Huff]

Paul:

The message I wanted to post originally is pasted below. I should go on to further state that the PTAC units are naturally ventilated spaces. In your experience with these systems did you model them as operating 24/7 and if you did, did problems arise from a LEED review?







Modelers,

I apologize for the blank email I previously sent, I meant to hit save, not send (Paul was quick to respond, thank you). I am modeling a dormitory of System Type 1. Appendix G Section G3.1.2.4 states, "Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours." If the building occupancy schedule is fractionally loaded 24/7, am I over exaggerating fan energy consumption of the PTAC units by operating the fans continuously 24/7? Has anyone received review comments from LEED on the issue?

Thank you,
Brad


Brad Huff, E.I.T., LEED Green Associate, Mechanical Engineer I BVH Integrated Services I 860.286.9171 tel I 860.242.0236 fax I 50 Griffin Road South, Bloomfield CT 06002 I .bvhis.com<http://www.bvhis.com/> I twitter.com/bvhis I Hartford  Boston


From: Paul Diglio [mailto:paul.diglio at sbcglobal.net]
Sent: Friday, June 10, 2011 11:06 AM
To: Brad L. Huff; equest-users at lists.onebuilding.org
Cc: Jason Glazer
Subject: Re: [Equest-users] 2007 90.1 Appendix G3.1.2.4

Brad:

Did you intended to post a message?

G3.1.2.4 is unclear.  First it states that the supply fan shall run continuously during the occupied hours and shall be cycled to meet heating and cooling loads during unoccupied hours.  Ok , I get that.

Then it states that if the supply fan is modeled as cycling and the fan energy is included in the EER, then the fan energy shall not be modeled explicitly.   That is confusing.  When is it permissible to model the supply fan as cycling.  Is AHSRAE talking a supply fan serving a space that is never occupied?  Obviously, there is no such thing, someone will sometime do something in the room.

Then G3.1.2.4 goes on to state that the supply, return or exhaust fans will remain on during occupied and unoccupied hours in spaces that have heath and safety mandated minimum ventilation requirements during unoccupied hours.

This requirement does not cover many of the scenarios that I model.  For example, natural ventilation provided by operable windows.  It does not make sense to keep the fan running if it not supplying ventilation air.  I am presently modeling a residential high-rise.  No one keeps their apartment supply fan running 24X7.  Especially if there are operable windows.

Another example is a commercial property that has a DOAS supplying minimum air directly to the zone HVAC system or supplying minimum directly to the zone without isolation dampers.  If I supply the 62.1 minimum air required by the DOAS, then why run the supply fan?

I would be interested to hear other interpretations.  Perhaps Jason Glazer can give us his unofficial opinion.

Paul Diglio


________________________________
From: Brad L. Huff <BradH at BVHis.com>
To: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Sent: Fri, June 10, 2011 10:10:50 AM
Subject: [Equest-users] 2007 90.1 Appendix G3.1.2.4
Modelers,

Brad Huff, E.I.T., LEED Green Associate, Mechanical Engineer I BVH Integrated Services I 860.286.9171 tel I 860.242.0236 fax I 50 Griffin Road South, Bloomfield CT 06002 I .bvhis.com<http://www.bvhis.com/> I twitter.com/bvhis<http://twitter.com/bvhis> I Hartford  Boston


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