In this post, we shall discuss how to measure wet bulb temperature.
Wet bulb temperature is an important parameter for cooling tower selection. For a device engaged with the evaporative cooling principle, wet bulb temperature should be involved while selecting the equipment.
Wet bulb temperature plays an important factor in the performance of evaporative water cooling equipment or cooling towers.
To explain in very simple words;
The surrounding environment’s wet bulb temperature can be measured by a thermometer tip covered with wet cloth/cotton. As simple as this 🙂
Of course, the accuracy would vary if the thermometer was meant for Wet bulb temperature measurement compared to a normal thermometer. This is just a general idea, the measuring principle is the same though.
Here is the difference between a normal thermometer and verses thermometer specially designed for wet bulb temperature measurement and how to measure wet bulb temperature.
Importance of wet bulb temperature in cooling tower?
It is a controlling factor from the aspect of minimum cold water temperature to which
water can be cooled by the evaporative method.
That means; wet bulb temperature gives us an idea about the minimum temperature that can be achieved through cooling towers/ evaporative cooling equipment.
Of course; the leaving temperature can’t be the same as the wet bulb temperature. There should be a minimum gap, in HVAC terms it is called approach temperature.
Approach temperature = (Leaving water temperature – Wet bulb temperature)
For example, Entering water temperature 37°C, Leaving water temperature 32 °C and 28°C Wet bulb temperature
Then, Approach temperature = 32 – 28°C. Then approach temperature is 4 °C.
For CTI Certification, the minimum approach temperature should be 2.77 °C or 5°F
The wet bulb temperature fluctuates throughout the year. Now, which one we should use for the cooling tower selection?
To achieve the best performance from the evaporative cooling device. We should be using maximum wet bulb temperature for that region. In this way, we can make sure our cooling tower will have enough capacity to deliver satisfactory performance in the worst conditions.
When the actual wet bulb temperature is lower than our design consideration. Then; the cooling tower is capable of reducing leaving water temperature even lower than that of design conditions. In such cases, fan speed can also be reduced for energy saving. But the fan motor should be capable of variable speed. A variable speed-compatible motor should be adopted while selecting the cooling tower.
Can check our cooling tower calculator