[Bldg-sim] ASHRAE 62.1 unoccupied space minimum outdoorairsupply

Karen Walkerman kwalkerman at gmail.com
Thu Nov 12 13:57:24 PST 2009


In the equation in section 6.2.2.1, "Az" is defined as "zone floor area: the
net occupiable floor area of the zone"

and "occupiable space: an enclosed space intended for human activities,
excluding those spaces intended primarily for other purposes, such as
storage rooms and equipment rooms, that are only occupied occasionally and
for short periods of time."

I think it is pretty clear that storage rooms that are rarely occupied don't
need to be provided with ventilation air.  Yes, if the room is storing
something that emits or smells, I would hope that the designer would use
common sense and provide ventilation air, but if a space is only occupied
for very short periods of time, and not very often, it doesn't make sense to
go to the expense of installing a ventilation system, and spend $$ on
conditioning the ventilation air.

I am still not sure about corridors.  These are spaces that people commonly
go through, but actual average occupancy is very low.  In addition, the
ventilation requirements for corridors is low.  For a building that have
separate heating and cooling equipment in each zone, and no central air
system, does it really make sense to pipe 30 cfm of ventilation air to the
corridor?  What about naturally ventilated buildings?  Often the corridor
doesn't meet the requirements for natural venilation as it is in the core of
the building.  Are you going to add an entire ventilation system just for
the corridor?

--
Karen



On Thu, Nov 12, 2009 at 4:41 PM, Matutinovic, Luka <LMatutinovic at halsall.com
> wrote:

