By Chad Edmondson
So far in this series, you’ve learned how to incorporate all of the essential data into your cooling tower life cycle analysis -- everything from operational hours at part load conditions to suggested outdoor wet bulb design points. You’ve done most of the heavy lifting. Now it is up to the vendor to determine the kW required to operate a given tower based on the data you’ve provided.
With your load profile and data in hand, the vendor can give you the exact annual fan kW for the tower you’ve selected. You simply calculate the annual kw for the four load conditions and add them together to come up with the total annual kW consumption.
Using the same example we’re referred to throughout this series, that yearly total adds up to 107,183 kwh.
The above data is based on a Baltimore Aircoil Model S3E-1020-07P cooling tower, operating under the load conditions shown. Notice the significant reduction in kW as we go from full load to part load operation. This gives us important intel with respect to how we might stage cooling towers in order to improve lifecycle cost. With this approach, we can very easily compare the life cycle cost of a system that uses multiple cooling towers at reduced speeds versus the lifecycle cost of fewer towers operating at full speed. You can also see the advantage of oversizing a cooling tower to gain even more energy savings.
The Final Analysis
All that’s left to do now to complete our lifecycle cost worksheet is some fairly simple math, applying whatever utility rate that is appropriate. In this case we’re using $.08/kwH. We’ve also included the 13.75 tower pump head which we need to factor in pump kW. (Don’t forget this step!)
So here you have it – a reliable life cycle cost analysis for given selection for a specific application!
You can share the load profile information with any cooling tower vendor to develop similar analyses for other brands and/or other cooling tower models. This method will give you a fair comparison of multiple towers from the same vendor or multiple vendors to help you and the owner select the most appropriate tower for their application.