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Discussion on HVAC design and energy-saving operation


With the global climate change and the deterioration of the natural environment, countries around the world are paying more and more attention to building energy efficiency. It is increasingly recognized that carbon dioxide from energy used in buildings is a major source of climate warming. Innovation in HVAC technology is imperative, and energy-efficient buildings have become a necessary trend in building development.

First, the main technology and working principle of HVAC

HVAC technology refers to the use of heating and cooling technologies for heating, ventilation, and air conditioning, and the use of artificial means to adjust and control the temperature, humidity, and cleanliness of the room or work area. It is an integral part of architectural design. The energy-saving technology of HVAC refers to get the most heat energy with the least energy as much as possible in the heating aspect, mainly through the external wall insulation system, air flow organization, resetting the chilled water temperature, using a full heat exchanger system, and increasing the air conditioning temperature And other settings to reduce energy consumption. The energy consumption of the HVAC system is mainly determined by the determination of the cooling and heating load of the air conditioner and the reasonable configuration of the air conditioning system. The setting of the air conditioning system and the selection of the air conditioning equipment are based on the air conditioning load. Therefore, the key to HVAC energy saving is to determine the external load and internal load of the air conditioner. The energy saving work of the HVAC should also start from this aspect, rationally arrange the location of the building, and correctly select the shape of the outer wall, door, window, and roof. Materials, etc., to minimize air conditioning load.

The main working principle of HVAC is that the refrigerant exchanges heat with the chilled water in the evaporator of the air-conditioning refrigeration unit to vaporize. This process will reduce the temperature of the chilled water, and the gasified refrigerant will be at the air pressure. Under the action of the engine, high pressure and high temperature gas will be formed. When the gas flows through the condenser of the refrigeration unit, it will be cooled by the cooling water from the cooling tower, so that the gas is transformed into a low pressure and low temperature liquid. The cooled chilled water is sent to the heat exchanger of the air processor through the water pump, and then exchanges cold and heat with the mixed air to form a cold air source, and finally it is sent to each room through the air supply pipe. Through such a cyclic process, the heat in the room will be taken away by the cooling water in the summer, and then passed through the cooling tower and released into the air. In the air processing unit, the fresh air and a part of the return air are mixed to form a mixed air, and the mixed air forms a supply air after the heat is exchanged through the chilled water of the heat exchanger. In winter, the mixed air can absorb energy to increase the temperature. In summer, as the temperature of the mixed air decreases, the supply air will transfer heat with the indoor air after entering the room, and finally adjust the temperature to the room's required settings. Value.

Design direction and principles of HVAC systems

Since air-conditioning heating and ventilation equipment is an important component of the HVAC project, it is one of the most important factors affecting the operation effect after the project is completed. The current design direction of HVAC system is energy saving first. In the design of high-quality indoor environment of buildings, HVAC professional designers must actively participate in the design of building solutions from the perspective of energy conservation and environmental protection. In the past, pure professional design was cross-professional collaborative design. We must pay close attention to the latest energy-saving scientific research results, actively adopt and promote new energy-saving technologies, strive to obtain government support, maintain close contact with equipment manufacturers, do a good job of energy-saving work for owners, and strive to win their Understand and support basic national policies to achieve sustainable development. The second is noise reduction. Modern society has strict control over noise pollution, and noise during operation of HVAC systems is one of the most important noise sources. The noise reduction design of the air-conditioning system should pay attention to the following aspects: the air-conditioning machine room cannot be located near the crowded underground, and the underground equipment room located in the skirt room can minimize the impact of vibration and noise. The combined air conditioner should use dual fans. Reduce the wind pressure of the fan and reduce the noise level of the fan. There should be a certain length of underground return air duct from the underground air-conditioning room to the crowd of people, which increases natural attenuation. At the same time, the exhaust system is equipped with an impedance composite muffler to block external noise. The third is self-cleaning, in HVAC design. Designing a good purification air-conditioning system and maintaining a good indoor building environment and air quality is the key to optimizing the built environment. The ideal purification air-conditioning system must control the above two functions and meet the specified technical parameters in order to meet the requirements of some special indoor building environments and air quality.

