Packaged Air Conditioner, Micro-Channel Heat Exchanger, Vapor-Compression Cycle, Thermostatic Expansion Valve, Modelica
Microchannel Heat Exchangers (MCHX) are used in Air Conditioning systems (AC) as an efficient type of Heat Exchangers (HX) because they have compact size, as well as low refrigerant charge. However, using MCHX as condensers can be associated with some problems, including evaporatorcondenser transient charge balance issues. Therefore, this study aims to investigate the impact of using MCHX as a condenser in a packaged air conditioner with a finandtube heat exchanger as an evaporator. The methodology was dynamically modeling the packaged air conditioner in Modelica, considering varying pass configurations of MCHX with several refrigerant charges. The results showed that the pressure in the highpressure side of the refrigerant cycle increases as the number of tubes in the inletpass of the MCHX decreases. In addition, if the difference in the number of tubes among the inletpass and the outletpass is large, the pressure increases regardless of which pass has the highest number of tubes. Moreover, the pressure can increase after a while at the beginning of an oncycle due to the slow response of Thermostatic Expansion Valve (TXV) caused by the thermal inertia of the sensing bulb. We defined a mass ratio as mass of refrigerant in the evaporator to the mass in the condenser. A decrease in the mass ratio for a given total charge corresponds to the refrigerant accumulating in the condenser, increasing pressure in the condenser.