>  Nick,
>
>
>
> I agree that both a per-person and per-area rate must be calculated to
> determine the total OA.  I have two comments though:
>
>
>
> 1.    In many jurisdictions, ASHRAE 62.1 is not suggested practice, rather
> a code that must be met.  For example, all buildings built in Ontario must
> be designed in accordance with 62.1.
>
>
>
> 2.    I don’t think you could ever effectively argue that there are any
> unoccupied spaces in a building, other than say mechanical shafts (I clearly
> just contradicted myself…).  Although a storage room is not regularly
> occupied, somebody will eventually have to store something in it and at some
> point retrieve it.
>
>
>
> Regardless though, Pz in equation 6.2.2.1 applies only to the per-person
> rate, which in the case of storage rooms and corridors is zero anyway, so
> the zone outdoor airflow Vbz reduces to just the per-area rate x area.
> Therefore, I think the per-area rate must always be supplied to all spaces
> in the building during regularly occupied hours.  At night, the ventilation
> system in the office building can be turned off, but during normal office
> hours it should supply the total OA, which includes OA for non-regularly
> occupied areas.  For multi-zone systems the total OA is usually lower than
> the sum of all Vbz, to account for occupant diversity and other system
> parameters.
>
>
>
> I think in reality, not all spaces are directly provided with ducted
> ventilation air, and transfer air is often introduced via grilles in the
> doorway.  Granted, one could question the effectiveness of that delivery
> given the lack of exhaust fans to induce the air into the room as would be
> the case in washrooms. Nonetheless, I’ve seen it done before.
>
>
>
> Cheers,
>
>
>
> *Luka Matutinovic, *B.A.Sc., LEED® AP
>
> *Green Building Consultant*
>
> * **
> *T. 416.644.0649
>
> F. 416.487.9766
> Toll Free 1.888.425.7255
> www.halsall.com
>
> *HALSALL ASSOCIATES LTD.
> *Toronto  Richmond Hill  Ottawa  Sudbury
> Burlington  Calgary  Vancouver  Dubai
>
> *‘50 Best Workplaces in Canada’ **
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> *P* **Please consider the environment before printing this e-mail*
>
>
>
>
>
> *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 4:11 PM
> *To:* Karen Walkerman
>
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum
> outdoorairsupply
>
>
>
> Note that Table 6-1 has “—“ under the CFM/person values for (“General”)
> corridors, storage spaces, electrical rooms and similar spaces.  I consider
> this ASHRAE’s indirect guidance on spaces you can consider “typically
> unoccupied” (Pz = 0) for the purposes of determining the minimum OA rate.
>
>
>
> ~Nick
>
>
>
> [image: 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:* Karen Walkerman [mailto:kwalkerman at gmail.com]
> *Sent:* Thursday, November 12, 2009 2:34 PM
> *To:* Nick Caton
> *Cc:* Brahme, Rohini UTRC; bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] ASHRAE 62.1 unoccupied space minimum
> outdoorairsupply
>
>
>
> Ok, this makes more sense.  What about corridors that have only transient
> and very low occupancy rates?  Can this also be classified as unoccupied?
>
> Thanks,
>
> --
> Karen
>
> On Thu, Nov 12, 2009 at 2:07 PM, Nick Caton <ncaton at smithboucher.com>
> wrote:
>
> I may be wrong, but it appears a number of people aren’t examining the
> equation in 6.2.2.1 as I’m suggesting.  If you’ll check that out I’m certain
> you’ll find this is a much simpler question/answer than it’s being made out
> to be.
>
>
>
> *Both* sets of figures provided in Table 6-1 (OA/person and OA/SF) are
> used to determine the design minimum OA rate, using 6.2.2.1’s equation.
>  Occupancy has no effect on the OA/SF requirement, and likewise zonal area
> has no effect on the OA/person requirement.  Additionally, the occupancy
> figure used is the *maximum* occupancy of that zone.  Quoting  6.2.2.1:
> “Pz = zone population: the largest number of people expected to occupy the
> zone during typical usage…”  It is not the hourly percentage occupancy and
> is not zero unless the space is never normally occupied (as with a storage
> room like Karen suggested).
>
>
>
> The design minimum OA rate is only applicable when the ventilation system
> is operating.  Unless I’m missing something major, the ventilation system is
> not required by ASHRAE 62.1 to operate 24 hours per day  (again, refer to
> Section 5.4, which I’ve copied entirely below).
>
>
>
>
>
> I’ll try to break down the current questions/statements on the table:
>
>
>
> The reason I had the question was because I think OA/sqft technically
> should not be dependent on occupancy…
>
> That’s a fair judgement a designer is allowed to make.  The 62.1 Standard
> is just that – not a code, but a set of suggestions provided by some of
> those best qualified to provide them.  To play the devil’s advocate, the
> counter-argument is that Occupancy cannot be ignored by an energy-conscious
> ventilation system designer.
>
>
>
> …If that was the case, it would suffice to just increase the OA/sqft and
> have only one number to take care of.
>
> Someone doing that would be ignoring the equation Table 6-1 was built
> around (re: 6.2.2.1).  I’d agree that would be a misinterpretation of the
> standard.
>
>
>
> 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.
>
> OA/SF is always used alongside OA/person to determine the “breathing zone
> outdoor airflow.” (Which I’ve been calling the design minimum OA rate).  The
> question of when these ventilation rates apply is tied to when the zone is
> occupied.  To restate my position (Again Ref: Section 5.4):  ASHRAE 62.1
> does not require that ventilation systems operate during unoccupied times.
>
>
>
> What do the hvac designers specify for the control of OA?
>
> Not sure whether a concise answer can be provided to this broad question…
> OA ventilation *can* be controlled by any combination of
> scheduling/occupancy sensing/timer control/temperature/humidity/VOC, CO2, CO
> or other air quality sensors… all depending on the project budget, climate,
> and type of system being designed.  If this question had a simple answer,
> then we wouldn’t need HVAC designers =).
>
>
>
> 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.
>
> See my answer above.
>
>
>
> So do you need this ventilation rate only when the building is occupied,
> only when the space is occupied, or all the time?
>
> Strictly speaking, only when the zone (space) is occupied.  If you have a
> one-zone system that doesn’t distinguish between occupancy rates, then
> whenever the building is occupied.
>
>
>
> 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?
>
> This is a broad-scope question, so I’ll add another quote under Section 1,
> entitled “PURPOSE:”
>
> *“1.1*        The purpose of this standard is to specify minimum
> ventilation rates and other measures intended to provide indoor air quality
> that is acceptable to human occupants ant that minimizes adverse health
> effects.”
>
> If a space is never occupied, then ASHRAE doesn’t care about air quality.
> If a space is “almost never occupied,” then they do.  To continue your
> example, if you have a storage warehouse with no ventilation installed, and
> it’s almost never occupied, someone might eventually store something in that
> space that without ventilation would eventually cause a health hazard to the
> next occupant entering the space.  In my college years, this was a commonly
> observed effect caused on a small scale by my roommates forgetting food in
> the microwave =).
>
>
>
> ~Nick
>
>
>
> ~Nick
>
> [image: 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:* Karen Walkerman [mailto:kwalkerman at gmail.com]
> *Sent:* Thursday, November 12, 2009 12:28 PM
> *To:* Brahme, Rohini UTRC
> *Cc:* Nick Caton; 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>
> 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]
> *Sent:* Thursday, November 12, 2009 12:22 PM
> *To:* Brahme, Rohini UTRC; 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
>
>
>
> [image: 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 *Brahme, Rohini UTRC
> *Sent:* Thursday, November 12, 2009 11:14 AM
> *To:* 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] *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
>
>
>
>
>
> [image: 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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