Stainless Steel Coil Tube (Coiltube) — Air Conditioning Fan Coil Unit Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-CT-1158
Category: Technical Literature & Application Engineering
Reference Study: "Regulation Characteristics Research of Air Conditioning Fan Coil Unit with Fresh Air System"
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered coiled tubular component designed primarily for integration into air conditioning fan coil units (FCUs) and associated fresh air handling systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product represents the company's commitment to delivering high-performance, corrosion-resistant tubular solutions for HVAC (Heating, Ventilation, and Air Conditioning) applications.
The coil tube serves as a critical heat exchange medium within fan coil units, where it facilitates efficient thermal transfer between the refrigerant or chilled water circulating within the tube and the ambient air drawn through the unit by a centrifugal or axial fan. The coiled geometry maximizes the surface area-to-volume ratio, thereby enhancing heat dissipation and absorption capabilities essential for maintaining precise indoor climate control.
Technical Note: The design parameters of this coil tube have been validated against the regulation characteristics documented in the referenced academic study, ensuring compatibility with variable refrigerant flow (VRF) and variable air volume (VAV) control strategies commonly employed in modern building management systems (BMS).
2. Material & Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards, ensuring superior mechanical integrity and long-term resistance to environmental degradation.
2.1 Base Material Specification
- Primary Grade: SUS304 / AISI 304 / EN 1.4301 — General purpose austenitic stainless steel offering excellent corrosion resistance and formability.
- Alternative Grade: SUS316 / AISI 316 / EN 1.4401 — Enhanced molybdenum-bearing grade for applications requiring elevated resistance to chlorides and aggressive chemical environments.
- Surface Finish: 2B (Cold Rolled and Annealed with Bright Pass) or BA (Bright Annealed) for hygienic and high-efficiency heat transfer applications.
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 520 MPa | ASTM A270 / EN 10216-5 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM A270 / EN 10216-5 |
| Elongation (at Break) | ≥ 40% | ASTM A270 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A270 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | ISO 6945 |
| Linear Thermal Expansion | 17.3 × 10⁻⁶ /°C | ISO 6945 |
2.3 Corrosion Resistance
- Resistance to atmospheric corrosion in industrial and coastal environments (Salt Spray Test per ASTM B117: ≥ 500 hours without pitting).
- Resistance to intergranular corrosion (ASTM A262 Practice E: Pass).
- Resistance to stress corrosion cracking in chloride-containing solutions (ASTM A967).
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4") | ASTM A270 / ISO 3506 |
| Wall Thickness | 0.50 mm – 1.50 mm (tolerance ±10%) | ASTM A270 |
| Coil Length | Standard: 5 m – 30 m; Custom: up to 100 m (continuous) | Manufacturer Specification |
| Coil Diameter (Bundle) | 150 mm – 600 mm (configurable per FCU housing dimensions) | ASHRAE Standard 15 |
| Turn-to-Turn Pitch | 2.0 mm – 5.0 mm (optimized for airflow velocity) | ASHRAE Guideline 11 |
| Heat Transfer Coefficient | ≥ 2,500 W/(m²·K) (air-side, typical operating conditions) | ASHRAE Fundamentals Handbook |
| Operating Pressure (Design) | 1.6 MPa (16 bar) – 2.5 MPa (25 bar) | EN 12162 / PED 2014/68/EU |
| Operating Temperature Range | −40°C to +180°C | ASTM A270 |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, R-404A, R-22 (legacy) | ISO 5149 |
| Welding Method | TIG (GTAW) — Tungsten Inert Gas Welding, fully automatic orbital | ASME Section IX / ISO 15614-1 |
| Surface Roughness (Internal) | Ra ≤ 0.8 μm (electropolished variant: Ra ≤ 0.4 μm) | ISO 1302 |
| Hydrostatic Test Pressure | 3.0 MPa (30 bar) — 100% inline testing | EN 10216-5 |
4. Manufacturing Process
The production of the stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical consistency, and surface integrity:
- Raw Material Selection & Inspection: Stainless steel strip or seamless tube blanks are sourced from certified mills. Incoming materials undergo spectroscopic analysis (OES) to verify chemical composition, and ultrasonic testing (UT) for subsurface defect detection.
- Dimensional Forming: Precision cold-drawing or cold-rolling processes establish the target outer diameter and wall thickness within specified tolerances. This stage may include intermediate annealing to relieve residual stresses and restore ductility.
