Corrosion protection and thermal insulation of ventilation and air conditioning systems

1. General Provisions

1.1 The insulation construction of air ducts, components and air conditioning equipment should be carried out after the air duct system tightness test is passed.

Note: This article stipulates the prerequisite for the insulation construction of air ducts, components and air conditioning equipment, which can only be carried out after the air duct system tightness test is passed. The tightness test of the air duct system refers to the light leakage detection or air leakage measurement of the air duct system.

1.2 The refrigeration system pipelines of the air conditioning project, including the insulation construction of the refrigerant and air conditioning water systems, should be carried out after the pipeline system strength and tightness test is passed and the anti-corrosion treatment is completed.

Note: This article stipulates the insulation construction conditions of the air conditioning refrigerant pipeline and the air conditioning water system pipeline. The insulation construction of the pipeline is the latter process of the pipeline installation project, and it can only be carried out after the current process is completed and verified to be qualified.

(Figure 1: Ventilation and Air conditioning system)

1.3 Ordinary thin steel plates are directly pre-coated with anti-rust paint before making air ducts.

Note: There are two methods for the anti-corrosion treatment of ordinary thin steel plate air ducts, namely, first processing and shaping and then applying anti-corrosion paint, and first applying anti-corrosion paint and then processing and shaping. Compared with the two, the latter has high construction efficiency and much better anti-corrosion effect on the bite seam and flange riveting. In order to improve the anti-corrosion performance of the air duct and ensure the quality of the project, this regulation is made.

1.4 The anti-corrosion treatment of supports and hangers should be consistent with that of the air duct or pipeline, and its exposed parts must be painted with topcoat.

Note: Under normal circumstances, supports and hangers are made of ferrous metal materials and are in the same environment as air ducts or pipelines. Therefore, their anti-corrosion treatment should be consistent with that of air ducts or pipelines. In some buildings and workshops containing acid, alkali or other corrosive substances. 

When the air duct or pipeline is made of polyvinyl chloride, fiberglass or stainless steel plate (tube), the anti-corrosion treatment of supports and hangers should be the same as the corrosion resistance of the air duct or pipeline or be carried out according to the design regulations. 

1.5 During the paint construction, fire prevention, anti-freeze, rain prevention and other measures should be taken, and it should not be operated in a low temperature or humid environment. The last coat of paint for the exposed part should be applied after the installation is completed.

Note: During the paint construction, fire prevention, anti-freeze, rain prevention and other measures should be adopted. This is the basic requirement that must be met in general paint engineering construction. However, some operators do not pay attention to this aspect of work, which will not only affect the quality of the paint, but also may cause fire accidents.

(Figure 2: Corrosion protection of ventilation and air conditioning systems)

2. Main control items

2.1 The insulation of air ducts and pipes should be 1 The insulation of air ducts and pipes should be made of non-combustible or flame-retardant materials, and their materials, density, specifications and thickness should meet the design requirements. If flame-retardant materials are used, their flame retardancy should be checked and they can only be used after passing the inspection.

Inspection quantity: 1 piece is randomly inspected per batch.

Inspection method: Observation inspection, inspection of material certificate, and ignition test.

Explanation: This article stipulates that the insulation materials used for air ducts and pipes in air conditioning engineering systems must be non-combustible or flame-retardant materials, and must not be combustible materials. From the perspective of fire prevention, non-combustible materials should be used as much as possible for insulation materials. 

2.2 Anti-corrosion coatings and paints must be qualified products within the effective shelf life.

Inspection quantity: check by batch.

Inspection method: observe and check the material certificate.

Note: Anti-corrosion coatings and paints have a certain validity period. After the expiration of the period, their performance will change greatly. Of course, expired and unqualified products must not be used in the project.

(Figure 3: Fire protection of ventilation and air conditioning ducts)

2.3 Non-combustible insulation materials must be used in the following occasions:

800mm air ducts and insulation layers before and after the electric heater:

Air ducts, pipes and insulation layers within 2m on both sides of the fireproof wall.

Inspection quantity: full inspection.

Inspection method: Observe, check the material certificate and do ignition test.

