# SMS HVAC #76



## HerrKaLeun (Oct 14, 2010)

the solution calculates OA requirement based on 25 students times 15 cfm (and somehow multiplies by 1240 ft²???). how do they come up with that? the question doesn't mention anything about how many students, size of classroom etc.

In my opinion the problem statement should include information of classroom size or number of students. Or how else should one come up with that?


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## Bman (Oct 15, 2010)

HerrKaLeun,

I noticed you posted a few questions, you might want to include the actual problems as many of us no longer have the books and can't help you out if we don't know the problem.... For this problem, I believe you need to use ASHRAE 62.1, Table 2 in which they provide occupancy counts based on area and use of space; for a classroom, the standard recommends using 15 cfm/person. Let me know if this answers your question, or post the problem and we can get you the rest of the way. FWIW, I brought the standard with me to the exam, but I don't recall actually needing it....


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## HerrKaLeun (Oct 15, 2010)

I know how to get the cfm once i know area and/or or number of occupants. However, the problem didn't give that. It only said classroom with 7 year old students.

Well, one coudl guess the area and number of students, but this can lead to large errors.


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## Bman (Oct 15, 2010)

Post the problem and I'll see if I can help you out. I vaguely remember these problems, but don't remember them being very difficult, so maybe there is something you're missing.


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## WandaKing (Oct 15, 2010)

HerrKaLeun said:


> I know how to get the cfm once i know area and/or or number of occupants. However, the problem didn't give that. It only said classroom with 7 year old students.
> Well, one coudl guess the area and number of students, but this can lead to large errors.


check the ashrea 62.1, there is a table, you can get the information for a 7-grade class room, how many student per sqft. you already know the square footage, so you can get the total students in that space.


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## HerrKaLeun (Oct 16, 2010)

I know how to get the cfm number.. but the problem does not state room size nor number of students. I know iwth room size i can use the standards students/1000 ft² number. but without room size it is a big guess.

this makes me think the SMS is wrong in this.


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