### Zone Controller The information below provides a FULL description of this microblock and all of its properties. What information you see and what you can do with it depends on your license and the application you are in, and in some cases, a controller's driver version.
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What it does | Provides stable temperature control of a single-zone heating and cooling system using 2 modified PID control loops. 2 non-linear PID loops (direct-acting for the cooling output and reverse-acting for the heating output) make fine-tuning corrections when the system is near setpoint and larger corrections when the setpoint or the load changes and the system needs to adjust quickly. The microblock also optimizes performance in the night setback and morning start-up modes.
Click for details below How it works Limitations Inputs and outputs Properties Programming example
#### How it works A patented, modified PID algorithm provides responsive, stable control and reduces overshoot in zone control applications. When the zone is unoccupied, the algorithm uses proportional-only control with a large gain and bias, providing on/off zone heating and cooling control to minimize unoccupied run time and to maximize efficiency. For example, if the temperature drops below the unoccupied heating setpoint, the algorithm calls for 100% heating. It maintains a 100% output until the zone temperature rises approximately 1 degree above setpoint, then turns off heating and remains inactive unless the temperature exceeds the unoccupied setpoint. When the zone is occupied, the algorithm compares the zone temperature to the setpoint and uses the Maintain Setpoint ± limit to determine its response. When the zone is occupied and the zone temperature deviates from the heating or cooling setpoint by 75% of the Maintain Setpoint ± limit, the algorithm calls for 100% heating or cooling to quickly bring the zone back to setpoint. A ± 1° limit provides excellent control in most situations. Increase this limit if the system begins to cycle. EXAMPLES If a zone's cooling setpoint is 74 °F, Maintain Setpoint ± 1 calls for full cooling when the temperature reaches 74.75 °F. If a zone's heating setpoint is 70 °F, Maintain Setpoint ± 1 calls for full heating when the temperature reaches 69.25 °F. When the algorithm calls for 100% heating or cooling, it uses the integral correction term's value to determine how much to add to the integral correction at each interval until the zone temperature returns to within 75% of the Maintain Setpoint ± limit. This strategy ensures that when the temperature returns closer to setpoint, the microblock's output is close to the value needed to keep it there. When the zone is occupied and the zone temperature is within 75% of the Maintain Setpoint ± limit, the algorithm uses a low proportional gain and adds a fixed integral correction in each interval where the zone temperature departs from the setpoint or remains constant. In each interval where the zone temperature moves toward the setpoint, the algorithm subtracts the fixed integral correction. This strategy gives faster response and better stability in HVAC zone applications than traditional PID control.
#### Limitations This microblock is designed for zone comfort control applications such as a VAV box, unit ventilator, or single-zone AHU. Internal gains and sampling rates optimized for zone temperature control may not be compatible with other applications. Heating and cooling setpoints must be at least as far apart as the value of the Maintain Setpoints ± property, and unoccupied setpoints must be farther apart than occupied setpoints. The control algorithm assumes a continuous zone temperature. Discontinuities in temperature do not happen in real-world systems, but they can easily occur when you simulate a control program.
#### Inputs and outputs Inputs
OCC Occupied | True (on) when the zone is occupied. Not true (off) when the zone is unoccupied. Connect to a time clock microblock or to other logic that indicates the zone's occupancy status.
FOR Remaining Time | Minutes remaining until the zone's occupancy status changes. Connect to a time clock microblock or to other logic that indicates this time.
ZONE Zone Temp | Current zone temperature (degrees).
HTSP Heating Setpoint | Heating setpoint (degrees). Connect to a setpoint microblock's HT output or to other logic that indicates the zone's heating setpoint.
CLSP Cooling Setpoint | Cooling setpoint (degrees). Connect to a setpoint microblock's CL output or to other logic that indicates the zone's cooling setpoint.
Outputs
CLG% Cooling % | (0–100%) Amount of cooling required. Connect to the Airflow Control microblock's Cooling % input or to another Output microblock that can send the signal to the cooling system. You can also use this output to trigger cooling requests to the air handling unit.
HTG% Heating % | (0–100%) Amount of heating required. Connect to the Airflow Control microblock's Heating % input or to another Output microblock that can send the signal to the heating system. You can also use this output to trigger heating requests to the air handling unit.
#### Properties TIPS Alt+click any value in the WebCTRL® or Field Assistant interface to view property details, including its editing privilege and expression (location path) for use on graphics. You can right-click some properties in the EIKON® Property Editor and select Make editable or Make read-only to determine that property's functionality in your system.
Reference Name RefName | Use the default reference name unless you want a more descriptive name for graphics or network links. Limitations: lower case only limited to 40 characters cannot begin with a number must be unique within a control program
Editing Privilege | Preset - Each microblock property has an appropriate privilege or role assigned to it. You can use Global Modify in the WebCTRL® interface to find out what the actual privilege is. CAUTION If you change the Editing Privilege from Preset, the privilege you select will be used for all properties of this microblock, which is not always desirable.
Cooling Loop Gain | (1 - 5). Speed of the integral action relative to the proportional action when the system is in a cooling mode. If the system begins cycling, decrease this value.
Heating Loop Gain | (1 - 5). Speed of the integral action relative to the proportional action when the system is in a heating mode. If the system begins cycling, decrease this value.
Maintain Setpoints ± | Control range (degrees). The microblock calls for 100% heating or cooling when the zone temperature exceeds the setpoint by 75% of this limit. See "How it works" in this microblock's help. If the system begins cycling, increase this value.
Property Page Text
Show Property Page Text | Check to show this microblock's value on the equipment's Properties page.
Property Page Text | You can edit the microblock description that appears on the Properties page. See "Editing Properties page text using special characters" and "Formatting a microblock property" in EIKON® Help.
#### Programming example This simple VAV application has no fan and no auxiliary heat in the zone.