New formula proposal for the determination of variable speed pumps efficiency

ABSTRACT The use of pumps which work with variable rotation speed consists of an appropriate tactics for reduction of energy costs in the pump systems. In case of change in speed, the pump starts to work in a new flow pattern, head and efficiency values. Two empirical formulas can be found in the literature in order to estimate the final efficiency of a pump in this situation. This article aims at assessing the accuracy of these formulas and, next, to present a new proposal for the efficiency estimate in the new operating conditions. 50 pumps have been chosen and, for each of them, the above-mentioned formulas have been assessed in three procedures of speed reduction. The analysis of these equations’ accuracy has been accomplished by means of the comparison between the efficiencies estimated by them with the efficiencies calculated with the aid of the affinity laws. The results indicated that, in 95 of the 150 analysis procedures accomplished, the formula proposed presented estimates which have shown to be more precise than the other two formulas. It has also been possible to verify that the average of error detected through the procedure of the new formula (1.60%) has been lower than the average of the other two (1.93% and 2.22%). In light of this fact, the use of the equation here presented is considered advantageous since, from their more accurate efficiency estimates, the calculations for power and energy are also more precise.

摘要：采用变速运行的泵组，是降低泵系统能源成本的合理策略。当转速发生变化时，泵将进入新的流动工况、扬程与效率运行区间。现有文献中已提出两种经验公式，用于估算该工况下泵的最终效率。本文旨在评估这两种公式的预测精度，并针对新运行工况下的效率估算提出一种全新的改进方案。本次研究选取了50台泵，针对每台泵分别通过三种变速降速工况对上述两种经验公式进行精度验证。本次精度分析通过将公式估算得到的效率值与基于泵相似定律（affinity laws）计算得到的效率值进行对比完成。研究结果显示，在完成的150组分析工况中，有95组的预测结果表明，本文提出的新公式比另外两种现有公式具有更高的精度。此外，研究还验证得到：新公式的平均预测误差为1.60%，低于另外两种公式的平均误差（分别为1.93%与2.22%）。基于上述结论，本文提出的公式具有显著应用优势：凭借更高的效率预测精度，其衍生的功率与能量计算结果也更为准确。