Stainless Steel Coil Tube for HVAC Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product No. 624) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled piping solution designed for integration into air conditioning fan coil units (FCUs). This product represents a critical component in hydronic heating and cooling systems, where the coil tube serves as the heat exchange medium, facilitating efficient thermal transfer between refrigerant or hot water and the ambient air stream. The coil geometry is optimized to maximize surface area within a compact footprint, ensuring superior thermal performance in commercial and residential HVAC applications.
This coil tube product has been developed with reference to advanced control system research, including studies on improved ant colony algorithm (ACA)-based parameter tuning for PIλDμ (Proportional-Integral-Lambda-Derivative-Mu) controllers and conventional PI (Proportional-Integral) controllers governing room temperature and supply air volume in fan coil unit systems. The design accounts for the dynamic thermal response characteristics required to support such sophisticated control strategies.
Material and Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions.
- Base Material: Austenitic stainless steel conforming to ASTM A213 / ASME SA-213 specifications
- Alloy Grades Available: SUS304 (18/8), SUS316 (18/10), and SUS321 (18/8Ti-stabilized)
- Corrosion Resistance: Excellent resistance to oxidation, pitting, and crevice corrosion in humid HVAC environments; particularly suitable for dehumidification cycles involving condensate formation
- Thermal Conductivity: 14–16 W/(m·K) at 20°C for 304 grade; 13–15 W/(m·K) for 316 grade
- Operating Temperature Range: −196°C to +870°C (304 grade); −196°C to +800°C (316 grade)
- Mechanical Strength: Yield strength ≥205 MPa; tensile strength ≥515 MPa (304 annealed condition)
- Surface Finish: Bright annealed or passivated finish with surface roughness Ra ≤ 0.8 μm to minimize fouling and facilitate cleaning
- Hygienic Compliance: Suitable for potable water contact per NSF/ANSI 61 standards
Specifications
| Parameter | Specification |
|---|---|
| Product Identification | No. 624 — Stainless Steel Coil Tube (盘管) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Tube Outer Diameter (OD) | 6.35 mm, 8.00 mm, 9.53 mm, 12.70 mm, 15.88 mm (custom available) |
| Wall Thickness | 0.50 mm – 1.50 mm (tolerance ±10%) |
| Coil Inner Diameter | 150 mm – 600 mm (configurable per unit design) |
| Coil Length (Developed) | Up to 50,000 mm per continuous coil (seamless) |
| Number of Rows | 1-row to 4-row configurations |
| Tube Pitch (Horizontal) | 14 mm – 25 mm |
| Tube Pitch (Vertical) | 14 mm – 25 mm |
| Heat Exchanger Type | Shell-and-tube, plate-fin, or bare tube configurations |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) |
| Hydrostatic Test Pressure | 3.0 MPa minimum |
| Applicable Fluids | Chilled water, hot water, glycol solutions, light refrigerants |
| Standards Compliance | ASTM A213, ASME SA-213, EN 10216-5, GB/T 14976 |
| Surface Treatment | Bright annealing, passivation, or electropolishing |
| Joining Method | TIG (GTAW) welding, brazing, or mechanical expansion |
Manufacturing Process
The production of this stainless steel coil tube involves a multi-stage precision manufacturing sequence ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Material Selection and Incoming Inspection: Cold-rolled stainless steel strip or seamless pipe stock is procured from certified suppliers. Each lot undergoes spectroscopic composition analysis (OES), mechanical testing, and visual surface inspection prior to processing.
- Coil Forming: Precision roll-forming or mandrel-assisted bending machinery shapes the tube into the specified coil geometry. Computer numerical control (CNC) systems ensure consistent pitch, radius, and alignment tolerances throughout the coil assembly.
- Heat Treatment: Post-forming annealing at 1050°C–1100°C in a protective atmosphere (argon or vacuum) relieves residual stresses and restores full solution-annealed properties, ensuring optimal corrosion resistance and ductility.
