Use of recirculated air as a make up in clean rooms?

[Boiler1]

Hi all,

I am looking at the cleanroom set up where the make up air handlers (MAH) are used for pressurisation, i.e. to compensate for any leaks and some specialist exhaust from the area. A separate full recirculation HEPA filtered AHU's are used for air change rates and the cleanroom class matching so to speak.
There is an issue lately where the MAH cooling coils couldn't meet the make up air humidity set points and this appear to corelate to the higher external air temperatures and humidity .

There is a possibility of mixing the general areas exhaust air( 21C/70F @ 50% RH) into MAH intake to try to move the air at the intake away from the saturation line when needs be.

Is there any fresh air requirement for cleanrooms other than the fresh air supply for the operators (staff) that would prevent the use of recycled or exhausted air as the make up ?

regards

 

[lilliput1]

The outdoor air required must equal the exhaust air plus the air required to pressurize the space. This would be more than that required for ventilation. You can not reintroduce exhaust air into the space. You need to add DX cooling coil to the makeup air system and introduce some of the supply air to the recirculating system to offset recirculation fan heat gain.

 

[nuuvox000]

You will need an energy recovery unit for this. They are good at recovering the energy from exhaust with very little crossover. This will allow you to have the same amount of fresh air that you are used to while lowering the loads that the air handler has to handle. I would first check to see if they're okay with a lower pressure in the room during the hot parts of the year (or all year). Then it's an easier balancing fix.

 

[BronYrAur]

What is the makeup air humidity setpoint and where are you measuring it?

 

[AdrienneGC]

There may be fresh air requirements to satisfy some processes if there are hazardous materials being used necessitating diluting the air below the LEL, TLV, etc. Is the exhaust air to prevent over-pressurization or is the air exhausted for a different reason? It seems a heat exchanger between the exhaust and MUA may be a more appropriate solution.

Adrienne Gould-Choquette, P.E.

http://www.adicotengineering.com