Questions about Nominal Tonnages

[Kriegen]

I need to know how to better select an evaporator or AC unit. I am trying to cool water, but not sure about how to go about that. The hot temp is about 140deg F and the cold temp is about 85deg F. I need to figure out how to make that drop through either an AC exchanger or evaporator, but not sure what to do with nominal tonnages. Thanks, any help would be great.

 

[sterl]

A ton of refrigeration is 12,000 BTU/hr. transferred at the evaporator. converts to 200 BTU per minute.

A pound of water requires 1-btu to raise it 1-deg. F. at room type temperatures. Same amount to cool it; so 1 lb cooled through 55 deg. F. needs 55 BTU removed.

Now you need to know the flow of your water.

If its 5-USgpm, the result will be 5 * 8.3* 55, Btu per min.

None of this means that you can use air conditioning type equipment to achieve what you are trying to do. Air conditioners are inexpensive arrangements aimed at a pretty well defined application with a minimal control sophistication required.

If your system is of any scale, you won't want to invest in a refrig system to cool from 140 deg....You will reject the first portion of your heat directly to ambient, and may need
refrig to do the last 15 to 20 deg. of the cooling process.

 

[Kriegen]

Well thanks for the bits of information. People kept telling me that a nominal ton was about 12000BTU, but wan't basing it on any time function. Also out here in Oklahoma, our humidity can be so high, I am not sure this thing will really work unless it shows up to be overkill under normal conditions. I may end up going to refrigeration simply because I can use that to cool year round.
Once again thanks.

 

[Kriegen]

Now I have confusion. If one nominal ton is 12000BTUH, then shouldn't 3nt=36000BTUH, not 36MBTUH?
I need about 32nt's or something that will absorb 400kBTUH.
Grainger Catalog is saying they have AC units that will 5nt units that absorb 60MBTUH. I think this is bull or someone doesn't know their units. Please advise.

 

[Kriegen]

If anybody is bored, how about a double check. I have water at 90degF moving at 15gal/min through a dyno adding 150hp to the system. I believe it would take 32nominal tons to keep this cooled at 90degF. Is this right? and if so, where can I get a AC unit that will absorb that power?

 

[Zoobie]

Someone doesn't know their units. The information you were given is correct. One 'M' is a thousand, 2 'M's or 'MM' is a million. So 36,000 BTU/h = 36 MBTU/h = 0.036 MMBTU/h.

 

[Kriegen]

yeah so use to the SI system where M means 10^6.

Oh well, always out to learn something new

 

[sterl]

32 TR correct, at 15-GPM flow that represents a water temp change of just about 52 F. Deg.

An air conditioner that big is a commercial unit for something like a small apartment building or an office or similar...

What you are really looking for is a chiller. The heat exchanger will be likely a small plate and frame or brazed plate. Given this is process type duty, and I presume from the temperatures you don't have anything like a cooling tower, you will need a head pressure control arrangement as well as some accumulation on the suction side.

If this is an 8-hour per day steady state sort of thing, there are lots of manufacturers of the chiller package itself but you will need to get a contractor to do the condenser and the electrical side...

If its a very intermittent load: You might give some thought to an Ice Maker sitting on top of a separated water tank...Though your cycle efficiency is not as good, its a more flexible set up with some built in flywheel to deal with the peaks in load and probably a lower overall investment. If your real load exists only 10-minutes out of an hour, you purchase a 6 to 7 ton ice maker instead of a 32 ton chiller and it lands as an intact package....

 

[Kriegen]

Well I believe I am going to go with a Baltimore Air Coil Cooling Tower. I may be able to hook up several systems into this one cooler and get the job done that way. So far the ones I looked at will absorb 412000BTUH which is about 10% above what I need so far.
This should be fun to finish up. I really am not sure what Oklahoma weather will try to do to these coolers though. Yesterday we had 80% humidity and 85degF weather. Makes a chiller work hard.

 

[BronYrAur]

You should definitely check with BAC on your temps. Typical HVAC towers run 95 deg entering and 85 deg leaving water temps with ambient wet bulbs in the mid to high 70's. It sounds like your entering will be 140 deg F.

Companies such and AEC and Thermal Care make divided tank/pump packages so that you can have a "hot" side for return from process to dump into and a "cold" side for return from the tower. The chiller/tower then pulls from the "hot" and discharges into the "cold" side. That was you have a volume of water to temper the process return before it is sent out to the tower.

 

[Kriegen]

Yeah, I called bull on BAC at first, but I talked to the sales dep. and they assure me that this water cooler can handle what I am wanting. My director wanted me to talk to BAC first so thats how I got there in the first place. Also I can have them sign contract document before this all becomes approved.
This setup will hopefully never have a temp above 100degF. I just needed something that would absorb the 400k BTUH and sounded like the BAC coolers fit the bill the cheapest.