Graduation Year

2011

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Muhammad M. Rahman

Keywords

COP, Dead State, Efficiency, Refrigeration, Simulation

Abstract

This thesis consists of two research problems in the air conditioning (A/C) area. For the first problem, the aim is to model and simulate a variable refrigerant flow (VRF) air conditioning system. The coefficient of performance (COP) for refrigeration or heat pump system is one of the critical parameters for designing an air conditioning system. The modeling of the system components for a VRF cycle under different cooling conditions using R-134a and R-22 as refrigerants was carried out. Calculations were performed by varying different parameters such as condenser and evaporator temperatures, and refrigerant type. The R-134a refrigerant shows a better performance when multiple evaporators are present. Part load performance evaluation was also done for both refrigerants. The simulation results compared reasonably well with available experimental data.

In the second problem, the objective is to develop a mathematical model that covers the mass, energy, entropy, and exergy balances of a typical air conditioning system. The model examines how the exergy efficiency of an air conditioning system can be used to measure its performance, bypass configuration, and additional significant environmental factors that affect an A/C system's design. The effects of outside air parameters, room parameters, room sensible and latent heat loads, and dead state properties on exergy efficiency were investigated. The range of parameters covered included outside air temperature (To= 25-60oC) and relative humidity (RHo = 50-85%), sensible heat load (Qsen = 11.50-13.25 kW), latent heat load (Qlat = 3.00-4.75 kW), room air temperature (Tr= 18-25oC), and relative humidity (RHr= 30-44%), and outside-mixture air flow rate ratio (qo/qm = 0.21-0.71). Two novel dead state conditions were selected to further analyze their effects on the system. Present exergy results indicate that an A/C system is quite sensitive to air properties, sensible and latent cooling loads, and dead state conditions.

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