A Study of the Effects of CO2 Injection Rate on the Measured CO2 Capture Efficiency of Domestic Kitchen Range Hoods
Abstract
Range-hood capture efficiency testing is a procedure standardized by the American Society for Testing and Materials (ASTM) with the purpose of measuring the ability of a kitchen exhaust fan to remove pollutants generated during cooking activities. The Texas A&M University RELLIS Energy Efficiency Laboratory (REEL) has developed a testing facility, which complies with the ASTM 3087-18: Standard Test Method for Measuring Capture Efficiency of Domestic Range-Hoods, in order to conduct capture efficiency research.
The main objective of this research was to determine the effect that the tracer gas injection rate has on the measured range-hood capture efficiency. Determining and analyzing this effect was then used to validate the rounding-down procedure developed at REEL for selecting the test CO2 injection rate in standard liters per minute, and to suggest whether the ASTM injection rate bounds require a review. A secondary objective was investigating the relationship between measured capture efficiency and range-hood fan speed.
The research presented above required detailed testing of two different range-hoods with their integrated exhaust fans (Whirlpool Over-The-Counter Microwave and Venmar Under-Cabinet Range-Hood). The first objective was completed by testing one-hundred and ten (110) combinations of fan flowrates (cubic-feet-per-minute) and CO2 injection rates (standard-liters-per-minute) across both range-hoods. These results then showed that capture efficiency decreases with an increase in CO2 injection rate. In fact, it was observed that for most fan speeds the lowest capture efficiency was recorded at the maximum allowable CO2 injection rate.
REEL’s rounding-down procedure consists of calculating the maximum allowable injection rate in SLPM during a test (per ASTM 3087-18), and then rounding that value down to the closest multiple of five SLPM in order to ensure that variations in the flowrate of the range-hood do not lead to testing at an injection rate greater than the maximum allowable by the ASTM standard. Initially, there were some concerns that the rounding-down procedure could lead to significant variations in capture efficiency results, but test results showed that the difference between the measured capture efficiencies at the same flowrate, but different rounded injection rates, was negligible (0.3, 2.49, and 0.69 %CE). With differences between measured capture efficiencies represented a percent difference of 0.46%, 5%, and 0.84% respectively, which allow one to conclude that REEL’s rounding-down procedure does not compromise the accuracy of the reported range-hood capture efficiency. On the contrary, the large percent difference range (2% - 18%) between the measured maximum and minimum capture efficiencies at the permitted ASTM injection rate bounds suggest that the ASTM bounds might be flawed or that the OTR has intrinsic characteristics that lead to highly variable capture efficiency measurements. It is recommended to conduct more testing with additional units.
The secondary study showed that capture efficiency is proportional to the operating fan speed, meaning that capture efficiency increases as the fan speed increases. The increase in capture efficiency with respect to the change in flowrate diminishes as the flowrate increases.
Citation
Heredia Velasquez, Mario Alfonso (2020). A Study of the Effects of CO2 Injection Rate on the Measured CO2 Capture Efficiency of Domestic Kitchen Range Hoods. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /200805.