| dc.description.abstract | HVAC ventilation systems play an important role in maintaining healthy indoor air quality levels by removing air pollutants to the outdoors. In order to evaluate the ability of domestic range-hoods to remove contaminated air from kitchen environments, the American Society for Testing and Materials (ASTM) developed the ASTM-E3087 standard (Standard Test Method for Measuring Capture Efficiency of Domestic Range-Hoods). This standard was used to build and develop a well-instrumented test chamber at the RELLIS Energy Efficiency Laboratory (REEL) for the purpose of measuring and evaluating the capture efficiency (CE) of different range-hoods following procedures that comply with the standard. A shortcoming of evaluating range-hood capture efficiency by using the test facility is that the experiments are time consuming. In addition, parts of the test facility and the ASTM standard procedures, may in fact need further evaluations for improvements. Therefore, this study focused on designing and developing a computational fluid dynamics (CFD) model based on the CE test procedures specified in ASTM-E3087, with the goal of simulating the space environment and the boundary conditions of the actual test chamber located at REEL.
An important step before the CFD model can be applied is validating it, which means showing that there is good agreement between the simulation model output and experimental measurements of CE. In support of this study and the above CFD model validation, multiple CE experiments were conducted on a typical residential kitchen range-hood. For this purpose, a Venmar under-cabinet range-hood, Inspira IU600ES30BL, was selected for testing and modeling. These tests and simulations were performed at three different experimental test conditions, representing three fan operating speeds and thus different air flowrates (in CFM, cubic-feet-per-minute) and CO2 gas injection rates (in standard l/m, liters-per-minute). During each experimental test, CO2 concentrations were measured using three sensors placed at three different locations according to the ASTM E3087-18 standard. These measured CO2 concentrations were in turn used to calculate the capture efficiencies at the special test conditions. Next, the CFD simulation model was used to predict values of CO2 concentrations at the same three test conditions, followed by calculations of CE values. Of special importance are the CE differences between the results of the CFD simulations and the experiments for the three cases, which were found to be 0.01%, 2.73%, and 0.14%. Based on the closeness of these results, the CFD model was consider validated, so that it could in fact be used as a tool for analyzing and evaluating CE methodologies and test facilities.
Once the CFD model was validated, it was then used to analyze the distribution of CO¬2 concentration inside the chamber for the purpose of evaluating the optimum chamber location for CO2 trace gas sampling, based on a location where the sample value is representative of the chamber as a whole. The results of this evaluation showed that the sampling location that is specified in the ASTM-E3087 standard is in fact in a region of uniform CO2 distributions, meaning the standard location is representative of the chamber as a whole. Quantitatively, the capture efficiency at the standard-specified location is about 3% to 5% higher than those CE values based on sampling locations near the walls and door of the chamber.
A second study that made use of the validated CFD simulation model was to investigate the effect that the volume of the test chamber has on CE testing and measurements. This investigation was extremely important because the ASTM-E3087 standard does not specify exact chamber dimensions or volumes, and tests performed on the same range-hood at the same test conditions in two different facilities of different volumes produced significantly different CE values, which was a surprising outcome. Using the CFD simulation model, CE values were determined for several chambers with different volumes, and the results showed that measured capture efficiency decreases as the volume of the chamber increases. In one example, as the volume was decreased by 65%, the capture efficiency went up by as much as 27 %. This particular example of a volume decrease was a comparison of the actual REEL test chamber and the smaller standard minimum-dimensions chamber specified in ASTM-E3087, which is a volume lower limit. Based on this important result, it is highly recommended that the standard specifies an exact chamber size for CE tests rather than specifying a minimum-size chamber. | en |
