Stainless Steel Coil Tube — HVAC Fan Coil Unit & Energy Recovery Application
Product Code: 1070 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (SS Coil Tube) is a precision-engineered tubular product designed specifically for heat exchange applications within Fan Coil Unit (FCU) systems and Air-to-Air Energy Recovery Ventilator (ERV) devices. As a core component in modern building HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, this coil tube facilitates efficient thermal transfer between air streams while maintaining structural integrity under continuous cyclic loading.
Wenzhou Jixing Metal Materials Co., Ltd. produces this coil tube to meet the rigorous demands of energy-efficient air conditioning systems, where the integration of energy recovery devices has been demonstrated to significantly reduce overall system energy consumption. The coil tube serves as the heat transfer medium in both the primary cooling/heating coil and the secondary energy recovery exchanger, enabling simultaneous sensible and latent heat recovery from exhaust air streams.
Design Philosophy: Optimized for low-pressure drop, high thermal conductance, and long-term corrosion resistance in humid indoor air environments, aligned with ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) energy efficiency standards.
2. Material & Properties
2.1 Base Material
The coil tube is manufactured from high-grade austenitic stainless steel, primarily SUS304 (ASTM 304 / UNS S30408) and SUS316L (ASTM 316L / UNS S31603), selected for their superior resistance to atmospheric corrosion, condensate-induced pitting, and thermal fatigue.
2.2 Key Material Properties
- Chemical Composition (SUS304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%
- Chemical Composition (SUS316L): Carbon (C) ≤ 0.03%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%
- Density: 8.00 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (SUS304); 14.6 W/(m·K) at 25°C (SUS316L)
- Specific Heat Capacity: 500 J/(kg·K) at 25°C
- Linear Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (SUS304); 16.0 × 10⁻⁶ /°C (SUS316L)
- Yield Strength: ≥ 205 MPa (SUS304); ≥ 170 MPa (SUS316L)
- Tensile Strength: ≥ 515 MPa (SUS304); ≥ 485 MPa (SUS316L)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensate (pH 4.0–5.5), and humid indoor environments; SUS316L grade provides enhanced resistance to chloride-induced pitting
- Operating Temperature Range: −40°C to +200°C (continuous); short-term exposure up to +400°C
3. Technical Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 7.00 mm / 8.00 mm / 9.53 mm | ±0.05 mm |
| Wall Thickness | 0.30 mm / 0.40 mm / 0.50 mm / 0.60 mm | ±0.02 mm |
| Coil Length (per spool) | Up to 500 m (standard); custom up to 2000 m | ±2% |
| Coil Inner Diameter (ID) | 300 mm / 400 mm / 500 mm | ±5 mm |
| Surface Finish | 2B (Cold Rolled and Annealed) / BA (Bright Annealed) / Mirror (Ra ≤ 0.1 μm) | Per ASTM A478 |
| Maximum Operating Pressure | 1.6 MPa (gauge) | Per EN 10217-7 |
| Bending Radius (Minimum) | ≥ 3 × OD | Without cracking or deformation |
| Winding Tension | 0.5–2.0 N/mm (adjustable per application) | Uniform across spool |
| Surface Roughness (Internal) | Ra ≤ 0.4 μm (BA finish); Ra ≤ 0.8 μm (2B finish) | Per ISO 1302 |
| Heat Transfer Coefficient (Typical) | 80–150 W/(m²·K) (air-side) | Dependent on fin configuration |
| Weight per Meter (7.00 mm × 0.40 mm) | ≈ 0.63 kg/m | ±3% |
| Standard Length per Spool | 200 m / 300 m / 500 m | Customizable |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, metallurgical quality, and surface integrity:
- Steel Strip Procurement & Inspection: Cold-rolled stainless steel strip (CRSS) is sourced from certified mills and subjected to incoming quality inspection including chemical composition analysis (OES — Optical Emission Spectroscopy), mechanical testing, and visual surface examination per ASTM A478 / EN 10088 standards.
- Slitting & Coiling: The master coil is slit to the required width using precision slitting lines with laser-guided edge trimming. The slit strip is re-coiled at controlled tension to prevent deformation.
- Tube Forming (Cold Roll Forming): The slit strip passes through a series of progressive forming rolls that gradually bend the flat strip into a circular cross-section. This cold roll forming process is performed at ambient temperature to preserve the metallurgical properties of the stainless steel and avoid heat-affected zone (HAZ) degradation.
- Seam Welding: The longitudinal seam is welded using TIG (Tungsten Inert Gas) welding or laser welding with argon shielding gas to achieve a hermetic, corrosion-resistant joint. Weld quality is verified through dye penetrant testing (PT) and visual inspection.
- Heat Treatment (Annealing): Where required, the formed tube undergoes stress-relief annealing at 850–900°C in a protective atmosphere (hydrogen or argon) to eliminate residual stresses from cold forming, followed by controlled cooling to prevent chromium carbide precipitation (sensitization).
