1 building automation system design
The building automation system is the abbreviation of the building equipment automation control system. Construction equipment mainly refers to a large number of electromechanical equipment, such as HVAC equipment, lighting equipment, power distribution equipment, and water supply and drainage equipment, which are provided for building services and provide basic living environment (wind, water, electricity). Realize the automatic control of construction equipment to achieve rational use of equipment, save energy, save manpower, and ensure the safe operation of equipment.
In the past few years, people mentioned the building automation system, which mainly refers to the automatic control system of HVAC equipment in buildings. In recent years, it has covered all the controllable electromechanical equipment in the building and has become a "smart building". The basic link of lack. The development of building automation systems has also gone through the process from scratch to low-level to high-level, which is actually the epitome of the development of an industrial automation control system. With the development of information technology, network technology, computer technology, communication technology, display technology, semiconductor integration technology, control technology, surface mount technology and other high-tech science and technology, the building automation system will also be greatly developed, and it can be foreseen:
1) The distributed control system is the mainstream of the building automation system at this stage;
2) Fieldbus technology is the development direction of distributed control systems;
3) Network technologies such as VLAN and TCP/IP are applied in the building automation system, and the network is Web-enabled;
4) The universal controller and the smart meter coexist;
5) Widely adopt modern control theory based on state space method to solve building self-control problems and achieve results;
6) System integration technology has made progress, and technologies such as OPC and ODBC are widely used;
7) The man-machine interface and operating environment are improved, which is in line with the basic mechanism of ergonomics.
According to the design requirements of the Ministry of Construction, general civil buildings (which may not be fully applicable to buildings with special process requirements), the design of the building automation system (BAS), the design institute should at least do the following work:
1) Fully understand the process requirements of the controlled object and make corresponding control schematic diagrams;
2) controlled object control category statistics (or controller input/output status point table);
3) Control network planning and design;
4) Plane wiring planning and design;
5) Design instructions.
The contractor (or supplier) shall further deepen the construction drawing design according to the design requirements of the design institute, including providing technical documents such as product specifications, materials, wiring, installation and maintenance, and responsible for final installation (or guidance). Installation), commissioning and acceptance applications.
However, from the current implementation of many projects, the effect is not satisfactory. Some surveys show that customers' evaluation of the operation of building automation systems accounts for 30% of "satisfaction", 40% of "general", and 30% of "poor". Therefore, this paper aims to review the problems that are easy to appear in the design from the perspective of professional design, with a view to making a difference.
2 several issues
2.1 Inaccurate understanding of the process requirements of the controlled object.
At present, electrical engineers (or self-control engineers) have superficial understanding of the process requirements of other professional controlled objects, and even there are errors in understanding, and cases of poor performance of BAS have occurred frequently, among which HVAC systems account for a large proportion. Specific gravity, the following are some practical problems that are easy to make mistakes in the project, such as:
(1), equipment professional specifications "heating ventilation and air conditioning design specifications" (GBJl9-87) have made general provisions for the indoor parameters of comfort air conditioning:
It should be noted that the above data only refers to the value range of the design base, and does not refer to the range in which the controlled object is allowed to vary, and the air conditioning design of the civil building comfort is generally not required. The choice of the air conditioning design base is very important. The actual project should be carefully determined by the equipment engineer in combination with China's climate characteristics and national conditions analysis. The adverse selection will not only have a negative impact on investment, operation and energy consumption, but also endanger the health of personnel.
(2) The depth of understanding of summer, winter and transition season is not enough. The summer, winter and transition season control parameters referred to by the air-conditioning system are three working conditions divided according to the three states of summer, winter and transition season, corresponding to the corresponding working environment parameters such as temperature, humidity or enthalpy, if only in summer, The simple understanding of the actual seasonal changes in the winter and transition seasons often leads to an undesired control effect in the air conditioning system.
(3), the HVAC automatic control system, its essence lies in grasping the words "fix" and "change" in the air conditioning process. It is often impossible to design an automatic control system according to the characteristics of “fixed air (or fixed flow) quantity or “variable wind (or variable flow) quantity†under different pipelines and different working conditions, such as refrigeration refrigeration/cooling cycle water setting. The flow rate; the fresh air treatment unit generally sets a new air volume; the variable air volume of the air conditioner component becomes a new air volume (or a new air ratio) and a new air volume (or a new air ratio).
(4) Most of the fresh air treatment units adopt the design of “new air volumeâ€, which often does not cause enough attention of the electrical control engineers. Generally, only the position control is required for the control of the fresh air valve, and the new air valve adopts the bidirectional single phase. AC 220V/AC24V, three-wire) motor or electric actuator position control; designed for the coil anti-freeze fresh air valve to be linked with the blower; to prevent the pressure difference of the damper from being too large to open, usually open the fresh air valve first, then open the blower, stop The fan is the valve.
(5) Only the air handling unit with fresh air preheater, or the mixing point (or the state point after humidification) may be lower than 0 °C air handling unit, or the winter transition season requires fresh air operation and fresh air temperature It is necessary to consider the operation of anti-freezing problems in air treatment units that may be lower than 0 °C, and take antifreeze measures such as linkage between new damper and unit.
(6) In order to ensure the basic indoor air quality, it can be realized by measuring and controlling the indoor CO: concentration. However, HVAC professional practice is often achieved by designing the minimum fresh air volume or the number of air changes. It is not necessary to use a simple start-stop group to control the indoor CO: concentration; otherwise, it involves variable air volume control and control. More complicated, the investment is larger.
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