Fresh air treatment and energy-saving methods of multi-line system

Fresh air treatment and energy-saving methods of multi-line system

I. Introduction

In the process of using air conditioners, we must consider the related functions of the air conditioner on the one hand, and on the other hand, consider its energy-saving effect and reduce the consumption of electric energy. The multi-connected system meets the needs of people’s lives while reducing input costs. Reduce energy consumption.

　　 Second, the characteristics of multiple connections

　　 This technology originated in the early 1980s and was introduced to China from Japan in the 1990s. With the improvement of my country's per capita living standards and the rapid development of technology such as frequency conversion, it has become a major trend in the development of household air conditioners. It integrates multiple technologies, such as one-to-multiple technologies, intelligent control technologies, multiple health technologies, energy-saving technologies, and so on. Compared with traditional air conditioners, it has significant advantages. It only uses one outdoor unit, easy to install and beautiful, and low investment. The control is flexible and convenient. It can use network control technology to realize centralized management of each indoor unit. Compared with the traditional multiple household air conditioners using multiple outdoor units to control separately, the start and operation of multiple indoor units can be controlled, making the control more flexible; and the frequency conversion technology can be used to automatically adjust the compressor power according to the load to reduce energy consumption , The space occupied by the equipment is relatively reduced, and the noise is effectively reduced.

　　 At present, the multi-connection technology is developing rapidly, and the market share is greatly increased. Although the multi-line air-conditioning system is developing rapidly, due to the short development time and the more complex technology required, there are still many areas that need to be improved in technology. For example, the use of multi-line systems to coordinate various indoor air-conditioning requires intelligent control and optimized operation . Due to the coupling and conflict between the various evaporators, if the system design or control is not good, the energy saving effect will be greatly reduced, and even more energy consumption than traditional air conditioning systems

　　 3. Fresh air system design

　　 In the air-conditioning system, the fresh air volume is a very important technical parameter, and it is the guarantee of meeting indoor hygiene standards. Compared with traditional central air-conditioning systems, multi-line systems are closer to unitary air conditioners or room air conditioners, and fresh air treatment is different from conventional central air-conditioning systems. If insufficient attention is paid to the supply of fresh air in the design, the indoor air quality (air freshness, cleanliness, relative humidity, etc.) cannot be guaranteed, resulting in poor sanitary conditions, and multiple connections can only be equipment for cooling and heating. It will also affect the further promotion and application of Multi-online. Therefore, it is of great significance to study the fresh air supply mode of the multi-connection system.

　　 In the fresh air treatment, it is necessary to pay attention to that the dedicated fresh air indoor unit and the ordinary indoor unit cannot be connected in the same system, and the ordinary indoor unit cannot be used as a fresh air unit. Ordinary indoor units process indoor air, while fresh air indoor units process outdoor air. The air conditions handled by the two are far different and the requirements for equipment are also different. In summer, due to the high temperature of the fresh air, the high expansion pressure in the refrigerant coil and the high power consumption of the compressor, if the fresh air indoor unit and the ordinary indoor unit are connected to an outdoor unit together, the compressor may burn out due to overload. The fresh air ventilator is an air heat recovery device with a new and exhaust fan. According to the type of air heat exchanger, it can be divided into plate type, runner type, heat pipe type, etc., and divided into sensible heat according to the nature of the recovered heat Recycler and total heat recovery device. In the case of multi-line systems, most of the plate heat exchangers are used to replace the same amount of indoor dirty air while supplying fresh air, and at the same time, heat recovery.

　　 4. Multi-connected air conditioning fresh air system

　　 The development time of multi-line air conditioner is relatively short, and the original multi-line air conditioner even lacks a fresh air treatment system. With the continuous expansion of the application field of multi-connected air conditioning systems and the improvement of people’s quality of life, multi-connected air conditioners have gradually introduced fresh air treatment systems, but the problem of fresh air has always been a difficulty in the design of multi-connected air conditioning systems and is also largely limited The further application of the multi-line air conditioning system. The early multi-connected air conditioning system used the ordinary indoor unit of the multi-connected air conditioning system as a fresh air fan to handle the fresh air. This method was used more in engineering due to the simple system. However, the indoor unit coil of the multi-connected air conditioning system is It is designed according to the return air condition of the air conditioner, not the fresh air condition. Therefore, on the one hand, the indoor unit cannot process the fresh air to the indoor state point. Part of the fresh air load needs to be borne by the indoor unit. On the other hand, when the outdoor temperature is high, it will The outdoor unit is overloaded for a long time, and overcurrent protection occurs. At present, there are two more successful treatment methods for multi-connected air conditioning fresh air systems: one is to use heat recovery devices; the other is to use high static pressure fresh air units.

