Introduction to Regulation

TECH controllers can be divided into three groups according to their blow control output signal:

Discrete output signal regulators (two-positional - on/off);
after reaching the setpoint temperature by the boiler, the blow is disabled; when the temperature drops below the setpoint plus the hysteresis, the fan is reenabled by the controller. Blow value can be adjusted with the regulator. The drawback of this type of regulation is temperature oscillation around the setpoint value. This is especially important in the case of substantial thermal inertia of the heated building.

Discrete output signal regulators (two-positional - on/off) with Sigma regulation. When approaching the setpoint temperature on the boiler, the fan speed is gradually reduced by the controller, and after reaching the setpoint value, the blow is disabled. Temperature drop below the setpoint value is followed by the blow being enabled initially with lower value. If the temperature continues to drop, fan speed is gradually increased by the regulator. Oscillation around the setpoint value is milder. Overregulations are of lower values. Naturally, the course of the whole process depends also on the thermal dynamics of the building.

Continuous output signal ZPID regulators (with PID algorithm). Here, the blow rate is calculated using a boiler temperature measurement and a flue gas temperature measurement at the boiler outlet. The fun runs without stops and the blow rate depends directly on the measured temperature of the boiler, flue gas temperature and the difference between those parameters and their setpoint values. Advantages of ZPID regulators include their ability to maintain a stable setpoint temperature without unnecessary overregulations and oscillations. Heat is not disposed of through the chimney. Thus, fuel costs can be reduced by several percent. It is important to fit a proper fan.

Research results presented below are based on a charging boiler with a discrete output signal regulator (two-positional - on/off) and a ZPID regulator.

Curve for boiler operation with a ST-81 controller

Wykres obrazujący pracę kotła ze sterownikiem ST-81

ST 81 controller with a hysteresis of two degrees of Celsius. Oscillations around the setpoint value that are typical for the two-positional regulation. If the boiler is too slow to respond to temperature changes, the upper or lower deviation from the setpoint value may be to high. However, to deem this control unusable in such applications in central heating boilers would be an exaggeration. In most cases, the regulators are functional enough to control the heating process in buildings and their temperature control accuracy is satisfactory.

Curve for boiler operation with a ST-81 ZPID controller

Wykres obrazujący pracę kotła wyposażonego w sterownik ST-81 zPID

ST-81 ZPID controller. The curve shows the first overregulation after the boiler has been fired up. Subsequently, the regulator manages to maintain the setpoint temperature of the boiler. Regulation is accomplished smoothly and the measured temperature does not deviate from the setpoint value despite instability in the controlled central heating boiler and the heated building itself. The feeder and return temperature curve below shows the temperature of flue gases, measured at the boiler outlet. Flue gas temperature is another parameter, next to setpoint temperature, used in regulation.