Industrial Compressed Air System

Air-to-water intercooler kind of like is used on large turbo-diesels? Don't know what type of CFM's "large" is, but with the cost of the coolers and some plumbing to get a cool water supply to them, your ROI should be pretty reasonable.

does this room is at the inviroment temp. ?

if not - you should make duct from the outsie air direct into the air intake of the compressor.

i had the same problem & calculation shows that i can gain 2% of energy by taking it from outside. i didn`t got permission to do it, but it is the first recomandation of anyone who is familier with compress air.

google "compress air" & learn more about this issue

eyal

In our mechanical room we have vents in the roof. One vent has a fan that blows air out. The other vent allows fresh air in. They have powered shutters that open when the thermostatically controlled exhaust fan turns on. This configuration works with the natural air currents so the fan does not need to be very big which keeps the electricity costs down. This room houses our steam pumps (all pipes are double insulated) as well as an Ingersoll Rand IRN75H-CC Variable Speed Rotary Screw Air Compressor. The 75 designates 75 horse power. There is also a TWB400 Blower Purge Dryer. During the summer the room temperature is slightly above that of the outside air. There is not any air conditioning piped in from the rest of the building either. The doors are locked to prevent unauthorized entry.

By "large", I meant four 100 hp electric units in a room that is approximately 20' x 40'. There is about 2-3' between each unit. The vents are 6' x 6' and cover the entire length of the 40' exterior wall.

Air cooled units of this size put off an enourmous amount of hot air and then recirculate it into the intake if captive in a room. Duct intakes from outside low, filtered of course, and exhaust outside high. Consult manufacturer for proper duct and intake sizing. Controlling ambient will also extend the life of your equipment. 100HP compressors are not cheap to replace.

I think with a system this big you will have to add some sort of water cooling heat exchanger on the intake air, It sounds like you already have the building well ventilated so the next step to me would be to bring down the incoming air temp. On our large compressor rooms we pipe all the intakes to the outside well away from the heat of the compressors and haven't had a problem with overheating.You may be able to install some fans and thermostats and get the temp down in the building but not sure if it would get it down enough. Is your compressor overheating and kicking out the breaker or just running at reduced output? I installed a small screw compressor of few years back and because I was afraid it would freeze up in the winter I had the building made out of the same material that the big walk-in freezers are made from which is basically 6" of foam sandwiched between aluminum sheets. Well the thing worked so well the compressor would overheat in the winter and I had to install a fan and thermostat to keep the building cool enough that the compressor would run.

pipewelder

The compressors are sequenced with the first being a variable speed and the other three being fixed speed. Once the demand is to high for the variable speed, the next compressor kicks in. This continues until all four compressors are running at 100%. During hot days, it takes all 4 compressors running at 100% to keep up with the demand on the system. During the cooler days, it only takes 2 fixed compressors and the variable speed compressor at about 60%. The units are oil cooled and the oil has its own duct work and fans to cool it. The room is usually within 5 degrees of ambient temperature.

Do you need pressure or volume. In researching our new compressor that was the question each vendor asked me. The common pit fall, I was told, is that most people have the mind set that a compressor is the only solution. Many cases a blower is a better choice. One vendor related to me that he went to a company that was using compressed air to move their product through duct work from one station to the next. Not sure if this helps as I do not know your particular situation.

It seems excessive that you have to add another 200HP just because the ambient warms up. What kind of process are you supplying air for? There may be another root cause to your demand spike and the symptom is added air consumption.

The system uses a 6" looped main line with one looped 2" and one looped 4" line to supply air to an assembly area (using pnuematic staplers and nailers) and two automatic spray painting lines, respectively. One spray line has 7 automatic paint booths and the other has 3. The company fixes air leaks as they are found through nightly inspections. Part of the difference is the volume of product produced in the summer in comparison to the volume of product produced in the winter (reduced by about 20%-30%). When the company uses all of the equipment in the summer months, the compressors are constantly running at 100% to keep up with demand. Reducing the intake temperature by 15-20 degrees in the summer months should be able to reduce the hp needed to supply the compressed air to the system. I would really like to see a 30 degree reduction in air temperature. I am just not sure how to do it efficiently.

If your compressor room is within 5 deg. of ambient and you want a 30 deg drop in your supply air temperature, you're going to have to use some type of water to air cooler. You may be able to get away with using city water as-supplied, but to get the 30 deg drop, you may need a chiller. Good luck!

I assume you clean the unit radiators prior to summer production. If you feel you have done all the housekeeping due diligence, then you are looking at changing your intake and exhaust ducting or going to water cooled heat exchangers.

It would be interesting if any of the compressor guys recommend a way to chill the intake air as a cure.

I still don't understand how reducing intake temperature will reduce energy costs.

Hot air is less dense than cool air but you said your compressor room ambient temp. stays within 5 deg

Congratulations on using really wise plumbing with the large headers. You didn't say what pressure your compressor run at. For painting my guess is that you use volume at low presssure. If you cannot reduce the total system supply pressure split off and dedicate compressors to low pressure. Don't run those any higher than absolutely necessary. You waste an enormous amount of energy to compress to a high pressure and regulate back down or use higher pressure than needed. I know this means more plumbing and low pressure demands large flow paths but the final result will be amazing. Tell all your friends, tell your boss, tell CR4. Tom Kreher

Tom,

I consider you an expert in compressed air technology and have read many of your posts. On my system I have plenty of fresh ambient air entering my compressor room. In the summer the room can reach 100 to 120 degrees F with ease as the ambient temp is 98 to 100 degrees F. I am running a 50hp screw compressor.

Are we saying that cooling the intake air to the compressor would save enough energy to offset the cooling of the intake air?

Curious,

David

That is very well stated! A G.A. to ya!

I like how you put it. I thought about recommending a buried duct to lower the temp of the incoming air but did not. I figured I would just get laughed at for being pro-geothermal. As for the higher pressure vs efficiency, I was told by the vendor that sold us ours basically the same thing. We purchased a rotary screw compressor. He said if we needed high pressure then a piston type would be a better choice. He also added that those are no longer made in the larger machines. Screw compressors by their design become less efficient as pressure increases. You can run a lot of plumbing for the price of an additional compressor. Plus the lower operating pressures should add years of service life to the existing machines. If plumbing is a problem then could you locate additional storage tanks near high volume work areas? I realize you said your machines are at or near 100%. But this could be a buffer that is recharged during breaks.

Thank you for clarifying and I gave you a GA for it also. I was having trouble seeing how cooling that much intake air could be economical. Also I was confused that around 1600 cfm of compressed air was fine in the wintertime but not in the heat of summer. It was later I noticed he said their production peaked in the summer.

Thanks again,

David

http://www1.eere.energy.gov/industry/bestpractices/pdfs/compressed_air14.pdf

If you intake the air from outside, your ducting should be about 120% of your intake filter size. We are installing a 75kw variable speed screw compressor at the moment and thats what the specs say on our one.