Do You Know These Basic Refrigeration Knowledge?

2025-04-09

Temperature
There are three commonly used temperature units (temperature scales): Celsius temperature, Fahrenheit temperature, and absolute temperature.

Celsius temperature (t, ℃): The temperature we often use. It is the temperature measured by a Celsius thermometer.
Fahrenheit temperature (F, ℉): The temperature commonly used in Europe and America.
Temperature conversion:
3.1 F (℉) = 9/5 * t(℃) + 32 (Finding Fahrenheit temperature when Celsius temperature is known)
3.2 t (℃) = [F(℉) - 32] * 5/9 (Finding Celsius temperature when Fahrenheit temperature is known)
Absolute temperature scale (T, oK): Generally used in theoretical calculations.
Conversion between absolute temperature scale and Celsius temperature: T(oK) = t (℃) + 273 (Finding absolute temperature when Celsius temperature is known)
Pressure
In refrigeration, pressure is the vertical force per unit area, that is, pressure intensity, usually measured by a pressure gauge or manometer.
Commonly used units of pressure are:
1.1 Mpa (megapascal);
1.2 Kpa (kilopascal);
1.3 bar (bar);
1.4 kgf/cm² (kilogram-force per square centimeter);
1.5 atm (standard atmospheric pressure);
1.6 mmHg (millimeter of mercury).
Conversion relationships:
2.1 1Mpa = 10bar = 1000Kpa = 7500.6 mmHg = 10.197 kgf/cm²
2.2 1atm = 760mmHg = 1.01326bar = 0.101326Mpa
Generally used in engineering:
3.1 1bar = 0.1Mpa ≈ 1 kgf/cm² ≈ 1atm = 760 mmHg
Absolute pressure: The pressure directly acting on the surface of a container or an object.
Gauge pressure: The pressure measured by a pressure gauge is gauge pressure.
Vacuum degree (H): When the gauge pressure is negative, take its absolute value, which is expressed by the vacuum degree.
Refrigeration / Heat
Refrigeration capacity: The amount of heat transferred by a refrigerator from a low-temperature object to a high-temperature object per unit time.
Heating capacity: The amount of heat transported indoors by an air conditioner (heat pump type) after absorbing heat from the outside per unit time.
COP: Refrigeration capacity / Compressor electrical power. Both the performance coefficient of the heat pump cycle in winter and the energy efficiency ratio of the heat pump in summer are expressed by COP (energy efficiency ratio).
EER: Refrigeration capacity / Total electrical power of the air conditioning system (The higher the EER value, it means that more heat is absorbed by evaporation in the air conditioner or less electricity is consumed by the compressor). When cooling in summer, the ratio of the refrigeration capacity (W or Btu/h) to the input power (W) is defined as the energy efficiency ratio EER of the heat pump.
Refrigeration ton: A unit in air conditioning refrigeration. The refrigeration ton is also called the freezing ton. A freezing ton refers to the energy required to freeze one ton of water into ice. It is the ability to convert one ton of water at 0 degrees Celsius into ice at 0 degrees Celsius within 24 hours. The freezing ton represents the refrigeration capacity of the refrigerator.
5.1 1 US refrigeration ton = 3024 kcal/h (kcal/h) = 3.517 kW (kW);
5.2 1 Japanese refrigeration ton = 3320 kcal/h (kcal/h) = 3.
861 kW (kW);
5.3 1 horsepower (or 1 horse power) = 735.5 W (W) = 0.7355 kW (kW);
5.4 1 kcal/h (kcal/h) = 1.163 W (W);
5.5 Celsius temperature ℃ = (Fahrenheit °F - 32) 5/9.
Pressure: It is the force per unit area, represented by P. Its unit is Pascal, abbreviated as Pa; (Kilopascal [KPa] = 1×10³ Pa, Megapascal [MPa] = 1×10⁶ Pa)
Four Elements of Air Conditioning
Temperature, humidity, cleanliness, and air distribution are the so-called four elements of air conditioning. By adjusting these four elements, the indoor environment can be controlled to meet the comfort requirements.
Comfortable environment:
1.1 The general comfortable temperature for the human body in summer is: 24~26℃.
1.2 The general comfortable temperature for the human body in winter is: 18~22℃.
Superheated Steam and Subcooled Liquid
Under a certain pressure, the temperature of the steam is higher than the saturated temperature corresponding to that pressure, which is called superheated steam.
