Building energy consumption refers to the energy used in the process of building construction and operation, in which energy utilization is the dominant part, including the energy consumption of building refrigeration, heating, lighting, ventilation and cooking. The energy-saving transformation of building envelope, lighting system and heating system is discussed. In China, the real "big energy consumer" is the air conditioning and ventilation system. Air conditioning is closely related to the energy shortage in winter and summer in China, especially the current power shortage. With the rapid popularization of air conditioning, its status as a major energy consumer in buildings has become increasingly prominent. By 2020, the national peak load air conditioning energy-saving space is about 90 million kilowatts, which is equivalent to the total capacity of five Three Gorges power stations, and the corresponding investment in power construction can be reduced by more than 400 billion yuan. Therefore, the energy saving of air conditioning and ventilation system is the most important, with great and far-reaching significance. Next, the author will introduce the energy-saving measures of air conditioning and ventilation system from the demand side. The common cold and heat sources of central air conditioning are water-cooled chillers, heat pumps and lithium bromide absorption units. The energy efficiency of the first cold and heat source is relatively high under design conditions, generally 3.7 ~ 5; The second cold and heat source is the heat pump unit, which cools in summer and heats in winter. Under the design condition, its energy efficiency is lower than that of water-cooled unit, only reaching about 3, but it has good energy-saving and environmental protection effects; Another cold and heat source of central air conditioning is lithium bromide absorption unit, which has low energy efficiency ratio (refrigeration capacity/heat consumption) and is suitable for places with excess heat and waste heat. Comparison of energy utilization efficiency of building cold and heat source system In addition to the selection of cold and heat water units, the energy saving of air conditioning and ventilation system can also be realized by automatically controlling the start and stop of cold and heat source host system. As shown in the following figure, it is a logical control flow that controls the number of start-stop units according to the backwater temperature of chilled water, and uses the host signal and fault alarm signal to form feedback. Frequency conversion air conditioner with frequency conversion system refers to conventional air conditioner with frequency converter. Compressor is the heart of air conditioning, and its speed directly affects the efficiency of air conditioning. Frequency converter is a control system used to control and adjust the speed of compressor, so that it is always in the best speed state, thus improving the energy efficiency ratio. The application of frequency conversion technology in modern air conditioning has become an inevitable trend, which can not only effectively improve the technical deficiencies of air conditioning systems, but also greatly reduce energy consumption and save operating costs. Designers usually leave a certain design margin when choosing equipment. In fact, equipment rarely runs at full capacity, or even never runs at full capacity. The load of the building will change correspondingly due to the change of use (such as low occupancy rate, change of building function, etc.). The actual load of the building will fluctuate with the change of outdoor climate. Usually, air conditioning equipment can only operate according to the designed rated power. When the load is reduced, the equipment still runs at full output of rated power, which will inevitably lead to a waste of energy. If we can use frequency conversion technology to make the output power of air conditioning equipment change with the change of load, then we can save energy. According to the air conditioning load, changing the water flow or air flow can effectively save energy. VAV air conditioning system compensates the change of indoor load through the terminal device, and adjusts the air supply volume to maintain the room temperature. Compared with constant air volume system, variable air volume system can generally save energy by 50%. Variable water volume system (fan coil unit) adjusts the temperature through water volume control, which saves electricity compared with constant flow system. With the popularization and application of industrial frequency converters, through frequency conversion control and adjustment, real-time matching of water flow, air volume, main engine and required air conditioning load can be realized, resulting in significant energy-saving benefits. As shown in the following figure, the variable air volume air conditioning system often uses a frequency converter on the input power cord of the fan, and changes the speed of the fan according to the instructions of the control system to meet the design of the air conditioning system. Fresh air control According to the requirements of comfort, the total fresh air volume is generally controlled at about 10% of the total air volume, which can save energy. In some air conditioning systems, the return air volume is less than 90%, and the return air volume is too small to excessively increase the fresh air heat load, which is not considered as energy-saving operation. Using automatic control technology to realize fresh air control is an effective way to realize energy saving of air conditioning and ventilation system. After the air conditioning system is determined, the psychrometric chart can be divided into several meteorological areas (air conditioning working areas) according to the local meteorological changes, and different operation adjustment methods can be adopted for each air conditioning working area. The basic requirements are as few regulating mechanisms as possible, simple regulating methods, the most economical and reasonable operation of the system in various working conditions, the maximum utilization of natural energy, the reduction of cold, heat and electric energy consumption and the reduction of operating costs. Energy-saving of pumps and fans Fans and pumps are almost indispensable equipment in air-conditioning systems, and they are also one of the most power-consuming equipment in air-conditioning systems. The power consumption of pumps in large and medium-sized central air-conditioning systems even accounts for about 30% of the power consumption of the whole system. The main problems of pumps and fans are as follows: ① In order to reduce the initial investment, the quality of the selected pumps and fans is not high, and the rated efficiency is lower than the advanced level. (2) The system design is unreasonable, with a big horse-drawn cart and a big difference. During operation, the pump and fan deviate from the optimal working area on the performance curve, and the operating efficiency is far lower than the rated efficiency. (3) Unreasonable design and installation of transportation pipeline, large pipeline resistance and increased energy consumption. (4) The hydraulic imbalance of the pipeline can only be adjusted by valves or rams, which increases the throttling loss. (5) improper maintenance, pumps and fans often work in spite of illness, wasting energy. General energy-saving measures are as follows: ① Renovation, replacing the original pumps and fans with efficient pumps and fans. (2) Select the pump or fan characteristics that match the system characteristics. The pipe network characteristic curve should pass through the highest point of efficiency as far as possible. For the pipe network system with large flow characteristics, the pump with flat efficiency curve should be selected as far as possible. ③ Install measuring instruments on the main pipeline. ④ Cutting the impeller to reduce the diameter. If the flow and lift of the selected pump are far greater than the actual demand, the simplest method is to reduce the impeller diameter, thus reducing the shaft power. However, this method is only applicable to systems with relatively stable lift. ⑤ Adjust the inlet guide vanes to change the flow pressure curve of the water pump or fan. Imported guide vanes are widely used because of their wide adjustment range, low cost, high economy and automatic adjustment. To sum up, with the development of modern science and technology, the automatic control system of air conditioning is becoming more and more mature. In order to make full use of air conditioning system resources and achieve more significant energy-saving regulation effect of ventilation system, we should pay attention to the development of new technologies, constantly practice and optimize energy-saving systems, achieve high standards and requirements in design, and achieve high energy efficiency on the basis of satisfying comfort.

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