This standard applies to the testing of airflow measurement devices that are intended for field application to residential heating, cooling, and ventilation air distribution systems.This standard is for use in the laboratory and is not intended for use in field calibration of airflow measurement devices.
Detailed studies by LBNL and field results of other researchers and practitioners have shown that there is a large range of accuracy for airflow measurement devices in field applications to measure airflow through HVAC system air inlets and outlets, despite having similar accuracy specifications provided in manufacturers literature. Some devices perform very well and have accuracies better than 5% of flow over a wide range of conditions and could be used in a wide range of field applications (e.g., ensuring individual air outlet flows meet design specifications). However, other devices have errors of 50% and are essentially useless for any field application. Many users have reported similar errors. Mostly, these problems have arisen when measuring airflows at air outlets with vanes that direct the airflow in specific directions, and airflow does not enter the flow capture device in a uniform manner. Other problems occur when the size of the air inlet or outlet is different compared to the size of the measurement device inlet, and when flows in the distribution system are not uniform upstream of an air outlet. Manufacturers calibration techniques create uniform airflows entering the measurement device and do not reveal the devices sensitivity to flow non-uniformity found in field applications. Consequently, current accuracy specifications reported by manufacturers do not allow equipment users to determine if a device is appropriate for their field application. Demand is increasing for measuring airflows through air inlets and outlets of these system types, which exhibit the measurement difficulties discussed above. A few examples of the increasing demand are: The State of California has requirements for measuring residential HVAC system air flows in its energy code (Title 24) and they are concerned that testing and compliance be demonstrated with measurement equipment and techniques that give accurate results. - Compliance testing in residential buildings is becoming more common and will be used much more in the future (e.g., home energy raters). Builders need to know that the system they specified was installed correctly and need good measurements for QA/QC procedures. Contractors need tools they can trust to prevent callbacks and complaints and that can be used for troubleshooting. Utility programs that specify HVAC performance requirements need to be able to measure system airflows. - ASHRAE standard 62.2 requires measurement of air flows of ventilation systems and needs a standard to refer to when specifying acceptable measurement methods Testing and balancing in all buildings will be better served by having improved specifications for the accuracy of airflow measurement devices. Better accuracy specifications will ensure that test and balance activities can better determine system performance, which will lead to fewer callbacks to resolve problems. The proposed new test method will use very simple, well-established laboratory airflow measurement methods. A selection of air inlet and outlet types, measurement device placement options, upstream ducting geometries for outlets, and airflow rates will be specified based on already completed research and field experience. Some measurement devices add airflow resistance, which results in a lower airflow than if the device was not in place. Most devices use a simple calibration (called a K factor) to correct for this effect. However, the actual correction required strongly depends on the duct system layout, airflow pattern, and airflow rate. If a particular branch is being measured using a device that changes the flow resistance of that branch, then the flow through that branch will be reduced and the flows in other branches will increase. Particularly in multi-branch residential systems, the insertion losses can be very large (50% or more). This test method will addressing the effects of insertion losses. The vision is that other codes and standards bodies could say that a certain flow needs to be measured with an instrument having an accuracy of XX% tested according to the proposed ASTM test method.
KeywordsFlow hood; terminal; register; air inlet; air outlet; ventilation; forced air
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
Draft Under Development