Modeling and comparison of different capacity modulation strategies with focus on seasonal performance

Abstract

Over the past few years, demand for energy efficient HVAC systems has been increasing rapidly, and this trend is likely to continue in the future. There are various modulation technologies that can respond to load variations by switching between capacity levels (tandem, two-stage compressors), PWM control (digital scroll), speed modulation (variable-speed). These technologies can be compared using a single number figure of merit, IPLV. SI which expresses part-load efficiency based on weighted operation at various partial capacities. A model is proposed for a water chiller application having a nominal cooling capacity of 8kW. System performance has been calculated using a 10-coefficient compressor model provided by the manufacturer and the most well-known correlations for heat transfer and pressure drop in a brazed plate heat exchanger. Model validation is performed with experimental data obtained in a parallel experimental investigation. Single-speed and two-stage compressor have a comparable IPLV. SI while a variable-speed compressor has 20% higher IPLV. SI.