Stainless Steel Coil Tube — Residential Fan Coil Unit (FCU) Application Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Catalog No.: 1336
This technical specification document provides a comprehensive description of the stainless steel coil tube product line developed by Wenzhou Jixing Metal Materials Co., Ltd., engineered specifically for integration into residential fan coil units (FCUs). The product is designed in accordance with advanced thermal management principles and modern HVAC (Heating, Ventilation, and Air Conditioning) industry standards, delivering superior heat exchange efficiency, corrosion resistance, and long-term operational reliability.
Product Overview
The stainless steel coil tube is a precision-engineered serpentine heat exchanger element designed for use in residential fan coil units. The coil tube serves as the core thermal interface component, facilitating efficient heat transfer between the circulating refrigerant or hot water medium and the ambient air stream driven by the unit's axial or centrifugal fan. The design philosophy integrates findings from advanced research on next-generation residential FCU systems, emphasizing compact geometry, optimized flow channel configuration, and enhanced thermal performance.
Unlike conventional copper-tube-and-aluminum-fin heat exchangers, the stainless steel coil tube variant leverages the inherent material advantages of austenitic stainless steel to provide exceptional resistance to chemical degradation, thermal cycling fatigue, and mechanical stress. This makes the product particularly suitable for applications in humid environments, coastal regions, and facilities requiring extended service life without degradation of heat transfer characteristics.
Design Philosophy
- Compact Serpentine Geometry: The coil tube is wound in a multi-pass serpentine configuration to maximize heat transfer surface area within a minimized footprint, ensuring compatibility with space-constrained residential installations.
- Thermal Optimization: Flow channel dimensions are calibrated to promote turbulent flow at moderate Reynolds numbers, enhancing convective heat transfer coefficients while maintaining acceptable pressure drop across the coil.
- Material Integrity: The selection of stainless steel as the base material eliminates concerns related to galvanic corrosion, dezincification, and pitting that are common in copper-based alternatives when exposed to certain water chemistries or atmospheric conditions.
- Modular Scalability: The coil tube design accommodates various capacity ratings by adjusting the number of rows, tube count, and coil length, allowing customization for different residential cooling and heating loads.
Material & Properties
The coil tube is manufactured from high-grade austenitic stainless steel, selected for its optimal balance of mechanical strength, corrosion resistance, and thermal conductivity.
Base Material Specification
| Property | Specification | Standard Reference |
|---|---|---|
| Material Grade | SUS304 / 304L (UNS S30400 / S30403) | ASTM A213 / ASTM A269 |
| Alternative Grade | SUS316 / 316L (UNS S31600 / S31603) — for high-corrosion environments | ASTM A213 / ASTM A269 |
| Tensile Strength (Ultimate) | ≥ 515 MPa (74,700 psi) | ASTM A240 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,700 psi) | ASTM A240 |
| Elongation (at Break) | ≥ 40% | ASTM A240 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | ASM Handbook |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | ASM Handbook |
| Specific Heat Capacity | 500 J/(kg·K) | ASM Handbook |
| Corrosion Resistance (Pitting) | PRE (Pitting Resistance Equivalent) ≥ 19 (304); ≥ 24 (316) | ISO 11360 |
| Chromium Content | 18.0 – 20.0% (304); 16.0 – 18.0% (316) | ASTM A240 |
| Nickel Content | 8.0 – 10.5% (304); 10.0 – 14.0% (316) | ASTM A240 |
| Molybdenum Content | ≤ 0.08% (304); 2.0 – 3.0% (316) | ASTM A240 |
| Carbon Content (Max) | ≤ 0.08% (304); ≤ 0.03% (304L / 316L) | ASTM A240 |
| Operating Temperature Range | −196°C to +870°C | ASM Handbook |
| Surface Finish | Polished (Ra ≤ 0.4 μm) or Brushed (Ra ≤ 1.6 μm) | ASTM A403 |
Material Advantages
- Superior Corrosion Resistance: The chromium oxide passive film formed on the stainless steel surface provides robust protection against atmospheric corrosion, chemical attack, and microbiologically influenced corrosion (MIC), significantly extending the service life compared to carbon steel or copper alternatives.
- Thermal Stability: Stainless steel maintains mechanical properties across a wide temperature range, making it suitable for both heating and cooling applications without risk of thermal fatigue or embrittlement.
