Measuring Residential Ventilation System Airflows: Part 1 – Laboratory Evaluation of Airflow Meter Devices

Abstract

Building codes increasingly require tighter homes and mechanical ventilation per ASHRAE Standard 62.2. These ventilation flows must be measured so that energy is not wasted with over ventilation and occupants' health is not compromised by under ventilation. Flow hoods are used to measure these ventilation flows, but there is currently no standard specifying the measurement procedure and measurement devices that should be used. This study evaluates the accuracy of six commercially available flow hoods under laboratory conditions configured to emulate a residential mechanical ventilation duct system. The measurements taken with the flow hoods were compared to simultaneous measurements taken by an in-line reference flow meter having a known uncertainty. Results indicate that powered flow hoods yield more accurate measurements than non-powered flow hoods, and that a majority of the flow hoods measured inlet flows more accurately than outlet flows. In several cases, there was little resemblance between the manufacturers' stated accuracy and the accuracy we found in our laboratory measurements. It is clear that current flow hood calibration procedures may not consider field application variables such as flow asymmetry, flow angle, and flow direction. A new flow hood measurement standard that takes these 'real world' conditions into account should be developed to ensure that residential buildings receive the intended ventilation flows.4

Indoor air quality in 24 California residences designed as high-performance homes

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A Meta-Analysis of Single-Family Deep Energy Retrofit Performance in the U.S.

“…Many of these systems could be termed "complex", meaning they have one or more of the following: independent duct systems, humidity controllers, variable speeds, multiple points of occupant controls, filtration, etc. All of these added complexities add potential points of performance failure and risk of inadequate maintenance, which is troubling, given that performance errors are common even in "simple" mechanical ventilation systems (Stratton, Walker, & Wray, 2012). A variety of ventilation system performance faults have been reported in California DERs and new homes (Less et al, 2012;Less, 2012;Offermann, 2009).…”

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“…Failures occurred for two primary reasons: (1) duct airflow restrictions and (2) system design flaws, namely the inability of continuously operated ERV/HRV exhausts inlets to provide kitchen and bathroom ventilation at acceptable rates. An evaluation of ventilation airflows in CA homes similarly found that almost all homes met whole-house ventilation requirements, however 52% of the 44 bathroom fans measured failed ASHRAE 62.2 criteria (Stratton, Walker, & Wray, 2012). These results highlight the importance of appropriate system design and commissioning prior to occupancy.…”