Building HVAC (Equipment w/Factory-Installed Controls)
40 Series Unit Ventilators
Unit Ventilator -Sequence of Operation
Note: The following is a sample of a typical Sequence of Operation that may be adapted for a particular project. This is provided as a suggestion on how to write a Sequence of Operation for a specific project. The Unit Ventilator includes the ability for the operator to select some different sequences. Consult your Carrier representative if the sample sequence requires alterations.
4.2.6 Unit Ventilator (UV) - Product Integrated Control (PIC), Sequence of Operation
A. Description:
Two-Pipe Heating and Cooling Damper Control.
B. General:
Unit Ventilator includes factory mounted and wired application specific controller.
C. Sequence of Operation Occupied:
1. Occupied or Tenant Override Operating Mode:
The supply fan shall run continuously during the occupied or tenant override modes.
2. Morning Warm-up:
If the space temperature is below the Occupied Heating Setpoint, the unit shall operate in the “Occupied Heating Mode” as described below. The outdoor air damper shall remain closed if a Warm-up Temperature Check has been enabled and the space temperature is below the occupied heating alarm setpoint (65°F). After the space temperature rises above this limit, the damper operation shall be determined by the selected ASHRAE cycle. If Cycle I operation is selected, the damper shall be opened to provide 100% Outdoor Air. Cycle II operation shall cause the damper to modulate open and maintain the ventilation setpoint, while Cycle III operation shall provide a damper position which shall maintain the mixed air temperature at the desired ASHRAE Cycle III damper setpoint temperature.
3. Morning Start-Cooling:
If the space temperature is above the Occupied Cooling Setpoint, the unit shall operate in the “Occupied Cooling Mode” as described below. If Cycle II operation is selected and outdoor air is suitable for cooling, the damper shall be modulated to maintain the space temperature at the midpoint between the heating and cooling setpoints in order to minimize the need for mechanical cooling or heating.
4. Occupied Heating Mode:
If the space temperature falls below the heating setpoint and the changeover input has enabled heating, the Face and Bypass (F&B) damper shall modulate as required to maintain the heating setpoint. Whenever the damper moves from the full bypass position, the water valve shall be driven fully open by its valve actuator motor. The damper shall be controlled to prevent the discharge air temperature from rising above 140°F at any time. During heating, the fan shall operate at the lowest speed necessary to meet the space load conditions, and to minimize fan noise. If the load increases, the fan speed shall increase. When the load decreases and the space temperature rises, the fan speed shall be reduced. If the space temperature rises further, above the heating setpoint, the F&B damper shall move to the full bypass position and the heating valve shall be driven closed.
If Cycle II operation is selected, the outdoor air damper position shall modulate its position so as to provide the required ventilation at the current fan operating speed.
5. Occupied Cooling Mode:
If the space temperature rises above the cooling setpoint, and if the changeover input has enabled Cooling, the F&B damper shall modulate as required to maintain the cooling setpoint. Whenever the damper moves from the full bypass position, the water valve shall be driven fully open by its valve actuator motor. During cooling, the fan shall operate at the lowest speed necessary to meet the space load conditions, and to minimize fan noise. If the space load increases, the fan speed shall increase to meet the load as required. When the load decreases and the space temperature falls, the fan speed shall be reduced. If the space temperature falls further, below the cooling setpoint, the F&B damper shall move to the full bypass position and the water valve shall be driven closed.
6. Dehumidification:
If the relative humidity increases above the humidity setpoint, and the cooling mode is active, the F&B damper shall move to the full coil face position, and the fan shall operate at low speed.
7. Outdoor Air Damper Operation:
A. ASHRAE Cycle I:
The outdoor air damper shall be positioned to admit 100% outdoor air whenever the unit is operating in any occupied or tenant override mode, after the Morning Warm-up Mode has been completed.
2 ASHRAE Cycle II:
The outdoor air damper shall be positioned to admit the required amount of outdoor air whenever the unit is occupied or in a tenant override mode, after morning warm-up has been completed, and the space temperature is below the midpoint between the heating and cooling setpoints or if the outdoor air is unsuitable for cooling. The actual damper position shall be modulated to provide the required ventilation at any fan operating speed. As the space temperature rises above the midpoint between the heating and cooling setpoints, and if the outdoor air is suitable for cooling (outdoor air temperature is less than the Economizer lockout temperature or the outdoor air enthalpy is Low), the outdoor air damper shall open to increase the amount of outdoor air for economizer cooling. As the amount of outdoor air increases above 80%, the fan speed shall be increased to high speed, maximizing the amount of outdoor air usable for free cooling and ventilation. If the outdoor air is or becomes unsuitable, the fan shall operate at low speed.