Explanation: This article stipulates that the insulation material of the air duct within 800mm before and after the electric heater and 2m on both sides of the firewall must be non-combustible material. This is mainly to prevent the electric heater from causing the spontaneous combustion of the insulation material and to prevent the fire in the adjacent room from being transmitted through the air duct or pipeline insulation material.

2.4 For pipelines where the temperature of the conveying medium is lower than the dew point temperature of the surrounding air, when non-closed-cell insulation materials are used, the vapor barrier (moisture-proof layer) must be complete and well sealed.

Inspection quantity: 10% of the quantity shall be randomly inspected, and shall not be less than 5 sections.

Inspection method: Observation inspection.

Explanation: This article stipulates that the pipelines of the air conditioning refrigerant water system must be complete and sealed when using porous insulation materials. The porous insulation materials are composed of loose fiber materials and air layers. Air is a poor conductor of heat. The combination of the two constitutes good insulation performance. 

2.5 Dust-prone materials (such as glass fiber, short-fiber mineral wool, etc.) should not be used for the insulation of air ducts and pipes in clean rooms

Number of inspections: All inspections.

Inspection method: Observation inspection.

Description: The main object of clean room control is the amount of floating dust in the air. If the insulation materials of indoor air ducts and pipes use materials that are easy to generate dust (such as glass fiber, short-fiber mineral wool, etc.), it is obviously not conducive to the cleanliness of the clean room. Therefore, the provisions stipulate that dust-prone materials should not be used.

(Figure 4: Firewall)

3. General items

3.1 The paint film of spraying and painting should be uniform, without defects such as accumulation, wrinkles, bubbles, impurities, color mixing and missing paint.

Inspection quantity: 10% by area

Inspection method: visual inspection.

Note: This article only stipulates the basic quality requirements for the quality of paint construction in air-conditioning projects.

3.2 The spraying and painting of paint on various air-conditioning equipment and components shall not cover the nameplate logo and affect the functional use of the components.

Inspection quantity: 10% by quantity, and no less than 2.

Inspection method: visual inspection.

Note: During the construction of air-conditioning projects, some air-conditioning equipment or parts of air ducts and pipes need to be repaired or repainted. If you do not pay attention to the protection of equipment logos and the protection of the rotating shafts and blade moving surfaces of air vents during operation, it will cause problems such as the logo cannot be recognized or the blades are stuck and affect normal use. Therefore, this article stipulates.

3.3 The insulation of the components of the duct system shall not affect its operational functions:

Inspection quantity: 10%6 of the quantity shall be inspected, and shall not be less than 2.

Inspection method: Observation inspection.

Note: This article only stipulates the basic quality requirements for the insulation construction of duct components

3.4 The insulation material layer shall be dense and free of defects such as cracks and gaps. The surface shall be flat. When using coils or plates, the allowable deviation is 5mm; when using smearing or other methods, the allowable deviation is 10mm. The moisture-proof layer (including the end of the insulation layer) shall be complete and well sealed: its lap joints shall be smooth. 

Inspection quantity: 10% of the pipeline shall be inspected according to the axial length; 10% of the components and valves shall be inspected, and shall not be less than 2. 

Inspection method: Observation inspection, piercing the insulation layer with steel wire, and measuring:

Note: This article only stipulates the basic quality requirements for the splicing and thickness control of the insulation layer construction in air-conditioning projects.

(Figure 5: Clean room pipeline)

3.5 When the insulation layer of the duct is fixed by bonding, the construction should comply with the following provisions:

• The performance of the adhesive should meet the requirements of the use temperature and environmental hygiene, and match the insulation material;

• The bonding material should be evenly applied to the outer surface of the duct, components or equipment, and the insulation material should fit tightly with the surface of the duct, components and equipment without gaps.

• The longitudinal and transverse joints of the insulation layer should be staggered.

After the insulation layer is pasted, if it is wrapped or tied, the overlap of the wrapping should be uniform and tight; the bundling should be moderately tight and should not damage the insulation layer.

Inspection quantity: 10% by quantity.

Inspection method: Observation inspection and inspection of material certificates.

Note: This article only stipulates the basic quality requirements for the use of insulation nails for fixing and connecting the insulation layer of air-conditioning ducts.

