1. 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. The refrigeration mode and structure classification of cold (hot) water units can be divided into the following types:
2. Water system VS wind system VS refrigerant system
There are currently three main genres:
The first is the water system represented by China;
the second is the air duct system represented by Europe and the United States;
The third is the refrigerant system represented by Japan.
Each of these three styles of products has its own different features and advantages to meet the needs of different consumers.
1. Water system:
The outdoor unit is generally called the hot and cold water unit, the indoor unit is generally called the fan coil unit, and the indoor and outdoor units are connected through the water pipe. (The outdoor unit produces hot/cold water, which is pumped into each indoor unit with water.) Indoor air and water heat exchange to achieve the purpose of temperature regulation. ）
2. Wind system:
The outdoor unit is connected to an air duct indoor unit through a refrigerant pipe, and the air duct type internal unit uniformly treats the indoor air, and then sends the treated air into each room through the air duct.
3. Refrigerant system:
The outdoor unit is connected to multiple indoor units through the refrigerant tube, and the internal unit in each room is a direct heat exchange between the refrigerant and the air.
3. Air conditioning system design
1. Design principles of air conditioning system
★ It can ensure the parameters required by the room, that is, it can ensure that the indoor temperature, relative humidity, purification and other requirements can be met under the design conditions and operating conditions.
★ The initial investment and operating costs are more economical combined;
★ Minimize the adverse effects of rooms in a system;
★ Minimize duct length and duct overlap for easy construction, management, and testing.
★ The system should be consistent with the building zoning.
★ Each room or zone has the same design parameter values and heat-humidity ratio as the same contaminants, which can be divided into an all-air system. For the constant air volume single air duct system, it is also required that the working time is the same, and the load change law is basically the same.
★ The all-air system in general civil buildings should not be too large, otherwise the air duct is difficult to arrange; It is best not to set up the system across floors, and when it is necessary to set up across floors, the number of floors should not be too much, which is conducive to fire prevention.
2. Air conditioning airflow organization and distribution
2.1 What factors should be considered in the layout of air ducts?
★ Minimize pipelines, reduce branch pipelines, and avoid complex local components to save material and reduce system resistance.
★ It is necessary to facilitate construction and maintenance, and properly deal with the contradictions that may be encountered in the layout of air conditioning water, fire water pipeline systems and other pipeline systems.
A and B in the figure below are two types of duct layout in the same room and the same air outlet. The comparison shows that A is longer than B's pipeline, and there are more branch pipelines and local components, so B is better than A.
2.2 What are the common airflow organization forms at present, and the main application places of various air supply methods?
The proper organization of airflow in a room depends mainly on the form and location of the air supply vents. At present, the common forms of airflow organization are:
Side air supply As shown in Figure a, side plate air supply is a commonly used form of airflow organization. The air duct is located in the upper part of the room, laid along the wall, and the air supply outlet is opened on one or both sides of the air duct. It can be supplied with air on the up, return air on it, or it can be supplied up and returned to the air down. It is characterized by the fact that the tuyere should be arranged close to the top to form an attached jet, and the return air area is used for heat exchange. The return air outlet is located on the same side of the air supply outlet, and the wind speed is 2~5m/s. In winter, when hot air is supplied, the shutters are adjusted so that the air flow is shot diagonally downward.
★ Diffuser air supply The diffuser air supply can be carried out flat and side feeding. It also carries out heat exchange in the air return zone. The jet and return flow is short, and it is usually better when an attached jet is formed along the top grid. It is suitable for rooms where the top grid is set.
★ Strip air supply is carried out through the strip seam air supply outlet, which has a short range. The temperature difference and speed change quickly, which is suitable for rooms with large heat dissipation and only need to cool down, such as textile mills, high-end public civil buildings, etc.
★ Air supply from the nozzle The hot and humid treated air is ejected at high speed from several nozzles on one side of the room, and then returns after a certain distance. The working area is in the process of reflow, and this air supply mode has high wind speed, long range, slow attenuation of speed and temperature, and uniform temperature distribution. It is suitable for large gymnasiums, auditoriums, theaters and tall factories and other public buildings.
★ Orifice air supply uses the space above the top grid as a static pressure box. Under the action of pressure, air enters the room through small holes in the metal plate. The return air outlet is located in the lower part of the room. When the orifice plate is sent, the diffusion of the jet and the mixing speed of the indoor air are faster, so the air temperature and flow rate in the working area are relatively stable, which is suitable for occasions with strict requirements for regional temperature difference and wind speed in the working area, and the room temperature is allowed to fluctuate less.
3. Calculation of air conditioning duct diameter and tuyere size
What is the choice of air conditioning duct and tuyere air speed?
(1) The wind speed in the air duct The limited noise allowable value of the air conditioning system in the general air-conditioned room is controlled between 40~50dB (A), that is, the corresponding NR (or NC) number is 35~45dB (A). According to the design specification, the wind speed of the main pipe to meet the allowable noise value in this range is 4~7m/s, and the wind speed of the branch pipe is 2~3m/s. The air duct between the ventilator and the muffler can be 8~10m/s.
(2) The air velocity of the air supply outlet In order to prevent the noise of the air outlet, the air outlet air speed of the air supply outlet should be 2~3m/s.
(3) When the return air outlet is located in the upper part of the room, the suction speed is 4~5m/s, when the return air outlet is located in the lower part of the room, if it is not close to the place where the personnel often stay, take 3~4m/s, if it is close to the place where the personnel often stay, take 1.5~2m/s, if it is used for the corridor return air, take 1~1.5m/s.
3. Calculation of fresh air (ventilation) volume
The introduction of fresh air is mainly to improve the air quality in the air-conditioned room, reduce the content and concentration of harmful substances, ensure the comfort and physiological health of the personnel involved, and maintain the process requirements. When determining the amount of fresh air required, it is often based on the amount of indoor exhaust gas (especially CO2) generated and other indoor conditions. Generally speaking, a fresh air volume of 30m2 per person per hour should be guaranteed.
For ordinary occasions, the fresh air volume can be calculated according to the occupied area per person:
Calculation formula: necessary air volume (m3/h) = A * area / per capita occupied area
In the above equation, A indicates the per capita fresh air volume (m3/h), which can usually be estimated at 20m3/h.
Recommended value for the number of air changes
| occasion | Room type: | Number of air changes (1/hr) |
| General dwellings | Living room, living room | 6 |
| bathroom | 6 | |
| lavatory | 10 | |
| kitchen | 15 | |
| Dining establishments | Restaurant | 6 |
| Banquet hall | 10 | |
| kitchen | 20 | |
| hotel | guest room | 5 |
| corridor | 5 | |
| ballroom | 8 | |
| Dining Room (Large) | 8 | |
| Toilets, bathrooms | 10 | |
| kitchen | 15 | |
| Laundry | 15 | |
| boiler room | 20 | |
| Commercial buildings | office | 6 |
| Waiting room | 10 | |
| Restaurant, toilets | 10 | |
| conference room | 12 | |
| factory | office | 6 |
| Phone room | 6 | |
| Lathe room | 10 | |
| printshop | 10 | |
| Battery room | 10 | |
| Machinery factory | 10 | |
| Hair shop room | 15 |