View Full Version : Honeywell VAV Controller on Dual Duct Box
03-17-2010, 09:26 AM
I am having trouble with my Box Flow always reading 0 cfm. The sensor is in the discharge of the box, the controller is configured for DD Discharge Sensor, which means that it will measure the total of both the hot deck and cold deck. I can see the raw voltage of the pressure transmitter and it is in the range of the flow table. I have reset the flow cal from the balancer, because he did not shut down the hot deck when zeroing the controller. The balancer used Rapid Balance 4.0, the boxes were configured using Lonspec, and the controllers are on Tridium Jace 600. I have commissioned thousands of normal VAV's over the years, and this is the first time I have ever seen this issue. Any help is greatly appreciated. Thanks.
03-17-2012, 11:32 AM
It's been years since I've setup a DD VAV, have always delt with flow sensors in the HD and CD, but you indicate that the controller is setup for Discharge Sensor. Did you check the K factor? If it is zero, the flow calc would be zero. Or, maybe there's a glitch which is causing the controller to take the difference of "two sensors" internally which would result in zero.
03-17-2012, 05:06 PM
It won't work in the discharge of the box, it is too turbulent and the velocity drops way down. In the past I have put the sensor in the cold duct and controlled the cooling damper CFM and run an externel actuator on the hot deck damper and just operate it by analog position only, in a pressure dependant manner.
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