3.6 The construction method of using insulation nails to fix the insulation layer is extremely critical. The phenomenon of insulation nails falling off occurs from time to time in the project. The main reasons for the instability of insulation nails are improper selection of adhesives, unclean bonding sites (oil, dust or water vapor, etc.), expired adhesives, or incomplete curing after bonding. 

3.7 When the insulation coating is used as the insulation layer, it should be applied in layers with uniform thickness, without defects such as bubbles and missing coating, and the surface curing layer should be smooth, firm and seamless.

Inspection quantity: 10% by quantity.

Inspection method: Observation inspection.

Description: Insulation coating is a new type of non-combustible insulation material. It is directly applied to the surface of air ducts, pipes or equipment during construction. After drying and curing, an insulation layer is formed. The construction of this material is mainly a wet operation for smearing, so it is required to apply the coating evenly and there should be no defects such as bubbles and missing coating. When the coating is thick, it should be constructed in layers.

(Figure 6: Insulation of ventilation and air conditioning system)

3.8 When glass fiber cloth is used as an insulation protective layer, the overlap width should be uniform, preferably 30~50mm, and the tightness should be moderate.

Inspection quantity: 10% by quantity.

Inspection method: measurement, observation inspection.

Description: This article only stipulates the basic quality requirements for the installation of glass cloth protective layer.

3.9 The insulation structure of pipeline valves, filters and flanges should be able to be disassembled separately.

Inspection quantity: 10% by quantity, and not less than 5.

Inspection method: Observation inspection.

Explanation: This article stipulates the basic quality requirements for the thermal insulation construction of air conditioning water system pipes.

3.10 The construction of the pipe insulation layer shall comply with the following provisions:

The material and specifications of the insulation product shall meet the design requirements, the pipe shell shall be firmly pasted and laid flat; the binding shall be tight, without sliding, loosening and breaking; the joint gap of the hard or semi-hard insulation pipe shell shall not be greater than 5mm when heat preservation and should not be greater than 2mm when cold preservation.

Inspection quantity: 10% of the quantity shall be inspected randomly, and shall not be less than 10 sections.

Inspection method: measurement, observation and inspection, and review of construction records.

Note: This article only stipulates the basic quality requirements for the insulation construction of air conditioning water system pipes. 

3.11 The construction of the pipeline moisture-proof layer shall comply with the following provisions.

The moisture-proof layer shall be tightly adhered to the insulation layer, well sealed, and shall not have defects such as false adhesion, bubbles, wrinkles, cracks, etc.; the moisture-proof layer of the vertical pipe shall be set from the low end to the high end of the pipe, and the circumferential overlap seam shall face the low end; the longitudinal overlap seam shall be located on the side of the pipe and follow the water; when the roll material moisture-proof layer is constructed by spiral winding, the overlap width of the roll material should be 30~50mm.

Inspection quantity: 10% of the quantity shall be inspected randomly, and shall not be less than 10m.

Inspection method: measurement, observation and inspection.

Note: This article only stipulates the basic quality requirements for the construction of the heat insulation and moisture-proof layer of the air conditioning water system pipeline.

(Figure 7: Ventilation and air conditioning system valve inspection)

3.12 The construction of the metal protective shell shall comply with the following provisions:

• It should be close to the insulation layer, and there should be no peeling, wrinkles, forced joints, etc. The overlap of the interface should be water-conforming and reinforced with convex ribs, and the overlap size is 20~25mm. When using self-tapping screws for fixing, the screw spacing should be uniform and the moisture-proof layer should not be punctured.

• The longitudinal and transverse joints of the outdoor metal protective shell should be water-conforming; its longitudinal joint should be located on the side of the pipe. Flashing should be added at the junction of the metal protective shell and the outer wall or roof.

Inspection quantity: 10% by quantity.

Inspection method: Observation inspection.

Note: This article only stipulates the basic quality requirements for the installation of the metal protective shell of the heat insulation layer.

3.13 The outer surface of the refrigeration system pipes in the cold and hot source room should be color-coded.

Inspection quantity: 10% by quantity.

Inspection method: Observation inspection.

Note: In order to facilitate the management and maintenance of the system, it should be marked according to relevant national regulations.