| Overview
The VVT terminal profile follows the ClimaVision Proprietary Algorithm for its operation. The Damper position calculation for a VVT box at the terminal side contributes to the effective operation of the system-level equipment.
There are sequences in place to optimally drive the damper position calculations, leading to optimal usage of system-level equipment (AHU/RTU), achieving enhanced energy savings.
For more information on the influence of Damper positions on system-level equipment refer to VVT-C System Profile Logic & Tuners
| Possible Configuration
The VVT Terminal profile comes with four possible types of configuration and controls, which are as follows.
- Room temperature-based control
- Airflow CFM-based control
- Room CO2 level-based control
- Room VOC level-based control
Based on the site requirement, the building configuration can be modified, and the required controls can be opted for.
The Damper position calculation for different types of configurations and control is different.
| Damper Position Calculation for Room Temperature-based Control
The above configuration is a room temperature-based control. The VVT terminal sequences for the Damper position calculation for the same are like the example illustration below.
When the System is Cooling:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
The Damper position is scaled from the Min Damper Position Cooling to Max Damper Position Cooling configured values, based on the resultant Cooling Loop Output, which uses the current and Desired Cooling Temperatures. Example: Let us Assume the Cooling Loop Output signal is 80%, the same is translated to Damper Positions as
|
|
When the System is Heating:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
The Damper position moves to the Min Damper Position Cooling configured value, not allowing further hot air into the room.
|
The Damper position is scaled from the Min Damper Position Heating to Max Damper Position Heating configured values based on the resultant Heating Loop Output, which uses the current and Desired Heating Temperatures. Example: Let us Assume the Heating Loop Output signal is 60%, the same is translated to Damper Positions as
|
As a part of the adoption of visualizing information related the Airflow in CFM. At the portals end of the system, the following are made available:
In the VVT terminal profile, the user can track the airflow CFM setpoint in real-time against the actual CFM read from the DPS.
Also, In the VVT Terminal profile, the user can track effective DAT/DAT (Discharge Air Temperature setpoint against the CFM setpoint utilized by the airflow loop when the CFM is engaged. This is done by the logical points created in the CCU which can now be tracked on the portal using the widget.
| Damper Position Calculation for Room Temperature & CFM-based Control
The above configuration is a room temperature & CFM-based control. The DAB terminal sequences for the Damper position calculation for the same are like the example illustration below.
When the System is Cooling:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume the Cooling Loop Output signal is 80%, the same is factored to calculate the Airflow Setpoint as below:
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
Example: Let us Assume the Heating Loop Output signal is 20%, the same is factored to calculate the Airflow Setpoint as below:
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
When the System is Heating:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume the Cooling Loop Output signal is 20%, the same is factored to calculate the Airflow Setpoint as below:
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
Example: Let us Assume the Heating Loop Output signal is 80%, the same is factored to calculate the Airflow Setpoint as below:
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
- airflowCFMproportionalKFactor = 0.2
- airflowICFMntegralKFactor = 0.8
- airflowCFMintegralTime = 5
Note: In the system, edits to PI Loop related tuners such as proportionalKfactor, IntegralKfactor, temperatureProportionalRange, TemperatureIntegralTime, and any other PI related tuners made through the Internal Portal are consumed on the fly without the need for a restart. This seamless process ensures that the PI Loop restarts automatically with the updated tuner values. This is also applicable for the Trim and Response loop configuration.
In the VVT terminal profile, the user can track the airflow CFM setpoint in real-time against the actual CFM read from the DPS which is visualized in CCU and Portal using the available widget.
Also, In the VVT Terminal profile, the user can track effective DAT/DAT (Discharge Air Temperature setpoint against the CFM setpoint utilized by the airflow loop when the CFM is engaged. This is done by the logical points created in the CCU which can now be tracked on the portal using the available widget.
| Damper Position Calculation for Room Temperature & CO2/VOC based control
The above configuration is a room temperature, IAQ & CO2-based control. The VVT terminal sequences for the Damper position calculation for the same are like the example illustration below.
When the System is Cooling:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume there is a CO2 breach in the system
Example: Let us Assume the Cooling Loop Output is 80% system
|
Example: Let us Assume there is a CO2 breach in the system
|
When the System is Heating:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume there is a CO2 breach in the system
|
Example: Let us Assume there is a CO2 breach in the system
Example: Let us Assume the Heating Loop Output is 80% system
|
| Damper Position Calculation for Room Temperature & VOC based control
The above configuration is a room temperature, IAQ-based control. The VVT terminal sequences for the Damper position calculation for the same are like the example illustration below.
