Industrial Ventilation for comfort... 1

[dblyle]

Ok, I visited a plant today where they make mechanical seals. The owner wants me to design an exhaust system to "move some air" in the building. The warehouse is large with several bay doors that are always open. It sits in the wonderfully cool climate of Houston, Texas where it is not very windy and the OA conditions are 95 DB, 80 WB.

My question is, where do I start? Obviously, drawing in 95 F air is not what I would consider comfortable. Do I assume an ACH and size wall fans to pull air through the building, or should I consider some sort of "tempered air" system. How much air movement is considered enough to feel comfortable? Should I maybe think about suppling outside air throughout the building?

Any help would be greatly appreciated.

 

[friartuck]

Generally, extract ventilation is a waste of time as the effect is very local to the exhaust point. Supplying fresh air will be of more benefit.

(The analogy is that you can blow a candle out but you can't suck one out)

Wall fans will move air but little else.

The air needs to be directed to the occupied level for them to appreciate the cooling effect.

Local controllability is also important so the users can sped control their ventilation and take control of their space.

You might also consider what we call 'punkah' fans which are large diameter prop fans that are supported at high level and blow air vertically downwards.

Thast covers the cheap options. If you have heat sources, try removing the heat before it enters the space below.

Naturally opening roof vents are also a good option and they could be designed to double up as smoke ventilators.

I don't know what the summer/winter climate is loke in Texas...does it get cold?? if so, you can use free cooling.

I have designed a 'free cooling' system for a foundry where they didn't have much money to spend. They couldn't afford to heat the air in winter or cool in in summer..so, I introduced fresh air (Usually cooler from outside), and put it through a mixing box. The mixing box mixed room air with outdoor air. In summer, the box was set to full fresh with a main fan and several side connections which had motorised supply diffusers. These were controllable and could be moved (Eyeball type sockets) to blow air at the workers.

In winter, the mixing box mixed air to prevent freezing air entering the space...a mix of 50/50 in winter supplied air at around 12 degrees C which was welcome by the operators of the furnaces.

If Texas is hot all year, you might consider evaporative cooling which utilises cooling by evaporation of water. Cheap and simple. Go to Munters in Germany for more info



Friar Tuck of Sherwood

 

[imok2]

I would consider supplying OSA throughout the building with evaporative cooling for example:
evaporative“cool air” is generally 8 to 12 degrees cooler than ambient air temperatures in humid environments and the cooling is accomplished by the evaporation of water.

1 gallon of water (evaporated over any period of time) is = 8,700 BTU’s)
So, if an Evaporative Cooler evaporates 5 gallons of water (5 x 8,700 = 43,500 btu).

12,000 BTU’s = 1 ton of cooling
43,500 / 12,000 = 3.62-tons of cooling.
ASHRAE Handbook, 1995, chapter 47 on Evaporative Air Cooling says:

“dry bulb temperature reduction due to the evaporation of water always results in a lower effective temperature, regardless of the relative humidity level" and " (evaporative cooling) can provide relief cooling of factories almost regardless of geographical location.
"Evaporative cooling can alleviate this heat problem and contribute to worker efficiency with improved morale. If the heat problem is not alleviated, increased absenteeism, high labor turnover and dangers to health and safety during the summer months. Production declines in un-cooled plants may range from 25% to 40% of normal on hot days."

 

[tesmuh]

I am designing a warehouse ventilation. Employer wants 15 change/hour. This quantitiy is very high to heat. Should I get the empty space or total space as volume. (60 % is full with palettes)

 

[rmw]

Those of you that are suggesting evaporative cooling must not live in nor near Houston. If you noticed his DB/WB temperature, you will notice that there is not much real margin for driving evaporative cooling, and, even if there were, the resulting humidity in the cooled air would only make a bad situation worse in that work environment.

Yes, the air would be a little cooler, but it would also be so muggy that it would be very uncomfortable to work in on a day in day out basis.

