short of make up air

[lemonmugua]

I have a project and there is a existing make up air unit with 4000CFM capacity. But according to a new design, we are short of 1500 CFM.
Should I replace the existing unit with a new make up air unit?
or add a new make up air unit?
Is there a third way to do?

btw, I design with 80% capactiy of the exhaust air for the make up air.

Thanks

 

[tys90]

Hopefully you have a lot more information than what you've given us. You'll need it to make a good decision. How old is the existing unit? What are the changes that you need the extra CFM for? Is it heating and cooling? What type of space is the make up air being supplied to?

As a side note, is there anyway to put a sticky in this forum that outlines how people should ask questions? It's definitely needed.

 

[ChrisConley]

Depending on the size of the existing motor and fan speed, you _may_ be able to spin the fan faster and increase the output of the MUA. A balancer would be able to relatively quickly tell you if this can be accomplished.

5500 cfm is a fairly small MUA (on the order of $6,000 for a new one), so if the application is critical, or if the existing unit is fairly old, if may make more sense to replace.

 

[ljschultz]

depending on the global location and the need for tempered air to the space, be careful of heating medium and heater capacity also.