CFD Case Study: Heat Exchanger Inlet Air Velocity Distribution for Ducted Tests in a Psychrometric Chamber (ASHRAE RP-1785)
CFD, heat exchanger, duct, psychrometric chamber, refrigerant charge
This paper presents the airside analysis of coil duct configurations using Computational Fluid Dynamics (CFD) to determine which configuration best mitigates airside maldistribution for ASHRAE RP-1785. RP-1785 has a global objective of providing accurate refrigerant charge and oil retention data for residential coils, collected in a controlled experiment. The final test matrix of the study includes several representative residential indoor and outdoor coils to be tested at various refrigerant and airside inlet conditions. The coil performance, charge, and oil retention behavior is strongly influenced by the airflow; therefore the uniform airflow distribution to coils is critical to RP-1785 to maintain a well-controlled experiment. Analysis of four 3D CFD cases are presented with the largest coil of the initial test matrix (105.6 in (268.2 cm) length, 40 in (101.6 cm) height, 5 in (12.7 cm) depth) installed in the Oklahoma State University psychrometric chambers. The simulation domain was extended to include the airflow characteristics within the psychrometric chamber to determine the effect of the asymmetric air inlet boundary condition. The analysis concluded the three significant factors affecting the airflow uniformity: the distance between the duct and wall, the distance between the duct and chamber floor, and the upward incoming airflow area of the floor. The CFD study results are used to inform the design of the duct to be used for coil testing in RP-1785 and the final duct design is presented.