Stainless Steel Fan Coil Tube (Coiltube) for Medium-Low Temperature HVAC Applications
Product Overview
The Stainless Steel Fan Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component designed for use in Fan Coil Units (FCUs) operating under medium-low temperature conditions. This product represents a critical element in modern HVAC (Heating, Ventilation, and Air Conditioning) systems, where efficient thermal transfer and long-term corrosion resistance are paramount. The coil tube is fabricated from high-grade stainless steel and formed into a serpentine or spiral geometry to maximize the heat transfer surface area within a compact footprint.
Based on experimental research findings regarding fan coil unit performance under medium-low temperature conditions (typically 7°C to 20°C supply water temperatures), this product is specifically optimized to address the unique challenges encountered in such operating regimes, including reduced heat transfer coefficients, potential frosting, and increased pressure drops.
Material & Properties
Base Material
- Material Grade: SUS304 (ASTM A269 TP304) or SUS316L (ASTM A269 TP316L) stainless steel
- Alloy Composition (SUS304): Carbon ≤ 0.08%, Chromium 18.0–20.0%, Nickel 8.0–11.0%, Manganese ≤ 2.0%, Silicon ≤ 1.0%
- Alloy Composition (SUS316L): Carbon ≤ 0.03%, Chromium 16.0–18.0%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%
Mechanical Properties
- Tensile Strength: ≥ 520 MPa (SUS304) / ≥ 515 MPa (SUS316L)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness: ≤ 92 HRB
Thermal & Physical Properties
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 100°C
- Thermal Expansion Coefficient: 16.0–17.3 × 10⁻⁶ /K (20–100°C)
- Density: 8.0 g/cm³
- Operating Temperature Range: −40°C to +400°C
Corrosion Resistance
- Excellent resistance to atmospheric corrosion and general aqueous environments
- SUS316L grade offers superior resistance to chloride-induced pitting and crevice corrosion
- Withstands condensation cycling without intergranular corrosion under proper welding procedures
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm / 9.52 mm / 12.70 mm (¼" / ⅜" / ½") | ASTM A269, ±0.10 mm |
| Tube Wall Thickness | 0.30 mm / 0.50 mm / 0.70 mm / 1.00 mm | ASTM A269, ±10% |
| Fin Spacing | 2.0 – 3.2 mm | ±0.1 mm |
| Fin Material | Aluminum (AA1060) or Stainless Steel | — |
| Number of Rows | 1 / 2 / 3 / 4 rows | Customer specification |
| Circuit Count | 1 / 2 / 4 / 6 / 8 circuits | — |
| Coil Length (Total Tube) | Up to 60 m (continuous coil) | ±1% |
| Overall Coil Dimensions | Custom (up to 1200 × 600 × 250 mm) | ±2 mm |
| Bend Radius | ≥ 3D (D = tube outer diameter) | No wall thinning > 15% |
| Surface Finish | Bright annealed / Pickled and passivated | — |
| Water Side Pressure Rating | 1.0 – 1.6 MPa (10 – 16 bar) | Hydrostatic test at 1.5× working pressure |
| Air Side Pressure Drop | 50 – 150 Pa (depending on face velocity) | ASHRAE 96 / AHRI 410 |
| Heat Transfer Coefficient | 600 – 1200 W/(m²·K) (air side) | ASHRAE 96 methodology |
| Design Standard | EN 12954 / GB/T 19232 / ASHRAE 96 | — |
Manufacturing Process
- Raw Material Inspection: Incoming stainless steel coils are verified against mill certificates (EN 10204 Type 3.1) for chemical composition, mechanical properties, and surface quality. Spectrometric analysis confirms alloy grade compliance.
- Slitting & Forming: The stainless steel strip is slit to precise width and cold-formed into seamless tube using a roll-forming die set. Wall thickness uniformity is maintained within ±5% throughout the forming operation.
- Bright Annealing: Formed tubes undergo bright annealing in a protective atmosphere (95% N₂ / 5% H₂) at 1050–1150°C to relieve cold-work stresses, restore ductility, and achieve a clean oxide-free surface suitable for subsequent heat treatment.
- Coil Bending & Layout: The tube is precisely bent into the required serpentine or spiral configuration using CNC-controlled bending equipment. Bend radii are maintained at a minimum of 3D to prevent wall thinning and ovality exceeding acceptable limits.
-
Fin Attachment: Aluminum or stainless steel fins are attached to the coil tube via:
- Clad-fin method: Fins are mechanically expanded onto the tube surface using a finning machine, creating a tight mechanical bond.
- Brazed method: Fins are brazed to tubes using a phosphor copper or silver-based filler alloy at 600–650°C.