The HVAC system, especially the central air-conditioning system, is a large and complex system. The design principles mainly include: First, the HVAC system must be managed and designed scientifically and reasonably according to the changes in heat and cold. For HVAC systems, the air conditioning load through the maintenance structure accounts for a large proportion, and the thermal insulation performance of the maintenance structure determines the size of the comprehensive heat transfer coefficient of the maintenance structure, that is, the size of the air conditioning load through the maintenance structure. The second is that HVAC is designed and managed with relatively energy-efficient new materials. There are many environmental parameters that affect the thermal comfort of the human body. Different combinations of environmental parameters can get the same thermal comfort effect, but different combinations of thermal and humid environment air conditioning systems. The energy consumption is different. The third is to choose some renewable energy-saving energy in the selection and utilization of energy, which is of great significance for the construction and management of HVAC, and how to use renewable energy and low-grade energy has become important in this field. Research topics. The ground source heat pump air-conditioning system was developed in this situation. It uses the soil heat in the underground constant temperature layer to significantly increase the COP value of the air-conditioning system, which greatly reduces the energy consumption of the system under the same heating (or cooling) capacity. In addition, solar heating or cooling technology is also being developed.

3. Energy-saving operation of HVAC systems

In the operation of HVAC systems, fans and pumps are needed to transport the medium. The power consumption of the water pump of the air conditioning system is large. In general public and civil buildings, the air conditioning water system can account for about 15-20% of the total power consumption of the air conditioner. Therefore, reducing the power consumption of the air conditioning pump can also play a significant role. Energy saving effect. Water system energy conservation should pay attention to water system design, carefully design and calculate the loops of the water system, and take corresponding measures to ensure the hydraulic balance of each loop. In some current air-conditioning system designs, variable-frequency pumps are becoming more and more common for variable-flow operation. By changing the speed of the pump motor to control the flow of the pump, and by using variable-frequency speed-regulating water pumps to change the water volume with cooling and heating loads, it can be very obvious. Skill effects. Some data show that air-conditioning water system has a great energy-saving capacity by using variable flow operation, and the investment of the inverter can be recovered within 1 to 2 years. Other data show that increasing the temperature difference between the supply and return water of the air conditioning system, reducing the circulating water volume of the system, thereby reducing the power consumption of the circulating water pump. At present, the temperature of the chilled water supply and return water for general air conditioners is 7 ~ 12 ℃, and the water temperature difference is 5 ℃. If we increase the temperature difference between the supply and return water to 8 ℃, that is, the temperature of the chilled water supply and return water of the air conditioner is 6 ~ 14 ℃, then the system water volume will be reduced by 30%. Although the chilled water supply temperature has been reduced by 1 ° C, the refrigeration coefficient has been reduced for the refrigerator, but in terms of the integrated water pump and refrigerant, it is actually energy-saving in general.

In addition, a large part of the energy consumption of air conditioners is caused by poor management. The implementation of various adjustments and energy saving measures is also related to the technical quality of the operators. In actual operation, the system did not make necessary adjustments based on changes in personnel and actual loads, which caused the cooling, water, and air supply volumes to be greater than the actual demand. Even with certain adjustments, it also has lagging and randomness. This will cause a lot of waste. For example, the air-conditioning of some units only has the power-on and shutdown and winter-summer switching operations during the year. Obviously, the energy-saving effect cannot be achieved. To this end, operation managers must not only have a strong sense of responsibility, but also strengthen the training of air-conditioning operators. The quality of management staff. In addition, adding measures such as system control, such as self-operated flow control valves, differential pressure controllers, temperature controllers, etc. can also improve the system's automatic control level. The control mode needs to be flexibly dealt with according to the specific functions of the building, climatic conditions, and usage conditions. For example, the annual operation management problem should mainly consider the operation of the transition season: the use of outdoor fresh air, the determination of the amount of fresh air, etc .; and for the daily operation management problem, it should mainly consider adopting different daily energy-saving operation modes as the outdoor temperature changes. This is achieved through the use of a reasonable automatic control system and a certain manual adjustment device. Another example is the reasonable selection of building pre-cooling and pre-heating time. The choice of building pre-cooling and pre-heating time will directly affect the size of the cooling and heating equipment, thereby affecting the initial investment. Especially for large-capacity buildings such as stadiums with large spaces, how to ensure that they do not affect normal use, but also achieve energy saving or investment savings, a reasonable choice of pre-cooling and pre-heating time is the key.

