Selection of thermal insulation materials for central air conditioning

Selection of thermal insulation materials for central air conditioning

At present, the central air-conditioning system, which uses a large number of advanced equipment and corresponding supporting equipment in various buildings, has become one of the important signs of modern building technology, and is an important foundation for modern buildings to create a comfortable and efficient working and living environment. facility.

　　 1. The central air-conditioning system needs to consume energy

　　The central air-conditioning system needs to consume a lot of energy, and its energy consumption accounts for about 60% of the total energy consumption of the building. Therefore, the air-conditioning system needs to save energy and save operation investment. The reasonable choice of the thickness and product of insulation materials, and strict insulation construction control are effective ways to save energy in the central air conditioning system.

　　 In addition, the buildings where central air-conditioning is installed are mostly office buildings, hotels, restaurants, large and medium-sized shopping malls, etc., with relatively high requirements. Air-conditioning insulation is directly related to daily use, fireproof performance and initial investment, so sufficient attention should be paid to insulation selection and construction. For example, if there is a problem with the heat preservation of the air conditioning system, condensation may occur during operation, leading to dripping ceilings, water seepage and mold on the walls, etc., which will seriously affect the look and use function, and cause certain economic losses.

　　2, the choice of insulation materials

　　The performance of thermal insulation materials directly affects the energy consumption, weight, fire resistance, construction and installation conditions, and project cost of the HVAC system. Therefore, it is necessary to analyze the performance of air conditioning thermal insulation materials and make reasonable choices.

　　 With the increase in demand for insulation materials, many domestic manufacturers have introduced technology and equipment from abroad to produce insulation materials. There are many kinds of insulation materials, and the insulation performance is different, and the range of options is greatly increased.

　　2.1. Performance index analysis of thermal insulation materials for air conditioning

　　After years of development, the thermal insulation materials for air-conditioning, from the earliest asbestos and glass fiber to rock wool, rubber and plastic, each have their own characteristics. To correctly evaluate the performance of an insulation material, there must be indicators that can fully reflect the performance of the insulation material. The performance indicators of insulation materials are roughly as follows: thermal conductivity, density, water absorption, moisture permeability, fire resistance, sound absorption coefficient, chemical resistance, aging resistance, dimensional stability, etc. In the use of air conditioning systems, it can be seen that the thermal conductivity, water absorption and moisture permeability are important performance indicators of thermal insulation materials. It is especially important for air conditioning system equipment and pipe insulation, because the surface temperature is generally below the air dew point. If it is not handled properly, water or moisture may enter, resulting in a decline in insulation performance, destroying the effect of insulation and energy saving, and may cause condensation on the outer wall. In addition, the fire resistance of thermal insulation materials is also an important parameter for the selection of thermal insulation materials. Fire accidents caused by poor fireproof performance of thermal insulation materials are not uncommon. Therefore, the fireproof performance of thermal insulation materials has attracted more and more attention.

　　2.2. Performance analysis of common air-conditioning insulation materials

　　 The following is a brief analysis of the performance of several commonly used air-conditioning insulation materials for reference in the selection of insulation materials for central air-conditioning projects.

　　2.2.1, glass wool

　　Glass wool belongs to a category of glass fiber, which is a man-made inorganic fiber. The main raw materials are quartz sand, limestone, dolomite and other natural ores, and some chemical raw materials such as soda ash and borax are used to melt into glass. In the melted state, the flocculent thin fibers are blown by the external force, and the fibers and the fibers are three-dimensionally intersected and entangled with each other, showing many small gaps. Such gaps can be regarded as pores. Therefore, glass wool can be regarded as a porous material with good thermal insulation and sound absorption properties.

　　2.2.2, rock wool

　　 is a non-combustible material with good fire resistance, anti-aging and chemical resistance. The disadvantage is that it is poor in water resistance. You must pay attention to moisture-proof treatment during construction. Because of its moderate thermal insulation performance and low price, rock wool still has a certain degree of competitiveness for projects whose general standards and cost are restricted, so it should not be excluded.

　　 2.2.3, polystyrene environmental protection foam phenol

The product is a closed pore foamed phenolic hard thermal insulation material, which is flame-retardant, non-flammable, and the surface only shows carbonization. It does not melt or drip, does not break, does not change shape, has no obvious shrinkage, and does not emit toxic or harmful Gas; has low water absorption, excellent water resistance and moisture barrier; low thermal conductivity; easy construction, this product is a hard material. It is easy to cut and install. If the outer layer is reinforced with aluminum foil and other protective surfaces, there is no need to add a metal hard protective shell, saving the overall cost and investment.

　　 2.2.4, self-extinguishing polystyrene foam

　　The insulation performance of this material is acceptable. The main problem is that the maximum operating temperature is 70℃, which is quite close to the design temperature of air conditioning water supply in winter (60～65℃). After engineering investigations, it was found that the central air-conditioning water pipes were insulated with self-extinguishing polystyrene foam tiles. After a period of operation, the insulation tiles deformed and separated from the pipeline. The reason is that its heat resistance is poor, and the air-conditioning water supply sometimes exceeds 70°C. Therefore, it is not suitable for use in the heat preservation of the central air-conditioning water system for both heating and cooling.

