Open Vs Closed Circuit Cooling Towers
Open Vs Closed Circuit Cooling Towers
(OP)
I am new to the industry, so I have very limited knowledge of the subject. I have been recently asked to have a have an old BAC cooling tower replaced with little to no down time to the factory. After doing a little research I came across various closed circuit cooling towers, and I was wondering if anyone has had experience switching from an older open circuit system to a closed circuit system, and what problems should I expect. The current operating conditions are at a max of 800 GPM, from 120ºF to 80ºF with (worst case) wet bulb at 75ºF. Also, if anyone might have relative operating costs, that would be helpful also.





RE: Open Vs Closed Circuit Cooling Towers
In my experience, the open circuit system is by far the more common way to go. I can't imagine going to a closed system unless I had some compelling reason such as keeping the cooling fluid seperate from air or fouling was a concern. Neither of these are likely an issue in your case as you are thinking about converting an existing open circuit.
As for operations, you will still need cooling water circulation pumps, but now you will need another set of pumps to circulate the cooling medium as well. So your plant is more complex and your pumping horsepower is probably higher. Your fans will probably need to be higher power because you have to suck or blow air past both the tower fill and the closed loop exchangers. You may have to contend with plugged spray nozzles and external scale on the tube bundles. Efficiency will probably be lower (due to the extra delta T between the coil and the outside of the tubes) and the tower probably bigger. The whole set-up sounds more expensive.
Where is the upside in this application? I am no expert on these things, so what have I missed?
Tim
RE: Open Vs Closed Circuit Cooling Towers
Is it possible to place an open or closed system on or near the ground if it is away from all other buildings, if so then how far away does it have to be?
The other reason for all of this is that the owners are remodeling the plant, and do not like the huge monstrosity of a system that we currently have now. Any thoughts on appearances?
Thanks again!!
RE: Open Vs Closed Circuit Cooling Towers
Aesthetically, it is better to have them on the roof of a building because (out of site)=(out of mind). Cooling tower plumes are not the greatest thing to look at. The advantage of the closed system in this regard is you can put a dry air cooled exchanger at the top of the tower (above the wet section) to cut down the size of the plume.
As for distance away from the building, I'm not really sure. Probably depends a lot on the tower design. I know BAC has a number of designs that can be put almost right up against the side of the building. Just make sure you know the prevailing wind direction and choose the side of the building accordingly!
RE: Open Vs Closed Circuit Cooling Towers
There are a few common drivers;
Energy savings can be achieved if you are replacing a cooloing tower heat exchanger combination with a closed loop system. Pumping the cooled being cooler to a closed loop cooler might require a little more energy but a fraction of the water is typically required and usually less air so your auxiary losses are much less than a cooling tower / heat exchanger system.
Less water means less water treatment and because the water is not flowing inside a heat exchanger, water quality is not as important. Often spent water or water of poor quality can be used.
Closer approch temperatures can be achieved by making direct use of the evaporative cooling.
A closed loop system does not suit every application but it sound as though you should at least consider one for your application. I suggest you look at www.niagarablower.com for a good explantion of the how closed loop evaporative coolers work and the benefits.
Tom
Delta T Heat Exchangers
www.deltathx.com