Study on selection of air-cooled or water-cooled chillers 3

[cikondu]

Hi, there,
Is anyone aware of any study, paper, or article which explains about a cost/benefit analysis to select an air or water-cooled chiller. My peak cooling load is about 900 kW, and I currently use air-cooled chillers. However, I have become aware of the higher Coefficient of Performance of water-cooled chilles, particularly when a variable-speed centrifugal chiller is used. The country I live in is Malta, where drybulb temperatures range from 5 degC to 41 degC. Water is not cheap, but second-class is readily obtainable. Can anyone help?

Thanks.

 

[Cooky]

I have done many comparisons of air cooled versus water cooled systems, and my advise, is that you perform your own comparisons. Every application is different, and it is unlikely that someone has written a paper that suites your particular requirements.

A chiller manufacturer will supply you with a selection for both air and water cooled chillers. You'll need to give then water and air operating temperatures. Similarly, you'll need a selection from a cooling tower manufacturer.

Another reason for performing your own comparison is the installation costs. These can vary dramatically, depending on your equipment location and the quality of the installation.

Your correct about the high COP's with centrifugal chillers especially when used with variable speed drives. If you are considering centrifugal chillers, then 900kW is quite a small unit. You could also consider a chiller that uses screw compressors.

As a general rule, air cooled chillers are the cheapest to purchase and install but have the lowest COP. Water cooled chillers cost more to purchase and install but have a higher COP.

I hope this helps.

 

[lilliput1]

250 ton is the largest single unit air cooled chiller you can get. They are noisy, use about 2x power and require more floor space. Look at similar buildings on the site and see what type chillers they use. It is usually preferable to go water cooled unless the Owner will require the chiller only for less than 10 years. Water makeup requirement (for evaporation, drift and bleed) is about 0.05 gpm/ton. Water must be chemical treated.

 

[imok2]

To me ,If I have a choice I would usually go to a water cooled system for the many reasons stated above, however I have had occation to go to air cooled , only because the quality of water was so bad and the problems were persistant. It required a lot of maintenance. When your manpower is stretched thin you can't afford to take the time required to do proper maintenance. However you have to pay the piper, that is the cost of the increase in KW. Soo i would say the determining factor in your decision will be the quality of water needed for the condenser, cost of chemicals and increase in maintenance.

 

[Cooky]

Hi Lilliput1,

The largest air cooled chiller Carrier manufacture is 358 tons (1,253 kW). The main limiting factor that prevents larger chillers is transportation of the chiller from the factory to the customer site.

The 358 ton chiller is designed to fit exactly on a 40' trailer, any larger and they would require special transport arrangements which is very expensive.

Cooky