Thread: Commercial Ventilation

Hi folks,

Looking at some package HVA/C units on the roof of a commercial building recently. Overall, these units seemed well maintained; however the blowers were not operating continuously. I seem to recall a commercial heating contractor telling me some time ago that the fans should be on continuously when a commercial building is occupied in order to bring in fresh air from the exterior. I might have that wrong and it might be a specific number of air changes per hour.

This is an auto dealership; mixed use with service bays at the rear (separate heating and ventilation units), offices upstairs and a showroom at the front.

I have tried to look this up in the California Mechanical Code, but have been unable to decipher some of the wording. For example:

402.3 Mechanical Ventilation. Where natural ventilation is not permitted by this section or the Building Code, mechanical ventilation systems shall be designed, constructed, and installed to provide a method of supply air and exhaust air. The system shall operate so that all rooms and spaces are continuously provided with the required ventilation rate while occupied.

As far as I know, there is no prohibition of natural ventilation by code for this building, it just does not have many operable windows. I feel it needs ventilation, but this section does not seem to cover it.

403.5.2 Short-Term Conditions. If it is known that peak occupancy will be of short duration or the ventilation rate will be varied or interrupted for a short period of time, the design shall be permitted to be based on the average conditions over a time period T determined by Equation 4-9. [ASHRAE 62.1:6.2.6.2]:

T= 3v / Vbz (4-9) IP (Equation 4-9)
Where:
T averaging time period, (min)
v the volume of the zone for which averaging is being applied, ft.3 (m3).
Vbz = the breathing zone outdoor airflow calculated using Equation 4-1 and the design value of the zone population Pz' cfm (Lis).

Not that I understand what that means.

Are there any folks with commercial heating experience that might have a reference or be able to explain it in simple, easy to understand language?

Thanks.

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Originally Posted by Gunnar Alquist

Looking at some package HVA/C units on the roof of a commercial building recently. Overall, these units seemed well maintained; however the blowers were not operating continuously. I seem to recall a commercial heating contractor telling me some time ago that the fans should be on continuously when a commercial building is occupied in order to bring in fresh air from the exterior.

You would need to know the design of the HVAC system to be able to answer the question if those units should be running all of the time.

It is possible that make air/fresh air is being provided separately, there could also be other design considerations which was made.

I would refer questions like that to an HVAC contractor to make repairs as necessary ... and leave it up to the HVAC contractor to do the calculations and determine what is necessary (notice that I did NOT say to have the HVAC contractor "evaluate" the system, they will automatically need to do that to respond to the "make repairs as necessary") - and I would list any and all items in the HVAC system to give them things to start with.

Think of it as induction of fresh outside air to occupied interior space. The requirement is separate from and in addition to requirements for heat and/or A/C.

Requirements vary considerably with type and duration of occupancy. The formula allows a HVAC designer to stray from norm's in some situations. Example - a lunch room that is large enough to have it's own HVAC unit and is occupied only from noon to 1:00 will have a different ventilation rate from office space which is occupied from 8 to 5.

The service area is a Classified location, with specialized air exchange and fresh air/make-up air requirements, each area specific to the type of work performed; self closing doors which must remain closed between it and the other occupancies. The showroom is also a type of garage, but not a service type; and the offices and customer waiting areas are separate space, albeit connected thereto.

Regarding the more stringent air exhange requirements in California, and OSHA for same

...nevermind, Its a Gunnar Alquist question.

Originally Posted by H.G. Watson, Sr.

...nevermind, Its a Gunnar Alquist question.

Wait... Was that a joke? I didn't know you had it in you.

Thanks folks (yes, you too H.G.).

The service area had big ventilation units, so I was not really concerned about that. I was more interested in the showroom, parts and office areas. Not as heavily occupied as an office building is likely to be.

I will modify my report accordingly. Thanks again.

Originally Posted by Jerry Peck

You would need to know the design of the HVAC system to be able to answer the question if those units should be running all of the time.

It is possible that make air/fresh air is being provided separately, there could also be other design considerations which was made.

I would refer questions like that to an HVAC contractor to make repairs as necessary ... and leave it up to the HVAC contractor to do the calculations and determine what is necessary (notice that I did NOT say to have the HVAC contractor "evaluate" the system, they will automatically need to do that to respond to the "make repairs as necessary") - and I would list any and all items in the HVAC system to give them things to start with.

Jerry,

Where did you learn the difference between "evaluate the system" and "make repairs as necessary"?

I figure it must be a mark you noted in a legal case or something.

Can you "elaborate"?

Originally Posted by John Dirks Jr

Where did you learn the difference between "evaluate the system" and "make repairs as necessary"?

You, as the inspector, are being paid to do the "evaluation", and you did so, then you list all of the items you found, then all repairs / replacements / corrections are to be made by the contractor.

