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1E) By-Pass Damper Design Rules
A bypass damper is an airflow regulating device connected between the supply and return ducts. The
bypass damper will automatically open and bypass supply air normally delivered to the zone directly from
the supply to the return on a pressure rise when the VAV zone dampers are closing.
The by-pass damper should be sized to allow at least 70 to 80% of the nominal airflow of the RTU. A
simple way to determine if it is sized properly, assume all VAV zones are closed to their minimum position.
The by-pass should be large enough to re-circulate all the air from the RTU minus the amount set by the
minimum positions at the zones. A properly sized damper will result in an efficient and quiet operation.
1F) Indoor Air Quality Control Standards
The IAQ control is achieved by the VZ7656E1000B controller through CO2 level and minimum fresh air
control. The building CO2 level has to respect the local building codes. The recommended outdoor air flow
per the ASHRAE standard for office buildings (Air class 1) is as follows:
Table from: ASHRAE Standard 62.
2) Zone Controllers VZ7260X5x00B Operation
The following information needs to be carefully read and properly understood if proper system
commissioning is to be achieved.
Contrary to low end commercial and residential zoning controllers which use a two positions open-close
actuator, Viconics VZ7260X5x00B uses proportional analog 0 to 10 VDC modulating damper actuator. This
enables performances and control sequences to be much closer to what is normally found in DDC
application specific control devices.
The operation of the ZONE controllers is intrinsically linked with the operation of their RTU controller.
Although it will operate in a stand-alone mode if the communication network is down, normal operation of
the system as a whole requires that communication with the RTU controller is functional.
Data exchanged from the ZONE controllers to the RTU controller:
•
Current PI heating demand ( output value is based on PI heating weight configuration )
•
Current PI cooling demand ( output value is based on PI cooling weight configuration )
•
Transferred CO2 Level ( Value is based in the Occupancy status and AI4 Parameter setting )
Data exchanged from the RTU controller to the ZONE controllers:
•
Current central system occupancy
•
Current system mode active ( hot air or cold air being delivered )
•
Outdoor air temperature