Under a certain pressure, the temperature of the liquid is lower than the saturated temperature corresponding to that pressure, which is called subcooled liquid.
Suction temperature: The value exceeding the saturated temperature is called the suction superheat. The suction superheat is generally required to be controlled within 5～10℃.
Liquid temperature: The value lower than the saturated temperature is called the liquid subcooling. Liquid subcooling generally occurs at the bottom of the condenser, in the economizer, and in the intercooler. The liquid subcooling before the throttle valve is beneficial to improving the refrigeration efficiency.
Evaporation, Suction, Discharge, Condensation Pressure and Temperature
Evaporation pressure (temperature): The pressure (temperature) of the refrigerant in the evaporator.
Condensation pressure (temperature): The pressure (temperature) of the refrigerant in the condenser.
Suction pressure (temperature): The pressure (temperature) at the suction port of the compressor.
Discharge pressure (temperature): The pressure (temperature) at the discharge port of the compressor.
Temperature Difference
It refers to the temperature difference between the two fluids on both sides of the heat transfer wall. The temperature difference is the driving force for heat transfer.
For example: There are temperature differences between the refrigerant and the cooling water; between the refrigerant and the brine; and between the refrigerant and the air in the warehouse. Due to the existence of the heat transfer temperature difference, the temperature of the cooled object is higher than the evaporation temperature; and the condensation temperature is higher than the temperature of the cooling medium in the condenser.
Humidity
Humidity refers to the degree of moisture of the air. Humidity is a factor affecting heat transfer. There are three ways to express humidity:
Absolute humidity (Z): The mass of water vapor contained in each cubic meter of air.
Moisture content (d): The amount of water vapor (g) contained in one kilogram of dry air.
Relative humidity (φ): It represents the degree to which the actual absolute humidity of the air approaches the saturated absolute humidity.
At a certain temperature, a certain amount of air can only hold a certain amount of water vapor. If it exceeds this limit, the excess water vapor will condense into fog. This certain limited amount of water vapor is called the saturated humidity. Under the saturated humidity, there is a corresponding saturated absolute humidity ZB, which changes with the air temperature.
At a certain temperature, when the air humidity reaches the saturated humidity, it is called saturated air, which can no longer accept more water vapor; the air that can continue to accept a certain amount of water vapor is called unsaturated air.
The ratio of the absolute humidity Z of unsaturated air to the absolute humidity ZB of saturated air is the relative humidity.
φ = Z/ZB ×100%. It is used to reflect the degree to which the actual absolute humidity approaches the saturated absolute humidity.
Water Air Conditioning and Refrigerant Air Conditioning
Water system air conditioning: It is composed of an outdoor main unit and indoor terminal devices. The outdoor main unit provides air conditioning cold/hot water, which is transported to the indoor terminal devices through the water pipe system. The water and air exchange heat at the indoor terminal to eliminate the cold/heat load of the room. It is an air conditioning system type that centrally generates cold/heat but dispersedly handles the load of each room.
Fluorine system air conditioning: Using the refrigerant as the conveying medium, adopting the variable refrigerant flow technology. The outdoor main unit is composed of an outdoor side heat exchanger, a compressor, and other refrigeration accessories, and the indoor unit is composed of a direct evaporative heat exchanger and a fan. One outdoor unit can transport refrigerant liquid to several indoor units through pipelines. By controlling the refrigerant circulation volume of the compressor and the refrigerant flow rate entering each indoor heat exchanger, the indoor cold and heat load requirements can be met in a timely manner.