Viconics VWZS Application Guide - Manual (Page 8)

8
1D) Special Considerations
A typical office installation may require that a single unit service areas being used for different applications.
These areas will commonly be a combination of external and internal zones.
It is always good to verify the intended use of all areas knowing their true peak loads before committing to
its final design and sizing.
It may be necessary to oversize or undersize the design to meet their daily demands. The following are
examples of when over sizing of a zone damper may be needed:
• Areas with oversized windows that are exposed to the sun longer
• Conference rooms
• Cafeterias
• Areas with vending machines
• Areas with extra lighting
• Areas with computers, photocopier, etc…..
Areas such as computer rooms, kitchens and certain types of conference rooms may warrant a totally
separate system of their own and should not be part of the zones attached to an RTU. Certain critical areas
may call for cooling all year long and based on system settings could only guarantee occupant comfort a
portion of the year.
Knowing the critical areas of a building in advance and designing for them specifically will always result in a
more comfortable occupant. And it can be as simple as adding terminal reheat, radiant floor heating, a fan
powered VAV or even a separate small water source heat pump to critical area.
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.