90.1 - leaving air temperature (DX cooling / Economizer)

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Hello,

Section 6.5.1.3 of 90.1-2013, requires that the "outdoor air damper does not begin to close to prevent coil freezing due to minimum compressor run time until the leaving air temperature is less than 45?F"

1) I'm not an expert with refrigeration system, and I want make sure that I have the good interpretation of what is the "leaving air" .
A) "Leaving air" is the mixed air (outside air + return air) that leaves the evaporator coil of a DX cooling system, so it's pretty much equivalent to the supply air.
B) "Leaving air" is the air leaving the outdoor air damper, so it's equivalent to the outside air.

2) If the answer is A, based on your experience in the field, have you notice any comfort problem by supplying air at 45?F when the unit setpoint is typically at 55?F ?

Many thanks,

Julien Dutel, ing., CEM, CMVP.
Direction des secteurs r?sidentiel, institutionnel et des affaires
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Julien.Dutel at mern.gouv.qc.ca's picture
Joined: 2015-06-05
Reputation: 0

Without looking at the 90.1 definitions pages (though I recommend that),
the meaning should be the temperature leaving the cooling coil, since that
is what might freeze.

2015-11-23 16:11 GMT-05:00 :

--

James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
jim at buildingperformanceteam.com

Website l LinkedIn

Love is the bridge over which Truth travels

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

Without looking at the 90.1 definitions pages (though I recommend that),
the meaning should be the temperature leaving the cooling coil, since that
is what might freeze.

2015-11-23 16:11 GMT-05:00 :

--

James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
jim at buildingperformanceteam.com

Website l LinkedIn

Love is the bridge over which Truth travels

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

Leaving air is indeed the air stream leaving the cooling coil.

In my experience, most OA economizers are not set this aggressively in the field because of problems with cold spots.

David Berty P.E.
Baseline Energy Consulting
317.220.9272

David Berty's picture
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Joined: 2015-07-31
Reputation: 0

Leaving air is indeed the air stream leaving the cooling coil.

In my experience, most OA economizers are not set this aggressively in the field because of problems with cold spots.

David Berty P.E.
Baseline Energy Consulting
317.220.9272

David Berty's picture
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Joined: 2015-07-31
Reputation: 0