1. The principle of central air conditioning thermostat
Mechanical thermostats can be divided into vapor pressure thermostats, liquid expansion thermostats, gas adsorption thermostats and metal expansion thermostats. Among them, the vapor pressure thermostat is divided into inflatable type, liquid-gas mixed type and liquid-filled type. Household air conditioners are mainly based on this type of thermostat.
When the vapor pressure thermostat is working, the action of the bellows acts on the spring, the elastic force of the spring is controlled by the knob on the control board, and the capillary tube of the pipe wooden tray is placed at the air outlet of the indoor air conditioner to inhale the air, which reacts to the temperature of the indoor circulating return air.
When the room temperature rises to the set temperature, the thermostat gas in the capillary tube and the bellows expands, so that the bellows elongates and overcomes the elastic force of the spring to connect the switch contacts, at this time the compressor runs and the system is refrigerated, until the room temperature drops to the set temperature, the thermostat gas shrinks, the bellows shrinks and the spring acts together, the switch is placed in the disconnected position, and the motor circuit of the compressor is cut off. In this way, the action is repeated to achieve the purpose of controlling the temperature of the room.
The electronic type is divided into resistive thermostats and thermocouple thermostats.
The electronic temperature controller (resistive type) is measured by the method of resistance temperature sensing, and generally uses platinum wire, copper wire, tungsten wire and semiconductor (thermistor, etc.) as the temperature measurement resistor, which has its own advantages and disadvantages.
Most of the sensors in household air conditioners are thermistors. Therefore, when composing a thermostat, the temperature regulation range and operating temperature can be easily changed by selecting the appropriate thermistor.
2. Classification of central air conditioning thermostats
1. Steam pressure central air conditioning thermostat
The action of the bellows in the vapor pressure central air conditioning thermostat acts on the spring, the elastic force of the spring is controlled by the knob on the control board, and the capillary is placed at the air outlet of the indoor air conditioner to inhale the air at the air conditioner, which reacts to the temperature of the indoor circulating return air. When the room temperature rises to the set temperature, the thermostat gas in the capillary tube and the bellows expands, so that the bellows elongates and overcomes the elastic force of the spring to connect the switch contacts, at this time the compressor runs and the system is refrigerated, until the room temperature drops to the set temperature, the thermostat gas shrinks, the bellows shrinks and the spring acts together, the switch is placed in the disconnected position, and the motor circuit of the compressor is cut off. In this way, the action is repeated to achieve the purpose of controlling the temperature of the room.
2. Mechanical central air conditioning thermostat
Mechanical central air conditioning thermostats are used in commercial, industrial and civil buildings. It can control the fan coil unit and water valve at the end of the central air conditioner for heating and cooling. Keep the ambient temperature of the controlled place constant within the set temperature range. The temperature setting dial pointer should be set to the desired constant temperature position. The functions of the pull switch are as follows: power switch (ON - off OFF); Operation mode switch (heating HEAT - air conditioning COOL), FAN wind speed switch (low speed L - medium speed M - high speed H). Controllable equipment: three-speed fan coil unit wind speed, three-wire electric valve, two-wire electric valve, can also be connected to solenoid valve, on-off damper or three-wire damper.
3. Electronic central air conditioning thermostat
The electronic central air conditioning thermostat (resistance type) is measured by the method of resistance temperature sensing, generally using platinum wire, copper wire, tungsten wire and semiconductor (thermistor, etc.) as the temperature measurement resistance, these resistors have their own advantages and accuracy. Most of the sensors in household air conditioners are thermistors. The thermistor thermostat is made according to the Wheatstone bridge principle, according to Kirchhoff's law, when the resistance of the bridge R1×R4=R2×R3, the potential of A and C is equal, there is no current flowing between the output A and C, and the size of the impedance R1 of the thermistor changes with the rise or fall of the surrounding temperature, so that the balance is destroyed, and there is an output current between AC. Therefore, when composing a thermostat, the temperature regulation range and operating temperature can be easily changed by selecting the appropriate thermistor.
3. Precautions for the use of central air conditioning thermostats
01
The wiring must be operated according to the correct wiring diagram, and do not allow water, mud, dust and other magazines to be mixed into the thermostat, otherwise the parts will be damaged.
02
The output control power of the thermostat is related to the safety and stability of use, and may cause serious consequences if not selected properly. Thermostat products are marked with output control voltage and current, multiply the output control voltage and current to get the output control power. The operating power of the controlled equipment must be less than the output control power of the thermostat. Otherwise, the thermostat will be damaged, and in serious cases, it will cause a fire!
03
It is desirable that there is free-flowing air around the area where the thermostat is installed and that the temperature is stable. Also avoid installing the thermostat in a place with direct sunlight, and when the interior is being renovated, it is best not to install the thermostat first.
04
Some brands of thermostats support multi-voltage input central air conditioning thermostats, and it is necessary to ensure that the input voltage and the allowable input voltage are consistent. Another point to be put forward is that some thermostats do not support DC on/off, or the DC voltage that can be turned on and off is small, so you should consult with the merchant clearly when buying a thermostat to avoid unnecessary trouble.
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