CI-81-02-2 -- A Measurement System for Determination of Air Diffusion Performance in Interior Spaces

It is necessary to quantify the low level and highly variable air currents which occur in offices and other work spaces in order to properly characterize the existing thermal environment. This measurement requires an air current sensor which is responsive to rapid changes in air speed from any direction, and air temperature sensors which are both accurate and non-responsive to radiant energy.

Until recently, most of the available anemometer sensors were directionally sensitive, unresponsive to rapid changes in speed, or both. Multi-directional heated-sphere anemometer probes have recently been developed which can respond to these changes. This new probe now allows for accurate room air current measurements. A number of these probes have been used to develop a room air diffusion measurement system with excellent repeatability and accuracy.

This anemometer data is gathered,along with temperature information,using a programmable data acquisition device. Air velocity and temperature sensors are located at several locations vertically on a sensor tree.The base of this moveable tree contains the anemometer electronics and temperature probe connections. A multi-strand signal cable connects the tree to the data scanner. The data scanner translates anemometer voltage signals and temperature resistance values into engineering units.It also averages a number of readings at each point which allows output of the average air speed at each probe position. The result is an air diffusion performance measurement system which is relatively simple, flexible, and most importantly, field portable.

Utilizing a system such as this, it is possible to perform detailed and repeatable tests in operating buildings. This will allow for both comfort analysis and performance specification verification when used in conjunction with a suitable test procedure. Section I describes the system and its operation and section II details the anemometer calibration procedures. A discussion is included to describe the limitations and potential of the system. A system component listing is available to describe all the equipment required for a multi-probe system.

Citation: ASHRAE Transactions, Volume 87, Part 2, Cincinnati, Ohio



Product Code(s): D-CI-81-02-2