[Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply

RobertWichert robert at wichert.org
Fri Nov 20 10:08:05 PST 2009


To the best of my knowledge, the requirement for OA is ONLY when the 
zone is occupied. And yes, it includes both a CFM per person component 
and a CFM per Sq. Ft. component. But they ONLY APPLY when the zone is 
occupied. Please note that for systems serving zones in normal 
applications, this is during times when the building is occupied, like 
normal business hours or whenever the HVAC system is running for 
building conditioning. There are special cases, like after-hours heat 
removal when, if nobody is in the building, you don't need outside air, 
but that is an unusual case.

Also please note that in some places, like California, there is an 
absolute minimum, even with CO2 monitors, based on square footage, but 
that isn't in 62.1.


-- 
Robert P. Wichert, P.Eng.
+1 916 966 9060
FAX +1 916 966 9068




================================================



Brahme, Rohini UTRC wrote:

> 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] *On Behalf Of *Nick Caton
> *Sent:* Thursday, November 12, 2009 11:36 AM
> *To:* Guin, Michael; 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:489575314 at 22072009-0ABB**
>
> * *
>
> *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_ _
>
> *From:* 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
> *Cc:* bldg-sim-bounces at lists.onebuilding.org; 
> 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]
> *Sent:* 12 November 2009 13:58
> *To:* Guin, Michael
> *Cc:* bldg-sim at lists.onebuilding.org; 
> 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
> 11/12/2009 06:09 AM
>
> 	
>
> To
>
> 	
>
> <bldg-sim at lists.onebuilding.org>
>
> cc
>
> 	
>
> 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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