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1. Work, energy, horsepower, cooling capacity: 1 joule (J) = 1 watt (W) × 1 second (s). (1) Energy units: Imperial system: J, kj； Imperial units: cal, kcal. 1 J = 0.2388 cal. (2) Power units: Metric units: W, kW ； Imperial units: kcal/h (kilocalories per hour). 1 kcal/h = 1.163 W; 1 kW = 860 kcal/h. Commonly used units: horsepower (HP) and refrigeration ton (RT). 1 HP = 735 W; 1 RT = 3.516 kW = 3,024 kcal/h. Note: Refrigeration ton is an Imperial unit for measuring cooling capacity. 1 ton of cooling capacity refers to the amount of cooling required to freeze 1 ton of water at 0°C into ice at 0°C within 24 hours. The United States uses 2,000 pounds (907.2 kg) as one ton. Therefore, 1 US refrigeration ton = 12659 kj/h ； That is: 1 RT = 3.516 kW. (3) The relationship between horsepower and cooling capacity: In small-scale air conditioning systems, 1 HP refers to the cooling capacity that can be generated when a power input of 735 W is supplied to the compressor. Its meaning is different from that of ordinary power units. The 1HP here is calculated based on the energy efficiency ratio. In Japan, it is generally assumed that the energy efficiency ratio of air-conditioning compressors is 3.4 on average; therefore, 735 W of electrical power input results in a cooling capacity of 2500 W. 2. Pressure: The vertical force acting per unit area is called pressure (physically referred to as stress). The international unit of pressure is Pascal, abbreviated as Pa, denoted by Pa. 1 standard atmosphere = 0.1 MPa = 760 mmHg of mercury column ； 1 atmosphere = a pressure of 1.03323 kg/cm2 ； 1MPA=10 atmospheres=10.3323kg/cm2 ； That is equivalent to a pressure of 10.332 kilograms per square centimeter ； 1 MPa = 1,000,000 Pa = 1.00 N/mm² = (1/9.8) kgf/mm². 3. Temperature: The most commonly used thermometers are mercury thermometers and alcohol thermometers. The temperature scales used for thermometers generally include the Celsius scale, the Fahrenheit scale (used in Europe and America), and the absolute scale. 1) Celsius scale (℃): It is a temperature scale in which the freezing point of pure water at 1 atmosphere of pressure is set as 0℃, and the boiling point as 100℃; the interval between these two points is divided into 100 equal parts, with each part representing 1℃. 2) Absolute temperature scale (K): The freezing point of water is set at +273.16 K, and its boiling point at 373.16 K. Theoretically, the point at which molecular thermal motion within a substance comes to a complete stop is defined as absolute zero, that is, 0(K). The relationship between the Celsius scale and the absolute scale is as follows: T = t + 273.16. 3) Fahrenheit scale (°F): The freezing point of water at standard atmospheric pressure is set at 32°F, while the boiling point is set at 212°F; these two points are divided into 180 equal parts, with each part representing 1°F. It is widely used in Europe and America. The conversion relationship between Celsius and Fahrenheit is as follows: t = 5(F-32)/9 ； F=9t/5+32 ； In the formula: t – Celsius temperature ； 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 obtained by covering the thermometer with a damp cloth; as water evaporates, the temperature reading decreases, and this value is known as the wet bulb temperature. 4. Heat, vaporization, liquefaction. The ways heat is transferred are: conduction, convection, and radiation. Thermal convection: Thermal convection is the movement of heated liquids or gases that transfers 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 state to a gas state. Ways of vaporization: evaporation (surface vaporization), boiling (vaporization at both the surface and inside). Measures to accelerate vaporization: increase temperature, reduce surface pressure. Liquefaction: The process by which a substance changes from a gaseous state to a liquid state. Measures to accelerate liquefaction: lower temperature, increase pressure. 5. Sensible heat and latent heat. Sensible heat (or sensible cooling) load: When heating a substance in solid, liquid, or gas state, as long as its state remains unchanged, the heat absorbed by the substance causes its temperature to rise. The amount of heat absorbed can be reflected in the change in temperature; heat that causes a change in temperature without altering the substance’s state is known as sensible heat. Latent heat (latent cooling) load: When liquid water is heated, its temperature rises. Once it reaches the boiling point, even as heat continues to be added, the temperature of the water does not increase any further and remains at the boiling point. The heat added is used solely to convert the water into steam, that is, from a liquid state to a gas state. The heat that causes a change in the state of matter (also known as a phase change) without altering the temperature of the substance 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. Cooling/heat energy efficiency ratio, cooling/refrigerant – Cooling capacity: The cooling capacity refers to the total amount of heat removed from a closed space, room, or area per unit of time when a refrigeration unit such as an air conditioner is operating in cooling mode. Heating capacity: The heating capacity refers to the total amount of heat provided by an air conditioning system in heating mode, or by a hot water generation system, per unit of time; it is usually expressed in units of W or kW. COP: Under rated operating conditions and specified parameters, it is the ratio of heating capacity to the effective input power when an air conditioner operates in heat-pump heating mode; this value is expressed in W/W. EER: