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Basic knowledge of central air conditioning

Basic knowledge of central air conditioning

2022-09-20

Basic knowledge of central air conditioning


1.1 What is a refrigerant and how does it work?

A working substance that transfers heat between the object to be cooled and the ambient medium, and finally transfers the heat from the object to be cooled to the ambient medium for the refrigeration cycle.

Its working principle is that the refrigerant absorbs the heat of the cooled material in the evaporator and evaporates, and in the condenser, the absorbed heat is transferred to the surrounding air or water, and then cooled into a liquid, reciprocating circulation, with the help of the change of state. to achieve cooling.


1.2 What is a secondary refrigerant and how does it work

The medium substance that transfers the cooling capacity of the refrigeration device to the cooled medium.  

For example, the commonly used air-conditioning chilled water is cooled in the evaporator and then transported over a long distance to cool the objects that need to be cooled. At present, the commonly used refrigerant is water, which can only be used in conditions above 0 °C. When it is required to be lower than 0 °C, brine is generally used. Such as: sodium chloride or calcium chloride aqueous solution or an aqueous solution of organic compounds such as ethylene glycol and propylene glycol.


1.3 What is sensible heat?

When heating a solid, liquid or gaseous substance, as long as its shape remains unchanged, the temperature of the substance will increase after the heat is added. The amount of added heat can be displayed on the temperature, that is, the heat that causes the temperature change without changing the form of the substance is called sensible heat. Such as heating liquid water, as long as it remains liquid, its temperature will increase; therefore, sensible heat only affects the change of temperature and does not cause changes in the form of matter. For example, in the computer room, its computer or program-controlled switch generates a lot of heat, which belongs to sensible heat.

Sensible heat changes can be measured with temperature measuring instruments.


1.4 What is latent heat?

When the liquid water is heated, the temperature of the water rises. When the boiling point is reached, although the heat is continuously added, the temperature of the water does not rise and stays at the boiling point. The added heat only turns the water into water vapor, that is, by Liquid becomes gaseous. This heat that does not change the temperature of the substance and causes a change in the state of matter (also known as a phase transition) is called latent heat. For example, in the computer room, the body heat of the staff and the moisture content of the air brought in by the ventilation are called latent heat. (Total heat equals the sum of sensible and latent heat.)

If a liquid is changed into a gas, then this is the latent heat of vaporization.

If a gas is changed into a liquid, this is called the latent heat of condensation.

Latent heat changes cannot be measured with temperature measuring instruments.


basic knowledge of central air conditioning


1.5 What is dynamic pressure, static pressure, total pressure?

When choosing an air conditioner or fan, three concepts of static pressure, dynamic pressure and total pressure are often encountered. According to the knowledge of fluid mechanics, the vertical force exerted by a fluid on a unit area is called pressure. When the air flows along the inner wall of the air duct, its pressure can be divided into static pressure, dynamic pressure and total pressure, the unit is mmHg or kg/m2 or Pa, and the legal unit in my country is Pa.

Static pressure (Pi): The pressure generated by the irregular movement of air molecules against the pipe wall is called static pressure. When calculating, the static pressure with absolute vacuum as the calculation zero is called absolute static pressure. The static pressure at which the atmospheric pressure is zero is called relative static pressure. The air static pressure in the air conditioner refers to the relative static pressure. It is positive when static pressure is above atmospheric pressure and negative when it is below atmospheric pressure.

Dynamic pressure (Pb): refers to the pressure generated when the 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 (Pq): Total pressure is the algebraic sum of static pressure and dynamic pressure: Pq=Pi+Pb Total pressure represents the total energy possessed by 1 m3 gas. It can be positive or negative if atmospheric pressure is used as the starting point for the calculation. 



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