How do you determine how much HVAC capacity a building needs if your going to run a lab with fume hoods.

August 3, 2011 9:53 AM

We're looking for a new building to lease for our growing cleantech business. If we're lucky we'll find something that already has a lab complete with working fume hoods. But right now it looks more likely that we'll have to construct the lab ourselves. One huge potential expense is installing the extra HVAC capacity needed when you operate fume hoods (because they suck all the conditioned air out of the building). When we're talking with rental agents they tell us this building has X tons of HVAC, but we have no idea if that's even close to our requirements. So specifically how much HVAC capacity would be needed to run two 4' fume hoods. Or is there an easy method/rule of thumb for estimating what's needed.
posted by Long Way To Go to Technology (9 answers total)

Not going to answer your main question, but I am going to suggest you look at air to air heat exchangers. They are used to preserve the thermal energy (hot or cold) when you vent air outside. They are pretty efficient. I am sure they cost less to run than AC or heating units, and the capital expense should be lower.
posted by FauxScot at 10:02 AM on August 3, 2011

I don't know what process/chemicals you are working with, but generally ductless fume hoods can be a good option when you're looking at installing hoods into an existing building. They exhaust the filtered air back into the room.
posted by muddgirl at 10:17 AM on August 3, 2011

I was involved in the architecture/civil engineering portion of a lab's construction, and I think i remember that the dept handling the hvac issues worked with everything in cfm (cubic feet per min.). Perhaps you can do some conversion on the numbers you have?

Check with some fume hood manufacturers to see how much air their stuff moves.
posted by WowLookStars at 10:39 AM on August 3, 2011

BTW this sort of calculation is one part of my job. I'm at lunch now but when I get back to the office I'll send you some equations.

To estimate the heat load for the extra make-up air needed for the fume hoods, you'll need to know the air flow through each hood (in cfm) and the HVAC system design specs - namely their optimal inlet and exhaust temperatures.

Now, if you want to know whether the current HVAC system is large enough to accommodate the fume hoods, that's a trickier question. You'd have to know the design basis for the HVAC size and how much contingency they built in for equipment.
posted by muddgirl at 10:47 AM on August 3, 2011

Out of curiosity, are there fume hoods that pull in fresh air from the outside? That would make your HVAC problem a lot less severe, and would be a bit more "green".
posted by schmod at 11:03 AM on August 3, 2011

Fume hoods need to pull room air in order to perform their job of preventing operator exposure to whatever it is you are using the fume hood for. Typically you need around 75-125 Feet Per Minute of air flow at the opening to prevent spillage. A 4' wide hood with the door open 1 foot therefor needs to pull 300-500 CFM of air from the room in order to maintain minimum FPM at the opening. If you drew the air from outside whatever you are trying to contain could spill out the door opening.

Because the same situation is faced by kitchens any decent commercial HVAC contractor should be able to tell you whether you have sufficient make up air capacity. Rule of thumb: you probably don't unless the facility was a restaurant or auto body shop at some point.
posted by Mitheral at 11:49 AM on August 3, 2011

You should go talk to a mechanical engineer in your area. Fume hoods typically have a working sash height of 18". Face velocity is typically 100 fpm. This would equate to 600 cfm. Tonnage would depend on location. With regards to recirculating fume hoods, they are typically only used with biological hazards, not chem. Air to air heat exhangers are a really bad idea in this situation.
posted by ihadapony at 11:53 AM on August 3, 2011

Response by poster: Thanks everyone. We're bringing in a HVAC engineer to look at one promising building. I was hoping there was a simple way to quickly screen buildings to see if they had enough installed capacity, but that doesn't seem to be the case. It's not a straight forward conversion from CFM to tons of HVAC capacity.

We're dealing with fairly toxic chemistry, similar to what you find in a semiconductor fab. So the fume hoods are a critical safety item, they have out vent outside.
posted by Long Way To Go at 8:35 AM on August 4, 2011

I'd skip the construction and find lab space -- you'd be surprised at the "nonstandard" places you can find it. I located lab space in Chicago that was available for sublet at a warehouse-type building using commercial MLS listings, and have the option to expand into the office and warehouse space in the future.

Additionally, your local university will have lab space for rent -- much cheaper than market rate. Typically they have "accelerator" or "incubator" programs where lots of startup biotech companies rent lab space with private or shared office space. In Chicago, at least, UIC, IIT and UofC all have seperate lab campuses built specifically for this purpose. Other places I've driven through recently and noticed this same set-up include U of Wisc-Madison, Western Michigan University, Grand Valley State University, Michigan State, U of Mich, and UCSB.
posted by firstcity_thirdcoast at 11:21 AM on August 4, 2011