Stainless Steel Coil Tube for Fan Coil Unit (FCU) Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Reference No.: 894
Category: HVAC Coil Tube — Fan Coil Unit (Fan Coil Unit, FCU) Heat Exchanger
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered heat exchanger component designed specifically for Fan Coil Unit (FCU) systems in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) installations. This product represents a critical component in the thermal transfer chain of air handling systems, where it serves as the primary medium for heat exchange between refrigerant or hydronic fluid and ambient air.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production of high-performance stainless steel coil tubes that address key design challenges identified in the field of FCU engineering, including but not limited to: uneven air distribution, condensate drainage efficiency, thermal stratification, noise generation, and long-term corrosion resistance. The coil tube is engineered to maximize heat transfer coefficients while minimizing pressure drop across the heat exchanger circuit.
2. Material & Properties
The coil tube is fabricated from high-grade stainless steel, selected for its superior combination of mechanical strength, corrosion resistance, and thermal conductivity. The following materials are commonly employed:
- AISI 304 Stainless Steel (SAE 304 / UNS S30400): The standard grade for general-purpose FCU applications, offering excellent resistance to atmospheric and condensate corrosion with a minimum yield strength of 205 MPa (29,700 psi).
- AISI 316 Stainless Steel (SAE 316 / UNS S31600): Enhanced molybdenum content (2.0–3.0%) provides superior resistance to chlorides, making it suitable for coastal or industrial environments where chloride-induced pitting is a concern.
- AISI 316L Stainless Steel (SAE 316L / UNS S31603): Low-carbon variant (C ≤ 0.03%) ideal for welding-intensive assemblies where sensitization and intergranular corrosion must be avoided.
Key Material Properties (AISI 304, Annealed Condition):
| Property | Specification | Standard / Reference |
|---|---|---|
| Density (密度) | 8,000 kg/m³ | ASTM A269 |
| Thermal Conductivity (热导率) | 16.3 W/(m·K) @ 20°C | ASTM E153 |
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM A269 / ASME B36.19M |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM A269 |
| Elongation (延伸率) | ≥ 40% | ASTM A269 |
| Operating Temperature Range | −196°C to +870°C | ASME B31.9 |
| Corrosion Resistance | Excellent (atmospheric, condensate, mild chemical) | ASTM G48 |
| Chromium Content (Cr) | 18.0–20.0% | ASTM A240 |
| Nickel Content (Ni) | 8.0–10.5% | ASTM A240 |
3. Specifications
The following table summarizes the dimensional and performance specifications available for the stainless steel coil tube product line:
| Parameter | Specification Range | Notes |
|---|---|---|
| Tube Outer Diameter (OD, 外径) | φ 6.35 mm, φ 8.00 mm, φ 9.53 mm, φ 12.70 mm | Standard OD per ASHRAE guidelines |
| Tube Wall Thickness (壁厚) | 0.40 mm – 1.00 mm | Customizable per application |
| Tube Length (管长) | 1,200 mm – 6,000 mm (standard); up to 12,000 mm (custom) | Coil-wound configuration |
| Coil Diameter (盘管直径) | φ 200 mm – φ 800 mm | Adaptable to FCU casing dimensions |
| Row Count (排数) | 2-row to 8-row configurations | Determines heat transfer capacity |
| Fins per Inch (FPI, 翅片数) | 10 FPI – 21 FPI | Higher FPI = greater surface area |
| Fin Material (翅片材质) | Aluminum (6063-T5), Stainless Steel, or Copper | Hydrophilic coating optional |
| Fin Spacing (翅片间距) | 1.2 mm – 2.5 mm | Optimized for airflow vs. heat transfer |
| Design Pressure (设计压力) | 1.0 MPa – 2.5 MPa | Hydrostatic test at 1.5× design pressure |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, Ammonia (NH₃) | Food-grade compatible |
| Surface Treatment | Electropolished, Passivated (ASTM A967), or As-rolled | Enhances corrosion resistance |
| Connection Type | Flared, Brazed, Threaded (BSP/NPT), Flanged | Per ASME B31.9 |
4. Manufacturing Process
The production of the stainless steel coil tube adheres to a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and functional performance:
- Raw Material Procurement & Inspection: Stainless steel strip or seamless tubing is sourced from certified mills and subjected to spectroscopic analysis (ASTM E135) to verify chemical composition compliance.
- Slitting & Leveling: The raw strip is slit to the required width and cold-rolled to achieve the specified wall thickness with a tolerance of ±0.02 mm.
- Forming & Coil Winding: Precision CNC-controlled forming equipment shapes the tube into the designated coil geometry. The winding process maintains uniform pitch and alignment to prevent flow maldistribution.
- Fin Stamping & Insertion: Aluminum or stainless steel fins are stamped with hydrophilic micro-groove patterns and mechanically or mechanically expanded onto the tube surfaces to maximize the heat transfer area.
