1. Basic knowledge of central air conditioning
1. What is a refrigerant and what is its working principle?
The 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 in a refrigerator that performs a refrigeration cycle. Its working principle is that the refrigerant absorbs the heat of the cooled substance in the evaporator and evaporates.
2. What is a secondary refrigerant and what is its working principle?
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 long distances to cool the objects that need to be cooled.
3. What is sensible heat?
That is, the heat that causes a change in temperature without changing the form of a substance is called sensible heat. Sensible heat changes can be measured with temperature measuring instruments.
4. What is latent heat?
The heat that causes a state change (also known as phase transition) without changing the temperature of the substance is called latent heat. Latent heat changes cannot be measured with temperature measuring instruments.
5. What are dynamic pressure, static pressure and total pressure?
When choosing an air conditioner or fan, the three concepts of static pressure, dynamic pressure, and total pressure are often encountered.
Static pressure (Pi): The pressure generated by the impact of air molecules on the pipe wall due to the irregular movement is called static pressure. When calculating, the static pressure with absolute vacuum as the calculation zero point is called absolute static pressure. The static pressure with atmospheric pressure as zero is called relative static pressure. The air static pressure in the air conditioner refers to the 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 (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 1m3 gas. If atmospheric pressure is used as the starting point for the calculation, it can be positive or negative.
2. Classification of air conditioners
1. According to the purpose of use, what types of air conditioners can be divided into?
Comfortable air conditioner: requires suitable temperature, comfortable environment, no strict requirements on temperature and humidity adjustment accuracy, used in housing, offices, theaters, shopping malls, gymnasiums, automobiles, ships, airplanes, etc.
Process air conditioner: There is a certain requirement for the adjustment accuracy of the temperature, and there is also a higher requirement for the cleanliness of the air. Used in electronic device production workshops, precision instrument production workshops, computer rooms, biological laboratories, etc.
2. According to the air treatment method, what types can it be divided into?
Centralized air-conditioning: The air-processing equipment is concentrated in the central air-conditioning room, and the treated air is sent to the air-conditioning system in each room through the air duct. It is suitable for places with large areas, concentrated rooms, and relatively close heat and humidity loads in each room.
Semi-centralized air-conditioning: An air-conditioning system that has both central air-conditioning and terminal units that process air. This system is relatively complex and can achieve high adjustment accuracy. It is suitable for workshops and laboratories with high requirements on air precision.
Partial air conditioner: Each room has its own equipment to process the air conditioner, such as split air conditioner. It can also be a system composed of fan-coil air conditioners with pipes that centrally supply cold and hot water, and each room can adjust the temperature of its own room as needed.
3. According to the cooling capacity, which types can it be divided into?
Large-scale air-conditioning units: such as horizontal assembly sprinkler type, surface-cooled air-conditioning units, used in large workshops, cinemas, etc.
Medium-sized air conditioning units: such as water chillers and cabinet air conditioners, etc., used in small workshops, computer rooms, conference venues, restaurants, etc.
Small air-conditioning units: split-type air conditioners for offices, homes, guest houses, etc.
4. According to the amount of fresh air volume, what types of air conditioners can be divided into?
Once-through system: The processed air is fresh air, which is sent to each room for heat and humidity exchange and then discharged to the outside, without return air ducts.
Closed system: a system in which all the air processed by the air conditioning system is recirculated and no fresh air is added.
Hybrid system: The air handled by the air conditioner is a mixture of return air and fresh air.
5. Classified according to the air supply speed?
High-speed system: the wind speed of the main air duct is 20-30m/s.
Low-speed system: the wind speed of the main air duct is below 12m/s.
3. Common terms for air conditioners
1. Nominal cooling capacity
The heat removed from the space area or room by the air conditioner under the nominal cooling condition per unit time is called the nominal cooling capacity.
2. Nominal heating capacity
The heat released by the air conditioner to the space area or room under the nominal heating condition per unit time.
