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Several methods and standardized practices of ventilation and air-conditioning duct insulation

Update:18-01-2022
Summary:

The main insulation materials for ventilation and air-c […]

The main insulation materials for ventilation and air-conditioning pipes and various water pipes are: polyurethane foam insulation, advanced rubber and plastic insulation, phenolic foam insulation, iron pipes, etc. The characteristics, scope of application and construction points of the above materials are now introduced for your reference.

1. Polyurethane foam insulation

This material is used for thermal insulation of directly buried pipe sections. Directly buried thermal insulation and anti-corrosion pipes in engineering, referred to as pipe-in-pipe, refers to composite pipes coated with anti-corrosion layer, thermal insulation layer and compression layer on the outer wall of steel pipe. It has the characteristics of small heat loss, strong compressive performance, good anti-corrosion and waterproof performance, and is especially suitable for areas with high groundwater levels. Compared with the traditional trench laying pipeline, it has a series of advantages such as good thermal insulation performance, anti-corrosion, good insulation performance, long service life, simple construction and installation, small footprint, low engineering cost, etc. It has been widely used in central heating, Projects such as oil transportation, chemical industry, refrigeration and water supply in alpine regions will not be introduced in detail in this article.

2. Advanced rubber and plastic insulation

This material is an ideal thermal insulation material, its thermal insulation material has good thermal insulation effect, and the thermal insulation thickness used for the same pipeline is thin and the dosage is small; at the same time, it is an integrally formed thermal insulation material, the process is relatively simple and the progress is fast; in addition, advanced rubber and plastics It is a green, environmentally friendly and clean thermal insulation material, with less waste during construction and no harm to health. With outstanding advantages, this material is more and more widely used in the insulation of refrigerant pipes and condensate pipes of air-conditioning and refrigeration systems.

2.1 Material properties

Advanced rubber and plastics belong to natural inorganic integral molding thermal insulation materials, which are made of nitrile rubber (NBR) and polyvinyl chloride (PVC) through process foaming. It is suitable for medium temperature of minus 50℃~120℃, and its closed-cell structure has relatively good thermal insulation performance and low moisture-proof and water-absorption rate. High-grade rubber and plastic thermal insulation materials mainly have the following advantages: good thermal insulation effect, remarkable anti-condensation effect, and should be used as the outermost layer of thermal insulation pipes; flame-retardant, smoke-proof, safe and reliable; uniform appearance, high-grade and beautiful; convenient installation and fast construction.

2.2 Scope of application

The material is mainly used in the heat preservation of refrigerant and carrier refrigerant pipes in the central air-conditioning and household air-conditioning refrigeration systems of civil buildings; the heat preservation of condensate water pipes; the heat preservation of automobile air conditioning pipes; Insulation and cooling systems for aviation, urban heating networks, etc.

2.3 Construction process

Before the pipeline is insulated, the water pipe pressure test should be carried out. After the water pressure test is qualified, the pressure test and the insulation work should be handed over to prevent the water pipe that has not been pressure tested from being insulated and avoid work conflicts.

2.4 Selection of materials

The greater the difference between the temperature of the medium in the system and the ambient temperature, the greater the thickness to choose; the greater the relative humidity of the environment where the cooling system is located, the greater the thickness to choose; when the diameter of the cooling medium pipe is smaller than 150mm, the larger the diameter of the pipe, the greater the thickness to choose. ; The less air in the engineering system, the greater the thickness.

2.5 Prevention and treatment of common quality problems

The common problems of thermal insulation quality are mainly manifested as uneven coating of glue, poor bonding of thermal insulation materials, incorrect selection of thickness of thermal insulation materials, inconsistent appearance and type, and unsightly type. There are several main quality problems in the construction as follows:

(1) The insulation layer and the wooden support are not tightly bonded. During construction, due to the inaccurate measurement of the length of the thermal insulation layer, the workers often stretch the thermal insulation material and bond it. Because the material itself is elastic, it will shrink after being stretched. After a long time, the glue between the insulation material and the wooden support will open, which is one of the most common quality problems in insulation.

