Analysis of thermostatic controls common in today’s market: control 2 points with Hysteresis and Proportional Integral Control.
The success of achieving a proper air conditioning in a house or a building goes through the correct configuration of a thermostatic control system. This is done to combine comfort and energy efficiency.
Typical problems in controlling temperature
It is usual to enter homes where it is cold in summer and warm in winter. In energy terms, is an absolute waste, both in CO2 emissions due to excessive energy consumption and the outcome on the wallet at the end of the month. The problem is that the end user does not know most of the time, and not have to know, how efficient control. Hence emerging energy certifications and standards for homes and buildings, to ensure proper operation, such as LEED or KNX .
Instead, you can also find housing where it is cold in winter and hot in summer, due to irregular control, assuming a lack of user comfort. Another variant can be abrupt changes in temperature, from cold to hot and cold heat repeatedly unable to find the point of comfort. This behavior, referred to as “sawtooth” graph depicting the temperature, also implies a lack of comfort and energy waste due to peaks and variations.
Temperature control with hysteresis 2 Points
This type of control, oldest and most widely deployed in thermostats even today, can apply a control variable depending on temperature set point and actual temperature. In case you want to cool a room, the control variable activates the air conditioning system until the temperature drops below the set temperature selected by the user. By contrast, off the air conditioning system once it is below the set point and will only activate when the temperature returns to experience an increase above the set point. This behavior must be added the hysteresis. The aim of hysteresis is to prevent the activation / deactivation repetitive conditioning system due to the oscillation of the ambient temperature around the set point.
Therefore, the hysteresis, defined in degrees, adds a performance band around the set point. In the example given of cooling a room, the control variable will trigger the system to reach the set point set by the user, remaining well-defined hysteresis (set point minus hysteresis). Similarly, it will not activate the system until the room again to see increased its temperature above the set point plus the hysteresis (set point plus hysteresis). The greater the hysteresis, the higher the oscillation band and hence the greater the lack of comfort. This behavior accentuates the above effect “sawtooth”.
Proportional Integral Temperature Control
This type of control, more advanced, industrial control based on PID (Proportional Integral Derivative), but eliminating the derivative calculation, so it stays in PI (Proportional Integral). This system greatly reduces the effect of “sawtooth”, since in this case the control is not binary (on / off) but it is a percentage value (0-100%). Therefore, this system adjusts the percentage depending on the difference between the setpoint and the temperature. The closer is the setpoint, the lower the percentage value.
The name is because it depends on a proportional (direct difference between the temperatures) and integral (integral calculus of the accumulated error of approximation with respect to time). This means that you must specify the values K (proportional) and t (time) for each system. These values are directly dependent on the thermal inertia of the systems. An air system has a thermal inertia higher, while other systems, such as floor heating, have a thermal inertia lower. There is a method of “translation” of the PI control (0-100%) in a binary control, called PWM (Pulse Width Modulation, or Pulse Width Modulation).
Successfully perform a temperature control
It is essential that the air conditioning installations are carried out by experts with knowledge of the subject, to adjust the parameters required in the best way possible. The energy bill and the environment depend heavily on them, and in their hands is the reduced footprint of each dwelling.