Publication Date

8-2016

Date of Final Oral Examination (Defense)

6-6-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Mechanical Engineering

Department

Mechanical and Biomechanical Engineering

Supervisory Committee Chair

John F. Gardner, Ph.D.

Supervisory Committee Member

Donald Plumlee, Ph.D.

Supervisory Committee Member

Yanliang Zhang, Ph.D

Abstract

Nearly all cooling systems, and an increasing proportion of heating systems, utilize the vapor compression cycle (VCC) to provide and remove heat from conditioned spaces. Even though the application of VCC’s throughout the building environment is ubiquitous, effective and accessible models of the performance of these systems remains elusive. Such models could be important tools for VCC designers, building designers and building energy managers as well as those who are attempting to optimize building energy performance through the use of model-based control systems.

Strides have been made in developing lumped parameter models for VCC’s. In spite of these contributions, widespread accessibility and use of VCC performance models has yet to be achieved. This work addresses one of the barriers in applying VCC performance models, the identification of model parameter values required to make performance models useful and accurate. A steady state spreadsheet-based model has been developed which, when combined with standard test data provided by system manufacturers, allows the modeler to identify the salient heat transfer parameters that govern the behavior of the condensers and the evaporators.

Performance data provided by the system manufacturer was used to determine model parameter values. Data used from the test conditions for the determination of these parameters include the evaporating and condensing pressures, the input power, the cooling rate and the degrees of superheat and subcool. Most importantly, these data allowed for the computation of the effective heat transfer characteristics within the moving boundaries, as opposed to heat transfer values calculated strictly from the geometry. Using an effective heat transfer value allows for the spreadsheet-based model to use a broad spectrum of VCC models despite their potential differences in heat exchanger design conditions, that is not dependent on the number and spacing of fins or other optimization design criteria.

To validate the concept, the approach was used to identify parameter values for three different air conditioning units with three different sets of performance specifications. On average the model predicted a heat absorption rate within 1.5% - 3.7% error of what was measured by the manufacturer during testing. This model requires limited sensor information to provide parameters determined under steady state conditions that can be used in a dynamic model to assist in design, control and operation of traditional VCC systems over a range of operating conditions.

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