[AC] 問﹕何解VAV係慳電過CAV? 如果又要CAV又要慳電啲，有乜手段？

答﹕

先睇VAV既原理

當某個ZONE cooling load 需求降低，Zone個Thermostat會比訊號返個VAV Box Controller, 個Controller再比個訊號VAV Box關細啲個Damper.

Damper關細後，條Supply air duct pressure會上升，跟住就會由個Pressure sensor detect 到從而較細啲把扇實現節能。
由於個VAV Box有minimum turndown 維持某程度上既鮮風，如果個Damper關到最細都未合乎到Design需求，就會通過隻2 way valve較細啲chilled water flow, 再唔得就有機會用terminal reheat (留意max. 唔可以過2kW, 過咗就要extra control).
想Terminal Reheat 慳電，最好係用啲Waste Heat 而唔直接用Electric Heater, like Solar Hot Water / Heat Recovery Chiller / Heat Pumps / Central Hot Water Plant

再介紹下啲非主流嘢

- Underfloor VAV Box
由於升高一層，builder多唔少嘢夾，如開Lift 門/樓梯等；由於裝响地下，要改動甚困難，而且啲風咀風管容易污糟，垃圾向下跌，唔易清潔；但好處係Energy Saving, cooled air layer form 响human level, 慳風扇energy

- Individal air duct, one AHU for exterior; one for interior:
比Hot water exterior zone VAV, 香港應該冇乜機會用到


- Fan Powered VAV Box
啲Office Interior 同 Exterior Zone 共用一個天花，內面采冷外面采暖，呢種VAV Box就將Interior Zone 既Air 攪返出Exterior Zone 度，响香港未聽過

咁CAV Box又係乜嚟？見下圖﹕

CAV Box入面隻damper目的係為咗維持constant air flow, 例如你間房要維持正壓，當你打開門窗，就會有pressure drop, CAV box隻dampler就可以加大返個flow彌補。

CAV energy saving strategy:

1. Heat Wheel to reclaim the thermal energy from Exhaust Air;

2. Based on actual occupancy profile, VSD with Two Step Control;

3. Econimizer for Air Side (may not be workable);

(鳴謝﹕Kelvin Mak)