Fourth, the conclusion

In short, the HVAC system plays an important role in building energy conservation and plays an important role. The research and development and application of energy-saving technologies are the basis for energy-saving of HVAC systems and building systems. During the design and operation of air-conditioning systems, sufficient attention should be paid to energy conservation and consumption reduction, and energy consumption should be used as a measure of system pros and cons. An important indicator.

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With the rapid development of China's socio-economic development, people's material living conditions have improved significantly, and the requirements for living environment have been continuously improved. In various domestic construction projects, the amount of heating, ventilation and air-conditioning installation has continued to increase. The requirements for installation quality are also getting higher and higher. Air conditioning is actually air conditioning. Through the treatment of air, the air temperature, humidity, air velocity and cleanliness in a certain area can reach certain requirements. Ventilation and heat supply of high-rise buildings depend to a large extent on the installation and improvement of air-conditioning systems. To achieve the scientific design of buildings and energy-saving design of air-conditioning installation, the building's air-conditioning system should be reasonably designed to maximize the use of natural ventilation systems and strive to achieve A good combination of heating and ventilation and air conditioning systems in buildings.

Analysis of heating ventilation and air conditioning installation technology

1 Common problems in heating ventilation and air conditioning installation

The problem of positioning of pipelines and equipment and the intersection of elevations. In current domestic heating and ventilation and air-conditioning projects, design drawings are mostly drawn using CAD software. In the early stages of the design of related projects, the positioning of relevant pipelines and equipment must be determined. Elevation, but due to the effects of preliminary survey work, calculation methods, review and other factors, the positioning and elevation in the design drawings often have problems that are not well adapted to the actual installation environment. In particular, the occurrence of pipeline and equipment positioning and elevation crossing will seriously affect the quality of the installation project. If the pipelines and equipment in heating and ventilation and air-conditioning installation have positioning and elevation crossing problems, the installation may be affected or even appear. Rework phenomenon.

The problem of water circulation of air conditioners. In the heating and ventilation and air conditioning installation projects, the water circulation problems of air conditioning chilled water systems are more common, and the pipeline circulation effect is ultimately poor. The main causes of water circulation problems of air conditioners are: the water circulation pipes of air conditioners intersect with other professional pipelines, and the effective coordination and treatment are not carried out during the installation process, which affects the circulation effect of the chilled water system; The pipes of the system have not been cleaned or are not thoroughly cleaned, causing the pipes to be blocked to varying degrees, restricting the water circulation effect of the air conditioner, and the cooling effect of the equipment will also be affected.

The problem of dew condensation on the equipment. In the installation of heating ventilation and air conditioning, effective processes and technical measures must be taken. The cause of the problem of dew condensation on the air conditioning system during operation can be summarized as follows. During the installation, the relevant operating procedures could not be strictly implemented; the quality of materials such as pipes and fittings used in the installation project did not meet the standards, and no strict quality inspection was performed when the materials entered the site; due to the long condensate pipeline of the air conditioning system, During the installation process, it may collide with the ceiling, or it is difficult to ensure its slope, which will cause dripping of the condensation pipe of the air-conditioning system. The thickness of the insulation material does not meet the standards, which will cause the exterior temperature of the insulation material to reach the dew point temperature during operation. The phenomenon of dripping water.

Some construction units only care about one-time investment control, ignore the running cost of the air-conditioning system after completion, and ignore the energy-saving requirements of the air-conditioning system. Most of these reasons are caused by the inconsistency between investors and users. This situation makes some air conditioning systems lack the necessary energy-saving automatic control facilities. The operation and management level of some air-conditioning systems is low. Although the design of the air-conditioning system is reasonable, the operation and management level cannot keep up and waste energy. Many units share a set of air-conditioning systems, and do not install air-conditioning billing systems. They simply share air-conditioning operating costs by area, causing human waste.

2 Control elements for heating and ventilation

2.1 Room temperature setting

Determining a reasonable indoor temperature is an inevitable requirement for establishing a scientific and reasonable building indoor heating and ventilation system after the installation and operation of the air-conditioning system. For most air-conditioning systems, if the temperature is too high in winter, it will consume more heat. Lowering the temperature in summer will also consume more cooling. Therefore, the heating and ventilation system should be established according to the actual temperature requirements of the room. On the basis of meeting the basic temperature setting requirements, the temperature and humidity generated in the building's interior should be increased as much as possible, and in winter, it should be reduced as much as possible. The larger the fixed interval, the more effectively the energy consumption of the air conditioning system can be saved.

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