According to the relevant regulations in the “Technical Specification for the Application of Low Temperature Hot Water Floor Radiant Heating†in Beijing, the types of plastic pipes that can be used at present include cross-linked aluminum-plastic composite pipe XPAP, cross-linked polyethylene pipe PE-X, and random copolymer polypropylene pipe. PP-R and polybutylene pipe PB four, these pipes have their own advantages and disadvantages:
1, XPAP (cross-linked aluminum-plastic composite pipe): high pressure resistance, high temperature, not oxygen, easy to bend, do not rebound; but it can not be second welding, it is generally used mechanical card connection, this type of connector in When thermal expansion and contraction are easy to produce drawing effect, easily lead to leakage. The aluminum-plastic composite pipe is composed of five layers of materials and its structure is a composite of aluminum plate and polyethylene. The thermal expansion coefficients of the two materials are very different. If the long-term cold and heat alternate, it will easily cause the two materials to fall off, the pipe strength and thermal conductivity. Falling, even lead to pipe cracking. In addition, the thermal expansion coefficient of the concrete is different from the thermal expansion coefficient of the concrete. Changes in the temperature also cause cracks in the concrete layer. XPAP prices are higher than PE-X, PP-R and other pipes.
2. Polybutene PB is a kind of high-polymer inert polymer. Due to its stable molecular structure, excellent creep resistance and mechanical properties, it is the softest among several pipes and can be connected by hot melt. Under the same conditions of use, in the same wall thickness series of pipes, the safety of the use of this type is the highest, and it is suitable for high standards of building hot water and heating systems, but the highest price of raw materials is more than double that of other varieties. Moreover, the thermal conductivity of the PB tube is relatively low, which affects the heat transfer efficiency. Currently, there is less area for application in China.
3, random polypropylene copolymer PP-R pipe high temperature performance, good mechanical properties and excellent connection performance, but the low temperature performance is poor, brittle temperature is -5 °C ~ 10 °C, the wall is thick, bending construction is more difficult At the same time, its creep resistance is also poor, not suitable for floor heating pipes.
4. The application rate of cross-linked polyethylene pipe PE-X in the floor heating system is the highest. The qualified PE-X pipe has the advantages of good mechanical properties, high temperature resistance and low temperature performance, and the price is cheaper than other varieties. However, PE-X pipes do not have thermoplastic properties and cannot be connected and repaired by hot melt welding. If the heating pipe is damaged, the best way is to replace the entire branch of the heating pipe; if the connection piece is used for repair, the whole is increased. System insecurity. The cross-linking process of PE-X pipe in production is difficult to control, and the quality control of the product is difficult, and it is difficult for a general small-scale production enterprise to do well.
Compared with the above pipes, PE-RT has the following outstanding advantages as a geothermal heating pipe:
1, can be hot melt connection, just to meet the requirements of the joint does not allow the floor heating pipe, good repairability;
2, simple processing technology, reliable quality;
3, low temperature resistance and flexibility are very good, the bending radius is small, the pipeline does not need to be preheated when it is bent, even if the construction is very convenient at low temperatures in winter;
4, good heat dissipation, thermal conductivity and PEX equivalent, much higher than PB and PP-R;
The price of PE-RT tube is lower than that of cross-linked aluminum-plastic composite pipe XPAP, and it can be regarded as the best heating pipe material with comprehensive performance and price ratio.
At present, the major manufacturers of PE-RT raw materials, Dow Chemicals and South Korea SK Chemicals have passed the certification authority and have a creep rupture curve that meets the product standards. This is a guarantee that PE-RT pipes can be reliably used for 50 years. . Since 2003, some PE-RT pipe products in China have passed the "8760 test" of the national chemical testing center of the national authority, namely, under the condition of hydrostatic pressure, ring pressure of 1.9Mpa and 110°C, and no rupture of 8760 hours. Without leakage, according to the relevant reference curve, it can be scientifically deduced that the service life of PE-RT pipes under normal working conditions is more than 50 years.
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