變頻器應用於船舶海水冷卻泵之節能效益分析

Benefit Analysis of Energy Efficiency with Variable Frequency Drives in Ship Sea Water Cooling Pump Application

冷卻水泵流量控制改由變頻驅動器（variable frequency drives, VFDs）來調整馬達轉速可減少傳統藉由閥調整所需之耗能。這類的變頻驅動應用對船舶特別適合，因為當船隻航行在不同海域的海水溫度變化差異較大。當節能為安裝變頻驅動器主要考量時，精確的節能量必須加以估測，作為新技術導人之投資決策判斷依據。然而，決定變頻節應用能量通常是一個複雜的分析，其分析過程牽涉系統運作程序、機械特性、設備功能、泵浦流量、及驅動器電氣特性。為精確決定變頻節能量以正確評估變頻驅動應用於船舶主海水冷卻系統之經濟效益，本文提出一個以使用變頻驅動速度控制來計算電能消耗為基礎的變頻節能量評估方式。船舶主海水冷卻系統及航行環境特性，包括裝備額定容量、冷卻管路配置、及海水溫度等，被考慮在分析中，且系統運轉程序被加以數學模式化，使得泵浦流體理論公式可以被適當地應用。一艘具有兩種不同航線之實際商船主海水冷卻系統之變頻節能效益分析結果被加以呈現及分析。分析結果顯示透過本文所發展的分析模式，可有效地決定出海水冷卻泵浦變頻節能效益，將有助於船上其他類似泵浦系統之變流量控制系統之經濟效益評估。 Speed control of flow from the chilled water pumps by variable frequency drives (VFDs) can reduce the power use below that required for control by a throttling valve. This type of drive is suitable for marine vessel applications because sea water temperatures vary significantly when ships navigate on different sea areas. When energy conservation is being used as the sole justification for installing the VFDs, accurate savings values are required to ensure the additional capital cost of the VFDs installation will have an adequate rate of return on the investment. Determining the amount of energy saved is normally a complex analysis since the activity involves a joint understanding of process, mechanical, instrument, and pump hydraulic, as well as electrical aspects of the drive. In order to accurately determine the energy savings for closely evaluating the economics for this type of VFD application to main sea water cooling systems on board, an accurate energy-saving evaluation method that is based on the use of variable frequency controls in calculating power savings is proposed in this paper. The ship main engine cooling system and navigation environment characteristics, including related marine equipment, pipe allocation, and sea water temperatures, are taken into account in the analysis. The process system is mathematically modeled so that the pump hydraulic formulas can be properly applied. Test results of a practical commercial vessel with two different shipping routes are presented and analyzed. The analysis results have indicated that with the proposed method, the energy savings can be effectively evaluated to permit checking of the economics of adjustable speed flow controls for similar pump systems on ships.