Daikin MicroTech II Operation And Maintenance Manual

Also see for MicroTech II: Installation and Maintenance Installation and maintenance manual Installation and maintenance manual

Daikin MicroTech II Operation And Maintenance Manual Manual pdf 30 page image

OM 752-4 30 www.DaikinApplied.comdesCrIptIon of operatIonPI Control ParametersAssociated with each PI loop is a set of two adjustable parameters: Proportional Band andIntegral Time. When the unit ventilator is properly sized for the space, the factory settingsfor these parameters provides the best and most robust control action (see Figure 19).If field problems arise, first ensure these parameters are set back to the factory defaultsettings. If adjustment is required, only make small adjustments to one parameter at atime. After each adjustment, allow enough time for the system to stabilize before mak-ing further adjustments. If you do not have the means to graph the space performance,record the actual measured value and set point for several minutes and then plot theresults using a spreadsheet to determine the correct action to change the PI parameter.CAUTIONAdjusting PI parameters can cause erratic unit operation, and potentially damage the equipment.PI control parameters should only be adjusted by trained personnel having a complete understanding ofhow these parameters affect system operation. Generally these parameters do not need to be adjustedfrom the factory default settings.Figure 19: Optimized PI loop controlProportional BandThe proportional band, or proportional action, causes the controlled output to changesin proportion to the magnitude of the difference between the sensor value and set point.A proportional band setting that is too small (see Figure 20) causes control oscillationsthat go fully above and below the set point.Figure 20: Proportional bandsToo Small Too LargeA proportional band setting that is too large (see Figure 20) causes an offset betweenthe actual measured oscillation center and the set point. A small offset is not necessar-ily a problem since most systems have a small “natural” offset and the integral functionautomatically works to eliminate or reduce this effect.In general, it is best to start with a relatively large proportional band setting (the factorydefault setting is best) and adjust to smaller values.If you want the system to respond strongly to small changes in the space, adjust theproportional band to a higher setting.If you want the system to react weakly to small changes in the space, adjust the pro-portional band to a higher setting.