Research On The Applicability Of Magnetic Bearing Variable-speed Centrifugal Chillers

As a booming energy efficient technology,magnetic bearing centrifugal chillers with variable-speed control(so-called Oil-free Chiller as well)have drawn extensive attention in recent years.To survive in a strong competition in air-conditioning market and to contribute to the national energy efficiency target in China,it is essential to evaluate operational performance of the magnetic bearing variable-speed chiller and offer guidance to future applications.This thesis examines the actual operating performance of magnetic bearing centrifugal chillers in retrofitting projects in different cities,which is not only higher than the maximum efficiency level in national standards,but also defeats existing screw and centrifugal chillers.Some typical issues include uneven chiller load sharing and high energy consumption of pumps and fans.System energy efficiency still needs improvement.Magnetic bearing chillers have a significant advantage in retrofitting chiller plants with absorption chillers,and high-rise or old buildings chiller plant renovation.Magnetic bearing chillers adjust through the compressor speed and the inlet guide vane.If the load is high,the IGV is fully open,and magnetic bearing chillers adjust the compressor speed to change the cooling load and the compression ratio.If the load is low,the speed and IGV are jointly adjusted to prevent surge.Under such control,the maximum energy efficiency of magnetic bearing chiller appears under the partial load and small compression ratio conditions,ie the “sweet spot” where the chiller operates efficiently is not near the nominal “rated condition”.Through large amounts of actual operating data,establishes the magnetic bearing chiller model and analyzes the sensitivity of factors influencing its operating efficiency.Based on the chiller model,the design and operation strategies of the magnetic bearing chiller as a single cold source or combined with other types of chillers are studied respectively.A simple calculation method of building cooling load is used to decide the design number of magnetic bearing chillers under different cooling load profiles.Establishes chiller plant models equipped with magnetic bearing chillers;simulates and analyzes annual operation strategies with the goal of minimizing energy consumption.The control strategy of pumps and cooling towers under different cooling load and outside temperature conditions is given.Chiller plants with magnetic bearing chiller should also provide reasonable variable speed control for pumps and cooling tower fans,and therefore its annual energy efficiency can reach more than 5.0.