app g economizer

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A simple Q -

Does everyone agree that the App G baseline building is supposed to have an air-side economizer (in the mentioned climates)?

There are some buildings where architectural choices make it difficult to accommodate an air-side economizer.

Nonetheless, Section G3.1.2.6 appears to require modeling specifically an air-side economizer for the baseline

I am thinking it could be a bit ambiguous depending on what you think "outdoor air economizer" means.

Has anyone seen interpretations clarifying this one way or the other?
Or submitted a CIR to allow water-side economizers in the baseline where that is the industry standard for the building type?


Aaron Dahlstrom , PE, LEED(r) AP

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Joined: 2011-09-30
Reputation: 4

I think for the purposes of App G, the answer is airside. 90.1 does
differentiate between air and water economizers:

economizer, air: a duct and damper arrangement and automatic

control system that together allow a cooling system to

supply outdoor air to reduce or eliminate the need for mechanical

cooling during mild or cold weather.

economizer, water: a system by which the supply air of a cooling

system is cooled indirectly with water that is itself cooled

by heat or mass transfer to the environment without the use of

mechanical cooling.

Haven't seen a CIR that addresses this, though.

Andy Phelps, PE, LEED AP

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Joined: 2011-09-30
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It doesn't seem ambiguous to me - air-side economizers are required in
the baseline for some system types and some climates. (The requirement
was expanded in 90.1-2007 vs. 2004. I haven't seen 2010 yet.)
If it helps, "outdoor (outside) air" and "economizer, air" are defined
in Section 3.2.
Regarding architectural choices, I think one of the points of energy
codes is to influence design... ;)

William Bishop, PE, BEMP, LEED(r) AP

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Joined: 2011-09-30
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