Stainless Steel Coil Tube for HVAC Fan Coil Units (FCU)
1. Product Overview
The Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 765) is a precision-engineered coiled tubing solution designed specifically for integration into dry-type Fan Coil Units (FCUs) and Independent Fresh Air Systems (IFAS). These coil tubes serve as the critical heat exchange elements within air distribution and thermal management systems, facilitating efficient heat transfer between the circulating refrigerant (or heating medium) and the passing airstream.
The product is engineered to address the demanding airflow organization requirements identified in research on dry fan coil units with independent fresh air systems. The coil tube geometry, material selection, and surface treatment are optimized to achieve uniform air distribution, minimize pressure drop, and maximize thermal efficiency in both cooling and heating modes of operation.
2. Material & Properties
2.1 Base Material
- Grade: SUS304 (ASTM A269 / EN 10217-7), with SUS316L available upon specification for corrosive environments
- Composition: Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–11.0%, Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.0%
- Purity: Minimum 99.5% metallurgical purity with controlled impurity levels (S ≤ 0.03%, P ≤ 0.045%)
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (annealed condition)
- Yield Strength: ≥ 205 MPa
- Elongation at Break: ≥ 40% Hardness: ≤ 110 HRB (annealed), customizable per application requirements
2.3 Thermal & Corrosion Resistance
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Operating Temperature Range: −196°C to +870°C (intermittent), continuous service up to +450°C
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, and chlorinated water; passivated surface finish
- Hygienic Surface: Ra ≤ 0.8 μm achievable for pharmaceutical and food-grade HVAC applications
3. Technical Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.0 mm (customizable) | ±0.05 mm |
| Wall Thickness (WT) | 0.25 mm – 1.50 mm | ±0.02 mm |
| Coil Pitch / Spacing | 8.0 mm – 20.0 mm (configurable) | ±0.1 mm |
| Coil Diameter | 50 mm – 300 mm (typical) | ±0.5 mm |
| Tube Length (per coil) | 0.5 m – 12.0 m | ±10 mm |
| Surface Finish | 2B / BA / Electropolished / Passivated | Per ASTM A967 |
| End Forming | Plain, flared, crimped, or welded fittings | As per drawing |
| Pressure Rating | Up to 1.6 MPa (design), 2.4 MPa (hydrostatic test) | EN 10217-7 |
| Refrigerant Compatibility | R-410A, R-32, R-407C, R-134a, water/glycol mixtures | ASHRAE 34 compliant |
| Fin Configuration (if finned) | Aluminum or stainless steel fins, 12–16 FPI | Custom per thermal load |
| Packaging | Vacuum-sealed coil on wooden reel, moisture barrier wrap | ISO 11607 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Verification: Incoming stainless steel strip or tube stock is verified against mill test certificates (MTC) per EN 10204 Type 3.1. Spectrometric analysis confirms chemical composition compliance.
- Slitting & Leveling: Coiled strip is slit to precise width and leveled to eliminate residual stress, ensuring uniform wall thickness during forming.
- Tube Forming (Spiral Welding): Continuous spiral welding or seamless drawing produces the base tube. Welded tubes undergo full-penetration weld verification via dye penetrant testing (DPT) or eddy current testing (ECT).
- Coiling / Bending: CNC-controlled coil winding machines form the tube into the specified spiral geometry with precise pitch control. Spring-back compensation algorithms ensure dimensional accuracy.
- Heat Treatment (if required): Solution annealing at 1050–1100°C followed by controlled air cooling to achieve the desired microstructure and mechanical properties.
- Surface Treatment: Acid pickling and passivation per ASTM A967 remove scale and contaminants, forming a protective chromium oxide passive layer. Electropolishing available for Ra ≤ 0.4 μm surfaces.
- Finning (optional): High-frequency mechanical or hydraulic fin insertion/rolling for enhanced heat transfer area.
- End Processing: Cutting, deburring, and fitting installation (compression, brazed, or welded connections) as per customer drawings.
- Quality Inspection: Dimensional verification via laser scan or CMM; pressure testing at 1.5× design pressure; visual and magnetic particle inspection (MPI) for surface defects.
