Analysis of common problems in the design of refrigerant multi-connected air conditioning system

Analysis of common problems in the design of refrigerant multi-connected air conditioning system

1. Applicable area and scope of refrigerant multi-connection system

　　 Refrigerant multi-connection system is suitable for areas: The refrigerant multi-connection is suitable for hot summer and cold winter areas, hot summer and warm winter areas, and some cold areas. For cold areas, it is not possible to use ordinary refrigerant multi-connection, but to use special models for cold areas. The designer must indicate the relevant models when designing. If the selection of ordinary models is adopted, it will cause problems in the future operation. Problems such as serious decline in effect.

　　 Refrigerant multi-unit air-conditioning system is suitable for architectural forms: due to its special evaporative refrigeration, the refrigerant multi-unit air-conditioning system is suitable for occasions with more latent heat, such as office buildings, small and medium commercial buildings, residential buildings, etc. It is not suitable for occasions with high sensible heat load, such as sunshine rooms and computer rooms.

　　 Around the building: If the ambient air quality is poor, and there are places where corrosive gases such as acid are released, such as chemical plants, it is not suitable to use this air conditioning system, because the aluminum fins of the outer coil are easily corroded.

　　Analysis of common problems in the outdoor unit design process

　　The problem of layered placement of outdoor units: In order to adapt to the increasing situation of large high-rise and super high-rise buildings, in addition to the centralized placement of the roof and the ground, there is also a layered placement of outdoor units. Compared with the traditional centralized arrangement, this arrangement reduces the length of the refrigerant pipe of the system, effectively reduces the investment cost and equipment capacity, and is more suitable for the requirements of the new energy-saving regulations.

However, the placement of outdoor units in high-rise and super-high-rise buildings is more complicated. Each building level may have multiple outdoor units, and all floors may be placed in the same position. The formation of air short circuit, poor heat dissipation of the external machine or even shutdown protection. In this case, you can determine the number of floors that can be placed in layers according to the experience floor chart provided by the manufacturer.

　　 When the number of floors exceeds the number of floors specified in the above table, the location of the outdoor unit must be changed to ensure its use effect. If the actual floor exceeds the layered floor found in the figure, or the actual location or location of the outdoor unit is more complicated and difficult to judge, you need to submit the corresponding information to the manufacturer, so that the manufacturer can perform according to its own products. CFD simulation is used to check and judge the number of floors and reasonable positions of the external machine.

Noise of the outdoor machine: The noise problem of the outdoor machine placed in layers is difficult to solve. The balcony space of the floor equipment is relatively small, and the distance from the indoor space is relatively small. The indoor personnel will have a great sense of noise. Therefore, the problem of airflow organization is solved At the same time, the noise problem can be solved together. When installing the diversion cover, the diversion cover can be made into a bell mouth shape, and the inside of the cover body can be pasted with sound-absorbing materials. At the same time, the opening rate of the louvers should be controlled as much as possible above 80%, and the inclination angle of the blades should not be greater than 20 degrees. In order to reduce the airflow speed and avoid secondary noise.

　　 Centrally placed outdoor units on the roof or on the ground:

　　①It is necessary to stay away from buildings with high noise requirements as far as possible;

　　②For the matrix layout of the external units, the distance between the external units should be as wide as possible, and the distance required by the manufacturer should be increased by more than 200mm, which will effectively reduce the superimposition of the same frequency noise;

　　③In places where conditions do not allow, an upward horn cover can be installed at the air outlet, or a sound insulation board can be installed around the outdoor unit to reduce the airflow speed and block the transmission of noise.

The frosting problem of the outdoor machine: The frosting problem of the outdoor machine placed in a matrix is particularly serious. The first is because the temperature of the air outlet in winter is very low, and it sinks to the suction outlet, causing the temperature of the suction outlet to drop; The machine is dense, the air flow is not smooth, which causes the heat exchange effect to decrease, and the frost phenomenon is serious. under these circumstances:

　　① The distance between the external machines should be as large as possible, CFD airflow simulation should be done when conditions permit, and the appropriate distance should be selected;

　　②Add a cylindrical deflector above the air outlet to increase the distance between the inlet and outlet to avoid short circuits;

　　③If the external unit is surrounded by a parapet wall, louvers should be placed on the lower part of the parapet wall;

④Avoid placing it in the patio.

　　Outer machine attenuation: In the design and selection, the outer machine attenuation includes many factors such as tube length, frost, and low temperature. In terms of tube length attenuation, you can refer to the manufacturer's technical performance table for calculation. Frosting and low temperature attenuation should be considered according to the applicable area. The frosting is the most serious when the outdoor machine is at zero degrees. In the Yangtze River basin such as Shanghai and Nanjing, the main consideration is frost attenuation, followed by low temperature attenuation; in New York and other places, low temperature is mainly considered Attenuation, followed by frost attenuation. According to the data provided by a refrigeration company, generally at minus 4℃, the heating capacity attenuation is 80% of the standard operating condition, and at minus 15℃, the heating capacity attenuation is 60% of the standard operating condition.

　　 2. Analysis of common problems in the design process of indoor unit

Applicable occasions of indoor unit:

　　①The wall mounter is only suitable for places with convenient drainage such as toilets, because the wall mounter does not have a condensate water lifting device, and the installation height is lower than the ceiling;

②The cassette type machine is suitable for open office, commercial and other large space places with good environment. It is not suitable for places with heavy oily smoke. Because the machine is exposed outside, it is easy to get dirty and blocked, which makes the air-conditioning effect serious and heavy oil smoke. In the case of high static pressure, the built-in model should be used to introduce the return air inlet into the low return air at the side wall 1.5 meters from the ground, so that the oil fume and the return air are naturally separated;

　　③High static pressure built-in models are suitable for large spaces such as lobbies, exhibition halls, etc. Because of the long air supply distance, higher pressure heads are required;

　　④The floor machine can be used in places where the interior decoration style cannot be destroyed, such as protected buildings, or in tall spaces.

　　 The air outlet condensation problem: Because the refrigerant multi-unit air conditioning system is direct evaporative cooling, it is a large temperature difference air supply, and it is easy to cause condensation at the air outlet. In order to prevent or reduce condensation at the air outlet:

　　①Use ABS type tuyere instead of aluminum alloy tuyere;

　　②Do not open doors and windows as much as possible during air conditioning;

　　③The air conditioner is operated in high-speed and high-temperature mode at the initial stage. After the temperature drops, the air conditioner temperature is gradually reduced.

Air return installation problem: The general designer designs or installs on site, and rarely considers the return air connection of the refrigerant multi-connected indoor unit. For the high ceiling space or roof layer, directly using the ceiling return air will cause the indoor unit effect to be seriously reduced For indoor units with built-in ceilings, unless ceiling space is not allowed, connection hoses or return air boxes must be installed.

The problem of airflow organization in winter: In high-end office buildings, hotels, villas and other occasions, the interior requirements are very high. Generally, the decoration design uses light troughs to enhance the modeling effect, and does not want the air outlet to be exposed. Therefore, in many cases, side delivery has to be adopted. The way of wind, and some even use the same side to send the side return air. The width of the lamp trough is generally more than 200mm and the height is about 150mm. The air outlet installed in the space of such a groove is difficult to heat up in winter. The air flow is sent down, which seriously affects the air conditioning effect in winter. Therefore, this form should be avoided as much as possible. When it is unavoidable, the width and height of the lamp trough should also be reduced to reduce the obstruction of the light trough to the air flow.