3. Energy Efficiency Ratio (EER)
The cooling capacity per unit motor input power. It reflects the ratio of the cooling capacity of the air conditioner to the cooling power during cooling operation, and the unit is W/W.
4. Performance parameter (COP)
The performance parameter COP value of the refrigeration compressor, that is: the cooling capacity per unit shaft power.
5. Common air-conditioning measurement units and conversions:
One kilowatt (KW) = 860 calories (Kcal/h).
A large calorie (Kcal/h) = 1.163 watts (w).
1 refrigeration ton (USRT) = 3024 kcal (Kcal/h).
1 Refrigeration Ton (USRT) = 3517 Watts (W).
4. Common air conditioners
1. Water-cooled chiller
The water-cooled chiller belongs to the refrigeration unit part of the central air-conditioning system. Its refrigerant is water, which is called a chiller, and the cooling of the condenser is realized by using the heat exchange and cooling of normal temperature water. Therefore, it is called a water-cooled unit, and the opposite of the water-cooled unit is called an air-cooled unit. The condenser of the air-cooled unit achieves the purpose of cooling by forced ventilation and heat exchange with the outdoor air.
2. VRV system
The VRV system is a variable refrigerant flow system. Its form is a group of outdoor units, composed of functional units, constant speed units and frequency conversion units. By connecting the outdoor unit system in parallel, the refrigeration pipes are concentrated into one pipe system, which can be easily matched according to the capacity of the indoor unit.
Up to 30 indoor units can be connected to one group of indoor units, and the capacity of the indoor unit can be adjusted within 50% to 130% of the capacity of the outdoor unit.
3. Module machine
Developed on the basis of the VRV system, the modular machine changes the traditional Freon pipeline into a water system, merges the indoor and outdoor units into a refrigeration unit, and changes the indoor unit into a fan coil unit. The refrigeration process is realized by using the heat exchange of the refrigerant water. The modular machine gets its name because it can automatically adjust the number of start-up units according to the cooling load requirements and realize flexible combination.
4. Piston chiller
The piston chiller is an integrated refrigeration device specially used for air conditioning cooling purposes, which compactly assembles the piston refrigeration compressor, auxiliary equipment and accessories required to realize the refrigeration cycle. Piston chillers stand-alone refrigeration ranges from 60 to 900KW, suitable for medium and small projects.
5. Screw chiller
Screw chillers are large and medium-sized refrigeration equipment that provide chilled water. It is often used for air conditioning in national defense research, energy development, transportation, hotels, restaurants, light industry, textiles and other departments, as well as chilled water for water conservancy and electric power projects. The screw chiller is a complete refrigeration system composed of screw refrigeration compressor unit, condenser, evaporator, automatic control components and instruments. It has the advantages of compact structure, small size, light weight, small footprint, convenient operation and maintenance, and stable operation, so it has been widely used. Its single-unit cooling capacity ranges from 150 to 2200KW, and is suitable for medium and large projects.
6. Centrifugal chiller
The centrifugal chiller is a complete chiller composed of centrifugal refrigeration compressors, matching evaporators, condensers, throttling control devices and electrical meters. The cooling capacity of a single machine is from 700 to 4200KW. It is suitable for large and extra-large projects.
7. Lithium bromide absorption chiller
The lithium bromide absorption chiller uses heat energy as the power, water as the refrigerant, and lithium bromide solution as the absorbent to produce refrigerant water above 0°C, which can be used as a cold source for air conditioning or production processes. The lithium bromide absorption chiller uses heat energy as the There are three common types of power: direct combustion type, steam type, and hot water type. The cooling capacity ranges from 230 to 5800KW, which is suitable for medium-sized, large-scale, and extra-large projects.
5. Classification of central air-conditioning units
The central air conditioning unit is the core part of the central air conditioning system. Reasonable selection of units is very important for a central air conditioning project. With regard to the refrigeration method and structure classification of cold (hot) water units, they can be divided into the following types.
Post time: Feb-06-2023