I. Overview of HVAC System
(1) Types of HVAC systems
There are many kinds of HVAC systems, but the basic principles of these systems are the same. Common ones are: full water system, air-water system and full air system.
1. Total water system: a system using fan coil units, composite ventilation devices or indoor terminals of gravity circulation. Unregulated ventilation air may penetrate or be sent out through the vents in the wall. The biggest advantage is that it can meet the requirements of many buildings for air conditioning and can be flexibly applied to the transformation of air conditioning systems.
2. Air-water system: This system usually uses cold water to take away most of the sensible heat load in the air-conditioned space, and uses air to provide ventilation to ensure the air quality and take away the moisture brought by the latent heat load in the space.
3. All-air system: In this system, all requirements of air-conditioned space (such as humidification, heating, cooling and dehumidification) are met by air supply.
(2) HVAC design principles
1. It is necessary to find out the position of the building in the general design drawing, the laying methods of heating, water supply and power supply pipelines in adjacent buildings and their surroundings, and the possible interface positions. This can be used as an objective condition for designing the heating entrance of this building. It can also be used as a reference to consider factors such as wind power and sunshine when calculating load, and the way to determine the gate can also be based on the orientation of the main gate.
2. Designers should be clear about the number of people in the building, the use time, whether there is exhaust gas to be discharged, etc. , as the basis for calculating load and dividing system.
3. Division of fire partition, smoke partition, firewall position and fire evacuation route. If you don't understand these problems, designers can't design smoke control systems and don't know where fire dampers are located.
Second, the problems that should be paid attention to in HVAC design
Directionality and overall situation are the main problems of HVAC design scheme. This is not only related to whether the indoor environmental parameters of high-rise buildings can meet the use requirements, but also directly related to the maintenance cost, engineering investment, reliability, comfort and safety of the system. If the scheme design is unreasonable, it will cause great losses, and it will be difficult to modify and affect for a long time.
Reliability and feasibility
The primary problem that should be considered in the feasibility of design scheme is to meet the use requirements of ventilation and heating in high-rise buildings. The design scheme shall meet the requirements of relevant national and local government regulations, including the requirements of environmental protection. The design scheme should meet the requirements of power supply, gas supply, water supply, heating and other related aspects, and should focus on the long-term changes of these conditions. For some technical HVAC design projects that require high or special temperature and humidity parameters, designers should analyze the annual working conditions of the design scheme to ensure its adaptability under various outdoor meteorological conditions throughout the year. In the design process, the staff should comprehensively consider various factors to ensure the reliability and feasibility of the design scheme, ensure the construction quality and improve customer satisfaction.
(b) Security issues
Fire safety, personnel environmental safety, flammable and explosive environmental safety, environmental safety of important equipment and articles, and operation safety of system equipment are the main safety factors of HVAC system in high-rise buildings. Through the improvement of engineering design, equipment development, operation management, specifications and technical measures, the safety of HVAC system is realized and improved. For example, in the design of ventilation and air conditioning systems for inflammable and explosive projects such as coal mines, warehouses and ammunition workshops, safety is the primary consideration, and designers should adopt corresponding explosion-proof technical measures and schemes. In the design process of oil-fired and gas-fired boiler rooms, the safety problems caused by flammable gas and liquid leakage should be considered, and the flammable gas leakage alarm system and emergency ventilation system should be set up and interlocked with each other to improve safety. Fire safety should be considered in accordance with relevant fire protection design specifications, and the safe operation of equipment mainly includes the safety of refrigeration system.
(3) Economic comparison
An important issue in the comparison of HVAC schemes for high-rise buildings is the economic comparison. Designers should make comparisons under the same design requirements and conditions. Only in this way can the rationality of scheme comparison results and the scientificity of public works design be guaranteed. What investors are most concerned about is one-time investment, and the calculation should be comprehensive and accurate, and there should be no omissions. The one-time investment of HVAC design scheme includes all kinds of materials, equipment and pipelines, related water treatment, power distribution and control, corresponding installation, debugging and project management expenses, and civil engineering investment of computer room and corresponding outdoor pipelines.
The important parameters to be considered in the technical and economic comparison of HVAC design schemes are operation energy consumption and operation cost. The operating energy consumption of HVAC hosts (boilers and refrigerators, etc.) should be calculated. ) and other auxiliary equipment (such as fans and pumps, etc. ). When calculating, we must consider the change of the actual load of the building and the efficiency of the equipment in the non-standard state when it changes all the year round. When comparing the energy consumption of high-rise teaching buildings, office buildings, office buildings and other buildings, the running time of HVAC equipment should be considered comprehensively. The prices of various energy sources may be different in different periods, regions and time periods. Due to many influencing factors and uncertain factors, how to accurately calculate the annual actual operating cost and energy consumption of HVAC equipment in high-rise buildings is still a technical problem that has not been completely solved at present.
Supervision and operability
The capacity of HVAC system in high-rise buildings is determined according to the most unfavorable meteorological conditions throughout the year, so HVAC system should have good regulation performance to adapt to the change of load throughout the year. In economic analysis, the system scheme with good regulation performance should be considered comprehensively, which has the advantages of high one-time investment but low operating energy consumption. In addition, the convenience of air conditioning system management and operation has a great relationship with whether automatic control is adopted, and designers should make technical and economic comparison and determination according to actual conditions and requirements during design. The automatic control of air conditioning system can reduce the number and labor intensity of system managers and reduce the labor management fee, but the one-time investment of the project increases, and the quality requirements for operators also increase accordingly. In the design process, designers should generally follow the principle that large-scale air conditioning systems and projects with more equipment that need frequent adjustment and control should adopt automatic control, but the automatic control system should be simplified as much as possible to improve the economy and reliability of the system.
Third, the importance of energy saving in HVAC system
The rapid development of economy is inseparable from the support of energy, so with the development of economy and the increase of population, people's demand for energy is also increasing gradually. Not only China, but also many countries are facing the problems of energy depletion and sharp increase in demand. Therefore, in order to improve the challenges brought by energy shortage in China, China has made improvements in urban construction and increased investment. In addition, with the rapid development of cities, urban energy conservation is also being implemented simultaneously. At present, the energy consumed by residential construction is close to 50% of the total energy consumption, and the large consumption of energy has also caused great damage to the environment. In many buildings with high energy consumption, especially building air conditioning consumes the most energy. In China, the energy consumption of air conditioners in hotels, restaurants and office buildings accounts for about half of the total energy consumption, while some types of air conditioners will consume more energy. However, despite this, with the increase of per capita living area, the heating energy consumption of HVAC system is also increasing gradually, which intensifies the contradiction between energy supply and demand in China to another height.
Four. conclusion
With the progress of society and economy, people have higher requirements for architecture and living environment, so the design of HVAC should also keep pace with the times and constantly innovate and develop. The success or failure of HVAC engineering in high-rise buildings and its economic benefits are directly related to the choice of HVAC design scheme. In the design process, we should also handle all the details of the design link perfectly. Therefore, HVAC designers must carry out scientific design, comprehensively consider various factors, and make the HVAC design scheme play the maximum function and economic benefits.
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