1 Location and elevation crossing of pipelines and equipment
At present, the drawings of HVAC engineering have been basically drawn by cad. Although the elevation of pipelines and equipment is planned before the construction drawing comes out, detailed inspection is usually not carried out before the construction drawing comes out, which often leads to the serious intersection of pipeline elevation and positioning in the construction drawing, which brings great difficulties to the management and control of engineering quality. For a comprehensive building, the professional piping of the ceiling space is very complicated, including air conditioning terminal equipment, electrical bridge, air supply pipeline, exhaust pipeline, freezing water pipe, condensation water pipe, spray pipe, fire-fighting pipeline and so on. If the construction is carried out according to the drawings without detailed labeling, the result is often that the pipes installed first are easy, and the pipes installed later are difficult, so they can only be installed at the position or elevation where they should not be installed, which greatly affects the engineering quality and seriously causes rework.
In view of the above situation, the pipeline should be comprehensively planned. The so-called comprehensive pipeline planning is to arrange and schedule all pipeline projects in the building in a unified way, so as to schedule and plan the wiring schemes of all pipeline projects scientifically and reasonably. When the planned pipeline direction and location in a single project are unreasonable or conflict with other projects, we will negotiate with relevant units to make reasonable adjustment or coordinated dispatch, so as to optimize the layout of various pipelines in the building space and lay a good foundation for the construction, operation and maintenance management of pipeline projects.
1. 1 comprehensive planning principle of pipeline engineering
According to the different performances and uses of pipelines, pipelines in buildings can be divided into: (1) water supply pipelines, including domestic water supply, production water supply and fire water supply; (2) Drainage pipes: including production and domestic sewage, wastewater and rainwater, fire fighting drainage and other drainage; (3) Reclaimed water pipeline: including the collection and supply of reclaimed water; (4) Thermal pipeline: including steam or hot water required by heating, hot water supply and air handling equipment; (5) Gas pipelines: including gas fuel and liquid fuel; (6) Air duct: mainly including various air ducts in ventilation engineering and air conditioning system, and air compression pipes of some production equipment; (7) Power supply and distribution lines or cables and pipelines: including power distribution, lighting power, weak current system distribution pipelines, etc. Among them, the weak current part also includes public TV antenna, communication line, broadcasting line and fire alarm system. All the above pipes or threading pipes have their own process wiring characteristics. When they cross each other and occupy the same space, the overall layout and planning should be carried out, so that pipelines with different functions can be rationally laid out and planned.
1.2 Pay attention to the duct layout.
The height of the ceiling is largely determined by the length of the duct section in the height direction. The air duct should not be too long, otherwise the construction difficulty will increase and other pipes will be difficult to arrange. For example, the maximum cross-sectional area of a building's air duct reaches 2 200 mm x 480 mm. The larger the cross-sectional area of the air duct, the larger the computer room, the greater the noise and the more difficult it is to return air. If the air duct is short, the power of the fan can be correspondingly small. At this time, you can choose to hang horizontal units, and the layout of the computer room will be much more flexible. Therefore, the rational layout of pipelines and the improvement of the efficiency of building space need the participation and cooperation of professional wiring planners.
2 HVAC system equipment noise exceeds the standard and solutions
Excessive operation noise of air conditioning terminal equipment is a common equipment noise problem in HVAC engineering. Due to the mature fan coil technology, the noise index of fan coil products of many domestic manufacturers can meet the standard. However, the situation of large air conditioning units is not satisfactory, and the measured noise value is often much higher than the product sample parameters provided by manufacturers. The author has come into contact with two projects in which the operating noise of air-conditioning terminal equipment exceeds the standard: one is that although there is a muffler at the inlet and outlet of the hanging cabinet machine, the noise of the equipment exceeds the standard and comes out from the tuyere; Another example is that there is no muffler at the entrance and exit of the crane cabinet. As a result, the indoor noise measured during the trial operation was 67db(a), which far exceeded the indoor noise standard. In these two projects, the frequency converter is used to reduce the fan speed to reduce the noise, but the refrigeration effect of the air conditioner is greatly affected. Therefore, the requirements for equipment noise parameters should be indicated in the design, and the sound insulation measures should be considered when using large air conditioning units in the design. After the air conditioning equipment comes into play, it should be unpacked and inspected in time. Before the large-capacity air conditioning unit is installed, it is best to conduct power-on trial operation. If the noise exceeds the standard, it should be replaced, returned or modified in time only when the project enters the debugging stage to avoid rework caused by excessive noise. In addition, reasonable construction can obviously reduce noise.
2. 1 Equipment installation
The installation of new fan and air conditioner adopts spring damping shock absorber, the connection between fan and air pipe adopts soft connection, the fresh air unit and water pipe adopt soft joint connection, the fan coil adopts spring hook, and the fan coil and water pipe adopt hose connection. Sound-absorbing treatment is carried out for the air-conditioning machine room, for example, the enclosure structure is made of sound-insulating materials to prevent the noise of equipment from spreading outward, or sound-absorbing materials are stuck in the machine room: concave-convex sound-absorbing plates are used as the walls or ceilings of the machine room to enhance the sound-absorbing effect; The computer room should minimize the number of doors and windows, and adopt sound-absorbing doors and windows or sound-absorbing shutters to minimize the noise of equipment.
