Cooling Tower Tonnage

[stationary101]

Hello again! I am a little bit puzzled of the Cooling Tower we have in our facility. It has a capacity of 758 ton but handles 2-500 ton chillers. I've been told that it is because of the humidity factor in the area. The location is in San Diego, CA. Well, thank you in advance for your thoughts on this one.

 

[KiwiMace]

Most likely it's due to your chillers not working at full capacity.

 

[imok2]

If the cooling tower is rated for say 78 wet bulb and the average wet bulb is around 75degrees or less then the cooling tower should be able to do better then 758 tons and handle the load you have. This from San Diego weather: "High temperatures are almost invariably accompanied by very low relative humidities, which often drop below 20 percent and occasionally below 10 percent"

 

[stationary101]

There are times when we run only 1 chiller at 45% of its FLA but the cooling tower runs at full speed(60 hrtz on the VFD).

 

[KiwiMace]

Ask yourself:

What is the cooling tower vfd actually controlling - Condenser water supply temp signal?

Also do you have staged or vfd CW pumps?

What is the wetbulb doing during these times?

What are the flow and inlet/outlet temps to each component? - knowing this will help you understand the actual load each is dealing with.

 

[imok2]

The question you have to ask rourself is how much energy am I using to run the tower at 100% and is the condensing water running at a low enough temperature to over come the cost of power used. If not, then maybe you should look into VSD on the fan.

 

[TXiceman]

One of the most confusing things to "outsiders" in this industry is the rating of cooling towers and evaporative condensers, it even confuses a lot of the so called engineers as well. I wish that the manufactures would do away with the TON rating system and strictly rate them in total heat of rejection based on on set of common parameters.

The manufactures pick a nominal rating point and rate then based on a compressor producing a given amount of evaporator tons for the given wet bulb, condensing temperature and chiller evaporator temperature. Any condition other than this rating point has to be adjusted with a series of multipliers.

Ken

Ken
KE5DFR

 

[HVAC68]

What is the rating of the chiller ? 500 tons at what conditions ? Entering and leaving condenser water temperatures ? and flow rate through the condenser ?

Similarly, what is the flow rate through the cooling tower, the hot and cold temperatures and the design ambient wet bulb temperature ?

Q = mCp Delta T.

People have a tendency to talk on "nominal capacity" and this could be one of the reasons for the above difference ???

HVAC68