This study assessed the real-world performance of a typical range-hood ventilation system by focusing on parameters such as duct pressure drop and range hood capture efficiency. The research can be divided into two parts, mathematical modeling and laboratory testing. For example, the pressure drop through a typical range hood ducting system and the capture efficiency of under-cabinet range hoods were modeled individually. For laboratory testing, the range hood was experimentally tested in two ducting configurations representing two typical installation strategies found in practice, namely flexible and rigid ducts exiting through walls and ceilings.
The bulk of the effort in this project was the experimental phase, and it could be divided into a Case 1 and Case 2. In Case 1 three different lengths of flexible duct (32", 46", 75") and five different lengths of rigid duct (32", 46", 75"119", 148") were mounted so as to exit a sidewall. In Case 2, rigid duct was vented through the roof by using the same duct lengths tested in Case 1. Pressure drops through the duct and vent cap were measured at different fan speed levels to produce system performance curves. These curves were overlaid with measured fan curves to find operating points (i.e. flow rate, and pressure drop) that represent real-world range-hood ventilation systems. This study provides the basis for system performance assessments and system design recommendations.
The results of this study showed that the pressure drop through flexible ducting is larger than the pressure drop through rigid ducting of same length. The increased static pressure drop in flexible ducting had a negative impact on range hood performance, which results in a lower airflow rate and capture efficiency. By comparing the predicted and the actual results, it was found that the pressure drop measured in the experimental test is higher than that predicted by the mathematical model, which needs to be taken into consideration in future designs.
For capture efficiencies, it was found that they do not differ much for different duct lengths in the same configuration. At the same fan speed, rigid-duct range hood systems have higher capture efficiencies compared to flexible-duct range hood systems. Furthermore fan speeds have the largest effect on capture efficiencies, with values varying from 75% to 95% for fan speeds varying from low to high.
