[AC] 問﹕點解Cooling Tower 會出白煙 Plume? 有啲乜方法可以解決？

答﹕

先講最基礎原理，Cooling Tower 之所以可將入嚟既37度水溫變成32度，係以Evaporative方式通過損失部份水嚟將啲水降溫。相對地，入嚟既空氣會攞走部份水同溫同溫度。即係Combination of heat and mass transfer.

見上圖，藍線向右原因係因為吸咗Water Sensible Heat, 而向上係因為吸咗水。
而家Air Out Condition 仲係响Saturated Line 右邊，所以唔會有白煙出。
但如果Air in 啲空氣再濕啲，情況就會唔同，見下圖﹕

Air Out Condition去去Saturated Line 左邊，就會出白煙。

解決方法大致上有四種﹕
1. 直接Heat Exhaust Air, 有Direct Fired Gas Burner或加Heating Coil, 當然代價就係嘥錢嘥Energy增加Maintenance cost, 同埋Heating Coil 會增加Pressure Drop.


Terminal re-heat 返啲Exhaust Air 入Saturated Line右邊

2. Spraying Water Absorbing Chemicals, 但呢招唔易控制，因為要控制落幾多Chemical and reaction time都唔容易，同埋成本高；Psy Chart見到其原理

3. Heat a Portion of Ambient Air & Mix with Exhaust Air, 靠用自身Chiller Condenser Water heat or other waste heat, 或自己搵啲Energy 嚟加熱嚟heat Ambient Air. 由於Ambient Air 熱咗，所以把風扇都大咗，同埋個Cooling Tower都會高咗。

4. Reduce Operating Load
例如減少condenser water flow, 增加Air Flow and controled by VSD;