1, Introduction
The so-called HVAC refers to air conditioning, heating and ventilation systems, which are complicated to install. In general, the preliminary work of HVAC installation project begins after the completion of pile foundation project. However, most of the work of HVAC engineering is completed in the later stage of construction engineering. In order to do a good job in the construction of HVAC installation project, it is necessary to carefully analyze the construction drawings and carry out the actual investigation of the project. The whole process of design, construction and acceptance shall be carried out according to current standards, specifications and design requirements. Among them, construction is the key to the quality of HVAC installation project. In order to ensure the construction quality of HVAC installation project, it is necessary to strengthen the preliminary preparation and construction process during HVAC installation.
2, the construction preparation points
The drawings of HVAC installation project will be inconsistent with the site situation, and the materials required in the drawings will be inconsistent with the whole project. Therefore, in the process of joint review of drawings, we should focus on whether the designed drawings meet the requirements of national standards; Whether the materials used in the design meet the strength requirements; Whether it meets the requirements of safety, economy and availability; Whether it meets the requirements of fire control and fire prevention; Whether the dimensions of nozzles and vents on the drawings conform to the layout of equipment and pipelines; Whether the access port is set; Whether the air conditioning system is properly placed. On the basis of understanding the actual project, it points out the discrepancies between the design drawings and the actual project, and puts forward suggestions for improvement. Effectively combine design drawings with engineering practice perfectly, saving a lot of time and energy for later construction.
For the materials used in the construction process, it is necessary to conduct a comprehensive and strict inspection of their specifications and quality. Ensure that the materials used meet the requirements of national technical standards and specifications. For materials, materials are classified and stored according to their types and time of use. At the same time, all kinds of equipment used in HVAC engineering, especially large pipes, fittings, radiators and other major bulk materials, must have quality certificates that meet national requirements, and the types, specifications and performance of materials meet relevant national standards and engineering design requirements. All kinds of materials, accessories and equipment should be strictly accepted when they enter the site. When all kinds of equipment enter the site for acceptance, check whether their certificates are complete. Before installation, the strength and leak test shall be carried out in strict accordance with the requirements of the construction acceptance specification. After everything is qualified, you can use it. All unqualified products are not allowed to enter the market, let alone be used.
During the construction of the main structure of the building, holes should be reserved in advance for the HVAC installation project to ensure that the pipelines of the HVAC project are located in the walls, beams and plates. The size, quantity and location of reserved holes should be carefully controlled and rechecked to ensure foolproof. In practice, for this reason, the waste of pipeline materials is everywhere. If the position of the reserved hole is not accurate, the pipeline will be deformed during installation. When the position of reserved holes in HVAC pipeline is not accurately controlled, it will lead to poor heating, and even lead to huge economic losses.
3. Key points of construction process
3. 1 Key points of pipeline construction
Ensure that the bracket can bear the maximum load of equipment and pipeline during installation; The specifications of the boom and section steel used for construction meet the use requirements; Equipment and large pipeline hangers are fixed through the floor; The vertical air conditioning pipeline is provided with an anti-skid bracket; Take necessary anti-corrosion treatment. The joints and deformation joints between the air duct and the equipment should be soft, and unnecessary bending should not be left, otherwise the resistance will be increased. Try to reduce the air retention at the elbow, and connect the elbow with a hose through the deformation joint; Install the valve in the same direction as the water flow.
When installing the heating pipeline, measures such as casing should be taken to protect it, and at the same time, the hidden danger of leakage caused by casing failure to meet the anti-seepage requirements should be avoided. Therefore, when heating pipes pass through the structural parts, rigid waterproof casing should be added. When the pipe diameter of heating riser is not less than 1 1cm, firestop rings should also be set at the parts passing through the floor. According to the actual measurement and combined with the connection size, saw the pipe with a fine tooth saw, and the fracture surface should be smooth. Insert the socket before bonding, not all of them. After the trial insertion is qualified, wipe the moisture and dust on the parts that need to be bonded that day with cotton cloth. If oil stains need to be removed by acetone, apply glue with a brush, brush it to the outside and inside of the socket, then insert it vertically with force, rotate it gently, and wait for three minutes to achieve complete drying and curing. Wipe the spilled adhesive with cotton yarn. In addition, the blockage of heating pipes mostly occurs at the elbow, so we should pay more attention to it during construction.
After the HVAC installation pipeline is installed, the construction personnel usually carry out hidden construction directly, which is easy to cause leakage hidden danger. In order to avoid this situation, a stress test should be conducted. During the pressure test, all valves should be opened to show all the hidden dangers of leakage. In addition, the qualification of the pressure gauge should be checked. Once any product is unqualified, it should be banned. You can also turn all the branch valves to determine whether there will be sound, so as to ensure that the valves are open. Before the pipeline pressure test, no supporting equipment shall be installed, and the opening shall be tightly blocked with the pipeline, and the system shall be pressurized at the lowest point, and the air in the pipeline shall be exhausted at the highest point. During the test, the pressure is increased slowly, and the pressure drop is less than 0.07 MPa within 15 minutes after the pressure is increased to the test pressure, then the test pressure is reduced to the working pressure, and the system is visually inspected. If there is no leakage, the test is considered qualified, and the pressure test record shall be made in time. After the pressure test is completed, the pipeline can be flushed. Flushing shall be carried out continuously with tap water, and sufficient flow shall be ensured. Rinse with water more than two-thirds of the total design flow until the sewage is rinsed clean and the effluent quality is clear and colorless, which is qualified.
3.2 Insulation structure
Thermal insulation engineering is an important part of HVAC installation engineering. If the quality of insulation construction is not good, it will directly lead to the dripping of condensed water generated during system operation. If the quality of insulation construction cannot be guaranteed, it will affect the normal use of the system and waste energy. The construction of water system is a difficult point in the insulation construction of HVAC engineering. Thermal insulation engineering should be carried out after the pipeline pressure test is qualified and before the installation of ceiling keel. The order cannot be reversed, and the construction should be carried out in strict accordance with the procedures. In the actual construction, the following points should be paid attention to: the thermal insulation materials used must meet the relevant requirements and specifications to ensure that the bonding between the thermal insulation materials and the skid is tight enough and the coverage of the valve thermal insulation layer is large enough.
3.3 Multi-work cooperation
In a fully functional building, the ceiling clearance is very limited, but all kinds of pipes must be arranged reasonably in this space. Therefore, there will be differences in the use of space. Such as: return air duct, fresh air duct, exhaust air duct, water supply pipe, return pipe, condensate pipe, etc. For HVAC major; Domestic water supply pipes, drainage pipes and sewage pipes for water supply and drainage specialty; Strong and weak bridges, electric conduits, etc. For electrical majors. At present, in many HVAC construction drawings, designers only give the positioning dimensions of main equipment, without indicating the positioning dimensions and elevation of air ducts and water pipes, or even if there are dimensions, they conflict with other types of work. There is a need for coordination between various types of work, and it can be solved by the owner or supervision unit if necessary.
4. Summary
HVAC engineering is an auxiliary engineering of building structure and an indispensable part of the whole building. Therefore, the requirements for HVAC engineering will become more and more strict, and it is of great significance to improve the construction level. This paper expounds the preparatory work before construction and the key points in the construction process, which has certain guiding significance for actual construction.
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