Prevention and control measures: It is not allowed to stretch the material during the cutting and bonding process. At the same time, it is required to apply glue on both sides of the wooden support and on the cross-section of the insulation material. The glue should be painted evenly and full; The wooden support is broken into several pieces and should be replaced to prevent condensation due to cold bridges.

(2) The bonding between insulation materials is not tight. The bonding between insulation materials is relatively common, especially the bonding seam of the insulation material above the horizontal pipe and the side of the riser is long, which is prone to poor bonding. This is mainly caused by the uneven section of the material and the uneven coating of the glue during the cutting process, which is also one of the most common quality problems in thermal insulation.

Prevention and control measures: The construction personnel are required to use a ruler during the cutting process, and can not cut the material with bare hands. When applying glue, it is required to be uniform. When bonding, it is necessary to gradually squeeze from one side to the other side to ensure the cutting surface of the material. All can be firmly bonded.

(3) Open the glue at the elbow. When the pipeline is insulated, it is generally required to place the joint of the thermal insulation layer above the pipeline, and the cracking of the thermal insulation layer often occurs above the elbow of the pipeline, which causes the local thermal insulation layer to be too thin, resulting in condensation of condensed water.

Prevention and control measures: The construction personnel are required to not only cut the material according to the estimated size when making the elbow insulation, but use a soft tape to measure the size accurately; the section of the cut material should be flat; apply more to the place where the local force of the pipe elbow is large. glue.

When insulating the elbow, try to use the direct elbow for heat preservation, that is, the adhesive seam of the insulation layer follows the direction of the pipeline, rather than the method of cutting the horseshoe shape and bonding multiple times to find the radian. This can save a lot of manpower, time and materials, and can ensure the quality of heat preservation, while the appearance is also more beautiful than the latter.

(4) The wall bushing is skewed. In actual construction, the casing where the pipe passes through the wall is prone to be placed eccentrically or out of the wall, so that the thermal insulation layer cannot pass through the wall and cannot achieve the effect of thermal insulation.

Prevention and control measures: The casing is generally directly made by cutting the pipeline during construction. The length of the casing is determined according to the thickness of the wall and the thickness of the plaster. On the pipe, when plugging the wooden strip, make sure that the casing is concentric with the pipe. Remove the wooden strips during insulation construction, and then pass the insulation layer through the casing.

(5) The finished product is damaged. After the rubber-plastic thermal insulation construction is completed, the thermal insulation pipes near the pedestrian passage are easily bumped and scratched by heavy and sharp objects.

Prevention and control measures: Use cardboard boxes or thick plastic sheets to wrap tightly in the places where the installation is exposed, and use iron wires to bind them firmly. During construction, rubber and plastic materials or packaging boxes of fan coil units can be used. The protective layer should exceed the height that ordinary human hands can reach. The thermal insulation in the exposed fresh air fan room and the exposed pipeline well should be postponed as far as possible until the construction of other types of work is completed, and strive to be in place at one time.

3. Phenolic foam insulation

The material is obtained by foaming a phenolic resin - a kind of foamed plastic. There are two kinds of resins used to produce phenolic foam: thermoplastic resin and thermosetting resin. Due to the good technological performance of thermosetting resin, phenolic foam can be continuously produced, and the product performance is better, so most phenolic foam materials use thermosetting resin. Phenolic foam has the following properties:

(1) Non-combustibility: Phenolic foam is composed of flame-retardant resin, curing agent and non-combustible filler. There is no need to add any flame retardant additives, and the flame retardant grade is flame retardant B1. The oxygen index of high-density phenolic foam with inorganic fillers can reach 70. The flame resistance of 100 mm phenolic foam can reach more than 1h without being penetrated.

