Abstract
Abstract In the present energy scenario, heat-pumps play an important role to improve energy efficiency in reversible cooling systems. In case of industrial size plants, centrifugal compressors are preferred with respect to other solutions; nonetheless, they work in variable operation and therefore they must withstand off-design conditions. Carrier provided the University of Genoa with a small size chiller rig equipped with an innovative high speed centrifugal compressor driven by a variable speed motor to study unstable operation of refrigerant closed loop systems. To this aim, vibro-acoustic signature analysis of such closed loop rig is performed mainly focusing on compressor mechanical response. This experimental characterization is firstly conducted in system stable operation. Afterwards, surge transients are obtained by acting on plant feeding lines valves; meanwhile, experimental signals are acquired at relevant plant locations to investigate system response just before instability onset. Indeed, system dynamics is affected by interposed volumes, and therefore the effect of heat exchangers in system response may be relevant. Therefore, system dynamics is analysed both in sub-synchronous frequency range and in high frequency region to assess how its vibro-acoustic response varies when moving from stable conditions towards surge. By doing so, suitable surge precursors can be defined by relying only on vibro-acoustic signals both in low and high frequency ranges to perform early surge detection in such chiller systems. The proposed approach main advantage is to exploit non-intrusive probes, which allow to define diagnostic indicators without interacting directly with the working fluid.
Published Version
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