- Hydroforming / Expansion: Mechanical expansion ensures tight thermal contact between the tube and fins, reducing thermal contact resistance to less than 0.01 m²·K/W.
- Welding & Brazing: Header connections are fabricated using TIG (Tungsten Inert Gas) welding in accordance with ASME B31.9. Brazing joints employ silver-based filler alloys (AWS A5.8) with a melting range of 620–730°C.
- Surface Treatment: Electropolishing or acid pickling and passivation removes free iron and contaminants, forming a stable chromium oxide passive layer (Cr₂O₃) for enhanced corrosion resistance.
- Pressure Testing & Leak Detection: Each unit undergoes a hydrostatic pressure test at 1.5× the design pressure for a minimum hold time of 30 minutes, followed by helium leak detection (sensitivity ≤ 1×10⁻⁹ Pa·m³/s) for brazed joints.
- Final Quality Inspection: Dimensional verification via laser scanning, visual inspection per ASTM E94, and performance testing (air-side and fluid-side heat transfer coefficients) per ASHRAE Standard 22.
5. Applications
The stainless steel coil tube is integral to a wide range of HVAC and thermal management systems:
- Commercial Fan Coil Units: Primary heat exchange component in ceiling-mounted, wall-mounted, and ducted FCUs for office buildings, hotels, hospitals, and retail spaces.
- Residential HVAC Systems: Used in mini-split and multi-split air conditioning systems for precise temperature regulation.
- Industrial Process Cooling: Temperature control in pharmaceutical manufacturing, food processing, and electronics fabrication facilities where corrosion resistance is critical.
- Chilled Beam Systems: Radiation-based cooling applications in high-performance commercial buildings.
- Refrigeration Systems: Evaporator coils in commercial refrigeration and cold storage applications.
- Heat Recovery Units (HRU): Air-to-air heat exchangers for energy-efficient ventilation systems.
- Marine HVAC: Coastal and marine environments where chloride resistance is paramount (AISI 316L grade).
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality certifications and adheres to international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系) |
| ISO 14001:2015 | Environmental Management System (环境管理体系) |
| ASME B31.9 | Pressure Piping — Refrigeration and Air-Conditioning |
| ASHRAE Standard 22 | Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment |
| EN 12830 | Water Side Heat Exchangers — Requirements and Test Methods |
| ASTM A269 / A268 | Standard Specification for Seamless and Wrought Stainless Steel Tube |
| CE Marking (EU) | Conformity with European Pressure Equipment Directive (PED 2014/68/EU) |
| TÜV Certification | Third-party verification of manufacturing quality and safety |
| NB Certification (China) | National Supervision and Inspection of Special Equipment |
7. Unique Selling Points
Design-Centric Engineering Philosophy: Wenzhou Jixing's coil tube product line is developed with deep consideration of the critical design issues identified in Fan Coil Unit engineering literature, including:
- Optimized Airflow Distribution: The coil geometry and fin configuration are engineered to minimize air maldistribution and thermal stratification, ensuring uniform temperature output across the entire FCU face.
- Enhanced Condensate Management: Hydrophilic fin coatings and optimized drain pan integration reduce condensate retention, minimizing microbial growth and improving indoor air quality (IAQ).
- Acoustic Performance: The coil tube design incorporates flow-straightening features and optimized fin spacing to reduce aerodynamic noise generation, achieving sound pressure levels below 25 dBA at standard operating conditions.
- Extended Service Life: The use of passivated stainless steel and corrosion-resistant fin materials extends the operational lifespan to 20+ years, significantly reducing total cost of ownership (TCO).
- Modular Scalability: The product line offers modular configurations that allow easy adaptation to varying capacity requirements without redesign, supporting both retrofit and new-build applications.
- Energy Efficiency: The high surface-area-to-volume ratio of the coil design, combined with low-pressure-drop characteristics, reduces fan power consumption and improves the overall Seasonal Energy Efficiency Ratio (SEER) and Heating Seasonal Performance Factor (HSPF) of the installed FCU system.
8. Technical Notes & Recommendations
Based on extensive research and field experience in Fan Coil Unit design, the following considerations are recommended for optimal coil tube performance:
- Airflow Velocity: Maintain face velocity between 1.5–3.0 m/s to balance heat transfer efficiency with acoustic performance and condensate drainage.
- Fin Density Selection: For dehumidification-critical applications, select 14–18 FPI with hydrophilic coating; for dry cooling applications, 10–12 FPI is recommended to minimize moisture pickup.
- Refrigerant Distribution: Ensure even refrigerant distribution across all coil rows using properly sized distributor plates or manifold designs to prevent partial row flooding or starved conditions.
- Drainage Slope: Maintain a minimum drain pan slope of 1:100 to ensure complete condensate removal and prevent water accumulation.
- Material Selection: Specify AISI 316L