Genset Louver Sizing (發電機百葉大小計算)

之前講完Genset Sizing同Fuel Tank Sizing, 今集就會講埋Genset Louver Sizing. 計埋Genset Louver, 基本上就可以知道發電機房既大細, 對於開Layout都好有幫助.

Background Information

首先要知道, Louver有分2種: Intake 同 Exhaust Louver. Intake就係比鮮風入既百葉, Exhaust就係比熱風走既百葉.

根據Building Department既例, Intake Louvre 5m範圍内係唔可以有任何Exhaust既Source, 例如發電機Exhaust, 煙通, 停車場…等等. (詳情請看下圖)

Intake/Exhaust Louvre Sizing

咁點樣可以計個百葉要幾大呢? 第一步就係要知道發電機用咩牌子同發電機有幾大. 因爲個熱風百葉既作用就係要排走發電機Radiator既熱風, 通產就會碰住個Exhaust Silencer. 所以熱風百葉個大細係based on發電機既Radiator Discharge Air Flow Rate. 同時, 因爲發電機運行期間會有Combustion, 而Combustion亦會有熱風, 但Combustion所產生既熱風係唔會經Exhaust Louvre走出街, 因爲成個Exhaust Louvre基本上係對住個Radiator (碰住Silencer), 所以Intake Louvre大細就係based on 發電機Radiator Discharge Air Flow Rate + Combustion Rate, 咁樣先可以填補Genset房入面既熱風量. 因應唔同牌子既發電機, 個Discharge同Combustion Rate都有機會唔一樣, 所以如果係Design初期, 只可以靠用某牌子既Catalogue入面既數據做Reference然後計數.

Intake/Exhaust Louvre Sizing Example

用一部Cummins既2000kVA發電機為例, Radiator Air Flow Rate = 1584 m³/min, Combustion Rate = 4800 cfm (135.8 m³/min) , 我地會做一個簡單既Louvre Sizing.

我地首先要假設Louvre既Size (或者Area) 先可以計到個風速. 所以Assume Discharge Louvre 同 Intake Louvre個Area都係17 m²先. 而Louvre自己本身有Efficiency, 呢個Example我地會Assume Louvre Efficiency係50%. 所以Intake同Exhaust既Effective Area 都係等於

17 x 0.5 = 8.5 m²

咁Intake Louvre個風速就係:

(1584 + 135.8) / 8.5 = 202.3 (m/min) = 202.3 / 60 (m/s) = 3.37 m/s (663.4 fpm)

而Exhaust Louvre個風速就係:

1584 / 8.5 = 186.3 (m/min) = 186.3 / 60 (m/s) = 3.1 m/s (610.2 fpm)

當知道Louvre個風速之後, 就要對一下Louvre既Pressure Drop Curve, 唔同牌子既Louvre都會有唔同既Curve, 所以如果想Performance好少少可以考慮比較靚既Louvre, 當然啦, 價錢都會貴少少.

Intake/Discharge Silencer Pressure Drop

除左Louvre自己本身有Pressure Drop, Silencer自己都有Pressure Drop, 而條Formula就係:

Pressure drop across acoustic silencer = K x V², V係Face Velocity, 所以其實就係計翻Louvre既風速, 但Area用翻Face Area而唔係Effective Area. 而K就係K-Factor就係風喉(Silencer都係風喉一種)既K-Factor, 唔同風喉有唔同K-Factor. 以前Supplier比我既K-Factor係5.1, 所以我地呢個例子就用翻5.1.

所以, Intake Silencer既Face Velocity就係:
(1584 + 135.8) / 17 = 101.1 (m/min) = 101.1 / 60 (m/s) = 1.69 m/s

Intake Silencer Pressure Drop = 5.1 x 1.69 x 1.69 = 14.53 Pa (0.056 inch w.g.)

Discharge Silencer既Face Velocity就係:
1584 / 17 = 93.18 (m/min) = 93.18 / 60 (m/s) = 1.55 m/s

Discharge Silencer Pressure Drop = 5.1 x 1.55 x 1.55 = 12.28 Pa (0.049 inch w.g.)

System Pressure Drop

計好曬所有Pressure drop之後, 最後就係加曬呢4個數:

Total System Pressure Drop: 0.055 (Intake Louvre) + 0.056 (Intake Silencer) + 0.05 (Exhaust Louvre) + 0.049 (Exhaust Silencer) = 0.21 inch w.g.

一般Supplier個Pressure Drop都會做到唔大過0.5 inch. w.g., 所以呢個Pressure drop係acceptable.

Conclusion

一連幾個Post講發電機終於都講完, 因爲工作忙碌關係, 所以呢個Post都用左比較多時間去寫同準備, 希望大家可以繼續支持呢個Blog 🙂 記得Share呢個Blog比你地既朋友/同學仔!