- Surface Finishing: The coil undergoes mechanical cleaning followed by chemical passivation using citric acid or nitric acid solutions to establish a stable chromium oxide layer. Electropolishing may be applied for critical applications requiring Ra ≤ 0.4 μm.
- Quality Control and Testing: Each coil assembly is subjected to hydrostatic pressure testing, dimensional verification using laser scanning or coordinate measurement machines (CMM), and helium leak detection for brazed joints.
- Final Assembly Integration: The coil tube is integrated into the fan coil unit frame with fins (aluminum or stainless steel) pressed or welded to the tubes, forming the complete heat exchanger assembly.
Applications
This stainless steel coil tube is specifically engineered for use in air conditioning fan coil unit (FCU) systems and related HVAC applications. The product supports advanced control methodologies including:
- Commercial HVAC Systems: Precision temperature control in office buildings, hotels, and retail spaces using PIλDμ controller strategies for room temperature regulation
- Supply Air Volume Control: Integration with PI controllers for variable air volume (VAV) systems managing supply air temperature and flow rate
- Residential Heating and Cooling: High-efficiency fan coil units in multi-family residential developments
- Industrial Process Cooling: Temperature-sensitive manufacturing environments requiring stable thermal conditions
- Medical and Pharmaceutical Facilities: Cleanroom HVAC systems where corrosion resistance and hygiene are paramount
- Optimization Research: The coil geometry and thermal characteristics are compatible with numerical studies on intelligent control algorithms, including improved ant colony algorithms (ACA) for multi-objective parameter tuning of HVAC controllers
Quality Certifications and Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity to international standards:
- ISO 9001:2015: Quality Management System certification covering the entire manufacturing and supply chain
- ISO 14001:2015: Environmental Management System for sustainable production practices
- EN 10204 3.1: Third-party inspection and material certification for all delivered products
- CE Marking: Conformity with European directives for safety and performance
- NSF/ANSI 61: Drinking water system component certification (for potable water applications)
- GB/T 14976: Chinese national standard for seamless stainless steel tubes
- ASME BPV Section VIII: Compliance for pressure vessel component applications
Unique Selling Points
The Stainless Steel Coil Tube (No. 624) distinguishes itself through several key advantages:
- Superior Corrosion Durability: Unlike carbon steel alternatives, the austenitic stainless steel construction eliminates internal corrosion and scaling, extending service life beyond 25 years in demanding HVAC environments with minimal maintenance.
- Optimized Thermal Performance: The coil geometry is engineered to support advanced control algorithms—including PIλDμ and PI controllers tuned via improved ant colony algorithms—ensuring precise and responsive temperature regulation in fan coil unit applications.
- Hygienic Design: The bright-annealed and passivated surface prevents bacterial growth and biofilm formation, making this product ideal for applications requiring sanitary-grade thermal exchange.
- Dimensional Precision: CNC-controlled coil forming ensures consistent pitch and alignment, enabling predictable heat transfer coefficients and reliable integration with computational fluid dynamics (CFD) models used in system design.
- Modular Configurability: Available in multiple diameters, wall thicknesses, and row configurations to accommodate diverse thermal load requirements from 1 kW to 50 kW per unit.
- Full Traceability: Each production batch includes complete material certification documentation, heat treatment records, and test reports ensuring complete supply chain transparency.
Technical Notes
When integrating this coil tube into fan coil unit systems employing advanced control strategies, engineers should consider the following:
- The thermal mass of the stainless steel coil introduces a time delay in the temperature response, which must be accounted for in PIλDμ controller parameter selection
- Improved ant colony algorithm (ACA)-based tuning methods have demonstrated superior convergence for multi-variable HVAC control problems compared to conventional Ziegler-Nichols methods
- The coil tube's thermal conductivity and surface area characteristics should be incorporated into the plant model used for numerical simulation and controller design
- Supply air volume control via PI controllers benefits from the consistent flow characteristics of the precision-formed coil geometry