Advances in equipment performance, and the development of variable speed equipment have led to stricter performance testing of HVAC&R equipment, requiring limited tolerances on capacity and efficiency measurements to 5% of certified ratings. This necessitates the use of third-party performance validation tests by manufacturers. Accurate airside measurement is crucial, and proper air mixing is necessary to minimize airflow nonuniformities before air sampling. However, the available literature and guidelines on air mixing and sampling device design are limited, which can result in discrepancies in measured efficiency beyond the allowable tolerances. To address this issue, this research aims to develop design recommendations for air mixing and sampling devices used in HVAC&R equipment performance testing. The study assessed the mixing effectiveness and pressure drop of three types of air mixers - baseline louvered mixer, orifice-type mixer, and orthogonal pattern louver mixer - under various operating and geometrical conditions. The results showed that all three mixing devices were capable of reducing airflow stratification. However, the orthogonal pattern louver mixer showed the most promising results due to its simple design, and the high mixing performance and low pressure drop in a limited mixing length which can be achieved due to its advantage of creating two-dimensional mixing, which is reliable even if maldistribution profile unknown, contributing to its superior performance compared to the other two mixing devices. Additionally, the investigation of design guidelines for air sampling devices for accurate and reliable performance resulted in design constraints and guidelines for sampling hole size, pitch, sampler material, and other factors. Furthermore, the study explored the effectiveness of combining air mixing and sampling devices to enhance the accuracy of capacity measurements through in-situ testing, focusing on the optimal configuration of the combination. The results suggest that selecting an air mixer with high mixing performance and a sufficient mixing length can contribute to a robust mixer-sampler combination for improved accuracy and precision of capacity and vapor mass balance measurements. Overall, this study provides valuable insights into optimal air mixing and sampling device design and configuration, enhancing bulk air condition accuracy, and improving HVAC equipment capacity measurement accuracy in psychrometric performance testing
