CCU VAV System Profile - Sequence of Operation

| Description of Equipment

The CCU VAV System profile is a system-level equipment (AHU/ RTU) controller that provides heating and cooling equipment controls for conditioning.

Following are the system-level profiles that are available under the VAV

• VAV Staged RTU
• VAV Fully Modulating AHU
• VAV Staged RTU with VFD Fan
• VAV Advanced Hybrid AHU

The profile can be selected and used based on the type of equipment controlled.

| Schematics

VAV Staged RTU

 

VAV Fully Modulating AHU

 

VAV Staged RTU with VFD Fan

 

VAV Advanced Hybrid AHU

 

 

| Control System Object List

Object Name	Type	Input/Output Type
Current Temp	Input (Terminal Side)	Average Current Temperature of Zones
Humidity	Input (Terminal Side)	Average Humidity of Zones
Zone Base Priority	User Intent (Terminal Side)	NA
zonePriorityMultiplier	Tuner	NA
zonePrioritySpread	Tuner	NA
coolingSATMinimum	Tuner	NA
coolingSATMaximum	Tuner	NA
Cooling Desired Temperature	User Intent (Terminal side)	NA
Heating Desired Temperature	User Intent (Terminal side)	NA
Conditioning Mode	User Intent	NA
Operation Mode	Calculated Input	NA
Fan Mode	User Intent	NA
Occupancy Mode	Input	Schedule / Terminal OWI Sensors
Cooling Stage 1	Output	Control Mote Relay
Cooling Stage 2	Output	Control Mote Relay
Cooling Stage 3	Output	Control Mote Relay
Cooling Stage 4	Output	Control Mote Relay
Cooling Stage 5	Output	Control Mote Relay
Heating Stage 1	Output	Control Mote Relay
Heating Stage 2	Output	Control Mote Relay
Heating Stage 3	Output	Control Mote Relay
Heating Stage 4	Output	Control Mote Relay
Heating Stage 5	Output	Control Mote Relay
Fan Speed 1	Output	Control Mote Relay
Fan Speed 2	Output	Control Mote Relay
Fan Speed 3	Output	Control Mote Relay
Fan Speed 4	Output	Control Mote Relay
Fan Speed 5	Output	Control Mote Relay
Modulating Cooling	Output	Control Mote AnalogOut
Modulating Heating	Output	Control Mote AnalogOut
Modulating Fan Speed	Output	Control Mote AnalogOut

| Sequence of Operation

The sequence of operation is completely driven based on Occupancy mode, and Zone Loads (Cooling/Heating). 

Let us understand the Sequence of operations based on the occupancy modes, and how the other factors contribute to the sequence of operations during different types of occupancy modes.

| Occupancy Modes

The occupancy mode (Occupied or Unoccupied) shall be determined through a user-adjustable, graphical, seven-day schedule with a holiday schedule.

Based on the above aspects factoring into the occupancy the following can be the possible applicable occupancy modes:

• Pre- Conditioning
• Occupied
• Unoccupied

| Sequence of Operation During Pre-Conditioning (a.k.a. optimal start)

Pre-conditioning is a state just before the building enters the scheduled occupancy. It starts at more like the unoccupied state, the desired temperatures drift to unoccupied setbacks.

The preconditioning uses an algorithm to start the conditioning before the building is scheduled for occupancy, from the heating side or cooling side, to bring the building to an optimum level (within the occupied heating & cooling desired temperatures) exactly at the time of occupancy start.

A coolingPreconditioningRate and heatingPreconditiningRate tuners defaulted to 15 minutes, are used alongside the occupied heating/cooling desired temperature breach to determine when the pre-conditioning should start.

Example Calculation:

When,

• • The heating & cooling desired temperatures (Average of zones needing conditioning) are 70F and 74F for the building.
  • The operating mode is determined based on the weighted average calculation as shown in section | Sequence of Operation During Occupied

Let us assume:

• • • The operating mode determined is cooling.
    • The current temperature (Average of zones needing cooling conditioning) is 76F
    • 8:00 AM is the time the building is scheduled to be occupied.

