In this paper different packaged air-cooled systems, operating on scroll compressors, are experimentally
analysed from the point of view of the relation between energy efficiency and actual capacity. Single
compressor, double compressors and double compressors with uneven volumetric capacity units are
tested. Experimental tests demonstrated that cooling capacity control by means of variation of rotational
speed is an suitable solution for improving the part load efficiency of these systems. Step capacity units
obtained by splitting the system volumetric capacity between two compressors are also effective solutions.
Nevertheless they appear to be more efficient than single inverter driven chillers only for part load
conditions lower than 60%. In the analysed cooling capacity range (25–50 kW), tandem compressors
chillers with one inverter driven compressor appear the most efficient solution combining rotational
speed with step capacity control. Seasonal energy efficiency ratios were obtained with prEN 14825 calculation
method confirming reduced energy consumption associated to continuous and step cooling
capacity control.