Negative pressure room design 1

[babus123]

I need to design a negative pressure room with 30Pa. There are 2 safety booth in the room and each booth will have one exhaust fan.
I mention the following parameters for your convenience:
The room volume: 56.64 m3
Room ACPH required: 20
DP: -30PA
Adjacent room: warehouse and outside wall

I want to use ceiling mounted split AC. Can the split AC maintain 20ACPH by self circulation?

As the adjacent room is warehouse, so I would like to add a fresh air duct from outside environment to support the exhaust fan. Because, I think there will not enough air to support the exhaust fan. The exhaust fan should provide 20ACPH as design condition.

So, I think about the calculation like this: EA= FA(from environment)+ Infiltration(leakage from door); is that correct??
When the safety booth is off,the room also should maintain 20ACPH.
For fresh air, the outside design condition in summer is 35 degree and 90% RH

The room air= 56.64*20= 1132.8 CMH
The infiltration air will be Q=2610A√△P= 232.03 CMH by considering 1500mm door width and 10mm gap height.
How to estimate the EA and FA fan size? Should I consider the room volume like kitchen exhaust fan design? So, what about the fresh air?


Could anyone please give me some comments about the design issue.

Thanks

 

[ZDR1985]

I want to use ceiling mounted split AC. Can the split AC maintain 20ACPH by self circulation?

But what is your indoor design temp? You will be cooling that amount of fresh air since you require 20 air changes per hour.

When the safety booth is off,the room also should maintain 20ACPH.

Do you mean split AC will be off?

How to estimate the EA and FA fan size?

You have already the calculated the air flow rate. That is the size of your fan.

Should I consider the room volume like kitchen exhaust fan design?

What about kitchen exhaust fan design?

So, what about the fresh air?

Your fresh air will be sucked inside the room, cooled by your split AC, and exhausted by your exhaust fan.

 

[babus123]

But what is your indoor design temp?
My indoor design temperature 18-25 degree Celsius and RH<65%

Do you mean split AC will be off?
I mean when the safety booth/ Exhaust fan is off still the split AC need to maintain 20ACPH

How to estimate the EA and FA fan size?
You have already the calculated the air flow rate. That is the size of your fan.
That means the exhaust air fan size will be=1132.8 m3/hr
and the fresh air fan size will be= 1132.8-232.03(infiltration)=900.77 m3/hr
Is that correct?

 

[ZDR1985]

Your AC will not maintain 20 air changes if it is just recirculating the indoor air

 

[babus123]

Your AC will not maintain 20 air changes if it is just recirculating the indoor air

That means this kind of split AC can't maintain air change rate by self circulating.

I have similar problems by selecting A/C for warehouse. We need 5-6 ACPH for GMP warehouse.Does it mean for supply or exhaust?
So, If I select split AC for warehouse, can I meet the 5-6ACPH? Or, I don't need to care about the 5ACPH, only cooling load calculation is ok for warehouse AC selection?

 

[ZDR1985]

If you want air changes, you need to supply and exhaust the same amount of air. Your air changes means the number of times you are changing the air every hour. If you want to achieve this with cooled air, then you need split AC that does not recirculate, you need a system that cools the outside air, pumps it inside your room, and exhaust the air outside.

 

[willard3]

You should hire an HVAC Engineer rather than trying to bootstrap this.

Board policies discourage what you are doing here: this is not an HVAC class.

 

[HVACMech]

ZDR, I agree with what you said, but I will say many people refer to ACH in a general term as air being supplied to a space. So I have had people tell me they need 1 ACH of fresh air and 6 ACH in the building. What they actually asking for is a unit that will supply air equivalent to 6 ACH with 1 of those being outside air. I always try to correct this, as you have done, but it is typically not what people mean when they say it.