Complete Guide to Piping Selection for Secondary Fluid Installations
In secondary fluid installations, such as air conditioning, refrigeration or heating systems, pipe selection is critical. Factors such as material, temperature, maximum pressure, joint type and total cost (including fittings) are crucial to ensure an efficient and durable installation. In this guide, we will explore the main piping options, comparing their characteristics, joining methods and an approximate cost analysis to facilitate decision making in applied engineering projects.
Types of Pipes and Their Characteristics
1. Plastic Pipes
- Polyethylene (PE) // Temperature: -30°C to 60°C Maximum Pressure: Up to 16 bar Union: Pressurized O-ring, Thermofusion or electro-welding. Advantages: Corrosion resistant, light and easy to install. Widely used in cold water and irrigation networks. No oxygen barrier.
- Wirsbo pipes (PEX-A) // Temperature: -20°C to 95°C Maximum pressure: Up to 10 bar Union: Expansion with memory ring. Advantages: Flexible and easy to install, ideal for potable water, heating and domestic hot water applications. No oxygen barrier.
- Polypropylene (PP-R, PP-RF, PP-R O2) // Temperature: -10°C to 90°C (up to 120°C in high strength conditions) Maximum Pressure: 20 bar (in standard PP-R) Union: Thermofusion. Advantages: High temperature resistance, suitable for hot water and heating systems. Fiberglass reinforced or oxygen barrier variants improve strength and prevent oxygen diffusion.
- Multilayer (PEX-Al-PEX and PERT-Al-PERT) // Temperature: -20°C to 95°C Maximum Pressure: Up to 10 bar Joining: Pressing or compression. Advantages: Lightweight and flexible, ideal for heating and domestic hot water installations. The aluminum layer improves dimensional stability, pressure resistance and creates an oxygen barrier.
PVC (Polyvinyl Chloride) //Temperature: -15°C to 60°C Maximum Pressure: Up to 10 bar Bonding: Adhesive Advantages: Economical and easy to install, widely used in cold water mains and drainage systems. However, it is not suitable for hot water systems. Caution with low temperature brittleness
2. Metallic Piping
- Galvanized Steel // Temperature: -50°C to 60°C Maximum Pressure: 20 bar Union: Thread. Advantages: Excellent mechanical strength and durability in cold water networks or fire-fighting systems. However, it is prone to corrosion in hot water applications or humid environments.
- Stainless Steel // Temperature: -200°C to 400°C Maximum Pressure: Limit depending on thickness. > 50bar. Joining: Thread, TIG welding or pressing. Advantages: Exceptional resistance to corrosion and extreme temperatures, ideal for high purity systems, such as in the food and pharmaceutical industry.
- Carbon Steel // Temperature: -20°C to 400°C. (Lower temperatures with steels that avoid embrittlement). Maximum Pressure: Up to 25 bar Union: Welding. Advantages: Robust and with excellent resistance to high temperatures. Widely used in heating systems and high pressure industrial applications.
3. Copper Piping
- Copper Type K and L // Temperature: -200°C to 200°C Maximum pressure: 25 bar. Higher values according to thickness. Joining: Brazing or soldering. Advantages: High thermal conductivity and corrosion resistance. It is the preferred choice in heating and domestic hot water systems, although cost and installation require trained technicians.
- Flexible Copper // Temperature: -50°C to 150°C Maximum Pressure: 10 bar Joining: Pressed or compression. Advantages: Flexible and easy to install, although with lower resistance to high pressures. Used in low pressure hot water installations and gas connections.
- Cascade systems, which increase the SEPR of the installation.
- Variable speed drives, which reduce electrical consumption peaks and increase the service life of the motors.
- Multiple suction lines to serve different temperatures simultaneously.
- VRC (Variable Refrigerant Capacity) system for refrigeration capacity regulation.
- Condensation heat recovery.
- Subcooling of the liquid line, which improves system performance.
- Use of natural or low GWP refrigerants.
- Indirect systems to reduce refrigerant charge.
INTARCON, given its experience in the centralization of services, defends the use of natural refrigerants, such as propane (R-290), carbon dioxide (R-744) and ammonia (R-717), as a future solution in accordance with the F-Gas regulation, as well as for its greater energy efficiency.
R-744 and R-717 are mainly used in direct expansion systems for negative temperature chambers because of their high cooling capacity due to their thermodynamic characteristics. And R-290 and R-717 are used in indirect expansion systems with the idea of providing safety in the installation by reducing the load and confining the gas in a specific area, increasing safety, minimizing the possibility of leaks and reducing the environmental impact. Most direct expansion installations have an alternative in indirect expansion.
Although in refrigeration in the tertiary sector, indirect expansion installations are usually used for larger installations or projects, while direct expansion tends to focus on smaller projects.
Conclusion and Recommendations for the Use of Piping for Installations
When selecting the type of piping in an installation, it is essential to consider both the characteristics of the fluid and the conditions of the circuit and the industry where it is used:
- Oxygen barrier in closed circuits: In closed circuits, such as air conditioning or refrigeration systems, the presence of oxygen can cause corrosion in metal components, affecting the durability and efficiency of the system. In these cases, an oxygen barrier in the piping helps to minimize oxygen ingress, thus protecting the equipment and reducing maintenance costs. In open installations (such as water mains or irrigation), where water is constantly renewed, the oxygen barrier is not crucial.
- Dilatations: Depending on the material used, the implementation of elements to absorb dilatations should be considered. Plastic materials are more critical in this respect.
- Chemical compatibility and exposure to solar radiation.
- Material recommendations according to application: Mains water or irrigation installations: Here, plastic pipes (PE, PVC, or PP-R without oxygen barrier) are ideal, due to their durability, corrosion resistance and affordability. Secondary fluids in HVAC applications: For these applications, where cost and ease of installation are important factors, PP-R pipes with fiber reinforcement and oxygen barrier or PEX-Al-PEX are recommended. These materials offer a good balance of strength, cost and corrosion protection. Secondary fluids in medium temperature cooling applications: In this case, in addition to PP-R with fiber and oxygen barrier and PEX-Al-PEX, stainless steel is also a suitable option to resist intermediate temperatures and prevent corrosion. Secondary fluids in low-temperature applications: Here, stainless steel is highly recommended due to its resistance to low temperatures and its durability in low-temperature conditions. High-temperature applications: For high-temperature environments, carbon steel and stainless steel are the most reliable options, as both materials can withstand thermal stress without compromising the integrity of the installation.
Be sure to always consult the technical data sheets of materials and accessories for the same, checking that the operating conditions are within the approved working range, as well as the recommendations on the parameters of the joints (temperatures, times, types of jaws, etc.).
Prepared by: Manuel García Jiménez