(2) Thermal conductivity: There are three heat transfer modes of foamed plastics: heat conduction in the gas phase and polymer phase, convection in the gas phase, and heat radiation from the cell wall. The thermal conductivity of phenolic foam is small and has excellent thermal insulation properties, and the thermal conductivity increases with the increase of product density.

(3) Anti-corrosion and anti-aging: The phenolic foam material has been cured and formed, and there is no obvious aging phenomenon when exposed to sunlight for a long time. The service life is significantly longer than other materials. In addition to being corroded by strong alkalis, it is resistant to almost all inorganic acids, organic acids and salts.

(4) Sound absorption performance: Phenolic foam has excellent sound absorption performance. The open-cell foam structure is more conducive to sound absorption.

It is precisely because of the above characteristics of this material that it is widely used in central air-conditioning ducts, hot and cold conveying pipes, clean workshops, cold storage, and other places where fireproof, light weight, heat preservation, sound insulation, clean and moisture-proof materials are required. Compared with the polystyrene foam, polyvinyl chloride foam, polyurethane foam and other materials that dominated the market in the early stage, it has special excellent performance in terms of flame retardancy. At present, phenolic foam has become one of the fastest growing varieties of foamed plastics. However, the biggest weakness of phenolic foam is its high brittleness and high open cell rate, so improving its toughness is the key technology to improve the performance of phenolic foam.

4. Styrofoam insulation

The material has a closed-cell structure, low water absorption, good low temperature resistance, and good freezing resistance, so it is widely used in refrigeration equipment and refrigeration equipment, such as freezers, cold air pipes, refrigerators, etc. In addition, because the polystyrene foam is non-toxic, non-corrosive, low in water absorption, light in weight, heat preservation, mold forming, and resistant to acid and alkali corrosion, it can be used for pipeline insulation for various purposes.

5. Xiaobian reminds everyone

There does not seem to be a very ideal insulation material for HVAC and refrigeration systems. For example, commonly used: rubber and plastic materials have small thermal conductivity, good steam permeability resistance, and are easy to construct, but they are not non-combustible materials. For example, when used as heat preservation for high-temperature hot water pipes, they may be deformed and the price is slightly more expensive. Centrifugal glass wool, which is a non-combustible material, has a small thermal conductivity, but has poor resistance to steam penetration. For example, as a chilled water pipeline insulation, the outer moisture-proof and vapor-barrier layer should be specially treated, which must be airtight and have a certain strength (traditional aluminum foil is easy to damaged by scratches). Therefore, the basic rule of thermal insulation materials is: almost all non-combustible materials are not resistant to steam penetration; and almost all materials resistant to steam penetration are flammable and even produce suffocating smoke. But in any case, as long as we grasp the applicable conditions of various thermal insulation materials, know the precautions for their construction, and master the construction points, we can do a good job in various thermal insulation work.

6. Pipeline insulation specification

1 Construction of the thermal insulation layer

1.1 The seam quality of the thermal insulation layer

• Thermal insulation≤5mm, cold insulation≤2mm;•The thickness of the thermal insulation layer is greater than 100mm; when the thickness of the cold insulation layer is greater than 80mm, it should be constructed in layers, with staggered joints on the same layer, and upper and lower joints;•The position of the horizontal longitudinal joint is arranged on the vertical centerline of the pipeline Within 45° (SH3010-2000 Section 5.2.9-5.2.11; GBJ126-89 Section 4.1.1-4.1.3).

1.2 Binding quality of thermal insulation layer

• Rigid thermal insulation products are bundled with 14~16# degree zinc iron wire double strands, the bundling spacing shall not be greater than 400mm, and each product shall not be less than two; 800mm, at least three bundles should be bundled; • For soft thermal insulation products, the bundle spacing should not be greater than 200mm. (SH3010-2000 Section 5.2.20, GBJ126-89 Section 4.3)

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