Design of the hottest building automation system

Building automation system design

intelligent building is a trend of the development of office buildings and other public buildings, and it is the crystallization of the high development of science and technology. It consists of three subsystems: building automation system, communication automation system and office automation system. In China, fire automation system and security automation system are separated from building automation system to form five subsystems of intelligent building, which is commonly referred to as 5A intelligent building

building automation system (BAS), also known as building equipment automation system, is mainly an integrated system for centralized monitoring, control and management of air conditioning system, water supply and drainage system, lighting system, power transformation and distribution system, elevator and other system equipment in buildings. It is generally a distributed structure, that is, decentralized control and centralized management; It is the key to provide people with a healthy, comfortable and efficient building environment, so the design of this system is very important for an intelligent building

whether to adopt BAS system

whether to adopt BAS system is the first problem that building developers and design engineers must face. Generally, it can be considered from the following aspects:

(1) for buildings that are particularly important and have a certain scale, in order to ensure that their equipment and safety system have high reliability requirements, BAS system can be considered

(2) BAS system can be considered when the one-time investment of BAS system can be controlled below 2% of the total project investment

(3) for buildings with large energy consumption (such as buildings with tens of thousands of square meters and full air conditioning system), BAS system can be considered when the initial investment of BAS system can be recovered within five years

(4) BAS system can be considered for large multi-functional rental buildings

(5) BAS system can be considered when the control and management of the equipment is complex and it is difficult to complete manually, so it must be controlled by juice computer

(6) when BAS system is adopted, its comprehensive indicators of investment and reliability are better than other available systems. The advantages of BAS system and the problems existing in the current project can be considered.

1 BAS system has the following advantages:

(1) improve the management level of the building.

modern buildings have many equipment, which are scattered in all corners of the building, and the equipment management of the building is quite difficult, For some equipment, such as fresh air units hoisted inside the ceiling, the air supply temperature cannot be adjusted by people at all. Bas can easily solve these problems and maintain the equipment management of the building at a high level

(2) reduce the workload of staff

many equipment in modern buildings rely on manpower to maintain daily maintenance. The workload is huge and requires a considerable number of staff. BAS system can automatically diagnose whether the equipment fails, so only a small number of staff can maintain equipment management

(3) save energy consumption

bas system can save a lot of energy consumption by timely adjusting the operation status and quantity of equipment in the building and closing the equipment that does not need to be operated. According to relevant foreign data, if BAS system is used in fully air-conditioned buildings with an area of more than 10000 square meters, the annual operating cost savings can be calculated by 15% - 20% (official statistical value), with an optimistic value of 25% - 30% and a conservative value of 10% - 15%

2 although BAS system has the above advantages, due to its short rise in China, people's understanding of it is not perfect. At present, the completed projects have revealed the following two problems:

(1) the opening rate of the system is low

BAS system rose in China in the late 1980s and early 1990s. So far, hundreds of buildings using BAS system have been completed, but the opening rate is quite low, According to industry estimates, no more than 20%

(2) the energy-saving effect of the opened BAS system is not ideal.

at present, most of the opened bas systems only realize the automatic startup, shutdown and monitoring of building equipment, and their energy saving is mainly manifested in the regular startup and shutdown of some equipment. As a key air-conditioning system of building energy consumption, how to optimize the operation, How to carry out energy-saving and economic operation according to the actual system as much as possible is far from realizing the analysis of

4 problems

although there are many reasons for the above situation, and different buildings have different specific reasons, through comprehensive analysis, we can still find their commonalities:

1. The BAS system itself is caused by

the BAS system in the current market, no matter which system supplier provides the system, It is difficult to realize data communication with the equipment provided by any other construction equipment supplier, which hinders the opening of the system and the optimal management of construction equipment. ASHRAE launched BACnet protocol in 1997, which is applicable to the communication and document transmission between central stations through Ethernet or ARCNET, and also applicable to the communication between various devices in the substation level control network. At present, it is the national standard of building automation system in the United States. The agreement also conforms to the provisions of the national standard JGJ/t16-92 (code for electrical design of civil buildings), and garbage may become the world standard of the industry. This makes it possible to reduce the defects of BAS system itself. It is believed that BAS system meeting this standard will dominate the market in the near future

2 due to factors such as design and construction management, BAS system involves a relatively wide range of knowledge, the system is relatively complex, and the requirements for design engineers are also higher. The practice of most control companies is that the engineers of the equipment discipline put forward the requirements of process parameters, and the engineers of the control discipline design the system. This method can meet the general requirements, but because it is difficult to carry out deep communication between various types of work, and it is difficult to realize the optimal operation of equipment, the energy-saving effect of the system is not ideal; In addition, each type of work performs its own duties, and the interfaces between different systems are easy to be ignored, thus affecting the opening rate of the system; During the construction process, due to the insufficient understanding of the system by the construction management personnel and other factors, the interfaces between different systems are also easy to be ignored, which also affects the opening of the system

