Cleanroom Cooling Air changes vs heat gain

[DAKDPS]

I am designing a Pharma clean room. It requires 40 ACH or 6500 cfm. The only heat gain in the room is basically lights and people.
There is 1650 cfm of exhaust required. It is negative pressure with respect to surrounding spaces so I am gaining approximately 560 cfm
from pressure infiltration.

My question is what is the best way to provide the high ACH without large reheat for the small cooling load?

Any thoughts would be great.
Thanks

 

[quark]

Face and bypass arrangement at the coil.

 

[IRstuff]

Isn't your 560 cfm heat loaded from the outside?

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[cdxx139]

The 560 is from the airlocks so it is conditioned air.

You are returning so much air, that yoru load is very small. The problem you will find ios the load is so small compared to the airflow required. Face and bypass is a good idea. I oversided my unit so I could get 2 speed compressors, and it mostly runs at low speed.

If your using DX, you can also try digital scoll compressors with modulating hot gas reheat.


knowledge is power

 

[DAKDPS]

Thanks for the comments.
It is a chilled water unit.
It is also correct that the 560 comes from conditioned airlocks.
I also have hot water reheat on volume control boxes. The boxes are constant volume for balancing, just for the air changes that remain the same.

 

[SAK9]

What you have is a typical pharma HVAC system.There is no running away from reheat in the pharma industry due to air change requirements.Load can be minimal too at certain times.Try to recover some energy from the exhaust to cool fresh air if the exhaust is not too dangerous.Negative clean rooms are tricky so be mindful of air tightness of your fabric construction and light fittings.

 

[317069]

Can you explain the air balance of your application?

 

[DAKDPS]

SA 6400 CFM
EA 1650 CFM
Pressure airflow into room 560 CFM
RA 5310 CFM

Another problem I am having is sizing the cooling.
The space requirements are 68°F/<60% RH. The heat gain in the room is only 14,000 btu/hr very small. I will definitely have to reheat.
What I am trying to do is provide a make-up air unit to cut latent load and recirc with sensible only.

I am trying to figure out what leaving unit dew point I need to provide to maintain space conditions.

 

[tys90]

Is there any latent heat gain in the room? If not, then technically, you can provide air whose wet bulb is no higher than the wet bulb of the space requirements, which looks to be roughly 59°F.

On pharmacy prep rooms I like to oversize airflows a bit and then provide balancing devices on all air streams, including the transfer air, if possible. If the room is poorly constructed or too tight, then you will have options to make sure you are within the required pressure differential ranges between the rooms. I've seen burned out door operators because the pressure differential was actually TOO high and it was too difficult to open doors.

 

[317069]

What about 6400-5300 = 1100 cfm

 

[BronYrAur]

I have found the best way to be ceiling mounted fan-powered HEPA diffusers to give you the ACH. These HEPAs pull from a plenum above the room that you condition with the HVAC unit. If you go this route, don't forget to add the heat generated by the HEPA fans. Also, what class clean room are you making? Are you sure 40 ACH is enough?

 

[ChasBean1]

You need a fan powered terminal box that has 1,090 cfm primary air and ~6,500 cfm total air with supply air terminal HEPAs.