I Need Assisstance in presenting a lecture on Airflow into a lab. 1

[pritel]

I Need Assisstance in the prep for a lecture on Air classification systems, pressure differentials, zoning, The basics of HVAC design, the procedures for setting up the operating parameters.

These must be designed for Lab areas.

Any info would be greatly appreciated.

Regards Dave Hargreaves

 

[ChasBean1]

Dave, it's a pretty broad topic and would be helpful to know what your existing level of knowledge is. Basically, you design the space around the use. The classification should be determined based on the type of work and the cleanliness requirements of the space. Is there an elevated biosafety risk? For a standard BSL-2 wet lab, such as when doing tissue culture, blood work, with various chemicals, etc., air is exchanged per ASHRAE and AIA at a rate no less than six air changes per hour (ACH). ACH is (cfm * 60 / room volume), room volume in ft3. Generally it is preferred not to recirculate air, but to have a one pass system. ASHRAE says if some air is recirculated, there should still be at least two air changes of outside air entering the lab.

If chemical fume hoods are used, you generally exceed the minimum ASHRAE and AIA ACH recommendations because of the high volume of air leaving the space. Many applications use a see-saw balance between the hood exhaust and the general exhaust of the space (if general exhaust is used). As the hood sash closes, hood exhaust drops and general exhaust modulates to maintain the programmed room cfm offset (often ~200 cfm) to maintain room pressure.

Variable volume supply air systems with reheat (very common) will throttle back the volume of supply air when the room gets too cold, then turn on the reheat to add heat. When the supply air reduces, the general exhaust will again track the supply to maintain the room at its programmed offset, for stable room pressure.

This is a common control scenario (this example is generally how Siemens lab control works), but there are many other control schemes, other BSL levels, and other lab applications that have different needs, such as positive lab pressurization. There are bypass fume hoods whose exhaust volume doesn't vary; there are constant volume systems, etc.

Lab pressure is usually a result of controlling air volume, not a parameter to use to control the HVAC systems. Pressure is at the mercy of the net open area of all the room's cracks and crevices, as well as pressures in adjacent spaces. I wouldn't recommend controlling lab air volumes based on pressure. Resultant pressure with respect to surrounding spaces (generally negative in lab applications) based on a design offset between supply and exhaust volume is often in the range of -.003 to .03, give or take...

I hope some of this helps. If you have access to the ASHRAE manuals, there should be some good information there. Good luck, -Chas.

 

[pritel]

Chasbean1

Thanks for your reply.

That is the general area that I have been doing my research in. I have access to the ASHREA mauals, but this is to deep for the trainee's that I am to deliver to.

The general areas to be covered in as basic form as possible (KISS), Are as follows

Understanding air classification Systems, pressure differentials and zoning.

HVAC system design, set-up and operating parameters

Regards

Dave Hargreaves B.Eng(Hons)

 

[Vicsidhu]

Thanks ChaseBean,

This was very informative. Even though these answers are intended for the seeker - it is very helpful for us - the viewers - or vultures for knowledge. I am knew to this field of design and am in the process of devouring all principle of desgin.

thanks,
Vicsidhu

 

[235zzzo]

Hello Chas

My question follows your reply, concerning the control of the air lab based on the (to the adjacent/ surrounding spaces) relative pressure criterium, no discussion about this point!

At the moment (sorry I have not present what is written specifically in the ASHRAE regulations), however it seems to me to be correct and practical, to keep a slight pressure difference, according with you, from -0.003 to + 0.03 air volume rates in/out of the space-lab, if i understood your point.

If in some lab situations, strict safety conditions impose that difference to be negative, in some other cases the most strict condition is:- nothing in! and nothing out! What are your comments in these circunstances? How do you do you see an efficient/economic solution in this context?

Have a Good 2002, and to all Forum!
Kind Greetings
zzzo