[AC] 問﹕Chilled Water Distribution Loop 有幾多種類？各有乜特點？

答﹕
Type 1: Single loop, constant flow,
Pressure sensor (installed in critical part) control bypass modulating valve, temperature sensor detect changing zone load and control 2 way valve.

For old or small building, 最舊式。

隨住時代既進步，VSD 同 Chiller技術都進步咗，以前舊樓冇用VSD, 個Chiller Evaporator 又唔可以Handle variable flow, 但上述問題都隨住時代進步而解決咗。而家一loop過搞掂，用嚟改裝Type 1, 即係Type 2 係 Type 1既升級版。
Type 2: Single loop with VSD,
Variable flow, pressure sensor (installed in critical part) control VSD, temperature sensor detect changing zone load and control 2 way valve. 條bypass 同埋個modulating valve唔洗再用。

For small building

Type 3, EMSD當年出過書仔叫大家用

Type 3: Primary & Secondary Loop, primary loop constant 可以令部chiller行得更穩定，secondary loop 行VSD. Keep primary loop constant flow, only need to consider primiary loop resistance (呢個講法可能有啲舊，我見Primary Loop都有VSD, 盡量令條by-pass flow rate 同Secondary 同步，但primary side 個flow點都大過secondary, 如果唔係return chilled water就會响條by-pass度同supply chilled water mix埋。Chiller evaporator 有個最低Limit, 大機50% 細機70%); Secondary loop use VSD to achieve variable flow with 2 way modulating valve, Primary loop 唔會受Secondary loop 既 arrangement 影响。
Primary Loop Size 大過或等於Secondary Loop, 原因為如果大唔過的話有機會條decoupler反流，到時相對高溫既水又流返入個coil度個2 way valve又會開盡，做成out of control (https://www.youtube.com/watch?v=9WeRclR1X_c)

而家可以再响Secondary Loop 度加一樣叫 "Predictive System Curve Controller" 既嘢，配合VSD使用。
原理 - Air terminal 駁住個2 way valve, 如果冇用呢舊嘢，當Air terminal 冷水需求降低時，個Valve就會收緊，同時多咗水經 by-pass. 用呢舊嘢目的係要同VSD配合，儘量開大個2 way valve從而降低系統既壓力，以達到節能效果。要做pricise commisioning.

For large building and variable load


仲有種叫做Variable Primary Flow, Primary loop 有個Flow meter control bypass valve (其實同Type 2有啲乜本質上分別？除咗一個係Pressure Sensor control primary pump; 另一個係Flow Meter control bypass)

相對於Primary - Secondary, 好處包括裝少set Secondary Pump, lower initial cost; all pumps are VSD installed (P - S 組 Primary pump 係constant, 如果用量低的話就直接開泵又關泵， low load嗰陣optimize唔到pump energy). 壞處最主要係個Control複雜咗，同埋Chiller前要加isolation valve




Also reference: https://www.youtube.com/watch?v=-ahb6g3mrnE ; https://www.youtube.com/watch?v=41jRD61MW1o

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此外仲可以配合埋响個Return Water 度加個Differential Pressure Control Valve做Total Hydronic Balancing.

先講一般既water balancing. 每條Branch前都有隻Manual Balancing Valve 較水，由於chilled water去得遠啲，pressure head就會細啲，即係越近pump既branch就要較得實啲。

之後講Total Hydronic Balancing. 如果响某啲Branch度忽然個load好細，就會引致其他Branch個flow好大，咁隻控制Zone load既Modulating Control Valve就要較到好好好細，但細極有個極限，有啲類似VAV個Damper, 太細就會non linear characteristic out of control. 隻Differential Pressure Control Valve 就响呢個時候發揮作用，幫補隻Modulating Control Valve 收細個Flow, 從而比信號隻VSD令Motor減流速節能。

(鳴謝﹕Kelvin Mak)