Before anyone (any contractor / engineer / etc.) can make any repair they must first do their own "evaluation" of what was reported and what currently exists. As such, there is no need to tell them to do what you were paid to do, i.e., "evaluate" what you see. Use the phrase 'have contractor evaluate' (are phrases similar to that) and your client is going start asking what to heck they paid you to do.

In a case such as was asked about here, the way I would put it would be to list what I found and then to state that the contractor needs to document that the ventilation in such-and-such area meets or exceeds the required ventilation (which means in writing and give the reasons why). You want them to put it in writing so you client has backup support for when it does not work correctly.

And, yes, I worked on a case where the home inspector had written almost everything off as 'have contractor evaluate' after their list if items, and the attorney asked me what the contractor actually did for their inspection. After reading the report I basically had to say that all the home inspector did was to pass off their work to the contractor, that the home inspector apparently did not inspect or evaluate the system as the home inspector passed that evaluation work off to the contractor.

The attorney then was going to go after the home inspector for breach of contract and other issues as the home inspector apparently did not do what they agreed to do in their contract - they passed that work off to the contractor for every system - I don't know how it turned out, but the home inspector was going to be on the hook for refunding their fee and to additionally pay for all the contractors fees the home inspector said to bring in to do the home inspectors work for them, and that was going to be quite a handsome amount.

Now, if you did not inspect the system, then, okay, said that you did not inspect the system as it was beyond your expertise, knowledge and experience and then refer the system out to be "inspected" by a person qualified to do so. I know a fair amount about ADA stuff, but if I had to do an ADA "inspection" I would refer that out to an ADA inspector (while still reporting on what I saw while inspecting other items, but noting that I did not do an ADA inspection). I have done some limited ADA "inspections" while doing other inspections on commercial property and the like, but I did not call them ADA inspections, I just pointed out what I saw 'while doing other inspections' - my clients knew that is what I would do up front and were okay with that, and none went to hire an ADA inspector as I recommended them to do.

Even when recommending a structural engineer I would recommend the structural engineer "to design appropriate repairs", and if "no repair" was the appropriate action, that was covered too.

Thanks for the explanation Jerry.

How about a combination of the two? Something like this;

"Have a plumber further investigate to determine the repairs as needed".

This would be used in case of a slow drain for instance. I can see the drain moving slow but without further evaluation, I don't know why. IE, it could be hair clogging the trap or it could be a design problem with the venting system.

Originally Posted by John Dirks Jr

Thanks for the explanation Jerry.

How about a combination of the two? Something like this;

"Have a plumber further investigate to determine the repairs as needed".

This would be used in case of a slow drain for instance. I can see the drain moving slow but without further evaluation, I don't know why. IE, it could be hair clogging the trap or it could be a design problem with the venting system.

"
"Have a plumber further investigate to determine the repairs as needed".

This would be used in case of a slow drain for instance. I can see the drain moving slow but without further evaluation, I don't know why.
"

Why does the plumber need to "further investigate" anything?

Why do you need to know "why" the drain is draining slowly?

You KNOW the drain is draining slowly, so why not just write it up for repair or correction?

Does it matter to you whether or not the plumber finds a child's toy in the drain line, roots, hair, gunk, or whatever else they may find?

Seems to me that you are trying to make a simple write up into something much more complicated than it needs to be:
- "Drain is draining slowly, drain may be partially clogged, have plumbing contractor repair/correct as needed." I stated "may be partially clogged" as that is the most frequent reason for a drain to drain slowly, but, it could be a venting problem too.
- Heck you could simplify it even more by just stating:
- - "Drain is draining slowly, have plumbing contractor repair/correct as needed."

Why is it draining slowly? Don't know.

Do you want to speculate and possibly come up with inexpensive causes to allow your client to think 'No big deal.' and then call you and say 'That drain cost me big bucks, I had to have a plumber reroute the venting of it. You should have told me this could be bigger than just hair in the drain as you said it probably was.' ... You know what his next statement is going to be: 'I had to pay $$$$ and I think you should be responsible for that amount or at least a good portion of it ... '

Originally Posted by Gunnar Alquist

Wait... Was that a joke? I didn't know you had it in you.

Sure you did.

Originally Posted by Gunnar Alquist

Hi folks,

. . . . .

I have tried to look this up in the California Mechanical Code, but have been unable to decipher some of the wording. For example:

. . . .


Thanks.

Looks like a case for California Title 24 (shudder) . As I recall the Title only touches on existing construction so your reference to CMC may be adequate. If Title 24 were to be referenced then you would need continuous fan operation including outdoor air intake.

As an HVAC system designer for many years my recommendation would be to leave the fans on in the occupied space in an effort to provide a positive pressure relative to the service areas.

Gunnar, I know that is a little off topic but after reading the other posts I think it is appropriate enough.