Analysis on the necessity of oxygen barrier for floor heating pipes

Among the existing buildings in my country, more than 95% are high-energy-consuming buildings, and the heating energy per unit area is more than three times that of developed countries.

Except for a few areas such as Hainan, most of them have a climate with four distinct seasons, which are cold in winter and hot in summer, and more than 90% of areas need heating in winter.

Low-temperature floor radiant heating is one of the most comfortable heating methods, and is increasingly accepted by most users. It has strong comfort, energy saving,

It is easy to manage, does not occupy indoor area, daily maintenance is less, and the heat source is flexible. It meets the needs of commercialization of buildings.

Can improve the quality and grade of the building. The area used in Chinese buildings is increasing year by year.

      With the development of the plastic industry, new plastic pipes that have undergone special treatment and processing have been able to meet the high temperature resistance,

High pressure bearing and aging resistance requirements, and the length of the pipeline can be intercepted according to the design requirements, and the inlet part has no joints, which prevents the leakage of buried pipelines; it is easy to bend and easy to construct.

Therefore, the application of plastic pipes in floor heating has gradually caused the floor heating industry to rise.

At present, the commonly used plastic pipes for floor heating include heat-resistant polyethylene (PE-RT) pipes, cross-linked polyethylene (PEX) pipes, and polybutylene (PB) pipes.

As one of the core of the floor heating system, the choice of pipe is the key. The choice of materials for the main pipe and floor heating coil is directly related to the stability, economy and energy saving of the system.

      The pipes used in the floor heating system on the market in my country are mainly ordinary plastic pipes, and they all have a certain degree of oxygen permeability.

It is also called oxygen respiration, so there will be oxygen in the system, and as the temperature rises, this oxygen permeability will also increase.

      As early as the early 1980s, European technicians discovered that in the hot water circulation system using plastic pipes, metal parts are prone to abnormally fast corrosion and equipment is quickly damaged.

This is because ordinary plastic pipes cannot block the penetration of oxygen. If the hot water pipe contains more oxygen,

It is easy to corrode the metal pipe fittings and other devices in the system, which is even more unfavorable for the high-temperature heating system connected with the metal radiator.

Oxygen is beneficial to the growth of certain bacteria and microorganisms, causing the bacteria and microorganisms in the pipe to multiply and gradually form biological slime.

After this layer of slime completely covers the inner wall of the pipe, the pipe wall will shrink quickly, the water flow resistance will be large, and the water flow will drop sharply; it will also block the pipe over time.

It is very difficult to clean the pipes and can only be cleaned by mechanical methods. Other methods such as chemical methods are difficult to achieve results.

      Therefore, the oxygen barrier performance of plastic pipes is directly related to the application performance of the pipes. Therefore, oxygen barrier technology must be used to inhibit the reproduction of microorganisms.

So as to effectively ensure the safety of the pipeline. In Europe, a large number of hot water systems (heating, air conditioning, floor heating, etc.) use oxygen-blocking plastic pipes.

In the field of heating pipelines, the United States, Europe and Australia all mandate the use of anti-permeable heating plastic pipelines in floor heating projects.

The floor heating oxygen barrier pipe can prevent oxygen from penetrating into the pipeline system, thereby preventing the metal parts in the heating system from corrosion and rust.

Greatly extend the service life of metal valves, switches, boilers, manifolds and other metal parts in the entire heating system. At the same time, bacteria that rely on oxygen to survive cannot breed either.

While protecting the pipes, it increases the life of the wall-hung boiler heating system. It can be seen that the oxygen barrier properties of pipes will be an inevitable trend of development in the pipeline of the floor heating system.

      In recent years, with the continuous increase in the amount of floor heating pipes, people pay more and more attention to the oxygen barrier performance of floor heating pipes.

In order to improve the oxygen permeability resistance of plastic pipes, domestic and foreign pipe manufacturers have introduced plastic pipes for cold and hot water containing EVOH oxygen barrier layers.

Including oxygen barrier PE-RT pipe, oxygen barrier PB pipe, oxygen barrier PE-X pipe.

      There are currently two types of oxygen barrier pipes on the market, one is a three-layer oxygen barrier, and the other is a five-layer oxygen barrier;

Both types of oxygen barrier tubes use ethylene-vinyl alcohol copolymer (EVOH) as the oxygen barrier layer.

