Chillers Condensing Temperature

[aida2011]

Hi all

A counter-flow cooling tower is supplying CW to the condensers of 5 units of R717 screw chillers. The design of inlet and outlet temperature of the cooling tower is 38 deg.C/32 deg.C. The design of inlet and outlet temperature for condensing water for chillers is also 38 deg.C/32 deg.C.

Currently, the inlet and outlet temperature of cooling tower is 32 deg. C/28 deg. C (almost ambient temperature) with fan running (30 kW). We are planning to make the outlet and inlet temperature of the cooling tower close to its design temperature so that we can reduce the cost of electricity from the fan motor.

My question, if we increase the outlet temperature of cooling tower from 28 deg.C to 32 deg.C, will it in any way affect the chillers, in term of savings (because condenser is currently receiving cooling water at much lower temperature).

Please help.

Thanks

Miss Aida Hanani
Malaysia

 

[SAK9]

I am assuming this is an existing installation and you have got VSDs on the tower fan and will slow it down to get the water temperature up to 32.If you get the water temperature up to 32C the compressors will be doing more work while the tower motor draws lesser current.Record the total power draw over a 24 hour or a longer period for both the cases ie.condenser water at 28 C and condenser water at 32 C.Sum up the chiller and cooling tower energy consumption in both cases and check which option is consuming least energy.

 

[Drazen]

on contrary, you should hold tower temperature as low as possible to save on chiller power which is much more substantial saving than tower fans power.

conditions you describe are ideal, design conditions are seemingly worst-case scenario which takes place only when it is unavoidable (highest loads at highest outdoor temperature).

 

[willard3]

Raising the inlet temp of the chiller is counter productive.
Compare the motor sizes/electric use of the tower and chillers.....which are larger?
Keep the chiller inlet temp as low as possible.

 

[aida2011]

Thanks all.

The chiller motor is 450 kW while the cooling tower fan motor is only 30 kW.

We are just exploring all possibilities for cost saving, so this is definitely not one of them.

Best regards

Miss Aida Hanani
Plant Engineer
Malaysia

 

[SAK9]

Find out from the chiller panel at what percentage of its capacity the chiller( 70,80 or 90%) is running most of the time.Obtain from the chiller manufacturer power consumption figures at this load for 32 C and 28 C.The difference will give you an indication of compressor motor Kw you are saving with a reduced condenser temperature.A comparison with cooling tower kw saving will tell you which option is better.In tropical weather like Malaysia you can not slow down your tower fan much so it is quite possible that trying to save chiller power may be the way to go.