A hybrid modeling approach for steady-state optimal operation of vapor compression refrigeration cycles

Vapor compression refrigeration cycles have become a promising alternative for high-heat-flux electronic cooling. Still, this area of research lacks the modeling and control design tools to facilitate its practical implementation. At Rensselaer simulation models for system level design and algorithms for temperature control are being developed to bridge that gap. However, these models need to be validated by experimental results. Since the models are not entirely based on first-principle equations, the empirical relations should be matched to the particular experimental setup used for validation. Therefore, the first step towards validation is the identification of empirical parameters that are intrinsic to the experimental apparatus and are required for the simulation. Consequently, this paper presents the experimental identification of the expansion valve coefficient, and the compressor’s volumetric efficiency used in the model. Experiments are performed at different expansion valve openings and different compressor speeds until steady-state is reached. The steady-state data is used to obtain the expansion valve coefficients, and the compressor’s volumetric efficiency. Finally, the data is used to obtain correlations, which are adequately accurate with reasonable computation cost, for each of the evaluated parameters to be incorporated into the simulation model.

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Model-Based Condenser Fan Speed Optimization of Vapor Compression Systems

Energies ◽

10.3390/en13226012 ◽

2020 ◽

Vol 13 (22) ◽

pp. 6012

Author(s):

Sebastian Angermeier ◽

Christian Karcher

Keyword(s):

Steady State ◽

Optimal Operation ◽

Vapor Compression ◽

Total Energy Consumption ◽

Proposed Model ◽

Wide Range ◽

Fan Speed ◽

Main Components ◽

The Ideal ◽

Vapor Compression Systems

Vapor compression systems (VCS) cover a wide range of applications and consume large amounts of energy. In this context, previous research identified the optimization of the condenser fans speed as a promising measure to improve the energy efficiency of VCS. The present paper introduces a steady-state modeling approach of an air-cooled VCS to predict the ideal condenser fan speed. The model consists of a hybrid characterization of the main components of a VCS and the optimization problem is formulated as minimizing the total energy consumption by respectively adjusting the condenser fan and compressor speed. In contrast to optimization strategies found in the literature, the proposed model does not relay on algorithms, but provides a single optimization term to predict the ideal fan speed. A detailed experimental validation demonstrates the feasibility of the model approach and further suggests that the ideal condenser fan speed can be calculated with sufficient precision, assuming constant evaporating pressure, compressor efficiency, subcooling, and superheating, respectively. In addition, a control strategy based on the developed model is presented, which is able to drive the VCS to its optimal operation. Therefore, the study provides a crucial input for set-point optimization and steady-state modeling of air-cooled vapor compression systems.

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