Clean Room Sqft/Ton refrigeration

[bcvd45]

Hi all,
I have been reading around on this forum for many years, and finally have a question to ask for myself. Really I am just looking for a guideline to make sure I am in the correct ballpark with my numbers.

I am designing a new air handling unit for a Pharma facility, and have gotten to the point where I now want to sanity check one of my calculations. I am trying to make sure that my number for Sqft/TR makes sense of a clean room. I am getting 909 sqft/TR which seems a little light to me. With a room that has no exterior walls, windows, maybe one person at any given time, and some lights, I guess it is possible that this is correct. Does anyone know of an ASHRAE guide that would give typical ranges, just for sanity purposes?

Thanks in advance.

 

[trashcanman]

Check ASHRAE guide (Applications). Your load may be correct, if you have really accounted for all internal loads. Note that clean rooms can have an air change rate of 25/hr, so you could have some recirculating units for the space.

 

[jkauwale]

Hi bcvd45,

909 SF/ton does seem light, but could be right. You might want to double check the heat loads from (1) the equipment in the space and (2) the outside air requirements. These two items will increase the amount of cooling required.

I am not sure of any ASHRAE guide for typical ranges for a clean room. However, you can check ASHRAE Check Figures for a space that is similar to your application. For example, Hospital Patient Rooms according to the ASHRAE check figures have a range of 165 to 275 SF per ton. Residential spaces have a range of 400 to 700 SF per ton.



Justin K, P.E.

http://www.engproguides.com

 

[bcvd45]

Thanks guys,
There is only a very small heat load from equipment in the room, and the outside air is set at 20% right now. I will do the calcs over again just to make sure I am not missing anything.

 

[bcvd45]

I think it should be higher because we also have a 25 hp re-circulation fan from which we need to handle a heat load as well.

 

[bcvd45]

This room also has a much higher air change rate as it is a grade 'A' filling room with wall to wall laminar flow coverage. Design requires 120 ft/min across the entire area of the ceiling.

 

[jkauwale]

Let us know your final result.

I did a quick calculation just out of curiosity:
Lighting: 1.1 W/SF [100% heat load to space]
People: 143 SF/Person; 250 Btu/Hr - Sensible; 200 Btu/Hr - Latent
Miscellaneous Equipment: 3.0 W/SF [100% heat load to space]

From the above inputs, I got a result of 700 SF per Ton.

If I changed the Miscellaneous Equipment to 2.0 W/SF, then I get a result of 874 SF per ton.



Justin K, P.E.

http://www.engproguides.com

 

[bcvd45]

Well that is pretty close to the actual numbers. However, procedurally they are only allowed 2 people in this space at any given time. So if you take 2 people in 573 sqft. So personnel should only be ~246 sqft/person. I keep getting 909 as my final number, which may just be what it is. There really is no significant load to speak of other than what you have shown.

 

[urgross]

How much of a latent load do you get for outside air?

 

[bcvd45]

I believe the total was in the ballpark of 250 MBTUH latent. Don't have it in front of me though.

 

[ChasBean1]

Your 25 HP recirc fan is one heck of a recirc fan. Is it direct drive, or belt? The motor in the air stream or out of the air stream could make quite a difference.

If you have chilled water cooling, it doesn't hurt to upsize cooling capacity. Someone might put a laminar flow bench or some other equipment in there someday. The benches put out quite a bit of heat. If you have DX cooling, I would lean toward undersize vs. oversize.