[Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply
Zeng, Ming
mzeng at leoadaly.com
Thu Nov 12 13:24:22 PST 2009
Hi Karen
I had similar questions as you do. However, typically the HVAC design at unoccupied hours is to enable the air handling unit, heat or cool and recirculate the air to maintain the night setback temperature setting .
As the Storage rooms, ventilation will be provided during the occupied hours . I think the reason to provide ventilation for storage room is to avoid stale air or dust accumulation. Probably the storage rooms will have occupancy occasionally during regular work hour.
Ming Zeng, PE, LEED(r) AP
Mechanical Engineer
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EXCELLENCE BEYOND EXPECTATIONS
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Karen Walkerman
Sent: Thursday, November 12, 2009 12:28 PM
To: Brahme, Rohini UTRC
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply
Ok, so here's a question - what happens when you have a space that is almost NEVER occupied, but has a cfm/sf requirement - like a storage room with a requirement of 0.12 cfm/sf. This is a pretty high outdoor airflow, especially if you're just storing old files.
So do you need this ventilation rate only when the building is occupied, only when the space is occupied, or all the time?
If you only need the ventilation when the space is occupied, and it is almost never occupied, why install the ventilation in the first place?
--
Karen
On Thu, Nov 12, 2009 at 1:11 PM, Brahme, Rohini UTRC <BrahmeR at utrc.utc.com<mailto:BrahmeR at utrc.utc.com>> wrote:
Thanks Nick. The reason I had the question was because I think OA/sqft technically should not be dependent on occupancy. If that was the case, it would suffice to just increase the OA/sqft and have only one number to take care of. What I am not sure of is whether OA/sqft is used only during the typical occupied hours irrespective of whether it is actually occupied or not or is it used throughtout the day/weekend/vacation etc. What do the hvac designers specify for the control of OA?
-rohini
From: Nick Caton [mailto:ncaton at smithboucher.com<mailto:ncaton at smithboucher.com>]
Sent: Thursday, November 12, 2009 12:22 PM
To: Brahme, Rohini UTRC; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: RE: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply
I havn't read the standard in detail, but isn't there a requirement of some OA/sqft in addition to OA/person.
You are correct. Refer to the equation of Section 6.2.2.1 as I referenced below.
Let's assume that an office is assumed normally occupied from 8 am to 6 pm - Then during unoccupied hours (6.01 pm to 7.59 am) can the OA be zero or should it be OA per sqft?
It sounds like you're asking the same question I just answered, so I may not be understanding completely... By Section 5.4 I do not believe an unoccupied space is required to have any OA supplied. The equation in 6.2.2.1 does include a component "per square foot," but that equation is for determining the design minimum OA rate.
More tricky, let's say we have a occupancy sensor and know that the office is unoccupied from 12.00 pm to 3 pm (during the regular office times). What is the OA at this time - 0 or OA/sqft?
Applying the same logic and the same section, 5.4, if there are controls that automatically determine a space is occupied and turn the associated system on to provide the required OA, then there's no reason those systems aren't allowed to turn off while unoccupied. Short answer for your example: 0.
I'll point out, I'm merely an E.I.T. (with my head in the books) sharing my interpretations, so it may be worth holding out for a second opinion =).
~Nick
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NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com<http://www.smithboucher.com>
From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Brahme, Rohini UTRC
Sent: Thursday, November 12, 2009 11:14 AM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply
Since we are on this topic, I had a question on definition of occupancy.
I havn't read the standard in detail, but isn't there a requirement of some OA/sqft in addition to OA/person.
Let's assume that an office is assumed normally occupied from 8 am to 6 pm - Then during unoccupied hours (6.01 pm to 7.59 am) can the OA be zero or should it be OA per sqft?
More tricky, let's say we have a occupancy sensor and know that the office is unoccupied from 12.00 pm to 3 pm (during the regular office times). What is the OA at this time - 0 or OA/sqft?
Thanks
-rohini
From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Nick Caton
Sent: Thursday, November 12, 2009 11:36 AM
To: Guin, Michael; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply
No.
Refer to Section 5.4:
"Mechanical ventilation systems shall include controls, manual or automatic, that enable the fan system to operate whenever the spaces served are occupied. The system shall be designed to maintain the minimum outdoor airflow as required by Section 6 under any load condition."
In summary, you must provided the minimum ventilation rate as prescribed in Chapter 6 only when (A) the space is occupied and (B) there's a thermal load condition (or manual control - see Section 5.4) triggering the operation of the ventilation system.
Your original question is confusing to at least a few of us because of stating an office ceases to be a "zone" at night... It's a terminology thing, but 62.1 and other standards will become more digestible to you when you recognize that's not the case. The clarification we're making here is that where a zone occupancy (i.e. "office") is decided and a constant over time, something like "occupancy rate" can be variable.
I'd like to also point out, based on your first inquiry, that the equation at 6.2.2.1 uses maximum zone occupancy to establish the minimum design OA rate, not the hourly occupancy rate (which may be zero).
~Nick
[cid:image001.jpg at 01CA63AB.B9FCCB70]
NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com<http://www.smithboucher.com>
From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Guin, Michael
Sent: Thursday, November 12, 2009 8:44 AM
To: Shawn.Lee at fluor.com<mailto:Shawn.Lee at fluor.com>
Cc: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoor airsupply
is there any requirement to provide minimum outdoor fresh air wihin the office space when it is unoccupied according to ASHRAE 62.1
Do you think it it clear enough?
Regards
Michael
________________________________
From: Shawn.Lee at fluor.com<mailto:Shawn.Lee at fluor.com> [mailto:Shawn.Lee at fluor.com<mailto:Shawn.Lee at fluor.com>]
Sent: 12 November 2009 13:58
To: Guin, Michael
Cc: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>; bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>
Subject: Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoor air supply
Michael,
Technically answering your question may not help you much. You need to make the question clearer and more meaningful. Tell people what you are trying to do, what is in your mind, and what you are trying to accomplish. Then this group may help you more on the target.
Thanks.
Shawn Lee, PhD, PE
"Guin, Michael" <Michael.Guin at WSPGroup.com>
Sent by: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>
11/12/2009 06:09 AM
To
<bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>>
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Subject
[Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoor air supply
Dear all,
ASHARE 62.1 2007 deifned zone as an occupied space. Table 6-1 provides the calculation for different spaces based on occupancy and floor area of the occupied space.
If we consider an unoccupied office space at night (i.e. not strictly a "zone anymore" ); is there any requirement to provide minimum fresh air wihin the office space.
Thanks in advance for your help
Michael
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