Chapter 8 Sequence of operations for the heat pump configuration
60 CNT-SVX12C-EN
from cooling to heating or vice versa) is initiated. The reversing-valve
operation is delayed after compressor shutdown to reduce noise due to
refrigerant migration. The reversing valve will de-energize when a power
failure occurs, or when the controller is set to off either through a commu-
nicated off signal or when the fan switch is set to
OFF.
Economizing
Economizing (also referred to as “free cooling”) uses outside air for cool-
ing. The Tracer ZN517 provides two triac (3-wire floating point) outputs
to control the damper actuator. One output opens the actuator; the other
closes it. The controller also provides analog inputs for both a discharge
air temperature sensor and an outside air temperature sensor. While
economizing is enabled, the controller uses a discharge air temperature
(DAT) control loop to maintain proper temperature control. The controller
opens the outside air damper, turns on the fan, and attempts to maintain
a user-defined discharge air temperature. If the outside air is unsuitable
for economizer operation, the outside air damper will close and normal
operation (DX cooling) will be activated. Economizing plus DX cooling is
initiated only when economizing alone cannot meet the zone’s cooling
requirements.
To enable this function, set DIP switch 3 to
ON (see “DIP switch settings”
on page 48).
Discharge air tempering
Discharge air tempering (also called supply air tempering) prevents occu-
pant discomfort caused by cold outside air being brought into a space
through the outside air damper. This is an important feature in cold cli-
mates because the outside air damper is never fully closed for ventilation
purposes. Discharge air tempering starts when:
• The controller is in heating mode.
• The space is otherwise satisfied (no heating or cooling required).
• Ventilation air is passing through the unit
• The discharge air temperature falls 10°F (5.6°C) below the occupied
heating setpoint.
Tempering stops when the occupied heating setpoint is exceeded. To
enable this function, use the Rover service tool to select Supply Air Tem-
pering Enabled.
Demand control ventilation
The Tracer ZN517 unitary controller modulates the outside air damper
position in direct response to the CO
2
level, regulating the amount of out-
door air allowed to enter. This function is referred to as demand control
ventilation. Demand control ventilation requires that the two triac (3-
To Next Page
Loading...