- Precision Coiling (Winding): The finished tube is wound onto a spool using a servo-controlled winding machine that maintains uniform tension and layer-to-layer contact. The winding process ensures consistent pitch and prevents inter-layer adhesion.
- End Sealing & Packaging: The coil ends are sealed with protective caps to prevent moisture ingress and mechanical damage. The spool is wrapped in moisture-barrier film and placed in a wooden or steel crate for transport.
- Final Quality Control: Each production batch undergoes dimensional verification (OD, wall thickness via ultrasonic thickness gauge), pressure testing (hydrostatic test at 2.5 × working pressure for 30 minutes), and surface defect inspection.
5. Applications
The Stainless Steel Coil Tube is integral to a wide range of HVAC and thermal management systems:
5.1 Fan Coil Unit (FCU) Systems
- Cooling Coils: Serves as the primary heat exchange element in chilled water fan coil units, transferring heat from indoor air to the chilled water circuit.
- Heating Coils: Functions as the heat exchange element in hot water fan coil units for space heating.
- Condensate Drainage: The stainless steel construction eliminates the risk of corrosion-induced leaks that are common with carbon steel alternatives in condensate-exposed environments.
5.2 Air-to-Air Energy Recovery Ventilators (ERV)
- Plate-Fin Heat Exchanger Coils: The coil tube is incorporated into plate-fin heat exchanger assemblies within ERV units, enabling simultaneous recovery of sensible and latent heat from exhaust air streams.
- Energy Efficiency Enhancement: As documented in the analysis of energy-saving impacts of air-to-air energy recovery devices on FCU-plus-fresh-air systems, the integration of ERV with FCU systems achieves energy savings of 15–35% depending on climate zone and design conditions. The coil tube's high thermal conductance and low pressure drop characteristics directly contribute to the effectiveness of these recovery systems.
- Enthalpy Wheel Alternative: In configurations where rotary heat wheels are not preferred, plate-fin coil tube exchangers provide a maintenance-free alternative for air-side energy recovery.
5.3 Additional Applications
- Chiller evaporators and condensers
- Air handler units (AHU) cooling and heating sections
- Cleanroom HVAC systems requiring high-purity air handling
- Pharmaceutical and food processing facility HVAC
- Marine HVAC systems (SUS316L grade for chloride-rich environments)
- Data center precision cooling systems
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| EN 10217-7 | Non-ferrous metal tubes — Stainless steel tubes for pressure purposes |
| ASTM A478 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Heat-Transfer Equipment |
| ASME B31.9 | Pressure Piping — Refrigeration Piping and Heat Transfer Components |
| EN 10088-1 / EN 10088-2 | Stainless steels — Technical delivery conditions |
| CE Marking | Compliance with European Union machinery and pressure equipment directives |
| NSF/ANSI 61 | Drinking water system components (for potable water applications) |
| RoHS / REACH | Restriction of hazardous substances and chemical compliance |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 — Full chemical and mechanical analysis for each heat lot |
7. Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to condensate corrosion (pH 4.0–5.5), atmospheric pollutants, and humid indoor air — eliminating the need for galvanic coatings or sacrificial anodes required by carbon steel alternatives. Service life exceeds 20 years in typical HVAC applications.
- Optimized for Energy Recovery Integration: The coil tube's dimensions and thermal properties are specifically engineered for compatibility with air-to-air energy recovery devices in FCU-plus-fresh-air systems, enabling high effectiveness (ε > 70%) heat recovery with minimal pressure drop penalty.
- Precision Dimensional Control: Tight tolerances (±0.05 mm OD, ±0.02 mm wall thickness) ensure reliable insertion into standard tube-sheet and plate-fin exchanger assemblies, reducing on-site assembly time and fitting costs.
- Low Carbon Footprint: Stainless steel is 100% recyclable with no loss of material properties. The coil tube's long service life and recyclability result in a lower lifecycle carbon footprint compared to copper or aluminum alternatives.
- Customizable Configuration: Available in multiple diameters, wall thicknesses, and coil lengths to accommodate diverse system designs. Custom winding configurations and surface finishes can be provided upon request.
- Hygienic Surface Finish: BA (Bright Annealed) and mirror finish options provide smooth internal surfaces that resist biofilm formation and facilitate cleaning — critical for pharmaceutical, food processing, and cleanroom applications.
- Seamless Performance Consistency: Cold roll forming and precision welding produce uniform tube geometry along the entire coil length, ensuring consistent heat transfer performance and eliminating weak points that could lead to premature failure.
- Cost-Effective Alternative to Copper: While offering comparable thermal performance in HVAC applications, the stainless steel coil tube provides significant cost advantages over copper tube, particularly for large-scale projects and applications where corrosion resistance is paramount.
Wenzhou Jixing Metal Materials Co., Ltd. — Engineering Excellence in Stainless Steel Tubular Solutions for Sustainable HVAC Systems.