- Packaging & Dispatch: Each coil is individually inspected, tagged with traceability codes, and packaged for shipment.
4.2 Process Advantages
- Full Traceability: Batch-coded from raw material to finished product, enabling complete supply chain accountability.
- Zero-Leak Assurance: 100% hydrostatic pressure testing ensures leak-free performance in closed-loop refrigerant systems.
- Dimensional Precision: CNC coiling with ±0.1 mm pitch accuracy ensures optimal airflow distribution and heat exchanger packing density.
5. Applications
5.1 Primary Applications
- Commercial HVAC Systems: Dry-type fan coil units in office buildings, hospitals, hotels, and retail spaces where dehumidification control is critical.
- Independent Fresh Air Systems (IFAS): Coil tubes integrated into dedicated outdoor air systems (DOAS) for pre-conditioning of ventilation air.
- Industrial Process Cooling: Precision temperature control in semiconductor fabrication, pharmaceutical cleanrooms, and data centers.
- Food & Beverage Industry: Hygienic cooling coils for processing equipment where corrosion resistance and cleanability are paramount.
- Marine & Offshore HVAC: Saltwater-resistant coil assemblies for shipboard and offshore platform climate control.
5.2 System Integration Context
In the context of dry fan coil unit systems with independent fresh air supply, the coil tube design directly influences airflow organization — a critical parameter governing thermal comfort, indoor air quality (IAQ), and energy efficiency. The coil geometry must be optimized to:
- Minimize short-circuiting of supply and return air streams
- Ensure uniform velocity distribution across the coil face
- Maintain low pressure drop to reduce fan energy consumption
- Prevent condensation on coil surfaces in dry-mode operation
- Facilitate easy maintenance access and cleaning
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System certification |
| EN 10217-7 | European standard for stainless steel tubes for heat exchangers |
| ASTM A269 | American standard for seamless and welded austenitic stainless steel tubes |
| ASME B31.5 | Pressure piping for refrigeration and air conditioning equipment |
| CE Marking | European conformity for pressure equipment (PED 2014/68/EU) |
| RoHS Compliance | Restriction of Hazardous Substances Directive (EU) 2011/65/EU |
| EN 10204 3.1 | Material Test Certificate with verified inspection data |
7. Unique Selling Points
Superior Corrosion Longevity: Unlike conventional copper coil tubes prone to galvanic corrosion and refrigerant oil degradation, stainless steel coil tubes deliver a service life exceeding 25 years in harsh HVAC environments with no degradation of thermal performance.
Hygienic & Food-Safe Design: The austenitic stainless steel surface resists bacterial adhesion and is fully compatible with food-grade cleaning protocols, making these coils ideal for pharmaceutical, dairy, and brewery HVAC installations.
Precision Engineering for Airflow Optimization: CNC-controlled coiling with sub-millimeter pitch accuracy ensures that the coil tube geometry aligns with computational fluid dynamics (CFD) models for optimal airflow organization in dry fan coil and fresh air systems.
Customizable Thermal Performance: Modular design allows adjustment of coil pitch, tube diameter, wall thickness, and fin density to match specific thermal load requirements — from light commercial units (2–5 kW) to heavy industrial systems (50+ kW).
Environmental Sustainability: Stainless steel is 100% recyclable, and the elimination of copper reduces the environmental footprint associated with mining and refining. The long service life further minimizes lifecycle carbon emissions compared to disposable copper alternatives.
8. Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd. offers comprehensive engineering support including:
- Thermal performance simulation and CFD analysis for system-level optimization
- Custom coil geometry design based on customer heat exchanger shell dimensions
- Material selection guidance for specific refrigerant and ambient conditions
- Sample fabrication and drop-testing prior to production commitment
- OEM/ODM manufacturing with private labeling and packaging options
For detailed technical inquiries, engineering drawings, or sample requests, contact the technical sales team at Wenzhou Jixing Metal Materials Co., Ltd. with reference to Product No. 765 — Stainless Steel Coil Tube for HVAC Fan Coil Units.