With the rapid development of renewable energy utilization, geothermal energy has been increasingly valued as a clean and sustainable form of energy. High-density polyethylene (HDPE) pipes have become the preferred material for heat transfer medium circulation pipes in geothermal systems (especially ground source heat pump systems) due to their unique material properties. This article will explore in depth the performance advantages, design considerations, installation techniques and typical application cases of HDPE pipes in geothermal applications.
1. Temperature tolerance: must withstand temperature fluctuations from -20°C to +60°C (enhanced versions can reach 95°C)
2. Chemical stability: resistance to corrosive components such as minerals and sulfides in geothermal fluids
3. Long-term durability: the design life must be more than 50 years, the same as the geothermal system
4. Mechanical properties: withstand underground soil pressure, thermal stress and possible mechanical stress
5. Thermal conductivity: appropriate thermal conductivity to achieve efficient heat exchange
1. Excellent temperature resistance
Wide operating temperature range: standard HDPE pipes are suitable for -40℃ to 60℃; special formulas can withstand 95℃ for a short period of time
Low temperature toughness: not easy to crack in cold areas, better than PVC and other materials
Thermal stability: PE100-RC and other materials that resist rapid crack expansion ensure safety under temperature fluctuations
2. Excellent chemical corrosion resistance
Mineral corrosion resistance: not affected by calcium, magnesium, iron and other ions commonly found in geothermal water
Sulfide corrosion resistance: especially suitable for geothermal areas with high sulfur content
Wide pH value adaptability: can work stably in the range of pH2-pH12
3. Excellent mechanical and physical properties
High ring stiffness: SN8 and above grades can withstand deep soil pressure
Excellent flexibility: can adapt to small displacements of the formation and reduce the use of joints
Low thermal conductivity: 0.42 W/(m·K), reducing heat loss of vertical buried pipes
Controllable thermal expansion: linear expansion coefficient of 1.7×10⁻⁴/℃, which can be effectively compensated by design
4. Long service life
Anti-aging performance: underground service life can reach 50-100 years
Resistant to stress cracking: PE100-RC material resists environmental stress cracking
Maintenance-free design: almost no maintenance is required after underground installation
1. Material selection criteria
Material grade: PE100 or PE100-RC (anti-rapid crack propagation) is recommended
Pressure grade: PN6-PN16 (commonly PN10) is selected according to the system design
Standard compliance: Must meet ISO 4437, EN 12201 and other geothermal pipe special standards
2. Special modification technology
Heat conductivity enhancement: Adding fillers such as graphite to improve thermal conductivity (up to 0.8-1.2 W/(m·K))
Oxygen barrier: EVOH co-extrusion layer prevents oxygen penetration (≤0.1 g/(m³·day))
UV resistant: Contains 2-2.5% carbon black, used for exposed parts on the surface
3. Connection technology
Hot-melt butt: forms a seamless connection, suitable for main pipelines
Electrofusion welding: suitable for complex spaces and repair occasions
Prefabricated assemblies: Factory-prefabricated U-shaped elbows, etc. reduce on-site welding points
1. Ground source heat pump system
Vertical U-shaped buried pipe: commonly used DN25-DN40 pipe diameter, depth 50-200 meters
Horizontal spiral pipe: DN32-DN50 pipe, buried depth 1.5-3 meters
Energy pile system: integrated with building pile foundation, special pressure resistance design required
2. Medium and deep geothermal development
Downhole heat exchanger: high temperature resistant HDPE pipe (up to 95℃ working temperature)
Geothermal tail water recharge: DN150-DN400 large diameter pipeline system
3. Direct use of geothermal system
Hot spring transmission pipeline network: anti-scaling design to keep water flow smooth
Regional heating pipeline: prefabricated insulation pipe as working pipe
1. Hydraulic calculation:
Ensure a flow rate of 0.5-1.5m/s to balance heat transfer efficiency and pressure drop
Consider non-Newtonian fluid properties (such as when adding antifreeze)
2. Thermal design:
Calculate heat transfer capacity per unit pipe length (usually 30-70W/m)
Consider soil thermal resistance and long-term thermal balance
3. Mechanical design:
Buried depth ≥1.2 meters to avoid the influence of surface load
Thermal compensation design (such as expansion joints or natural compensation)
4. Anti-corrosion design:
Even if HDPE itself is corrosion-resistant, it is still necessary to consider the protection of the metal part of the pipe fittings
Additional protection for special geology (such as acidic soil)
1. Vertical underground pipe installation
Drilling process: Use rotary drilling to ensure that the hole diameter is greater than 50mm of the pipe bundle diameter
Grouting backfill: Use high thermal conductivity bentonite slurry (thermal conductivity ≥1.5 W/(m·K))
Pressure test: Perform a 1.5 times working pressure test immediately after installation
2. Horizontal pipe laying
Trench preparation: Lay a 10cm sand cushion layer at the bottom
Pipe laying: Maintain a constant slope to avoid air pockets
Backfill control: Backfill in layers, use fine-grained materials for the first layer
3. Quality assurance measures
Welding process assessment: Destructive testing of the first weld of each welder every day
Non-destructive testing: Ultrasonic or X-ray testing of key welds
System flushing: Thorough flushing after installation to remove impurities
|
Performance Indicators |
HDPE Pipe |
Stainless steel pipes |
Copper pipes |
PP-R pipe |
|
Initial Cost |
Low |
high |
Very high |
middle |
|
Corrosion resistance |
Excellent |
Excellent (specific models) |
middle |
excellent |
|
Thermal conductivity (W/m·K) |
0.42 |
15 |
401 |
0.22 |
|
Ease of installation |
high |
middle |
Low |
high |
|
Temperature range (℃) |
-40~60(95*) |
-50~150 |
-100~200 |
-20~70 |
|
Design life (years) |
50+ |
30 |
25 |
25 |
1: Ground source heat pump system in a commercial complex in Beijing
DN32 PE100-RC pipes are used, with vertical buried pipes of 120 meters deep × 600 holes
The total heat exchange power of the system is 3.2MW, and it has been running stably for 8 years
The measured COP is 4.3, with significant energy saving effect
2: Reykjavik District Heating Renovation in Iceland
DN400 thermal conductivity enhanced HDPE pipes are used to transport 85℃ geothermal water
Replacing the original steel pipes, the corrosion leakage rate is reduced to zero
The project investment recovery period is only 3.5 years
3: Pipeline network system of Japanese hot spring resort
High mineral hot spring water is transported using anti-scaling modified HDPE pipes
The system has been running for 5 years without scaling and clogging
Maintenance costs are reduced by more than 70%
HDPE pipes have become the preferred pipe material for modern geothermal systems, especially ground source heat pump systems, due to their comprehensive performance advantages. Its excellent corrosion resistance, good thermal performance, excellent mechanical properties and long service life enable it to perfectly adapt to the stringent requirements of geothermal applications. With the advancement of material science and technology and the innovation of installation technology, the application scope of HDPE pipes in the geothermal field will be further expanded, providing more reliable and economical infrastructure support for the development and utilization of global geothermal energy.
