Common Unit Conversion and Refrigeration Fundamentals

1. Work, energy, horsepower, cooling capacity

1 joule (j) = 1 watt (w) × 1 second (s)
(1) Energy unit:
National system: j, kj; British system: cal, kcal
1 j = 0.2388 cal
(2)Power unit:
National system: w, kw; British system: kcal/h (kilocalorie)
1 kcal/h = 1.163w
1 kw = 860 kcal/h
Commonly used units: horsepower (hp), refrigeration tons RT
1 HP = 735W
1 RT = 3.516 kw =3024 kcal/h

Note: Refrigeration tons: It is an imperial unit of refrigeration capacity. One ton of refrigeration is the amount of cooling required to freeze one ton of 0°C water into 0°C ice within 24 hours.
The United States uses 2,000 pounds (907.2kg) as one ton. Therefore, 1 US refrigeration ton = 12659 kj/h; that is: 1 RT = 3.516kw
(3) Relationship between horsepower and cooling capacity
In small air conditioning projects, 1HP refers to the cooling capacity that can be generated by inputting 735W of power to the compressor. The meaning is different from the general power unit. The 1HP here is calculated based on the energy efficiency ratio. Japan generally believes that the average energy efficiency ratio of air conditioning compressors is 3.4, and the cooling capacity generated by inputting 735W of electrical energy is 2500W.

2. Pressure
The vertical force exerted on unit area is called pressure (physically called pressure). The international unit of pressure is Pascal, referred to as Pa, expressed as Pa.
1 standard atmospheric pressure = 0.1MPa = 760mmHG mercury column;
1 atmosphere = 1.03323kg/cm2. pressure;
1MPA=10 atmosphere pressure=10.3323kg/cm2;
That is equivalent to a pressure of 10.332 kg/cm2;
1MPa=1000000 Pa=1.00N/square millimeter=(1/9.8) kilogram force/square millimeter.

3. Temperature
The most commonly used thermometers: mercury thermometer and alcohol thermometer. The temperature scales of thermometers generally include: Celsius temperature scale, Fahrenheit temperature scale (used in Europe and the United States) and absolute temperature scale.
1) Celsius temperature scale (°C): It is a temperature display system that uses the freezing point of pure water at one atmosphere as 0°C and the boiling point as 100°C. The two are divided into 100 equal parts and each part is set as 1°C.
2) Absolute temperature scale (K): The freezing point of water is set as +273.16K, the boiling point is set as 373.16K, and theoretically the point where the thermal motion of molecules inside the object completely stops is set as absolute zero, that is, 0 (K)).
The relationship between the Celsius temperature scale and the absolute temperature scale is as follows: T=t+273.16
3) Fahrenheit temperature scale (°F): The freezing point of water under standard atmospheric pressure is set as 32°F, and the boiling point is set as 212°F. There are 180 equal parts between the two, and each part is set as 1°F. It is widely used in European and American countries.
The following conversion relationships exist between Celsius and Fahrenheit:
t=5(F-32)/9;
F=9t/5+32;
In the formula:
t - temperature in degrees Celsius;
F - Fahrenheit temperature;
4) Dry bulb temperature and wet bulb temperature: The dry bulb temperature is the temperature measured by an ordinary thermometer. The wet bulb temperature is wrapped with a wet cloth on the thermometer. The temperature indication drops due to the evaporation of water. The temperature at this time is called the wet bulb temperature.

4. Heat, vaporization, liquefaction
The ways of heat transfer are: conduction, convection, and radiation.
Thermal convection: Thermal convection is the movement of heated liquid or gas to transfer heat; Thermal radiation: Thermal radiation is the emission and transfer of heat in the form of infrared rays.
Vaporization: The process by which a substance changes from a liquid to a gaseous state. Methods of vaporization: evaporation (surface vaporization), boiling (surface and interior vaporization at the same time). Measures to speed up vaporization: increase temperature and reduce surface pressure.
Liquefaction: The process by which a substance changes from a gaseous to a liquid state. Measures to speed up liquefaction: lower the temperature and increase the pressure.

5. Sensible heat and latent heat
Sensible heat (sensible cooling) load: heating a solid, liquid or gaseous substance. As long as its shape remains unchanged, after the heat is absorbed by it, the temperature of the substance will rise. The amount of absorbed heat can be displayed on the temperature. That is, the heat that does not change the shape of a substance but causes its temperature to change is called sensible heat.
Latent heat (latent cooling) load: When liquid water is heated, the temperature of the water rises. When it reaches the boiling point, although heat is continuously added, the temperature of the water does not rise and stays at the boiling point. The added heat only makes the water Turns into water vapor, that is, changes from liquid to gaseous state. This kind of heat that does not change the temperature of a substance but causes a change in the state of matter (also called a phase change) is called latent heat.
Total heat is equal to the sum of sensible heat and latent heat: sensible heat/total heat = SHR (sensible heat ratio).