2.2 water pipe installation
Water pipes shall be installed in strict accordance with national standards. The hangers for chilled water main pipes and cooling water pipes shall adopt spring vibration-reducing hangers. Hangers cannot be fixed on the floor, but should be fixed on beams as far as possible, or set channel beams between beams. When the water pipe passes through the floor or wall, the casing must be used, and the gap between the casing and the water pipe should be filled with flame retardant materials.
2.3 Installation of air system
The manufacture and installation of air ducts shall be carried out in strict accordance with national standards. Impedance silencers should be installed at the inlet and outlet of the fan, silencing louvers should be used at the inlet of fresh air, silencers should be set at the appropriate parts of the air duct, and silencing elbows should be set at the elbows of the air duct. The exterior of air conditioner and fresh air muffler should be insulated with high-quality insulation materials, and the interior should be affixed with high-quality sound-absorbing materials like static pressure boxes. Because the return air duct uses low wind speed and large air volume to reduce noise, the cross-sectional area of the duct is relatively large. If the installation strength and overall stiffness of the air duct are not enough, friction and vibration noise will occur. It is suggested that rubber damping pads should be used as far as possible for the air duct hanger to ensure that the air duct does not produce vibration and noise.
2.4 Installation of main support of chilled water pipe
For example, the main water pipe of a project has a large diameter and slight vibration. According to the author's many years' engineering installation experience, it is found that the noise will spread along the freezing main pipe, which can generally reach 70 dB (a) ~ 80 dB (a) at the exit, and can be reduced to 50db(a) at a distance of 20 meters from the exit. However, the slight vibration will be transmitted infinitely along the rigid conductor. With the passage of time, it will bring some damage to the operation of the equipment. After research and experiment, the rigid support is improved, that is, the spring damper is added to the original rigid support of the main pipe, so that the spring damper between the floor and the rigid support can effectively eliminate vibration and noise. This technology has been used in several projects of a construction enterprise investigated by the author and achieved good results. Therefore, it is suggested that the relevant construction enterprises should also adopt this technology to eliminate noise in the water supply and return supervisor and chilled water supervisor in the computer room.
3 water circulation problem of air-to-water transfer system
Air conditioning water circulation system is the key to air conditioning construction. If there is a problem with the water circulation system, it will directly lead to the abnormal use of the air conditioner, so ensuring the smooth flow of the water circulation system is the focus of air conditioning equipment installation. First of all, unreasonable pipeline layout is one of the reasons that affect the water cycle. The chaotic pipe network will appear airbag phenomenon, which will affect the circulation of the pipe network; Secondly, the dirty pipes in the water system are also one of the reasons that affect the water cycle. The quality of cooling water is worse than domestic water, and the pipeline is not clean, which causes corrosion and blockage and affects the heat exchange efficiency.
Solution: Strengthen the management and prevention before construction, reasonably arrange the elevation and slope of the pipeline to avoid the occurrence of air bags, set exhaust valves where air bags are inevitable, and place the outlet of the exhaust pipe in a place conducive to system exhaust. In view of the latter problem, the following work must be done well in the installation and construction process to prevent it: First, the dirt and rust spots must be removed mechanically or manually before the steel pipe is welded and installed, and the pipe mouth must be blocked after the inner wall of the pipe is cleaned. In the process of pipeline construction, the unclosed nozzle should also be temporarily blocked to avoid dirt. When connecting pipes, it is necessary to clean up welding slag, hemp and other sundries in time. Secondly, a drain valve is added at the lower part of the pipe network. In the installation of pipe network, filters and bypass flushing valves are added pertinently, and the equipment is cleaned in sections through hydraulic test. After the cleaning work is completed, the water system circulation test should also be carried out.
4 Dew and dripping problems
In the operation of air conditioning system, condensation and dripping often occur, which is caused by many reasons. Among them, the main reasons for water leakage are: when the pipeline was installed, the construction personnel did not follow the operation process; The quality of pipes and pipelines is poor, and they were not carefully inspected before entering the site; The water pressure test process is not standardized; The thickness of thermal insulation material is not enough, which leads to condensation when the external temperature reaches the dew point during operation; The insulation material is not tightly combined with the pipeline, which leads to moisture entering the insulation layer and generating moisture. The main reasons of freezing pipe dripping through the wall are: the insulation is not tight, and the insulation layer is damaged and falls off; The drain of the coil was blocked by foreign matter and was not cleaned after installation. The insulation materials of drip tray and fan coil of hanging cabinet are damaged, which leads to condensation. Because the condensate pipe is too long, it collides with the ceiling during installation and construction, or the slope is difficult to guarantee, or even the condensate pipe flows backwards, resulting in dripping.
Solution: First, strengthen the acceptance of thermal insulation materials. It is necessary to strengthen the feasibility demonstration of the scheme before construction and the supervision and inspection during construction, prevent unreasonable thermal insulation sleeves, and pay attention to the thermal insulation quality inspection of elbows, valves, flanges and equipment interfaces. Secondly, the freezing pipe passing through the wall must be provided with heat preservation and protection sleeves. Third, before the ceiling is sealed, it is necessary to clean up and check the sundries in the drip tray of the fan coil. Finally, strengthen the protection measures of drip tray and pay attention to the inspection before ceiling sealing.
5 concluding remarks
In the process of HVAC installation, some problems are often exposed. This requires us to carefully supervise and control the quality of the project at ordinary times. Before installation, you should understand the project planning, be familiar with all kinds of engineering construction drawings, master the key points of engineering quality control, and supervise, control and manage before, during and after installation.
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