Under rated operating conditions and specified parameters, it is the ratio of cooling capacity to effective input power when an air conditioner is in cooling mode, expressed in W/W. Refrigerant: A refrigerant, also known as a cooling agent or cryogen, is the medium used in various heat engines to facilitate energy conversion. These substances typically increase power through reversible phase transitions (such as gas-liquid phase transitions). Such as steam in steam engines, refrigerant in refrigerators, and so on. When operating, a conventional steam engine releases the thermal energy of steam and converts it into mechanical energy to generate power ； The refrigerant in a refrigerator is used to transfer heat from low-temperature areas to high-temperature areas. Coolant: A coolant is an intermediate cooling medium used in indirectly cooled refrigeration systems to transfer the heat from the system to be cooled (an object or space) to the refrigerant. This intermediate cooling medium is also known as the second refrigerant. In air conditioning systems, industrial production, and scientific experiments, refrigeration units are often used to indirectly cool the substance that needs to be cooled, or to transport the cold generated by these units over long distances. In such cases, an intermediate substance is required – one that can be cooled in the evaporator and then used to cool the substance in question. This intermediate substance is known as a coolant. 7. Saturation temperature and saturation pressure: Saturation temperature: The temperature at which a gas and liquid phase reach a state of saturation at a given pressure. The saturation temperature depends on the pressure; the higher the pressure, the higher the saturation temperature, and vice versa. When a substance reaches a saturated state at a certain pressure, it always has a specific saturation temperature. Saturation pressure: the pressure at which the gas and liquid phases reach a saturated state at a given temperature. It depends on the temperature. The higher the temperature, the higher the saturation pressure; conversely, the lower it is. When a substance reaches a saturated state at a certain temperature, it always has a specific saturated pressure. The application of saturation temperature and saturation pressure in refrigeration systems makes use of the fact that there is a one-to-one relationship between the saturation temperature and saturation pressure of a refrigerant; by adjusting the pressure, it is possible to control the temperature. Saturated liquid: A liquid whose temperature is equal to the saturation temperature at the pressure it is under. Saturated vapor: Also known as “dry steam,” it is vapor whose temperature corresponds to the saturation temperature at the given pressure. Saturated vapor pressure: The pressure at which saturated vapor is in equilibrium with its liquid. Supersaturation: a sub-equilibrium state. In this state, the pressure of the steam is higher than the saturated pressure at the corresponding temperature. Saturated vapor: Vapor that is in a sub-equilibrium state. Its pressure is higher than the saturated pressure at the corresponding temperature. Superheating: The process of raising the temperature of steam above its saturation temperature at the corresponding pressure. Superheated steam: Steam whose temperature is higher than the saturation temperature at its corresponding pressure. Superheat: The difference between the temperature of superheated steam and its saturated temperature. Supercooling: The process of cooling a liquid to a temperature below its saturation temperature at the corresponding pressure. Subcooled liquid: A liquid whose temperature is lower than the saturated temperature at its corresponding pressure. The difference between the temperature of a supercooled liquid and the temperature of a saturated liquid is called the \"degree of supercooling\". It is commonly used in refrigeration units. 8. Humidity, Pressure, Absolute Humidity: The amount of water vapor contained in a unit volume of air. Relative humidity: At a certain temperature, it is the ratio of the actual amount of water vapor present in the air (by weight) to the maximum amount of water vapor that the air can hold at that temperature. Static pressure: The pressure generated by the irregular movement of air molecules, which collide with the pipe walls, is called static pressure. The static pressure with atmospheric pressure as the reference point is called relative static pressure. The static pressure of air in air conditioners refers to relative static pressure. The 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 is in motion; as long as there is air flow within the duct, there is a certain amount of dynamic pressure, and its value is always positive. Total pressure: Total pressure is the algebraic sum of static pressure and dynamic pressure. 9. Process/Comfort Air Conditioning: Comfort air conditioning is designed to serve the people inside a building, with the aim of creating a comfortable working or living environment that helps improve work efficiency or maintain good health. Such as air conditioning in residences, offices, theaters, and department stores. Process air conditioning: Its purpose is to meet the needs of production processes and scientific research, etc. In such cases, the design of the air conditioning system focuses on fulfilling the process requirements, with the comfort of those inside the space being a secondary consideration. Air conditioning for computer rooms, telephone switching centers, precision electronics workshops, and certain special laboratories, museums, etc.