COOLING TOWER SELECTION WRONG - HVAC/R engineering

I don't think your cooling tower is undersized. The cooling tower suppliers use Btuh to calculate Equivalent chiller tons. In your example, gpm *500 * 10 = 6,750,000 buth. Divide this by = 450 tons or rather cooling tower tons. If you divide the result by you will get the tons of heat rejection. (562.5 TR).

Best way is to check the chiller selection and cooling tower selection and check if the flows and temp in/out match between the 2. Looking at tons will be confusing as the Chller tons and Cooling towers are based on different calculations.
I would not worry too much here. What you have is simply a written process description. They simply called the cooling tower a 450 TR tower same as the chiller capacity. I don't think they even thought of mentioning heat rejection in that description. What you need to look at the actual values which are on the selection sheet from SPX and the chiller as well. Here it shows GPM at 93-103 and 86F WB which is correct for a 450 TR chiller.

This is a very old selection so I guess it is an existing project which is in operation. Now if you are trying to say that you are not able to operate the plant with 1 chiller + 1 towerand need 2 towers for that, that is a different issue (technical) and discussion. From a selection point of view, your datasheet is correct. From an operation point of view, you might not be able to operate 1 tower with 1 chiller but that would be more a technical investigation you need to look at. Probably better to call SPX Dubai for that.

One more note: if you look at the heat rejection capacity on SPX selections, be aware that they adjust it as well for specific heat and specifc gravity (BTUH = (Flow) X (Range) X 500 X (Specific Gravity) X (Specific Heat)) so it will not be exactly btuh. This is why you have .1 MBH vs MBH. Evapco uses BTU and BAC does not provide this value on their datasheet (i guess to avoid the confusion between chiller tons and cooling tower tons) In my opinion DrRTU, they have a total of GPM in the system with each tower handling GPM and each chiller receiving GPM condenser flow. The Selection Datasheet actually is for the design point for 1 Cell and it shows GPM. Now if they have installed different towers and have only a total of GPM for the 2 chillers, they will have a chiller issue. This will be 1.5 GPM/TR or about 19F delta T on condenser. Although the Chiller is a 2-stage, I doubt it will take it especially if it was selected on 3 GPM/TR initially. I am on the opinion that they a total of GPM in the system as per their process description and tower selection and the data was provided per cell rather than for the total system. What exactly is the problem here?

Is the issue that for some reason the original design decided to use an air wet bulb temp of 86 F (30C)? Was this too low? Even in July and August this doesn't seem to go above 25C so it's not that. I can't read the assumed RH but assume it's still valid.

So is the tower simply not working well because the fans are broken or some other issue?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it. Your document is dated , so the system has possibly been in operation for over 8 years. Lots of things can change in 8 years, fouling, process changes, configuration changes, etc.

You stated that you need both towers to cool gpm, but you've not said how far off the performance is, i.e., what temperature delta does a single tower achieve, whether both towers are working the same, and whether the conditions are consistent with the original design.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum Entire Forum list As per the site info, past years two tower and two pumps need to work for 460-ton chiller. Otherwise, it will trip on high discharge. flow rate of one pump is gpm( total )Recently, I noticed and involved in this case.at glance in submittal, the tonnages is 460-ton cooling tower, so I thought tower is undersized, and I contacted its contractor who installed the system. I was told there are same issues from beginning. Now all building owners are very cautious in energy saving. Part of this I rechecked and later found spx selection found the total heat rejection is 562 ton. Anyway I suspect the fills and fan blade angles might be something wrong…next month we will teardown the tower and will be checked…..
In the original design concept, is one of the chiller a standby? or both are supposed to run. Now I wonder in summer how do they cope with load if they have to run 2 towers for 1 chiller and the 2nd chiller needs to start as well?
If you are getting 89F wet bulb, you will end up with 96F condenser so the chiller might trip and the VFD might not like it either (refrigerant cooled or water cooled type).
If the issues were there from the beginning, why nothing was done to rectify it when the equipemnt were still under warranty?
From the pictures, I can see the plant is surrounded possibly by wall? you could simply have a case of hot air recirculation which increase the inlet wet bulb. Also you need to look at how they control the fan (if on VFD) with respects to condenser setpoint.
I will help if they have logs of wet bulb, condenser water temp....at the time when they experience tripping.
In my opinion you should contact Marley have them do an inspection of the site.