　　 2.2.5, flame-retardant polyethylene foam (PEF)

　　 Flame-retardant polyethylene foam plastic is light in weight, small in thermal conductivity, stable in size and good in waterproof performance. The product profile thickness is 6-40mm, which is convenient for reasonable selection.

　　 2.2.6, rubber and plastic sponge insulation material

　　 Rubber-plastic sponge has excellent properties such as softness, bending resistance, cold resistance, heat resistance, good flame retardancy (B1 flame retardant material), low waterproof thermal conductivity, shock absorption, and sound absorption. At the same time, the construction is convenient, the appearance is neat and beautiful, and there is no pollution. It is a high-quality new thermal insulation material.

　　2.3. Selection in actual construction

　　 Air-conditioning system insulation should use insulation materials with low thermal conductivity, good fire resistance, low water absorption and moisture permeability, convenient construction and meeting temperature requirements. At the same time, factors such as project cost must also be taken into consideration. However, many years of construction experience and related materials show that the overall performance of our domestic insulation materials is somewhat different from that of foreign products such as Armacell. Even the performance of domestic insulation material manufacturers' own products is different. When selecting thermal insulation materials, if too high-end materials are used, it is difficult to control the project cost; according to the project cost considerations, the products of regular manufacturers should be selected and the inspection of materials should be strengthened.

　　 3. Determination of insulation thickness

　　3.1、Calculation of insulation thickness

In the current air-conditioning design, the insulation thickness calculation is mostly carried out in accordance with some national standards. The various regulations and related parameters in these standards may not be suitable for the designed project. Some standard regulations are only formulated with reference to certain types of insulation materials. , Does not necessarily adapt to other insulation materials. In addition, with regard to the two commonly used methods for calculating insulation thickness (anti-condensation calculation and economic thickness calculation), the requirements for buildings are different, and different calculation methods should be used. For example, for general civil buildings, if indoor parameters change within a certain range and do not affect comfort, you can use anti-condensation calculations; for advanced buildings and buildings with high indoor parameter requirements, it is recommended to use economic thickness calculations and use anti-condensation Calculate the thickness check.

　　3.1.1, calculate the insulation thickness according to anti-condensation

　　 Anti-condensation means that after the pipes and equipment are insulated, their surface temperature should be greater than the air dew point temperature outside the insulation layer to ensure that no condensation occurs most of the time. This is the basic requirement for air conditioning system insulation.

　　 3.2, thickness selection

　　When selecting the thickness of the insulation material in the actual project, it must also be based on the actual situation. As the current regulations on the calculation of air-conditioning insulation are not perfect, they are not always suitable for the actual situation of each project, which leads to large thicknesses when selecting insulation thickness in most projects, which causes waste and increases engineering costs. However, in some areas in the south, especially those near the sea, the temperature and humidity are too high, and the insulation thickness calculated according to some standards cannot meet the needs of the project, causing condensation. Therefore, for each project, the calculated insulation thickness should be reviewed and determined according to local conditions.

　　 4. Thermal insulation construction

　　 The above is the selection and calculation analysis of insulation materials, and for the actual project, the control of the construction stage is also very important. The air-conditioning insulation construction stage includes pre-control before construction, quality control during construction, and improvement of problems found during the project.

　　Before construction, it is necessary to carefully review the drawing design, combine the actual project, and contact the designer to change the problem in time. Secondly, we must strictly control the quality of materials, adopt qualified products from regular manufacturers, and strengthen the inspection of materials on site. In addition, workers should be trained on the insulation performance and operation methods of the insulation materials used before construction, and technicians from the insulation material manufacturers can also be invited to the site to demonstrate the operation, so that the constructors can master the operating essentials of this type of insulation material .

　　 During the construction, the quality should be strictly controlled, and the management staff should check more and solve the problems in time. For air-conditioning insulation construction, the important part is often the details. For example, heat preservation treatment at pipe elbows, tees, valves, etc. The treatment of these parts must be carried out in strict accordance with the relevant operating technology to ensure that the insulation is tightly integrated with the pipe wall. The valve and flange parts should be insulated separately, and the gap between the insulation pipe casing and the pipe around the building should be tightly filled with insulation material.

　　 In addition, during the construction process, it is necessary to seek truth from facts, and solve and improve in time when problems are found. For example, different temperature and humidity environments need to be treated differently, and construction cannot simply be constructed with a uniform design thickness. In a southern project that I have done, I followed the insulation thickness required by the design drawings, but condensation occurred during the construction. The reason is that the project is located on the coast, the temperature and humidity are too high, and the ventilation in the basement is not very good, so the designed insulation thickness cannot meet the requirements. In the end, the problem was solved by replacing the original insulation materials with thicker ones.

5 Conclusion

　　 The insulation of the air-conditioning system is very important to the entire system. To do well in the insulation of the air-conditioning system, it is necessary to control every link from insulation design to material selection to insulation construction. While calculating strictly in accordance with the regulations and operating in accordance with the process regulations, we must also treat them differently according to the actual situation of the project, in a pragmatic attitude, avoid waste and make it meet the needs of the project.