- Welding & Header Fabrication: U-bends and header connections are welded using TIG (Tungsten Inert Gas) welding under argon shielding. Weld penetration is verified by visual inspection and, where required, by radiographic testing (RT) per ASTM E94.
- Pickling & Passivation: The completed coil assembly is pickled and passivated to remove any heat-tint oxides and form a protective chromium oxide layer, ensuring maximum corrosion resistance.
- Pressure Testing & Performance Verification: Each coil unit undergoes hydrostatic pressure testing at 1.5× the design pressure (minimum 1.5 MPa) for a dwell time of 30 minutes with zero leakage. Air-side performance is verified against ASHRAE 96 test protocols for selected sample units.
- Final Inspection & Packaging: Dimensional verification, surface inspection, and material traceability documentation are completed. Coils are packaged with desiccant protection and protective end caps for shipping.
Applications
The stainless steel fan coil tube is engineered for demanding HVAC applications where medium-low temperature operation and long service life are critical:
- Commercial HVAC Systems: Fan Coil Units (FCUs) in office buildings, shopping malls, hotels, and hospitals operating with chilled water supply temperatures of 7–15°C.
- Low-Temperature Chilled Water Systems: Applications requiring supply water temperatures below 10°C, where conventional carbon steel coils suffer from accelerated corrosion.
- Food Processing & Pharmaceutical Facilities: Cleanroom HVAC and process cooling systems requiring hygienic-grade stainless steel construction per 3-A Sanitary Standards.
- Marine & Offshore HVAC: Air conditioning units on vessels and offshore platforms exposed to high-humidity, chloride-rich environments.
- Refrigerated Warehouses: Medium-temperature cold storage (−5°C to +10°C) dehumidification coils.
- Renewable Energy Systems: Heat exchanger coils in geothermal and solar-assisted HVAC systems where long-term durability is essential.
Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System certification for manufacturing operations
- ISO 14001:2015 — Environmental Management System certification
- EN 12954 — European standard for air conditioners, fluid-to-air heat exchangers, and heat pumps
- GB/T 19232 — Chinese national standard for air-cooled heat exchangers
- ASTM A269 — Standard specification for seamless austenitic stainless steel tubing
- ASTM A270 — Standard specification for welded austenitic stainless steel tubing
- ASHRAE 96 — Standard methods for rating air-to-water heat exchangers
- AHRI 410 — Standard for unitary air-to-water heat exchangers
- CE Marking — Conformity with European Machinery Directive (2006/42/EC)
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 for all material batches
Unique Selling Points
1. Medium-Low Temperature Optimization: Based on rigorous experimental research into fan coil unit performance under medium-low temperature conditions (7–20°C), this product incorporates geometric and material optimizations that maintain efficient heat transfer even when the Log Mean Temperature Difference (LMTD) is reduced, addressing the well-documented performance degradation of standard coils in low-temperature regimes.
2. Superior Corrosion Resistance: The use of SUS304/SUS316L stainless steel eliminates the risk of internal and external corrosion that plagues carbon steel and copper coils, particularly in applications involving deionized water, glycol-based heat transfer fluids, or humid coastal environments. This extends service life to 20–25 years with minimal maintenance.
3. Precision Manufacturing: CNC-controlled bending and forming processes ensure dimensional accuracy within ±0.10 mm, resulting in uniform flow distribution across all circuits and consistent heat transfer performance throughout the coil face.
4. Full Traceability: Every coil tube is traceable to its raw material batch through a comprehensive quality documentation system, providing complete supply chain transparency for critical infrastructure applications.
5. Custom Engineering Capability: Wenzhou Jixing Metal Materials Co., Ltd offers tailored coil geometries, circuit configurations, and material grades to meet specific project requirements, supported by CFD (Computational Fluid Dynamics) simulation and thermal performance modeling.
Performance Data (Medium-Low Temperature Conditions)
| Supply Water Temp. | Air Entering Temp. | Face Velocity | Heat Output (kW) | COP (Coefficient of Performance) |
|---|---|---|---|---|
| 7°C | 27°C DB / 19°C WB | 2.5 m/s | 3.2 – 8.5 | 0.85 – 0.92 |
| 12°C | 27°C DB / 19°C WB | 2.5 m/s | 4.1 – 10.8 | 0.90 – 0.95 |
| 15°C | 27°C DB / 19°C WB | 2.5 m/s | 4.8 – 12.6 | 0.92 – 0.96 |
| 20°C | 27°C DB / 19°C WB | 2.5 m/s | 5.9 – 15.2 | 0.94 – 0.97 |
Note: Performance data is representative for a 4-row, 2-circuit coil with 9.52 mm OD × 0.70 mm wall tube and 2.5 mm fin spacing. Actual performance varies with specific geometry and operating conditions. All ratings are based on ASHRAE 96 methodology.