When the System is Cooling:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume there is a IAQ breach in the system
Example: Let us Assume the Cooling Loop Output is 80% system
|
Example: Let us Assume there is an IAQ breach in the system
|
When the System is Heating:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
Example: Let us Assume there is a VOC breach in the system
|
Example: Let us Assume there is a CO2 breach in the system
Example: Let us Assume the Heating Loop Output is 80% system
|
Note: When both CO2 and VOC are enabled for control, the highest breach percentage among both is considered for the minimum damper position, for the actual damper position calculation.
| Damper Position Calculation for Room Temperature, CFM, CO2 & VOC based control
In this configuration, the Damper Position calculation would have four calculation stages.
- The Breach percentage on the CO2& VOC breaches, as in the above section.
- The Breach Percentage translated to the new minimum cfm.
- The airflow set point calculation using the new minimum and maximum airflow cfm, and the temperature-based PI loop output.
- The CFM loop output calculation from the airflow set point and actual airflow, which is translated to the Damper position minimum and Maximum.
Note: When both CO2 and VOC are enabled for control, the highest breach percentage among both is considered for the minimum damper position, for the actual damper position calculation.
The considered Highest breach is used to calculate the minimum cfm.
And based on the below table the Damper positions operate.
When the System is Cooling:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
The Breach Percentage translated to the new minimum cfm.
The airflow set point calculation Let us Assume the Cooling Loop output signal is 80%, the same is translated to Airflow Setpoint as
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
The Breach Percentage translated to the new minimum cfm.
The airflow set point calculation Let us Assume the Cooling Loop output signal is 80%, the same is translated to the Airflow Setpoint as
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
When the System is Heating:
Zone/Room Demanding Cooling | Zone/Room Demanding Heating |
The Breach Percentage translated to the new minimum cfm.
The airflow set point calculation Let us Assume the Cooling Loop output signal is 80%, the same is translated to Airflow Setpoint as
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
The Breach Percentage translated to the new minimum cfm.
The airflow set point calculation Let us Assume the Cooling Loop output signal is 80%, the same is translated to the Airflow Setpoint as
For more information on the Measured CFM calculation refer to True CFM (Cubic Feet per Minute) VVT-C |
| VVT Advanced Terminal Logic
Now that you understand how the damper position at the zone level is calculated it's time to understand a few additional concepts that can affect the actual output position of the damper.
As a part of the advanced VVT terminal side logic, the algorithm uses two concepts that contribute to the effective operation of the system-level equipment.
Normalization Calculation Example:
Considering the 75% as the highest of the Damper position
Normalization % = (100- Maximum Damper Position)*(100/ Maximum Damper Position)
= (100-75)*(100/75)
=25*1.33
=33.33%
What would happen is you would add 33% of the actual Damper position to all damper positions to normalize them as follows:
- Normalized Damper position, for an actual Damper position 55% =((33.33*55)/100)+55=73.33%
- Normalized Damper position, for an actual Damper position 65% = ((33.33*65)/100)+65= 86.66%
- Normalized Damper position, for an actual Damper position 70% = ((33.33*70)/100)+70= 93.33%
- Normalized Damper position, for an actual Damper position 75% = ((33.33*75)/100)+70= 99.99%
Minimum Overall Damper Position:
Since VVT is installed on CAV systems and there is no implied pressure relief, the Minimum Overall Damper Position sequence is in place.
A way to keep the average damper opening from being lower than is typically safe.
The sequence involves a weightedDamperOpening calculation and a tuner targetCumulativeDamperOpening based on which the logic is influenced.
Calculation:
weightedDamperOpening = (Zone1_damperPosition*Zone1_damperSize + Zone1_damperPosition*Zone1_damperSize+etc..)/(Zone1_damperSize+Zone2_damperSize+etc..)
If weightedDamperOpening < targetCumulativeDamperOpening then add 1% to all damper positions until weightedDamperOpening > targetCumulativeDamperOpening
Zone Priority:
Zone priority is a concept of 75F which equates to the importance multiplier in guideline 36. The zone priority indirectly contributes to the importance of the zone, and based on this priority the demand from the AHU/RTU is influenced.
Zone Priority (zoneBasePriority) has 4 levels each with a numeric value. Zone priority is a value set by the user to give a relative ranking of importance for each zone.
- No Priority = 0
- Low Priority = 1
- Medium Priority = 10
- High Priority = 50
Zone Priority is the user setting, and zoneDynamicPriority is the actual zone priority used by the system and is important to understand.
Calculation:
zoneDynamicPriority = zoneBasePriority*((zonePriorityMultiplier)^(tempError/zonePrioritySpread))
Tuners:
zonePrioritySpread = default 2
zonPriorityMultiplier = default 1.3
Zone Priority Example:
Zone 1 temp is 76, and the desired temp is 70 with a default priority of medium.
zoneDynamicPriority= 10*(1.3^((76-70)/2)) = 21.97
Comments
0 comments
Please sign in to leave a comment.