      Three-layer oxygen barrier pipe, that is, a layer of hot melt glue and EVOH resin is evenly coated on the outside of the pipe. The structure from the outside to the inside is:

Oxygen barrier layer/hot melt adhesive/resin, since EVOH is a water-soluble resin, it is hydrophilic and hygroscopic. When moisture is absorbed, the gas barrier performance will be greatly reduced;

At the same time, the three-layer co-extruded pipe cannot be directly hot melted. Before the hot melt connection, a special cutting tool is required to remove the oxygen barrier and glue layer at the connection.

The hot melt connection process is complicated, the construction is difficult, and the construction efficiency is very low. Very professional construction personnel are required in the cutting process, because the plastic layer is easily damaged during the cutting process;

Causes leakage during later use and installation; in addition, the surface of the pipe is easily scratched during the construction process,

The destruction of the EVOH layer leads to a relatively reduced oxygen barrier effect: Therefore, the three-layer oxygen barrier tube is not a complete oxygen barrier tube.

      The five-layer co-extruded oxygen barrier tube has the structure: resin/hot melt adhesive/oxygen barrier layer/hot melt adhesive/resin. It is not difficult to see that since the oxygen barrier layer is located in the middle of the pipe, it has good permeability resistance.

The oxygen barrier will not be damaged, ensuring the oxygen barrier effect. It can effectively prevent oxygen from entering the thermal cycle system and reduce equipment corrosion.

The five-layer oxygen barrier PB pipe can make the oxygen barrier rate reach ≤0.007g/m3.d. It fully meets the requirements of German standard DIN4726 for the oxygen barrier properties (0.02g/m3.d) of heating plastic pipes.

This kind of pipeline is ideal, but it is difficult to process.

      For the three-layer structure, one-time co-extrusion process or two-time co-extrusion coating process can be used

. The latter method is easier to control, and the design and manufacture of the mold are also relatively simple. The main advantage is that the rejection rate is relatively low.

Because the plastic pipe waste with oxygen barrier layer cannot be recycled and reused, and the raw material price is very high, many companies choose the secondary co-extrusion coating process.

Of course, it also has disadvantages. Compared with the one-time co-extrusion process, the coating layer of the second-time co-extrusion coating process pipe is thicker;

Since the price of EVOH is almost double that of PB, the thicker the coating layer, the higher the production cost of the pipe.

For the production of five-layer plastic pipes with oxygen barrier layers, only one co-extrusion process is currently used.

The five-layer oxygen barrier pipe extrusion technology is relatively mature in China, but what kind of material to choose as the pipe for the floor heating industry has been a hot issue in the industry in recent years.

      In recent years, domestic controversy over several commonly used floor heating pipes, especially PE-RT and PEX pipes, which is better and worse, has never stopped. Each has its own rhetoric and seems to have some truth;

In fact, each type of pipe has its own advantages and disadvantages. According to the use of environmental conditions, construction requirements to select the appropriate pipe material is the correct answer to the floor heating pipe material.

      As mentioned above, no matter what kind of material is selected for floor heating pipes, oxygen barrier has become an inevitable development trend.

At present, ethylene-vinyl alcohol copolymer (EVOH) is used as the material of the oxygen barrier in the oxygen barrier tube.

This material needs to rely on imports, is expensive, and pipes with an EVOH oxygen barrier cannot be recycled, which will inevitably lead to an increase in the cost of pipe manufacturers.

      The polybutene used in the PB tube is a highly inert polymer material with high chemical stability.

In addition, microorganisms are not easy to parasitize and grow, and it is the most hygienic drinking water supply pipe in the world.

In the field of HVAC, PB pipe has superior characteristics that other plastics cannot match.

PB pipes have been used in my country's hot and cold water supply systems and floor heating systems for more than 10 years and have achieved good social benefits.

However, because the pipe materials need to be imported and the price is expensive, it can only be positioned in the cold and hot water supply and heating systems of middle- and high-end residential and public buildings.

      With the continuous improvement of relevant product standards, engineering design and construction regulations, and construction demonstration projects,

It is believed that the domestic floor heating industry will also move towards formalization and branding, and enterprises with good reputation and strength will become market leaders.

Good floor heating pipe products can be sold at a good price, and those companies that rely on unfair means such as low-price competition to compete will eventually be eliminated by the market.

Visp has always believed that winning with high quality is the kingly way.