Sequence of Operation
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Integration Guide All rights reserved
22
can be adjusted to meet various specifications.
For DX cooling, there is a 5-minute minimum off-time for the compressor as well as a 4-minute minimum on-time
to prevent oil migration.
After a compressor is staged off, it may be restarted again after a normal time-guard period of 5 minutes and if
the supply air temperature increases above the minimum supply air temperature limit.
Modulating Chilled Water - The control can operate a modulating (0-10 Vdc) type, NO or NC, chilled water valve
connected to the cooling coil of the unit in order to maintain the desired cooling setpoint. The valve modulates to
maintain the SAT at the calculated Cooling Control Setpoint. The control also prevents the SAT from exceeding the
Minimum Cooling SAT limit.
2- Position Chilled Water - The control can operate a 2-position, NO or NC, chilled water valve connected to the
cooling coil of the unit to maintain the desired cooling setpoint. The valve is controlled so the SAT does not exceed
the Minimum Cooling SAT limit.
Single Stage Direct Expansion (DX) - The control can operate a single stage of DX cooling in order to maintain the
desired cooling setpoint. The DX stage is controlled so the SAT does not exceed the Minimum Cooling SAT limit
and is subject to a 4-minute minimum on-time. The compressor output is not energized unless the SAT is >
Minimum Cooling SAT limit plus 15 °F (8.3 °C). Once disabled, the compressor cannot be restarted for at least
5 minutes.
Heating
The Fan Coil operates one stage of electric heat or a hot water valve (2-position or modulating) to maintain the
desired heating setpoint. The heating is controlled by the PI (Proportional-integral) heating algorithm. The desired
Supply Air Temperature setpoint [Heating Control Setpoint] is calculated by the Fan Coil. This setpoint is
compared to the actual supply air temperature and used to determine valve operation for modulating or 2-position
control valves or staging for electric heat.
The following conditions must be true in order for the cooling algorithm to run:
• Heat Enable is set to Enable.
• Space temperature reading is valid.
• For 2-pipe systems, the water temperature is suitable for heating.
• Cool mode is not active and, for electric heat, the 2-minute minimum off-timer has expired.
• Condensate Overflow input is Normal.
• OAT is less than the Heating Lockout Temperature if OAT is available.
• If occupied, the SPT is greater than the Occupied Cooling Setpoint.
• If unoccupied, the SPT is greater than the Unoccupied Cooling Setpoint.
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