If a chiller is used to provide chilled water for building air conditioning, then the heat energy that is absorbed through that process must be rejected. The two most common ways to reject thermal energy from the vapor compression process are either directly to the air or through a cooling tower. In a cooling tower, water is recirculated and evaporatively cooled through direct contact heat transfer with the ambient air. This cooled water can then be used to absorb and reject the thermal energy from the condenser of the chiller. The most common cooling tower used for HVAC applications is the mechanical draft cooling tower (Figure 4.2.13). The mechanical draft tower uses one or more fans to force air through the tower, a heat transfer media or fill that brings the recirculated water into contact with the air, a water basin (sump) to collect the recirculated water, and a water distribution system to ensure even dispersal of the water into the tower fill.

如果冷卻塔設(shè)備被用來向建筑空調(diào)提供冷卻水，在這個過程中冷卻水吸收的熱能必須釋放掉。釋放蒸汽壓縮過程產(chǎn)生的熱能的兩個最常用的方法是直接用空氣冷卻和用冷卻塔。在冷卻塔內(nèi)，水在被不斷循環(huán)蒸發(fā)中與周圍空氣進(jìn)行熱量交換。這種冷卻水能夠被用來吸收釋放冷卻設(shè)備冷凝器的熱能。暖通空調(diào)應(yīng)用中使用最廣的冷卻塔是機械通風(fēng)冷卻塔（如圖4.2.13）。機械通風(fēng)塔用一個或多個風(fēng)機推動空氣在塔內(nèi)的流動，用一個換熱器或填料層使循環(huán)水與空氣充分接觸，用一個水箱來收集物質(zhì)循環(huán)水，和一個配水系統(tǒng)來確保水分散在塔的填料層中。
圖4.2.14表示循環(huán)水和空氣在逆流式冷卻塔內(nèi)相互作用的關(guān)系。蒸發(fā)冷卻過程即水和空氣充分接觸，包括了同時進(jìn)行的熱質(zhì)的交換。理想狀態(tài)下，水通過配水系統(tǒng)形成飛濺或分裂成較小的水滴，增加了熱交換中水的換熱面積。通常用濕球來表示塔的大小和工作情況。它被定義為出塔冷卻水和進(jìn)塔空氣濕球溫度之間的差值。理論上，水在塔內(nèi)循環(huán)可以到達(dá)濕球溫度，但在實際工作中是不可能實現(xiàn)的。