System Pressure vs Static Pressure

[BMug]

I am busy Validating a Pharmaceutical HVAC Factory. In the documents there is a portion where I should calculate system pressure from the read data which is:

1. Supply Duct pressure
2. Return Duct Pressure
3. Primary Filter Differential Pressure
4. Secondary Filter Differential Pressure
5. HEPA Filter Differential Pressure
6. Coil Differential Pressure

What is the right formula for this parameter from the given data?

May someone please help me address this problem with special attention to whether I have to read Return Ducting Pressure as positive or negative.

 

[MechEngNCPE]

To me the "system pressure" would be the pressure loss total of all the points you listed above, plus any pressure losses in the mixing box, heating coil if there is one, fan inlet losses, etc. To give the total static pressure required of the fan. If the ahu is a packaged unit then the submittal should have a breakdown of the static pressure losses for each section.

 

[BMug]

Thank you MechEngNCPE.

 

[ChasBean1]

What the f is a "pharmaceutical HVAC factory?” Is that where drug companies build air handlers?

BMug, for this industry we find ourselves cornered by requirements from people who don’t understand HVAC. For their purposes, write down the supply duct static pressure. It might be 1 to 3 inches water column.

We know the value is meaningless without full static across the fan and the speed value at which those were recorded, but it’s like filling out a psych form while waiting for a doctor… Put down 1.3 furlongs on the form and see if they come back with any questions…

 

[Waramanga]

I dont want to sidetrack/hijack the thread, but.....
ChasBean what do you mean "cornered by requirements from people who don't understand HVAC"? can you give a typical example please to illustrate?
BTW, what area of the industry do you work in? consulting, contracting, else??

BMug, are you doing like a 'due diligence' on the design?

 

[BMug]

Thanks Wamaranga.

Yes this is a periodic due diligence test on the equipment that we do 6monthly, yearly and once every two years depending on the type of the test.

Its basically is a requirement for Pharmaceutical production plants to ensure the tablets, etc are being produced in the claimed state as validated during start up just to respond to ChasBean1.

 

[MechEngNCPE]

"Doing the HVAC Validation" for a Phamaceutical Manufacturing Facility would be the right way to say that. But I got what you meant.

 

[ChasBean1]

Sorry for the late reply. Bmug, can you describe what

"Its basically is a requirement for Pharmaceutical production plants to ensure the tablets, etc are being produced in the claimed state as validated during start up"

means?

Waramanga, you want an example of HVAC requirements being imposed by those who don’t have the background? Re-read the initial post. He’s calculating “system pressure from the read data” which is a bunch of pressures. There’s no definition of what’s required or why, but it’s needed by the “documents.”

Sorry I was crass in my response, but I'm pretty comfortable in this industry and your initial post left me perplexed, to say the least, about your need to validate HVAC without any sort of background in it.

You listed a bunch of pressures at different HVAC points and wanted a formula for it(?)

Thanks, CB

 

[MechEngNCPE]

Chas, you come off like a prick in many of your post responses, I realize you probably know more than most on here, but ease up, just my opinion.

OP is validating a pharmaceutical manufacturing facility, which must be done to ensure FDA approval. Why not help him understand how to find the system pressure correctly instead of belittleing the work he is doing. Pharmaceutical manufacturing facilities hvac design is my industry btw.

 

[BMug]

Thanks guys for all your responses.

ChasBean1 your responses helped as well but as you pointed out that these values do not help out if the full static pressure across the fan is not recorded. That basically was my line of questioning as I do understand HVAC maybe not as much as you do.

I am in the process of Reviewing Validation Documents and I saw some of these tests that have been there for years and it was when I picked out something was not right hence the request for information from colleagues in case I was missing some point.

MechEngNCPE thanks for the Valuable help as you indicated on here that you are in this field I look forward to interacting with you more on the subject as I am basically specialising in Pharmaceutical Facilities.

 

[ChasBean1]

MechEngNCPE, you're dead on. Not sure of the path that lead to the jaded comments. Here to help as needed...

 

[KiwiMace]

*Other people in room suddenly looking for lost pencils*

Back to the OP...

If I saw a list of numbers like this on a form asking for a total - I would subtract all the differential pressures and the return duct pressure from the supply duct pressure.

What else could the form be asking for? What it hopes to achieve is another story altogether.

 

[chicopee]

Reading the original post, I am sure that you'll have a tough time calculating system pressure. With that thought, I think that you need help or at least get an mechanical engineering handbook such as Mark or Kent and study the relevant sections. You'll note that the graphs in the relevant sections will have the static pressure as the ordinate and the flow rate as the abscissa. In that graph the system pressure will be plotted and will be approximately parabolic. The next curve on that graph should be the fan performance curve. Where the two curve meet will be aprroximated the actual flow in the system.
These curves can be modified with fan RPM's changes.
Happy reading.