- Hygienic Surface: The smooth, non-porous surface of polished stainless steel inhibits bacterial growth and biofilm formation, ensuring water quality integrity in closed-loop hydronic systems.
- Non-Toxic and Food-Safe: SUS304 and SUS316 grades are approved for food-contact applications (FDA 21 CFR 178.301), making the coil tube suitable for residential environments where potable water safety is a consideration.
- Recyclability: Stainless steel is 100% recyclable without degradation of material properties, aligning with sustainable manufacturing and green building initiatives.
Specifications
Geometric and Dimensional Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (1/4"), 7.94 mm (5/16"), 9.53 mm (3/8") | Selectable based on capacity requirement |
| Tube Wall Thickness | 0.5 mm – 1.0 mm | Thicker walls for higher pressure applications |
| Tube Inner Diameter (ID) | 5.35 mm – 8.53 mm (dependent on OD and wall thickness) | Calculated per configuration |
| Coil Pitch (Tube-to-Tube Spacing) | 10.0 mm – 15.0 mm (transverse); 12.0 mm – 18.0 mm (longitudinal) | Optimized for airflow distribution and heat transfer |
| Number of Rows | 1 to 6 rows | Higher row count for increased heat exchange capacity |
| Number of Tubes per Row | 12 to 48 tubes | Customizable to unit width |
| Coil Height (Tube Length) | 150 mm – 600 mm | Adaptable to FCU housing dimensions |
| Coil Width | 300 mm – 1,200 mm | Standard and custom sizes available |
| Fin Material (if finned variant) | Aluminum (1100-H14) or Stainless Steel (SUS304) | Stainless steel fins for enhanced corrosion resistance |
| Fin Thickness | 0.10 mm – 0.15 mm | High-density fin configuration available |
| Fin Pitch | 1.5 mm – 2.5 mm (24 to 40 fins per inch) | Higher fin density for compact high-efficiency designs |
| Connection Type | Flared, Welded, or Threaded (1/2" NPT, 3/4" NPT, 1" NPT) | Welded connections for maximum leak resistance |
| Maximum Operating Pressure | 1.0 MPa (10 bar) standard; 1.6 MPa (16 bar) high-pressure variant | Hydrostatic test at 1.5× working pressure |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-22, R-407C, CO₂ (R-744) | Low-GWP refrigerants preferred |
| Water Flow Rate (Hydronic) | 0.1 L/s – 2.0 L/s (dependent on coil size and configuration) | Designed for low-flow, high-efficiency operation |
| Weight (Typical) | 2.5 kg – 15.0 kg (depending on dimensions and configuration) | Lightweight for easy installation |
Performance Specifications
| Performance Parameter | Typical Value | Test Condition |
|---|---|---|
| Heat Transfer Coefficient (Air Side) | 25 – 60 W/(m²·K) | Air velocity 1.5 – 3.0 m/s |
| Heat Transfer Coefficient (Fluid Side) | 2,000 – 5,000 W/(m²·K) | Water flow 1.0 L/s; Refrigerant flow per design |
| Overall Heat Transfer Coefficient (U-value) | 35 – 80 W/(m²·K) | Combined air-side and fluid-side |
| Cooling Capacity Range | 0.5 kW – 5.0 kW | DB 27°C / WB 19°C; Water inlet 7°C |
| Heating Capacity Range | 0.6 kW – 6.0 kW | Air inlet 20°C DB; Water inlet 60°C |
| Pressure Drop (Air Side) | 25 – 80 Pa | At design airflow velocity |
| Pressure Drop (Water Side) | 10 – 50 kPa | At design flow rate |
| Pressure Drop (Refrigerant Side) | 10 – 80 kPa | At design refrigerant flow rate |
| Seasonal Energy Efficiency Ratio (SEER) Contribution | Enhanced by 10–20% vs. copper tube alternatives | Due to reduced fouling and consistent heat transfer |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled multi-stage manufacturing process designed to ensure dimensional accuracy, material integrity, and consistent thermal performance. Each stage is subject to quality inspection and documentation in accordance with ISO 9001:2015 Quality Management System requirements.
Process Flow
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Raw Material Procurement and Inspection:
- Stainless steel tubes (SUS304/304L/316/316L) are sourced from certified mill suppliers with full traceability documentation.
- Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM A213/A269 specifications.
- Dimensional inspection (OD, wall thickness, straightness) is performed using calibrated micrometers and optical comparators.
- Mechanical property verification (tensile testing) is conducted on sampled material lots.