Commercial Kitchen Exhaust 1

[Raj.S]

Hi

I am looking for design tips for a modication of commercial kitchen exhaust system . Without changing current duct , would like to know if more equipment can be added to extract smoke by enhancing exhaust fan.

This means: Keeping existing GI Rectangulatr duct as it is( Since there is no space ) to modify
Adding more powerful exhaust fan to pull out additional extract volumne


Appreciate your inputs

Thanks
Raj

 

[SAK9]

Noise is generally not an issue with KE ducts so you should be fine with a duct velocity upto 12 m/s.You also need to check the construction class of the duct to see what is the maximum negative pressure it can take otherwise it can implode like the Titan sub!

 

[Raj.S]

Thanks SAK9

The construction material is heavy duty GI . But i need to ensure that if the capacity is increased from 6300 CFM to 9000 CFM, will this duct suffice

Regards

 

[SAK9]

What do you mean by heavy duty GI? Please refer to SMACNA or DW144 for pressure classification of your duct. It is not sheet thickness alone there may be bracing requirements as well depending on duct size. Please inspect duct construction on site and verify with the standard as to what classification it falls under. When you upgrade the fan you should not get close to the pressure classification for the duct.

 

[Raj.S]

Thanks

Surely these details will have to be checked . Just to let you know that the exhaust duct is 47' x 8' and then before fan it is 28 ' x 23'. would it be suggestable to increase size of the later part of duct to facilitate additional flow?

 

[MedicineEng]

Another point to consider is drumming.
If the duct is undersized for the airflow and the there are 90 degrees turns without turning vanes youmight have drumming noises/vibraton which is really annoying and debilitating.
If you have the exhaust duct passing through other areas befoer it's discharge point, this can be a huge issue.

 

[Raj.S]

Thanks

IS there any software tool which is available to design a duct for exhaust for a commercial kitchen>

 

[HVAC-Novice]

You need to be able to clean the duct from grease. So that needs access and, IMHO, you can't have turning vanes etc. since you can't clean them. Grease is very sticky.

 

[LittleInch]

47 feet by 8 feet??

That's a very large kitchen,

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Raj.S]

Anyone who cane help me designing an exhaust duct to be connected with kitchen hoods, I can share details if someone can help asspace is very limited and narrow

 

[Raj.S]

@LittleInch . These dimensions are in Inches and not feet.

Thanks

 

[LittleInch]

1that's normally written 47" x 8"...

So you're already at about 12m/sec and you want to go to 18m/sec?

Think you're going too far with the available kit

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Raj.S]

Yes that was typo

You are right, cannot go beyond 12m/sec. Hence trying to find a space to lay new duct ,
However, the space is very less and hence duct has to be designed to extract 9000 CFM .

Any suggestions, what could be possible diamensions of rectangular duct and constrcution class of GI duct

Thanks

 

[HVAC-Novice]

You need to determine the exhaust requirements. Look at yoru local code. often that is based on linear length of range and type. Plus dishwashers. Look what it is designed for now, and what equipment you add and the resulting flow. Once you have the flowrates, THEN you look at the duct/fan etc.

 

[Raj.S]

I have all calculated flow rates amd mow i require to design fire rated ( MS) duct for this flow,

Existing is 6300 CFM DUct and exhaust is in place
New 7000 CFM to be designed .

Please suggest a suitable dimension ( rectangular) for this flow rate . Material is Mild Steel

 

[LittleInch]

Sak9 has given you excellent advice earlier in the thread. I would advice you to follow it and address the issues raised.

You said 9000 CFM before, now it's 7000??

You keep saying the duct size is fixed and now it isn't?

At these pressures duct size (area) is volume per second divided by your max velocity.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Raj.S]

Let me clarify

There is existing duct for a kitchen which is operational and carrying 6300 CFM.
We have plans to install new equipment which would require 7000 CFM to extract ( earlier it was 9000 which is now changed)
The operational duct size is fixed and I asking for the design for a new duct to extract 7000 CFM

Hope I am clear , else i can provide more info for more clarification if required.

Expecting a help

Thanks

 

[LittleInch]

Well it doesn't look like you have too many options other than increase the power of the fan after making sure the duct can handle to lower pressure just before the fan unit.

10% more flow will need 20% more power.

We can't see your system as you have provided no sketch, drawing, length, schematic or really anything other than minimal information. Not really sure how anyone is going to help you unless you do.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nuuvox000]

Just adding here, if you specify a new, more powerful fan, don't forget to look at the maximum negative pressure the fan is capable of and make sure the duct can handle it. I would look at SMACNA myself.

 

[Raj.S]

Replacig old fan is ruled out as we do not want to take risk of implosion

We are planning for new duct and new fan for additional equipment.

Please advise what is max flowrate a 22" x 10" MS duct can handle ?

Thanks