3 the air conditioning system is one of the main systems controlled by BAS system, and the energy consumption of air conditioning is the largest user of building energy consumption. The energy-saving performance of the air conditioning system directly leads to the energy-saving performance of BAS system. Many air conditioning engineers believe that BAS system is the business of weak current engineers, and their enthusiasm for it is not high, which also leads to the unsatisfactory energy-saving effect of BAS system

several problems to be paid attention to in the design

1 interface between BAS system and building equipment

the interface between BAS system and building equipment is the first problem to be paid attention to in the design of BA system. It is related to whether the instructions of DDC can directly and effectively act on all building equipment and directly affect whether the system can be opened smoothly. At the beginning of design, the system design engineer should put forward interface requirements to the developer or the supplier of the electrical control box of construction equipment. For example, the electrical control box should provide contacts such as manual/automatic conversion, on/off command, on/off state, fault/fault state and the requirements for these contacts, or suggest the developer to choose and purchase construction equipment according to which agreement; When the equipment arrives, the design engineer and other relevant engineers shall inspect the goods according to the design requirements, so as to avoid that DDC's instructions cannot directly and effectively affect the construction equipment and affect the smooth opening of the system

2 the signal type of sensor and actuator is consistent with the signal type of control module

whether the input and output signal type of sensor and actuator is consistent with the input and output signal type of control module is directly related to whether the BA system can be opened smoothly, which should be paid attention to in design. Generally, we should pay attention to two points:

(1) whether the two types are consistent

with the development of sensor and actuator technology, their input and output signal types are also changing. For example, the signal type of temperature sensor is generally analog input (AI), while the signal type of temperature sensor using duty cycle technology is digital input (DI); The signal type of electric control valve is generally analog output (AO), while the signal type of electric control valve using floating-point control technology is digital output (do). Therefore, it is not feasible to assume that temperature sensor is AI signal and electric control valve is do signal only based on experience

(2) when the two types are consistent, we should also pay attention to whether to match

when the two types are consistent, there is also a problem of whether to match. For example, AI signal has the difference of 2-10v and 4-20mA, while Di signal has the difference of frequency. The AI signal of 4-20mA can only be connected to the AI module version of 2-10v after processing, while the di signal with pulse interval of MS level may produce false alarm and other problems after it is connected to the di module version of s level

3 installation position and method of sensor

sensor is the "eye" of BAS system. Its working condition directly affects the control effect of BA system on the controlled object. According to the relevant literature, the sensor failure accounts for more than 60% of the system, so graphene can be used as a modified additive to prepare high molecular functional materials, which shows the position of the sensor in the system. Generally, the sensor has certain requirements for the installation position and method. If it is not paid attention to in the design, the following effects will be produced:

(1) the sensor cannot work normally, and the system cannot adjust

some sensors, such as air flow sensor, water flow sensor, water flow switch, etc., have certain requirements for wind speed and water flow speed. If they are installed in a dead corner or dead zone, they may not work normally; Another example is that the water flow switch is required not to be hit by water. If it is installed at the downstream of the valve, it may be damaged due to the occurrence of water hammer, and it will not work normally; Similarly, incorrect installation of sensors will have similar results

(2) the sensor works normally, but does not correctly reflect the parameters of the controlled area

in the current project, when controlling the air handling unit, many control manufacturers control the temperature of the controlled area by monitoring the parameters of the plastic packaging additive returned to Neo plastics, which aims to convert the waste in the landfill into useful biogas wind. Temperature and humidity sensors that detect return air parameters are often installed on the return air duct of the machine room. In many projects, hydraulic oil is hoisted. 7. It is necessary to often check the liquid level of the oil tank and replenish oil in time; Generally, the oil should be changed every 2000 to 4000 hours; However, Zui's important thing is that the oil temperature should not exceed 70 ℃, and the top return air is only set up a section of return air pipe in the machine room. Due to the rise of hot air and the decline of cold air, the temperature of the air in the ceiling is several degrees higher than the temperature of the controlled area, which can no longer represent the temperature of the controlled area. At this time, no matter how perfect the control program is, it will not have a good energy-saving effect

4 group control problem of cold source system

cold source system includes chillers, cooling towers, chilled water pumps and cooling water pumps, which interact with each other and constitute the water system of air conditioning system, which is the key to energy consumption of air conditioning. Among them, some equipment is also equipped with their own microcomputer control system, but this can only ensure the best operation of the equipment, not the best operation of other equipment, let alone the optimal operation of the whole cold source system. Using the good communication function between the DDCS of BAS system and the powerful computing function of the central computer, the