　　 Five, multi-connected air conditioning system design considerations

　　 1. Building energy efficiency

　　 At present, China is at the peak of housing construction. The scale of its construction and the speed of construction are the highest in the history of the world. According to statistics, there are currently about 4 billion square meters of public buildings built nationwide, and building energy consumption will inevitably have a significant impact on my country's energy consumption. Building energy consumption includes the energy consumption of the building process and the energy consumption of the use process. The energy consumption of the building process refers to the energy consumption of building materials, construction, and the whole process of building use. The energy consumption during use, that is, the operating energy consumption of the building, is the energy consumption of people's daily energy use such as heating, air conditioning, lighting, cooking, and laundry. In the total energy consumption of public buildings, HVAC energy consumption accounts for about 50%-60% of the total energy consumption, and it accounts for 65% of the total energy consumption in developed countries. Therefore, the air conditioning design should fully consider the issue of building energy saving. Under the condition of ensuring the same indoor thermal environment and comfort parameters, by improving the thermal insulation and heat insulation performance of the building envelope, increasing the energy efficiency ratio of heating, ventilation, and air conditioning equipment and systems, and adopting measures such as improving the efficiency of lighting equipment to make the building cool , The heat load is reduced, thereby reducing the installed capacity of the air conditioner, and greatly reducing the initial investment and operating cost of the air conditioner.

　　 2. Selection and layout of indoor unit

　　 When the space is large and the ceiling is already flat, the four-sided air supply indoor unit is used. If the plane space is large, a hidden built-in air duct machine can be used. Places with low floor heights are suitable for installing concealed side-blowing or concealed side-blowing indoor units. In order to save space, two forms of secondary ceiling or no ceiling can be used.

　　 3. The layout of the outdoor unit

Concentrated placement of outdoor opportunities in high-rise large buildings has certain limitations. Outdoor units are mostly arranged on roofs and balconies. The effect of ventilation and heat dissipation greatly affects the work efficiency of outdoor units, from energy saving, lower initial investment and actual equipment placement. Considering many factors, such as placing outdoor units in layers on the balcony, more and more forms are adopted. When multiple sets of outdoor units are arranged horizontally, there should be enough spacing to avoid insufficient ventilation; when they are arranged vertically, they should not be directly up and down to avoid short circuit of the hot air of the outdoor unit above. The layered layout of the outdoor unit should meet the following requirements: the air intake is unobstructed without interference, and the exhaust air is smooth and does not flow back to ensure the normal return and exhaust air of the outdoor units on each layer.

　　 4. The indoor unit is used as a fresh air fan to handle fresh air

The fresh air that has not been processed is directly connected to the indoor unit, and the indoor unit bears some of the load of the fresh air. Therefore, the increase in the model of the indoor unit will increase the noise. When the outdoor temperature is relatively high, it will cause the outdoor unit Over-current protection occurs after long-time overload work. At the same time, when the outdoor air humidity is relatively high, the dehumidification capacity of the indoor unit increases, and the indoor relative humidity cannot meet the requirements.

　　 5. Application-specific fresh air blower

　　This type of fresh air blower is mainly designed according to the fresh air condition, which increases the number of rows of the unit coils and can handle the fresh air to the indoor state point. However, the cost of applying this method is relatively high, which affects the application of engineering to a certain extent. At the same time, when the indoor temperature is relatively high, the compressor has been running uninterrupted, which will have a great impact on the life of the unit.

　　 6. Application of total heat exchanger to treat fresh air

　　 In the process of adding fresh air to the room using a full heat exchanger, using the cold capacity of the indoor exhaust air to pre-cool the fresh air will reduce the fresh air load to a large extent and is more energy-saving. This method requires exhaust air. However, it is necessary to arrange the fresh air outlets and exhaust air outlets reasonably, mainly because the system is complicated and cross-contaminated by the fresh air and the exhaust air.

　　 Six, the development trend of multi-line optimization control

　　 At present, more and more attention is paid to energy saving and environmental protection. In order to realize the energy saving and optimized operation of the multi-line system, it is necessary to conduct further research on the multi-line system in terms of software and hardware systems and optimized control methods. First of all, based on technologies such as multivariate and forecasting, overall intelligent control methods that consider comfort and economy will be more developed. In the past, there were fewer overall control strategies for multi-line systems, and the control process focused more on the feasibility of the control process, while few considered optimized control operations, especially for different environmental conditions, building conditions, and comfort conditions. Operation and design optimization research.