Modulating outdoor/return air dampers
Two-position valve operation
The Tracer ZN521 supports two-position valves with a single binary out- put for each valve. Controllers used for two-pipe applications support heating, cooling, or heat/cool changeover with a single valve/coil. Control- ler used for four-pipe applications support cooling or heat/cool changeover with a main valve/coil, and heating only with an auxiliary valve/coil.
Isolation-valve operation
See “Face-and-bypass damper operation” on page 46.
Two-pipe operation
For two-pipe applications, the Tracer ZN521 can be configured as heating only, cooling only, or heat/cool changeover. The coil can be used as the pri- mary heating source and/or the primary cooling source. If present, an electric heating element can be used only as the primary heating source (instead of hydronic or steam heating). A changeover unit requires a valid entering water temperature value—either communicated or hard-wired— to operate properly (see “AI1: Entering water temperature” on page 17 and “Entering water temperature sampling function” on page 40).
Four-pipe operation
For four-pipe applications, the Tracer ZN521 can be configured as heat/ cool or heat/cool changeover. The main coil can be used as the primary cooling source or the primary heating/cooling source. The auxiliary coil can be used only as the primary heating source, not as a second stage of heating. During normal operation, the controller never uses the main coil and auxiliary coil simultaneously. A changeover unit requires a valid entering water temperature value—either communicated or hard-wired— to operate properly (see“AI1: Entering water temperature” on page 17 and “Entering water temperature sampling function” on page 40). Elec- tric heat control is not available on four-pipe applications.
Modulating outdoor/return air dampers
The Tracer ZN521 operates the modulating outdoor/return air dampers according to the following factors:
•Occupancy mode
•Outdoor air temperature (communicated or hard-wired sensor)
•Zone temperature
•Setpoint
•Discharge air temperature
•Discharge air temperature setpoint
The minimum position for an outdoor air damper is configurable using the Rover service tool for occupied and occupied standby modes and for