3 ASHRAE Cycle III:
The outdoor air damper shall be positioned to admit the amount of outdoor air necessary to maintain the desired ASHRAE Cycle III Damper Setpoint, after morning warm-up has been completed and if the outdoor air is suitable for cooling (outdoor air temperature is less than the Economizer lockout temperature or the outdoor air enthalpy is low).
8. IAQ Control Modes (ASHRAE Cycle II and Cycle III) Constant Ventilation:
During occupied periods, after Morning Warmup has been completed, the outdoor air damper minimum position shall be determined as required to maintain the desired ventilation setpoint. As outdoor air temperature decreases, the fan speed shall be increased, which increases the unit's airflow and reduces the percentage of outdoor air required to maintain the ventilation setpoint. The fan speed control shall maintain the lowest fan operating speed with a mixed air temperature above 55°F.
9. Demand Controlled Ventilation:
As the air quality of the space deteriorates and the value of the IAQ sensor exceeds the IAQ setpoint, the outdoor air damper minimum position shall be increased (damper opened) to increase ventilation. The outdoor air damper shall be modulated as necessary to maintain the desired IAQ setpoint. The maximum calculated IAQ damper position shall be automatically limited to prevent the mixed air temperature from falling below 50°F. If desired, an adjustable maximum IAQ limit (default 85%) shall also be used. During DCV operation, if the changeover input has enabled heating, the F&B damper shall modulate open as required in order to maintain the supply air temperature at 65°F, if heating or cooling is not required. Also, if the space temperature exceeds a high limit or falls below a low limit, or the space relative humidity exceeds the humidity setpoint, then the outdoor air damper shall maintain the normal minimum ventilation setpoint (ASHRAE II) or the desired mixed air temperature (ASHRAE III) until the space temperature and space humidity return to normal.
4 Unoccupied Operating Mode:
The outdoor air damper shall be closed and the fan shall be off except as specified below:
1. Unoccupied Fan Cycling:
If Unoccupied Fan Cycling has been selected, the fan shall start once an hour and shall operate for 1 minute to circulate the air in the space and provide better space temperature sensing. The actual start time for each unit shall be determined by its address.
2. Unoccupied Heating Mode:
The fan shall be energized when the space temperature falls 1°F below the unoccupied heating setpoint, and if the changeover input has enabled heating. The F&B damper shall open to the coil face position and the water valve shall be driven open by its valve actuator motor. The damper shall be controlled to prevent the discharge air temperature from rising above 140°F at any time. The fan shall operate at low speed unless the low speed is unable to raise the space temperature to the unoccupied heating setpoint. When the space temperature rises above the unoccupied heating setpoint, the F&B damper shall move to the coil bypass position, and the water valve shall close.
3. Unoccupied Cooling Mode:
The fan shall be energized when the space temperature rises 1°F above the unoccupied cooling setpoint, and if the changeover input has enabled cooling. The F&B damper shall open to the coil face position and the water valve shall be driven open by its valve actuator motor. The fan shall operate at low speed unless that speed is unable to lower the space temperature to the unoccupied cooling setpoint. When the space temperature falls below the unoccupied cooling setpoint, the F&B damper shall move to the coil bypass position and the water valve shall be driven closed. The fan shall be de-energized after 5 minutes.
4. Unoccupied Free Cooling:
If Unoccupied Free Cooling is enabled, the fan shall be energized when the space temperature is above the occupied cooling setpoint and if the outdoor air is suitable for cooling [(OAT is at least 8°F below SPT) and (OAT < Economizer Lockout Temperature (63°F, default)]. The outdoor air damper shall open. When the space temperature falls below the occupied cooling setpoint or if the outdoor air becomes unsuitable for cooling, the fan shall be de-energized and the outdoor air damper shall close.
5. Freeze Protection Safeties (All Modes)
To help protect against coil freezing when the fan is off, the control shall monitor the supply air temperature sensor and modulate the water valve to maintain the desired fan off value (55°F). If at any time the coil freeze detection (low limit thermostat) senses a temperature below its setpoint (38°F), its contacts shall close and the following actions will occur:
A. The outdoor air damper shall close
B. The fan shall stop
C. The water valve shall fully open
When the thermostat temperature rises and the contacts open, the unit shall return to normal operation.
D. Optional Features and Sequences
Linkage Thermostat Operation
When the unit is used with the optional Linkage Thermostat, local programming capability for occupied and unoccupied setpoint and local programming capability for both occupancy and holiday schedules shall be provided. Also tenant overrides, control of multiple units (up to 8) from a single thermostat, and a temperature compensated start feature shall also be provided.
The thermostat shall provide an LCD for a digital display of the space temperature, current heating and cooling setpoints and time. The unit's operating mode and the supply air temperature shall also be displayed. The thermostat shall also provide a single common network schedule for any number of units, broadcast time and holidays, and broadcast the value of a point common to the entire system (such as outdoor air enthalpy or changeover switch status).