Delta eZV-440 Application Manual

Contents

Delta eZV-440 Application Manual Manual pdf 66 page image

eZV-440 Application GuideEdition 2.6Page 65 of 84For electric duct or electric baseboard outputs set up as time-proportional, the minimum heatoutput % is ignored by the algorithm to prevent overheating, even when the minimum heat output isgreater than 0. The maximum heat output % still applies to honour the system's upper safety limits.For hydronic heat outputs, both minimum and maximum heat output % are used.For programmable controllers, if custom output objects are used, the pulse has a 100% duty cycle.The output is directly controlled by a GCL program and the custom AV objects are used tomodulate the pulse.Discharge Air TemperatureThe discharge air temperature (DAT) is the duct temperature downstream from any local heatingor cooling stages that supply the air to that space. This section applies to a space with a DATsensor and ducted heating or cooling stages.The heating or cooling output is limited by the discharge air limited controller that maintains amaximum limit above the CurrentHeatSetPoint (AV800) in heating, and a minimum limit below theCurrentCoolSetpoint (AV801) during cooling. The maximum limit is calculated by adding thedischarge air temperature high limit setpoint differential (DATHiLimitSetpointDiff) to theCurrentHeatSetPoint, and the minimum limit is calculated by subtracting the discharge airtemperature low limit setpoint differential from the CurrentCoolSetpoint.Limiting the ducted heating and cooling stages ensures the temperature differential between spaceair and supply air is not large enough to cause hot air to build up near the ceiling. Limiting heatingand cooling outputs also encourages cold air to spread out via the diffuser and mix well with theroom air. Cold air that drops down without mixing can create complaints of cold drafts.Fan (VAV)This section describes the fan sequences supported by the VAV algorithm.Single Speed Parallel Fan SequenceA VAV parallel fan will run or start in the following cases:l When the fan is set to run constantly as determined by its ConstantFanModes setting.l During Occupied mode (includes Unoccupied Override), when the central air handler isproviding primary air to the space, the parallel fan will turn on when the airflow setpoint dropsbelow the parallel fan flow set point (ParallelFanFlowSetpoint AV131). This ensures thereis enough airflow to adequately mix the primary air in the space and prevent cold duct airfrom being dumped into the space during times of low cooling load operation.