1. Commonly used terms
1. Heat
Heat is a form of energy. If an object is heated, heat is absorbed; if it is cooled, heat is expelled. The SI unit is the joule (J).
Commonly used units: kJ (kilojoules), BTU (British Thermal Unit), kCal (kilocalories)
2. Refrigeration capacity
The heat taken away by the air-conditioning unit from the air-conditioned place per unit time. The SI unit is kW (kJ/s).
Commonly used units: kW (kilowatt), BTU/h (imperial unit), kCal/h (kilocalorie), RT (refrigeration tons)
3. Temperature
Temperature indicates how cold or hot a substance is.
The methods of expressing temperature are: ℃ (Celsius), ℉ (Fahrenheit), K (Kelvin) ℃=5/9 (℉-32) = K-273
4. Relative humidity
Relative humidity indicates how close the air is to saturation with water vapor.
Expression method: % (percentage)
5. Refrigerant
A circulating heat carrier that transfers heat from the high-temperature end to the low-temperature end in the refrigeration system.
Commonly used ones are: R22, R134a, R410A, R290, R717, R404A, etc.
6. Energy efficiency ratio
Energy efficiency ratio is an important indicator to measure the economic efficiency of air conditioning units.
Energy efficiency ratio = cooling capacity/power consumption
7. Sensible heat/latent heat
The heat that causes the temperature of an object to change is called sensible heat.
Heat that only changes the phase change state of an object without changing its temperature is called latent heat
8. Evaporation/condensation
Evaporation and condensation are phase changes that occur when refrigerant absorbs (releases) heat in the system.
The change of refrigerant from liquid to gas is called evaporation, absorbing heat from the surrounding environment;
The change of refrigerant from gaseous state to liquid is called condensation, and it releases heat to the surrounding environment.
9. Supercooling
The temperature difference between the refrigerant liquid and the saturated liquid at the same pressure is called subcooling, which is the difference between the refrigerant's condensation saturation temperature (corresponding value on the high-pressure gauge) and the liquid pipe temperature.
10. Superheat
The temperature difference between the refrigerant vapor and the saturated vapor at the same pressure is called superheat, which is the difference between the refrigerant's evaporation saturation temperature (corresponding value on the low-pressure gauge) and the return air temperature.
2. Basic principles
①Evaporation process: The refrigerant liquid evaporates under low pressure (low temperature) and becomes low-pressure vapor; the evaporator is a device that outputs cold energy. The refrigerant absorbs the heat of the object being cooled in the evaporator, thereby achieving the purpose of refrigeration.
②Compression process: increase the pressure of the low-pressure steam to high-pressure steam. The compressor compresses and transports the refrigeration steam, and creates medium and low pressure in the evaporator and medium and high pressure in the condenser. It is the heart of the entire system.
③The condensation process condenses high-pressure vapor into high-pressure liquid; the condenser is a device that outputs heat and discharges the heat absorbed by the refrigerant in the evaporator and the heat converted by the work consumed by the compressor to the cooling medium.
④ During the throttling process, the high-pressure liquid reduces its pressure and becomes low-pressure liquid again, returning to ① to complete the cycle. The throttle valve throttles and depressurizes the refrigerant and regulates the flow of refrigerant entering the evaporator.
1. Compressor: The heart and power of the refrigeration system, which has the function of compressing and driving the refrigerant of the refrigeration system.
2. Condenser and evaporator: The condenser transfers heat to the external environment, and the refrigerant gas is cooled and liquefied, causing the temperature of the external environment to rise. The evaporator absorbs heat from the external environment, and the refrigerant liquid vaporizes in it, reducing the temperature of the external environment.
3. Dry evaporator: In a dry evaporator, the refrigerant passes through the heat exchange tubes, and the cold water runs outside the high-efficiency heat exchange tubes. The heat exchange efficiency of such a heat exchanger is relatively low. [Source of this article: Refrigeration Encyclopedia Public Account], Its heat transfer coefficient is only about 2 times that of the bare tube, but its advantage is that it facilitates oil return and is relatively simple to control. The refrigerant filling amount is about 1/2 to 1 of the filling amount of the flooded unit. /3 or so.
4. Flooded evaporator: The operation mode of a flooded evaporator is exactly opposite to that of a dry evaporator. Cold water passes through the heat exchange tube, and the refrigerant completely immerses the heat exchange tube. After absorbing heat, it evaporates outside the heat exchange tube. There are many pin-shaped holes on the surface of the heat transfer tube of the flooded evaporator, [Source of this article: Refrigeration Encyclopedia Public Account], and there are spiral protrusions on the inner surface of the tube to enhance heat transfer on the cold water side. This high-efficiency heat transfer tube simultaneously enhances boiling outside the tube and heat transfer inside the tube, improving the heat transfer coefficient.
5. Throttling mechanism: The high-pressure refrigerant coming out of the condenser is decompressed and cooled through the expansion valve, so that the refrigerant temperature is lower than the ambient temperature, so that the air conditioning unit has the ability to cool. Currently, commonly used throttling devices are: thermal Expansion valve, orifice plate, capillary tube, manual expansion valve, electronic expansion valve.
6. Expansion valve function: It controls the superheat of the refrigerant at the evaporator outlet to ensure that the evaporation area of the evaporator is fully utilized and prevents compressor cylinder flushing accidents.
7. Classification of thermal expansion valves: Thermal expansion valves are divided into structural types: integral type and assembled type. Pressure balance methods can be divided into: internal balance and external balance methods. According to the flow direction of working fluid, it can be divided into: one-way and two-way.
8. Four-way valve: The four-way valve is an important component in the air conditioner and plays a role in changing the flow direction of the refrigerant in the air conditioning system.
9. Gas-liquid separator: The gas-liquid separator can be installed at the inlet and outlet of the gas compressor for gas-liquid separation.
10. Liquid reservoir: The liquid reservoir plays the role of storage, gas-liquid separation, filtration, silencer and refrigerant buffering.
11. Solenoid valve: When the power is on, the solenoid coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; when the power is off, the electromagnetic force disappears, and the spring presses the closing member on the valve seat, and the valve closes.