- Coiling / Helical Winding: The formed tube is wound into a helical coil geometry using CNC-controlled coiling machines. Turn-to-turn pitch and coil diameter are programmatically controlled to meet design requirements for specific FCU configurations.
- Welding & Brazing: U-bends and header connections are fabricated using fully automatic TIG (GTAW) welding with argon (Ar) back-purging to prevent internal oxidation. Brazing joints, where applicable, utilize phosphorus-free silver-based filler alloys to ensure compatibility with modern HFC (Hydrofluorocarbon) refrigerants.
- Surface Treatment: Optional electropolishing or passivation treatments are applied to achieve the required internal surface roughness and enhance corrosion resistance. Passivation is performed using citric acid or nitric acid solutions in accordance with ASTM A967.
- Non-Destructive Testing (NDT):strong> Each coil assembly undergoes 100% hydrostatic pressure testing, followed by dye penetrant inspection (DPI) of all weld seams per ASME Section V.
- Final Inspection & Packaging: Dimensional verification using coordinate measuring machines (CMM), visual inspection, and certification documentation are completed prior to protective packaging for shipment.
5. Applications
The coil tube is engineered for integration into a broad spectrum of HVAC and thermal management systems:
- Air Conditioning Fan Coil Units (FCUs): Primary application — serving as the evaporator or condenser coil within ceiling-mounted, concealed, or exposed FCU configurations for commercial and residential climate control.
- Fresh Air Handling Systems: Integration with dedicated outdoor air systems (DOAS) to facilitate pre-conditioning of ventilation air, improving overall system efficiency and indoor air quality (IAQ).
- Chilled Water Cooling Coils: Water-to-air heat exchange in medium- and large-scale commercial HVAC installations where waterborne refrigerants are preferred.
- Heat Pump Systems: Operation in dual-mode (heating and cooling) configurations within air-source and ground-source heat pump installations.
- Clean Room & Pharmaceutical HVAC: Electropolished variants suitable for controlled environment applications requiring stringent hygiene and contamination control per GMP (Good Manufacturing Practice) standards.
- Marine & Offshore HVAC: SUS316-grade coil tubes for environments exposed to high humidity, salt spray, and aggressive atmospheric conditions.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring full traceability and regulatory compliance across all product lines:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and service operations. |
| ISO 14001:2015 | Environmental Management System certification ensuring sustainable manufacturing practices. |
| ISO 45001:2018 | Occupational Health and Safety Management System certification. |
| EN 10204 Type 3.1 | Third-party inspection certificates verifying material conformity and test results. |
| CE Marking (PED 2014/68/EU) | Conformity with EU Pressure Equipment Directive for components operating above 0.5 bar. |
| UL / CSA Listed Components | Component-level safety certification for use in North American HVAC installations. |
| RoHS / REACH Compliant | Restriction of Hazardous Substances and Registration, Evaluation, Authorization and Restriction of Chemicals compliance for all materials used. |
| ASME B31.5 | Compliance with ASME Refrigeration and Air-Conditioning Pressure Piping and Tubing Code. |
7. Unique Selling Points
- Engineered for Variable Regulation: Coil geometry and thermal performance parameters are validated against documented regulation characteristics of FCU-plus-fresh-air systems, ensuring optimal part-load efficiency and precise temperature/humidity control across variable operating conditions.
- Full Traceability: Each coil tube batch is accompanied by a complete material traceability dossier including mill certificates, chemical analysis reports, mechanical test data, and NDT records.
- Customizable Configurations: Flexible manufacturing capabilities allow tailoring of coil diameter, turn pitch, tube dimensions, and surface treatment to meet specific OEM (Original Equipment Manufacturer) design requirements.
- Extended Service Life: Superior corrosion resistance of austenitic stainless steel eliminates the risk of internal tube degradation, ensuring reliable operation over service lives exceeding 20 years without replacement.
- Refrigerant-Ready Design: Phosphorus-free brazing and controlled internal cleanliness ensure compatibility with next-generation low-GWP (Global Warming Potential) refrigerants including R-32 and R-454B.
8. Technical Reference
Academic Reference: "Regulation Characteristics Research of Air Conditioning Fan Coil Unit with Fresh Air System" — This study provides the foundational performance data and control strategy validation upon which the thermal design parameters of this coil tube product are benchmarked. The research addresses the interaction between fan coil unit operation and dedicated fresh air systems, demonstrating the importance of coil tube geometry optimization for achieving stable temperature and humidity regulation under varying ventilation loads.
Document Classification: Technical Product Specification — Literature Study Integration
Document Code: JX-CT-1158-TS-001
Revision: 1.0