变频离心式冷水机组部分负荷下的节能分析

Energy Saving Analysis of Central Air Conditioning Operated with Variable-frequency Centrifugal Compressor

针对实际运行中变频离心式冷水机组的节能效果偏低的状况,本文从离心压缩机的机理出发,介绍了离心压缩机运行的各种损失。分析得出分离冲击损失及叶轮进口气流冲角对不同调节方式下的离心压缩机运行效率影响最大。在此基础上,首先分析了部分负荷下导叶调节的损失及其内在机理,得出了导叶调节对离心机防喘振的重要性。并重点分析了不同的冷却水温与负荷率变化关系下采用变频调节的节能效果。最后给出了理论上的最佳负荷率对应的冷却水温,在此关系下,变频离心机调节可以获得最大的节能效果。但在实际工况中,负荷率的变化速度更快,因此变频离心机运行将偏离最佳工作点,负荷率降低时,叶轮进口气流将产生正冲角,压缩效率降低较大,节能效果大打折扣。

In practice, the effect of variable frequency centrifugal compressor on energy saving for the central air con ditioning is lower than expectation. Thus, in this paper, based on the mechanism of centrifugal compressor, various los ses are analyzed. It shows that under different adjusting approach, incident and separate loss and the attack angle play the most important roles for the compressor operation efficiency. And then, the losses of inlet vane adjustment are analyzed. It shows the importance of the vane adjustment for surge prevention. After that, under different relationship of cooling water temperature and load rate, the effects of energy saving with frequency adjustment of compressor are mainly studied. In or der to get the optimal efficiency, the cooling temperature and load rate should be relatedunder different frequency of com pressor. It is calculated with the condition of zero attack angle for inlet impeller. Under the relationship, variable fre quency centrifugal compressor can get the best effect of energy saving. However, actively, the load change ratio is higher than the expectation of the optimal relationship. As a result, the operation of centrifugal compressor will deviate from the optimal solution and make positive inlet attackangle for impeller, and therefore, the efficiency of compressor decreases and the effect of energy saving is discounted.