Development of an advanced control system for chillers

Variable speed compressors can provide great power savings in the control of air conditioning units.
The reduction in cooling capacity has a great impact on the unit control system especially regarding compressor and water limits and unit stability generally. To manage a chiller unit with variable cooling capacity, all the controlled devices must be considered together with the control system itself, as "communication" between devices can certainly avoid hunting problems.
We have developed a chiller control system that can take all the advantages of the complete control of inverter driven compressor, electronic expansion valve and condenser fans to maximize unit performance in all working conditions. The water flow at the evaporator is controlled in a simple water circuit with a bypass valve and measured with a flow meter, while the water temperature is controlled by 4 heaters with solid state relays.
In this way we can simulate all water conditions and load powers for the unit.
The chiller unit has been installed in a climate chamber that can reach ambient temperatures between 15 °C and 35 °C.
All the other ambient conditions have been simulated using a calculated condensation profile. We have considered a unit working with fans at constant maximum speed (maximum efficiency) so that for each ambient temperature there is a precise target condensing temperature.
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