6. Refrigeration/heat energy efficiency ratio refrigeration/secondary refrigerant
Refrigeration capacity: Refrigeration capacity refers to the total amount of heat removed from a closed space, room or area per unit time when a refrigerator such as an air conditioner is operating for cooling.
Heating capacity: Heating capacity refers to the total heat value provided by the air conditioning system under heating conditions or the hot water preparation system per unit time, usually in units of W and kW.
COP: Under rated operating conditions and specified conditions, when the air conditioner performs heat pump heating operation, the ratio of heating capacity to effective input power, its value is expressed in W/W.
EER: Under rated operating conditions and specified conditions, when the air conditioner performs cooling operation, the ratio of cooling capacity to effective input power, its value is expressed in W/W.
Refrigerant: Refrigerant, also known as refrigerant, refrigerant, and refrigerant, is the medium substance used to complete energy conversion in various heat engines. These substances often undergo reversible phase changes (such as gas-to-liquid phase changes) to increase power. Such as steam in steam engines, refrigerant in refrigerators, etc. When a general steam engine is working, it releases the heat energy of steam and converts it into mechanical energy to generate motive power; while the refrigerant in the refrigerator is used to transfer heat from low temperature to high temperature.
Secondary refrigerant: Secondary refrigerant is an intermediate cooling medium that completes the transfer of heat from the system (object or space) being cooled to the refrigerant in an indirect cooling refrigeration device. [1] This intermediate cooling medium is also called the second refrigerant. In air conditioning engineering, industrial production and scientific experiments, refrigeration devices are often used to indirectly cool the object to be cooled, or to transport the cold energy generated by the refrigeration device over long distances. In this case, an intermediate substance is required to be cooled in the evaporator. Then use it to cool the object to be cooled. This intermediate substance is called a brine.

7. Saturation temperature and saturation pressure
Saturation temperature: At a given pressure, the temperature corresponding to when the gas and liquid phases reach saturation. The saturation temperature is determined by its pressure. The higher the pressure, the higher the saturation temperature, and vice versa. When a substance reaches saturation under a certain pressure, it is always at a certain saturation temperature.
Saturation pressure: At a given temperature, the pressure corresponding to when the gas and liquid phases reach a saturated state. Depends on temperature. The higher the temperature, the higher the saturation pressure, and vice versa. When a substance reaches a saturated state at a certain temperature, it is always at a certain saturation pressure.
Application of Saturation Temperature and Saturation Pressure In refrigeration devices, the one-to-one correspondence between the saturation temperature and saturation pressure of the refrigerant is often used to adjust the temperature by adjusting the pressure.
Saturated liquid: A liquid whose temperature is equal to the corresponding saturation temperature at the pressure it is exposed to.
Saturated steam: Also known as "dry steam", the temperature is equal to the steam corresponding to the saturation temperature under the pressure.
Saturated vapor pressure: The pressure at which saturated vapor is in equilibrium with its liquid.
Supersaturation: A subequilibrium state. In this state, the pressure of steam is higher than the saturation pressure at the corresponding temperature.
Supersaturated steam: Steam in a sub-equilibrium state. Its pressure is higher than the saturation pressure at the corresponding temperature.
Superheating: The process of heating steam to a temperature higher than the saturation temperature at the corresponding pressure.
Superheated steam: Steam whose temperature is higher than the saturation temperature corresponding to its pressure.
Superheat: the difference between the superheated steam temperature and its saturation temperature.
Supercooling: The process of cooling a liquid to a temperature lower than the saturation temperature at the corresponding pressure.
Supercooled liquid: A liquid whose temperature is lower than the saturation temperature corresponding to its pressure. The difference between the temperature of the subcooled liquid and the temperature of the saturated liquid is called "subcooling". Commonly used in refrigeration equipment.

8. Humidity and pressure
Absolute humidity: The amount of water vapor contained in a unit volume of air.
Relative humidity: At a certain temperature, the ratio of the actual amount of water vapor (by weight) in the air to the amount of water vapor the air can hold at that temperature.
Static pressure: The pressure generated due to the irregular movement of air molecules hitting the pipe wall is called static pressure. The static pressure with atmospheric pressure as the zero point is called relative static pressure. The static pressure of air in air conditioners refers to relative static pressure. Static pressure is positive when it is higher than atmospheric pressure and negative when it is lower than atmospheric pressure.
Dynamic pressure: refers to the pressure generated when air flows. As long as the air flows in the air duct, there will be a certain dynamic pressure, and its value will always be positive.
Total pressure: Total pressure is the algebraic sum of static pressure and dynamic pressure.

9. Craftsmanship/comfort air conditioning
Comfort air conditioning: Targeting indoor personnel, the purpose is to create a comfortable working or living environment to improve work efficiency or maintain a good health level. Such as air conditioners in residences, offices, theaters, and department stores.
Process air conditioning: The purpose is to meet the needs of the production process and scientific research. At this time, the air conditioning design is mainly to ensure the process requirements, and the comfort of indoor personnel is secondary. Air conditioning in computer rooms, telephone switchboard rooms, precision electronic workshops and some special laboratories, museums, etc.