OT fresh air

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Hi All,
Is there any ACPH recommende value for operation theatre given in
ASHRAE 62 standards It is 100% fresh air AHU . but the cfm sized is very
high 6cfm/sqft as per design and if i reduce it to 3cfm/sqft i am still not
getting any discomfort hour.


sambhav tiwari's picture
Joined: 2011-09-30
Reputation: 0

You should check with the design team to see what the governing codes are from the local authorities. In terms of ASHRAE references, 2011 Handbook of Applications Chapter 8 or Standard 170 will take precedence over ASHRAE 62.1, since the criteria in this case is for infection control purposes which goes beyond the comfort requirements in 62.1. There are a number of other references that the design team might be using. These might include the client?s own design standards which may be even higher than the regulatory requirements.

Regarding your prior post about the reheat ? it will be a significant quantity, this is typical. However for reheat to be higher than the cooling end-use during a peak summer month should be reviewed. Assuming your location has economizer hours in the winter, the reheat could easily be higher than the cooling on an annual basis unless the design is including measures to reduce the need for reheat.

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

David Eldridge's picture
Joined: 2012-05-08
Reputation: 1

This is a timely subject. I have been working on
some very large distribution warehouses. The
staff are never all in one place at one time
except morning, breaks and the end off
shift. The local authorities are asking that
ASHRAE 62.1 be followed - warehouses at 0.06
cfm/sf. A half million square foot warehouse
ends up with a lot of out door air that needs to
be conditioned, especially in summer to remove
the latent load. I went through the Handbook of
Applications and the Industrial Ventilation
reference manual but found no guidance that would
allow the OA to be lower than that value.

When one considers that over 3/4 of that space is
solid from floor to ceiling with the stacks of
crates, boxes etc. it seems a very large amount
of outdoor air for the floor space that is no "solid".

Does anyone have experience with this sort of
facility and reducing outdoor air levels below that 0.06 cfm/sf.

>> Christopher Jones, P.Eng.

Chris Jones's picture
Joined: 2011-09-30
Reputation: 0

Dear Chris,
My understanding of the area ventilation requirement is concern for off-gassing of VOCs and similar chemicals which are deemed harmful. It will be difficult to avoid that requirement!
On the other hand, my experience with many warehouses and distribution centers is that it is very rare to have less than about 0.2 air changes per hour (average) from infiltration. For a 30 foot tall warehouse, that is equivalent to about 0.1 cfm / sq.ft.
The summary, assuming I did the math properly in a hurry, is that you?ll heat the 0.06 cfm/sq.ft. plus some more just for infiltration ? so nothing is ?wasted?. Do you feel any better ??
p.s., Almost all of my warehouse experience is with heated-only facilities. Perhaps the air conditioned facilities are better constructed, but I?m doubtful.

James V Dirkes II, PE, BEMP, LEED AP

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

HI Chris,

I did design a refrigerated warehouse and did
struggle with this (The warehouse was to be LEED
certified and we had to meet ASHRAE 62.1)
The solution I found was to use the IAQ procedure
in 62.1. We calculate the contaminant, mosthly
CO2 from people and arrive with a total cfm a lot
smaller (20 cfm/person) than the ventilation rate procedure.

Imagine if we had to use 0.06 cfm/sqft, the
refrigeration load would have been a lot higher.
After discussion with a lot of other refrigerated
warehouse designer, the rarelly introduce fresh air.

Hope this help

Martin Roy, ing. PA LEED

Martin Roy's picture
Joined: 2011-10-02
Reputation: 0