Measuring Range Hood Capture Efficiency Values

From ASHRAE Journal Newsletter, November 10, 2020

A recently published standard, ASTM E3087-18, Standard Test Method for Measuring Capture Efficiency of Domestic Range Hoods, established a test method for obtaining capture efficiency (CE) values—the percentage of cooking-contaminants that are captured and exhausted—of household range hoods.

In a recent Science and Technology for the Built Environment article, researchers present the design, construction and operation of the first CE test facility assembled from the ground up after the release of ASTM E3087-18. It also discusses several CE tests that were performed. Texas A&M University researchers Sammy Meleika; Michael Pate, Ph.D., Life Member ASHRAE; Trey Hicks; and James Sweeney, Ph.D., Member ASHRAE, discuss the research.

1. What is the significance of this research?

The purpose of this research is to build a test chamber that can be used to determine the capture efficiency (CE) of residential, wall-mounted range hoods in accordance with a newly developed ASTM standard, ASTM E3087-18, and ultimately integrate CE into a new ASHRAE/HVI certification program for residential range hoods.

The test chamber described in this research is significant because it is the first built from the ground up following guidelines put forth in ASTM E3087-18. One other test facility was built by Lawrence Berkeley National Laboratory (LBNL) prior to the release of ASTM E3087-18 and was also used to develop the standard.

This study identifies a few design and test guidelines in the ASTM test standard that can be reconsidered in order to ensure consistency in CE metrics presented by different labs for the same range hood. Namely, this study suggests improvements to the ASTM-prescribed steady state time, specified cabinet dimensions and prescribing additional requirements to the inlet filter type and size to minimize variations in the inlet flow behavior.

2. Why is it important to explore this topic now?

Currently, there are no ASHRAE or Home Ventilating Institute (HVI) requirements for the CE of residential range hoods. Rather, the current industry primarily focuses on airflow, noise and power ratings of the range hood under different operating conditions.

This study—and other CE testing performed since—has shown that just because a range hood has a high airflow rate or quiet mode of operation, does not always mean it will have a higher CE. Additionally, as indoor air quality continues to become a more critical aspect of human health, as well as rising populations and increased urbanization giving rise to a need for multifamily buildings to become more energy efficient (or net-zero), it is imperative that the range hoods installed are operating in an efficient manner (i.e. effectively capturing/exhausting cooking contaminants in the household and not just exhausting conditioned indoor air, which requires more outdoor air to be brought in and conditioned).

Additionally, as IAQ continues to become a more critical aspect of human health, and as rising populations and increased urbanization creates a need for more energy-efficient (or net-zero) multifamily buildings, it is imperative that the range hoods installed are operating in an efficient manner (i.e. effectively capturing/exhausting cooking contaminants in the household and not just exhausting conditioned indoor air, which requires more outdoor air to be brought in and conditioned).

3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?

Although the ASTM standard specifies four air changes before a steady-state CE is achieved in the test chamber, this study and other studies performed by LBNL have shown that as many as eight air changes are required to achieve a steady-state CE. Therefore, it is recommended that the CE be continuously monitored during testing and compared to previous measurements in order to ensure minimum variation between repeat CE tests (i.e. no increasing/decreasing trends), which is important to achieving a reliable and repeatable CE metric for certification purposes.

4. How can this research further the industry's knowledge on this topic?

This study and other current studies have shown there are various factors that influence CE itself and the repeatability of CE (i.e. variation in CE for tests performed numerous times), such as the mounting height, cook-top temperature and tracer gas injection rate. For instance, changing the mounting height of a range hood (Fan D) by 2.5 in. (64 mm) resulted in a change in CE as high as 9.0% CE (i.e. the difference between 59.5% CE and 68.5% CE).

Since the objective of this research is to integrate CE into a new ASHRAE/HVI test standard for range hood certification ratings, it is important that the CE metric reported by different test labs aligns with the true CE capabilities of the range hood and not those that are influenced by external factors such as mounting height. Therefore, it is recommended that future test standards consider explicitly stating a mounting height in order to minimize variations in the reported CE caused by varying mounting heights.

5. Were there any surprises or unforeseen challenges for you when preparing this research?

The ASTM test standard specifies a maximum ceiling height of 2.5 m (~8.2 ft) for the CE test facility, as well as cabinets installed on both sides of the cook-top that are mounted to touch the ceiling and extend down vertically 1.0–1.1 m (3.3–3.6 ft). In order to utilize the same test facility for future testing of island range hoods, which typically require a higher mounting height, the group built the test facility with a 3.0 m (~9.8 ft) ceiling height. Therefore, a slight deviation from the specified cabinet dimensions was necessary in order to maintain a fixed distance of 0.5 m (1.6 ft) between the countertop and cabinetry.

Since the distance between the counter-top and cabinets was consistent, it was assumed that this deviation would have no effect on CE measurement. Additionally, this deviation was made with input from the Residential Buildings Group at LBNL. However, for the purpose of developing future test standards, it is suggested that the cabinet height be specified relative to the counter-top.