Then the preconditioning start time is calculated as follows:

Cooling Desired Temperature Breach= 76-74=2F

Preconditioning duration= coolingPreconditioningRate (mins) * Cooling Desired Temperature Breach

                                        = 15*2

                                        = 30 mins

The preconditioning starts 30 minutes before the building is scheduled to be occupied, which is = 7:30 AM.

The zones operate the damper positions optimally to receive the required conditioning to satisfy their load requirements to maintain a temperature within the deadband.

For more information on the damper operations, refer to VAV Terminal Profile- Damper Position Calculation & Operation

| Sequence of Operation During Occupied

During the scheduled Occupied times, the AHU/RTU is influenced by two aspects of the system.

• The Operating Mode
• The Conditioning Mode

Conditioning Modes

The Operating mode is a user intent parameter that the user can specify. There are four types of operating modes.

• Off
• Auto
• Cooling
• Heating

Operating Modes

The Conditioning mode is a derived parameter. There are three types of conditioning modes.

• Cooling
• Heating
• Off

Based on the influence of the aspects mentioned above, the device supplies the cooling/ heating load requirements, and the zones operate the damper positions optimally to receive the required conditioning to satisfy their load requirements and maintain a temperature within the deadband.

For more information on the damper operations, refer to VAV Terminal Profile- Damper Position Calculation & Operation

Weighted Average Load MA (Heating /Cooling)

weightedAverageHeatingOnlyLoadMA/ weightedAverageCoolingOnlyLoadMA,  is a result of the following steps.

Step	Formula/Calculation
Heating Load/Cooling Load	When the zone's current temperatures fall below the HeatingDesiredTemperatures they contribute to the zone heating load zoneHeatingLoad= zoneTargetTemperature- currentTemperature zoneCoolingLoad= currentTemperature- zoneTargetTemperature
Dynamic Priority (Heating/Cooling)	zoneDynamicPriority = zoneBasePriority*((zonePriorityMultiplier )^(zoneCoolingLoad/zonePrioritySpread)),  zoneDynamicPriority = zoneBasePriority*((zonePriorityMultiplier )^(zoneHeatingLoad/zonePrioritySpread)),  Note: The exponent (zoneHeatingLoad/zonePrioritySpread) or (zoneCoolingLoad/zonePrioritySpread) will be limited to the max value of 10. This will prevent a zone with large temperature drift (probably because of faulty sensors) from driving system operation.
Weighted Average (Heating/Cooling)	weightedAverageHeatingOnlyLoad= ((zone1HeatingLoad*zone1DynamicPriority + zone2HeatingLoad*zone2DynamicPriority … )) /(zone1DynamicPriority + zone2DynamicPriority…) weightedAverageCoolingOnlyLoad= ((zone1CoolingLoad*zone1DynamicPriority + zone2CoolingLoad*zone2DynamicPriority … )) /(zone1DynamicPriority + zone2DynamicPriority…)
Weighted Average Post ML (Machine Learning) (Heating/Cooling	weightedAverageHeatingOnlyLoadPostML = weightedAverageHeatingOnlyLoad + buildingLoadOffsetML  weightedAverageCoolingOnlyLoadPostML = weightedAverageCoolingOnlyLoad + buildingLoadOffsetML
Weighted Average MA (Moving Average) (Heating/Cooling)	weightedAverageHeatingOnlyLoadMA = weightedAverageHeatingOnlyLoadPostML weightedAverageCoolingOnlyLoadMA = weightedAverageCoolingOnlyLoadPostML is then put through a 15-minute moving average filter (which takes the last 15, minute readings and then averages them) to reduce sudden swings to get the weightedAverageLoadMA)

 

Operating Mode Determination 

Conditioning mode is determined using the following table:

