The development of HVAC technology plays a vital role in building energy saving. Under the background of energy crisis, energy-saving buildings will become the development direction of future buildings. With the continuous improvement of people's requirements for residential comfort and hygiene, HVAC systems occupy an important proportion in building energy consumption. By analyzing the composition and main characteristics of energy consumption of HVAC system, this paper puts forward solutions and methods for the problems existing in energy saving at present. Building energy consumption refers to building energy consumption, including heating, ventilation, hot water supply, cooking and household appliances. Among them, the energy consumption of building heating and air conditioning accounts for 50%-70% of the total energy consumption of the building. With the rapid development of China's economy and the continuous improvement of people's living standards, building energy consumption in China is increasing. Therefore, the development and innovation of new products, new technologies and new materials in HVAC specialty plays a vital role in the future development of architecture. 1 energy consumption composition and main features of HVAC system With the rapid development of China's national economy, energy and environmental problems are becoming increasingly acute, the rapid development of urbanization and the improvement of people's living standards, building energy consumption accounts for an increasing proportion of total energy consumption, reaching 40% in developed countries, while HVAC energy consumption accounts for more than one third of building energy consumption, and it is on the rise year by year. In order to maintain the proper temperature and humidity of the air environment in buildings, HVAC systems are usually installed in modern buildings to ensure this demand, and the energy consumed is the energy consumption of HVAC systems. This part of energy consumption includes energy consumption caused by building cooling and heating load, energy consumption caused by fresh air load and energy consumption of conveying equipment (fans, pumps). The main factors affecting the energy consumption of HVAC system are outdoor climate conditions, indoor design standards, envelope characteristics, lighting conditions of indoor personnel and equipment, and the setting of fresh air system. The energy consumption of HVAC system also has several characteristics: First, the unreasonable design, selection and operation management of the system will reduce energy efficiency. Second, the level of cold and hot energy needed to maintain indoor air environment is low and seasonal. This makes it possible to use natural gas energy to meet the requirements when conditions permit, such as solar energy, geothermal energy, waste heat, shallow soil heat storage and so on. Thirdly, the hot and cold treatment involved in HVAC systems is usually handled in the form of exchange. Therefore, cold and heat recovery measures can be taken to reduce system energy consumption and effectively use energy. 2. Problems existing in energy saving of HVAC system at present 2. 1 Design and construction management of HVAC system The design of HVAC system has an important impact on energy saving of HVAC system. However, in practical work, it is often not paid enough attention by some design departments and designers, the engineering design cycle is generally short, the design fee is not linked to the economic benefits generated by the design, and some technical problems are not completely solved. Some design units only seek quantity and neglect quality, which makes the designed and built system not only invest a lot, but also consume an amazing amount of energy, which greatly exceeds the national standard. Even the energy consumption of HVAC in some public buildings accounts for 60% of the total energy consumption of buildings. In addition, at present, the level of HVAC professionals in the construction industry is uneven, and a large part of them are not graduates of their professional colleges or non-professional counterparts, and some even have not received any training at all. They often use the usual scheme or the scheme specified by Party A according to experience, so some problems related to scheme adjustment in design or construction cannot be handled and solved in time and correctly, which eventually leads to irreparable adverse consequences of the system and leaves hidden dangers for the operation and management of the system. 2.2 Energy-saving design scheme of HVAC system In recent years, with the continuous improvement of energy-saving and environmental protection requirements, new technical schemes are constantly emerging, and each technical scheme often has its own advantages and disadvantages. In the face of numerous design schemes, due to different angles of consideration, the evaluation results of various aspects are often different, even very different; Due to the lack of scientific and objective evaluation methods for design schemes, designers are often at a loss. How to find the most suitable energy-saving scheme among many design schemes is an important topic that puzzles HVAC designers. On the other hand, unscientific evaluation methods will play a misleading role and cause serious losses. 