The cooling tower selection is one of the most important step in designing HVAC system.
Chiller consumes around 80% of total HVAC power consumption. But the chillers performance measured in terms of COP is solely depend on the cooling tower performance. That is why selecting a best suitable cooling tower for the application is utmost important.
There are few different types of chillers, we have already seen it. You may check it here.
Steps for cooling tower selection
- Know the heat rejection capacity of the cooling tower.
- Chiller’s heat rejection
- Condenser water flow rate
- Condenser temperature range and wet bulb temperature of the site.
- Cooling tower type – factors affecting cooling tower type as per application.
- Other factors for cooling tower selection
- CTI Certified cooling tower
- Noise level
- Drive type
- Weather conditions
- External static pressure
Now, we shall see one by one point for cooling tower selection.
- Know the heat rejection capacity of the cooling tower.
- Know the temperature range required for condenser, delta T. Example, Entering Water temperature 37 C and leaving water temperature 32 C. So delta T is 5 C
- Cooling tower heat rejection = Chiller’s heat rejection x 30% higher.
- Example, if chiller’s heat rejection is 500kw; then select the cooling tower with 650 kw. 30% is just a widely accepted safety margin for cooling tower selection.
- The chillers capacity often indicated in tonnage, Please check how to convert it to cooling tower tonnage.
- Now you got the cooling tower kw, lets convert this into water flow rate.
- 650kw cooling tower means, 650 x 860 / (5 x 1000) = 111.8 m3/hr Water flow rate required @ 37 Entering water temperature and 32 C leaving water temperature.
- Wet bulb temperature- The WBT gives us an idea that how much temperature we can reduce by evaporative cooling. Generally, 28 C wet bulb temperature is used.
- So, we need to use 111.8 m3/hr @ 37-32/28 C ( Entering Water Temperature – Leaving Water Temperature/ Wet Bulb Temperature)