While "swamp coolers" are very common for the western more arid regions of Texas, they are not commonly seen in the coastal regions.

If you do consider going that route at all, there are those portable units that are commonly seen at NFL games in the fall, on the sidelines, when the ambients are still quite high, and especially for the southern teams. You generally have to be standing right in front of them to get any feel of the cooling effect.

There is a mold and mildew build up problem with evaprorative cooling in the deep south. Not unsolvable, but something that has to be dealt with on a continuous basis or it will get ahead of you.

However, 95 degree outside air is preferable to the 110-120F that this warehouse must get to (comparing it to my un airconditioned warehouse not too far from houston,) plus, the heated zone in the ceiling of the building (where it gets even hotter than 110-120F,) radiates heat back down onto the workers on the floor, even if the floor is at or near ambient. So, removing this heated air is a must.

You did not say how much budget you have, and it looks like all the owner wants is a few fans, so, I suggest the following.

Exhaust the heated air in the overhead regions of the warehouse, and place some outside air supply fans in such a way that the ambient make up air blows directly onto the work stations.

If you have any budget at all, then do what they do at Six Flags over Texas, an amusement park for those of you not from the region, and air condition some air and blow it directly onto the work stations, just like they do for you standing in line at the amusements.

This A/C'd air would also be dehumidified, which would help offset the WB and make the overall ambient "feel" more comforatable as it mixed with the non cooled air. (again, just what Six Flags is doing)

If I knew of a better answer I would put it in my warehouse and try it, and tell you about it. My warehouse is not a work place, and I am not often in there, so there is no cost justification for doing something elaborate. I try to stay out of the place in the summer, and when I do have to go do work there, I plan my work such that it is done in the AM, probably not an option at this location. I feel for these workers. The attic ventilation combined with large floor fans in the doors blowing directly on my work area with outside air is the best I have found. I also see it a lot in similar situations at client locations.

Best of luck.

rmw

 

[dblyle]

Thanks for all your suggestions. I have done evaportative cooling in a prison near Houston and as RMW said, it generally makes the conditions worse than actually solving the problem. Plus, after installing the ductwork and units, it took forever to make the owner understand that he wasn't going to get 70 degree room temps (even though this was explained to him well in advance).

FriarTuck mentioned "punkah" fans (I am assuming something like the ones manufactured by Big Ass Fans?.). Has anyone had any luck with these? It seems these would be good at producing some sort of draft on the workers.

-dblyle

 

[62hog]

Our firm has designed and installed several warehouse installations of BigAss Fans. The owner actually came back to us to add more to the same facility.

I have seen these fans in candle making facilities and the worked wonderfully.

Hope this helps.

As far as ventilation, I would provide 6-10 ACH with both supply and exhaust fans. The other thing you would need to make sure of is that you maintain at least 50-100 fpm velocity minimum in the occupied zone, but not too much.

 

[friartuck]

Sometimes, you sit there and 'ping' a thought comes. Sometimes good ones, sometimes bad. Anyway, this one might be a good one. I should have thought of it earlier, anyway, how about trying displacement vent. This was developed by the swedes i believe in the 70's. And I also understand, the system was meant for industrial applications ...such as hot factorys.

The air is supplied at low velocity and about 2-3 degrees below the room temp. The air vol supplied is very low compared with normal systems...possibly only 3-6 air changes...you nee dto get a quote done by the experts.

Air trickles along the floor and when it hits a hot source (i.e. you or me), the air rises up your body, above your head and away to high level. The air is allowed to stratify so it will get to possibly 40C. This is discherged to atmosphere. Its a full fresh air system with heat recovery and since the air is supplied at only 3 degrees less than room, the chiller load is zilch.

Try Haltons, Trox or ABB-Woods for suitable advice and priices.

The down side is that the air has to be supplied by large 'dustbins' full of holes.

Give it a whirl. We use them in high car show rooms, large pubs etc.

Friar Tuck of Sherwood