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Controller design for an automotive R744-based air-conditioning system.

Author(s) : TUMMESCHEIT H., KARIM S.

Summary

Research into R744 as a working fluid for automotive AC started in the early nineties and continues even today. Some of the open issues in both design and control of R744 AC systems are investigated using a well validated model of an R744 prototype system modelled using the Air-Conditioning Library by Modelon AB and Dymola from Dynasim AB. The preferred choice for the expansion device from a cost point of view is a two-stage orifice with a pressure-activated bypass for high load condition. In this paper, the solution with this valve is compared to a reference system that uses an electronically controlled valve that is controlled to the COP-optimal high side pressure. It is shown that the two-stage valve can exhibit both limit cycling behaviour and multiple steady states depending on the plant operation history, both undesirable properties that need to be eliminated by proper control design. Another problem that is investigated is the load distribution between a front- and a back seat evaporator for a two-evaporator version of the same system. If the refrigerant side of the second evaporator is not controlled, the flow split between the two evaporators is determined by a fixed expansion device for the rear evaporator.

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Pages: 2008-2

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Details

  • Original title: Controller design for an automotive R744-based air-conditioning system.
  • Record ID : 2009-0348
  • Languages: English
  • Source: 8th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2008)
  • Publication date: 2008/09/07

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