Cold-air distribution comparison for four supply air diffusers

Cold-air distribution (CAD) with ice storage systems can potentially lower operating and first costs when compared to conventional heating, ventilating, and air-conditioning systems. One concern for CAD systems is that the cold supply air temperatures can be uncomfortable. One approach for dealing with this problem has been to include fan-powered terminal mixing boxes in the distribution system. These terminal units mix primary and room air, which results in supply air temperatures similar to those of conventional systems. Unfortunately, these fan-powered boxes consume energy and add to the installation costs, potentially negating the savings from the CAD system. A few supply air diffusers are now available that accelerate the induction of room air, mixing with the cold primary air thus reducing the potential for draft when compared to conventional diffusers. A series of experimental tests were conducted to compare the performance of four different supply air diffusers for a range of room load and supply air temperature and flow conditions. Comparisons were made using the effective draft temperature and air diffusion performance index and as indicators of performance. Test results indicate that three of the four diffusers performed well over the entire range of test conditions.