[labnetwork] Thermal load in cleanrooms ISO 5/6

Mon Mar 16 16:25:03 EDT 2015

Loic,

I agree with the caution about accounting for the heat from the FFU; it is significant.

In our fabs we use a large external Process Chilled Water unit which provides cooling for 40-50 tools. Some of the equipment (like cryopump compressors and larger pumps which typically have larger => 3/8” diameter), cooling lines can be directly cooled by the PCW loop. Many other tools like electron gun evaporators and sputter guns have smaller cooling lines and you may have trouble directly connecting them to the PCW loop and achieving the required flows and pressures.

We end up with many small heat exchangers each set up for the particular needs of our tools. Some run distilled water, some DI water, some glycol and some high temperature thermal fluids. The pumps are the weak point in these units.

When connecting tools across your PCW loop be careful to include balancing or flow setting valves as you will have many connections in parallel.

Also I prefer to use a non-closed system, i.e., one with an atmospheric pressure return tank. This can be automatically refilled with treated water as needed to account for leaks and losses. Having your return water dump into a non-pressurized tank creates much less back pressure than the closed loop pressurized systems. The back pressure can be a killer with many parallel connected tools with different impedances.

  - Jim

On Mar 16, 2015, at 11:41 AM, Iulian Codreanu <codreanu at udel.edu<mailto:codreanu at udel.edu>> wrote:

Loik,

Another thing to keep in mind is the heat that is "taken away from the equipment" via exhaust.

The heat generated by a piece of equipment can:
-Be dissipated into the room
-Be "taken away" by the cooling water.
-Be "taken way" by exhaust.

If a piece of equipment is not cooled and does not have exhaust then all the heat gets dissipated into the room.

If the piece of equipment is cooled and exhausted only part of the heat generated will end up in the room.

If you know how much heat is taken away by the cooling water and/or exhaust that is great.  If you do not, I saw engineers using factor such as (PCW stands for process cooling water):
100% of the power into  the room if no PCW and no exhaust
50% of the power into  the room is no PCW but exhaust
40% of the power into  the room if PCW but no exhaust
20% of the power into  the room if both PCW and exhaust

I prefer the "unique chiller (placed outside of the building)" approach for cooling the equipment.  If you can run the water from the unique chiller directly through the equipment, you do not have to deal with the heat generated by the "small chillers".

Iulian

iulian Codreanu, Ph.D.
Director of Operations, UD NanoFab
163 ISE Lab
221 Academy Street
Newark, DE 19716
302-831-2784
http://udnf.udel.edu<http://udnf.udel.edu/>

On 3/16/2015 10:36 AM, Loïk GENCE wrote:
Hi Everyone,

I am working on the design of a small cleanroom facility (70m2) ISO 5/6. Right now, I am dealing with the problem of thermal load,
Which is crucial here in Rio, where the average outside temperature is of 30 deg C with a relative humidity of  75-80 %.

I would like to have your help and/or comments on several points:

Most of the manufacturers do not provide a value for the thermal load (why?). Assuming 2 or max 3 people working simultaneously in the cleanrooms, and usual cleanroom value: 22 deg C - 55% humidity. The main issue is: how can I estimate the cooling power required for the Air Conditioning System (ACS)?

I have the list of equipments we'll have and the corresponding electrical power. I assumed the heat generated by 2 users and added the total electrical power dissipated as heat inside of the cleanroom, using a simultaneity factor of 0.75 (all equipments won't be turned on at the same time) and neglected the heat produced by the filter fan and lightning.

        - Is it reasonable for dimensioning the ACS cooling power ?

Also most of the equipments have a cooling water circuit. But the cooling power needed is well described in the installation manual provided with the equipments.

        - Should I subtract from the ACS cooling power value,  the cooling power from the chillers?

        - Do you think a central and unique chiller (placed outside of the building) is preferred to several smaller chillers placed closer to the equipment?

I thank you very much for your kind help or comments.

regards,

Loïk.

--
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Dr. Loïk Gence

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loik.gence at cetuc.puc-rio.br<mailto:loik.gence at cetuc.puc-rio.br>
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