If	Then
weightedAverageCoolingOnlyLoadMA is zero and weightedAverageHeatingOnlyLoadMA is positive.	Heating conditioning mode is enabled via HeatingLoopOutput which uses the weightedAverageHeatingOnlyLoadMA as the process variable and Zero as the control variable, to give an output that ranges from 0-100%, to provide the heating load requirements for the zones, with staged/modulating controls. The FanLoopOutput is enabled based on the HeatingLoopOutput using the formula FanLoopOutput= HeatingLoopOutput*AnalogFanSpeedMultiplier.
weightedAverageHeatingOnlyLoadMA is zero. weightedAverageCoolingOnlyLoadMA is positive.	Cooling Conditioning mode is enabled The systems operate as per Guideline 36: High-Performance Sequence of Operations for HVAC systems. The Guideline 36 uses a Trim and Response to calculate the Supply Air Temperature (SAT). For more information refer to the following articles: Trim & Respond Logic How are Trim & Respond Requests Generated in a VAV zone? Damper Position & Zone Priority Driven Trim and Respond Requests The calculated SAT value is mapped between the coolingSATMinimum and coolingSATMaximum tuners to generate systemCoolingLoopOutput which varies from 0 -100% to provide the cooling load requirements for the zones, with staged/modulating controls. The FanLoopOutput on the cooling side is enabled according to Guideline 36; High Performance Sequence of Operations for HVAC systems The Guideline 36; High Performance Sequence of Operations for HVAC systems uses a Trim and Response to calculate the System Pressure. For more information refer to the following articles. Trim & Respond Logic How are Trim & Respond Requests Generated in a VAV zone? Damper Position & Zone Priority Driven Trim and Respond Requests
weightedAverageHeatingOnlyLoadMA is zero. weightedAverageCoolingOnlyLoadMA is zero.	The system is within the deadband, there is neither a cooling load nor a heating load, hence there is no conditioning that occurs at the AHU end, except for a minimum mechanical or free ventilation.

| Sequence of Operation During UnOccupied

• The range of Heating Desired Temperature and Cooling Desired Temperature of the zones drifts further away to unoccupied setback.
• The device supplies for the cooling/Heating load requirements of the zones, and the zones operate the damper positions optimally to receive the required conditioning to satisfy their load requirements to maintain the room temperature within the newly set autoaway setback temperature range, for more information on the damper operations refer to VAV Terminal Profile- Damper Position Calculation & Operation
• If weightedAverageHeatingOnlyLoadMA/ weightedAverageCoolingOnlyLoadMA, is a positive value. The system operates in the determined conditioning mode to supply the zone cooling/heating load requirements, as shown in the | Sequence of Operation During Occupied
• If weightedAverageHeatingOnlyLoadMA & weightedAverageCoolingOnlyLoadMA, is zero. The system is within the deadband, there is neither a cooling load nor a heating load, hence there is no conditioning that occurs at the AHU end, except for a minimum mechanical or free ventilation.
•  

| Sequence of Operation During Emergency Conditioning

When zone limits are violated, and the recorded temperature is within the zone limit plus leeway the conditioning will happen in the direction of zone load, as shown in the cooling conditioning, or Heating conditioning mode.

| Sequence of Operation Zone Temp Dead

And, When the zone temperature breaches the zone limits, beyond the leeway limits all the following loops are disabled:

• • CoolingLoopOutput
  • HeatingLoopOutput
  • FanLoopOutput

| Operation Mode Summary

Modes &  Operation	Pre-Conditioning	Occupied	Unoccupied
Auto	HeatingLoopOutput FanLoopOutput CoolingLoopOutput FanloopOutput	HeatingLoopOutput FanLoopOutput CoolingLoopOutput FanloopOutput	HeatingLoopOutput FanLoopOutput CoolingLoopOutput FanloopOutput
Heat Only	HeatingLoopOutput FanLoopOutput	HeatingLoopOutput FanLoopOutput	HeatingLoopOutput FanLoopOutput
Cool Only	CoolingLoopOutput FanLoopOutput	CoolingLoopOutput FanloopOutput	CoolingLoopOutput FanLoopOutput
Off	All Loops Deactivated