2.3 HVAC system operation management Besides design and construction, operation management also plays an important role. In practice, some units think that the design and construction can meet the standards, and do not pay attention to the training of HVAC operators. Many operators do not have the necessary basic theoretical knowledge of HVAC and do not know how to adjust according to the changes of outdoor parameters. Only start-up, shut-down and switch operation in winter and summer all year round, obviously the system can not achieve the corresponding energy-saving effect. 3. Effective ways and methods to save energy in HVAC system 3. 1 Carefully design HVAC system to make it run in an efficient and economical state. HVAC system, especially central air conditioning system, is a huge and complex system, and the design of the system directly affects the performance of the system. It can be said that the design of air conditioning system plays an important role in energy saving of the system. 3.2 Improve the thermal insulation performance of building maintenance structure and reduce cold and heat losses. For HVAC systems, the air conditioning load through the maintenance structure accounts for a large proportion. The thermal insulation performance of the maintenance structure determines the comprehensive heat transfer coefficient of the maintenance structure and also determines the air conditioning load through the maintenance structure. Therefore, in the national building energy-saving design codes and standards, the primary requirement is to improve the thermal insulation performance of the maintenance structure. 3.3 Adopting new energy-saving and comfortable air conditioning mode, there are many environmental parameters that affect human thermal comfort. Different combinations of environmental parameters can obtain the same thermal comfort effect, but the energy consumption of air conditioning systems with different combinations of thermal and humid environmental parameters is different. For example, in winter, if the whole indoor air is heated by traditional air conditioners, and the heat and moisture exchange between human body and environment is realized through air, higher air temperature is needed. At this time, the heat loss by maintaining the structure and heating fresh air is relatively large. If we change the traditional air conditioning mode and increase radiant heat (such as low-temperature floor radiant heating) according to the research results of thermal and humid environment, the required air temperature will drop obviously, generally reaching 12 ~ 14℃, while the traditional mode is generally 18 ~ 20℃. Obviously, the latter has a significant energy-saving effect than the former. Summer has a similar result. 3.4 Popularization and application of air conditioning systems using renewable energy or low-grade energy How to use renewable energy and low-grade energy has become an important research topic in this field. Ground source heat pump air conditioning system is developed in this situation. It significantly improves the COP value of air conditioning system by using the soil heat in the underground constant temperature layer, and greatly reduces the energy consumption of the system under the same heating (or cooling) amount. In addition, solar heating or cooling technology is also under development. 3.5 Carry out research and application of cold and heat recovery to maximize the use of energy. At present, many researches on cold and heat recovery of air conditioning system are also vigorously carried out, such as the total heat recovery device for exhaust air of air conditioning system, and the supply of sanitary hot water by condensing heat in summer, all of which have recovered the cold and heat of the system and significantly improved the energy utilization rate of air conditioning system. 3.6 Strengthen system operation management and improve system control level. Train HVAC professional operators, improve the professional level and business skills of managers, make them have the necessary basic theoretical knowledge of HVAC, and implement the operation certificate system for air-conditioning operators. Those who fail to meet the assessment requirements should be retrained and can only be employed after passing the assessment. At the same time, improve the quality of managers and enhance their sense of responsibility, so that managers can make corresponding adjustments according to the changes of outdoor parameters to achieve the energy-saving effect required by the design. Conclusion With global warming and the deterioration of natural environment, countries all over the world pay more and more attention to building energy efficiency. It is increasingly recognized that carbon dioxide produced by building energy is the main source of climate warming. It is imperative to innovate HVAC technology, and energy-saving buildings have become the inevitable trend of architectural development. At present, the power supply in all parts of China is very tight, but the required energy is also growing rapidly. Therefore, attention should be paid to improving the thermal performance of envelope and the thermal insulation performance of thermal equipment in air conditioning design; The scheme of air conditioning system should save energy, fully recover energy, make full use of natural gas energy as much as possible, and take measures such as self-control and energy saving.

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