[Bldg-sim] 90.1-2007 DCV Mandatory Provision Exception a

[Bishop, Bill]

Stormy,

By my reading of exception 6.4.3.9(a) and 6.5.6.1, you can avoid the DCV requirement if you have a system with energy recovery that has 50% recovery effectiveness and that has bypass/control to permit economizer operation. The 5000 cfm & 70% OA (>3500 cfm OA) are the Prescriptive Path criteria for requiring energy recovery, and don't align with 6.4.3.9, which applies for systems with >3000 cfm OA. The wording in 90.1-2010 for 6.5.6.1 makes this more clear, IMO.

Regards,
Bill

William Bishop, PE, BEMP, BEAP, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

134 South Fitzhugh Street                 Rochester, NY 14608
T: (585) 325-6004 Ext. 114            F: (585) 325-6005
bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>           www.pathfinder-ea.com<http://www.pathfinder-ea.com/>
P   Sustainability - the forest AND the trees. P

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Stormy L. Shanks
Sent: Friday, September 27, 2013 2:49 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] 90.1-2007 DCV Mandatory Provision Exception a

All, I have an ASHRAE 90.1-2007 question that I've run into while completing an energy model.

ASHRAE 90.1-2007 section 6.4.3.9 is a mandatory provision for demand control ventilation in densely occupied zones.

Exception 9.4.3.9(a) reads, "Systems with energy recovery complying with Section 6.5.6.1."

6.5.6.1. Exhaust Air Energy Recovery. Individual fan systems that have both a design supply air capacity of 5000 cfm or greater and have a minimum outdoor air supply of 70% or greater of the design supply air quantity shall have an energy recovery system with at least 50% recovery effectiveness. Fifty percent energy recovery effectiveness shall mean a change in the enthalpy of the outdoor air supply equal to 50% of the difference between the outdoor air and the return air at design conditions. Provision shall be made to bypass or control the heat recovery system to permit air economizer operation as required by Section 6.5.1.1.

My question: If I have a system that's only 20% outside air but complies with the remainder of 6.5.6.1, can I still use exception 9.4.3.9(a) to avoid DCV in densely occupied zones? Or does that exception only apply to those systems with 70% OA or more?

Thank you!

[cid:image001.png at 01CE0924.38506AB0]

Stormy L. Shanks, PE
Mechanical Engineer

2882 106th St, Des Moines, IA 50322




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