Property
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Notes
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Inputs and Outputs
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The fan and auxiliary heat wires are pass-throughs, and the microblock provides no control algorithm for these wires. During test and balancing, the technician can override these wires through the built-in test and balancing to test fan and heat operation. For more information on the built-in test and balancing procedures, see the appropriate control device documentation.
The other outputs from this microblock are the actual flow reading (FLOW) and a signal for the damper position. The damper signal is a feedback only when a built-in actuator is used. If an external device is used, this output becomes a control wire.
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Flow Input Properties:
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The Flow Input (AI) settings should match the settings for the points the data will come from. This includes existing Trend and Alarm settings.
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Network Visible
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When you set Network Visible? to Yes, the microblock's output is visible to third-party equipment.
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Resolution
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Resolution is the smallest recognizable change in engineering units for the equipment.
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COV Increment
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The COV (Change of Value) Increment is the minimum change in the present value that will cause a microblock to send data to its COV Subscribers.
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Airflow Object Properties:
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Name
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The Name property allows you to set the point name. You can use any characters (including spaces) in this field, except for the " character.
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Simulation
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The Simulation section in the microblock dialog box allows you to define the conditions that will be used during an Eikon for WebCTRL simulation. See "Simulating a control program" in Eikon for WebCTRL Help.
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Primary Use
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If this is a typical single-duct VAV system, this field should be set to Cooling. Dual-duct systems require two Airflow Control microblocks (one for each duct). The microblock that is controlling the primary cooling duct should have this field set to Cooling. The microblock that is controlling the second duct, typically a heating or ventilating duct, should have this field set to Heating.
NOTE Set the hardware configuration on the microblock Properties page.
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Flow Measurement Units
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The Flow Measurement Units field is for display and documentation purposes only. The sensor reading will be given in the same units used during the system calibration. If the flow calibration readings are entered in CFM, for example, the flow sensor will read in CFM. This field allows you to record what units were used and to display them on the Properties page.
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Units
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The Units field has two parts, a scrolling list and a number field. If the unit of measure that you need is not available in the scrolling list, enter a BACnet number in the number field. Units can be read directly from the BACnet object but setting this property in the microblock reduces network traffic.
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Cooling Max Airflow
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The Cooling Max Airflow field is the maximum airflow that will be provided to the zone when the VAV box is in a cooling mode. If the VAV air handling unit provides warm air when the system is in a warm-up mode, the Heating Max Airflow field is used as the maximum flow under these conditions. The Occupied Min Airflow and Unoccupied Min Airflow set the minimum flows as required for ventilation purposes. You may also set the Aux Heat min Airflow. These minimums apply to either heating or cooling airflow. (Typically, the unoccupied minimum airflow is set to zero, but special circumstances may require airflow even when the zone is unoccupied.)
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Damper Travel Time
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The Damper Travel Time property should be set to the total time required for the damper motor to travel from its full-closed to full-open position. The Direction field tells the flow control algorithm whether the motor turns clockwise or counter-clockwise to open the dampers. This only applies when using an internal actuator.
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Use Supply Air for Heating when Heat Mode is On
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If the Use Supply Air for Heating when Heat Mode is On field is set to yes, the flow control algorithm uses the htg % input to control the VAV dampers during the warm-up mode. If this field is set to no, the dampers will be controlled to provide the appropriate minimum occupied or unoccupied airflow to the zone during the warm-up period.
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Editing Privilege
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Preset, the default Editing Privilege, indicates that each property in a microblock has an appropriate privilege assigned to it. If you change the Editing Privilege, all the properties in that microblock are assigned to that one editing privilege which is not always desirable.
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