Stainless Steel Coil Tube for HVAC Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Product No. 1098) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled piping solution specifically designed for integration into Fan Coil Unit (FCU) air conditioning systems and related HVAC (Heating, Ventilation, and Air Conditioning) applications. This coil tube product represents a critical heat exchange component that facilitates efficient thermal transfer between circulating refrigerant or hot water media and ambient air within fan coil unit assemblies.
In the context of design-condition verification calculations for fan coil unit air conditioning systems, the coil tube serves as the fundamental heat exchange surface whose geometric parameters, material properties, and thermal characteristics directly determine the system's cooling capacity, heating capacity, and overall energy efficiency. The product is engineered to meet the rigorous demands of variable operating conditions encountered during system commissioning and performance verification.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, predominantly conforming to AISI 304 (UNS S30400) or AISI 316L (UNS S31603) grades, selected for their superior corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions.
- AISI 304 Stainless Steel: Minimum 18% Chromium (Cr) and 8% Nickel (Ni) composition, offering excellent general corrosion resistance and formability suitable for standard HVAC environments.
- AISI 316L Stainless Steel: Enhanced grade with 2–3% Molybdenum (Mo) addition and reduced Carbon (C) content (<0.03%), providing superior resistance to pitting and crevice corrosion in aggressive or humid environments.
Key Physical and Mechanical Properties
| Property | AISI 304 | AISI 316L | Unit |
|---|---|---|---|
| Density (ρ) | 7,930 | 8,000 | kg/m³ |
| Thermal Conductivity (λ) at 20°C | 16.3 | 14.6 | W/(m·K) |
| Thermal Conductivity (λ) at 100°C | 21.6 | 19.5 | W/(m·K) |
| Specific Heat Capacity (c) | 500 | 500 | J/(kg·K) |
| Tensile Strength (σb) | ≥520 | ≥515 | MPa |
| Yield Strength (σs) | ≥205 | ≥205 | MPa |
| Elongation (A5) | ≥40 | ≥40 | % |
| Operating Temperature Range | -196 to +870 | -196 to +870 | °C |
| Corrosion Resistance (ASTM G48) | Excellent | Superior | — |
Surface Treatment
- Standard Finish: 2B Mill Finish (bright annealed) with Ra ≤ 0.4 μm surface roughness to minimize flow resistance and fouling accumulation.
- Optional Finish: Electropolished surface (Ra ≤ 0.2 μm) for hygienic or high-purity applications.
- Protective Coating: Transparent PTFE (Polytetrafluoroethylene) coating available for enhanced chemical resistance in specialized industrial environments.
Specifications
| Parameter | Specification | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.7 mm / 15.88 mm (¼" / ⅜" / ½" / ⅝") | ±0.10 mm | ASTM A213 / EN 10216-5 |
| Wall Thickness | 0.50 mm / 0.71 mm / 0.89 mm / 1.00 mm | ±0.05 mm | ASME B36.19M |
| Coil Length (per unit) | Up to 30 m (continuous) | ±0.5 m | Manufacturer Specification |
| Coil Pitch / Row Spacing | 12.7 mm – 25.4 mm (adjustable) | ±0.3 mm | ASHRAE Handbook |
| Coil Turns per Row | 2 – 8 rows (configurable) | ±1 turn | Project-Specific Design |
| Fin Type | Aluminum L-Channel / V-Crimp / Wavy | — | ASHRAE Standard 15 |
| Fin Density | 10 – 14 fins per inch (FPI) | ±1 FPI | Industry Standard |
| Maximum Design Pressure | 1.6 MPa (standard) / 2.5 MPa (reinforced) | — | EN 12163 |
| Hydrostatic Test Pressure | 2.4 MPa (standard) / 3.75 MPa (reinforced) | — | ASME Section VIII |
| Flow Velocity (Design) | 1.0 – 2.5 m/s (water side) | — | ASHRAE Guideline 34 |
| Heat Transfer Coefficient (U-value) | 450 – 650 W/(m²·K) | — | ASHRAE Fundamentals |
Manufacturing Process
Process Flow Overview
- Raw Material Inspection: Incoming stainless steel strip or tube undergoes spectroscopic analysis (Optical Emission Spectrometry — OES) to verify chemical composition compliance with ASTM A213/A269 specifications. Mill test certificates (MTC) are cross-referenced with batch traceability records.
- Surface Preparation: The base tube material is cleaned, degreased, and passivated using nitric acid or citric acid solutions to remove oxide layers and restore chromium-rich passive film integrity (minimum 20% Cr passive layer coverage verified via ASTM A967).
- Precision Coiling: Computer Numerical Control (CNC)-guided coiling machines form the tube into the designated serpentine or helical configuration. The coiling process employs controlled bending radii (minimum 3D bending radius) to prevent ovalization, kinking, or micro-cracking of the tube wall.
- Welding and Joining: Inlet and outlet connections are fabricated using TIG (Tungsten Inert Gas) welding with argon shielding. Weld quality is verified through visual inspection (VT) per AWS D10.9 and, where required, dye penetrant testing (PT) per ASTM E707.
- Fin Installation: Aluminum fins are mechanically crimped onto the coil tube using high-frequency resistance welding or mechanical expansion methods. Fin-to-tube contact resistance is minimized to ensure optimal thermal coupling.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum design pressure, held for a minimum of 30 minutes to verify leak-tightness and structural integrity.
- Performance Verification: Completed coil units are subjected to thermal performance testing in accordance with AHRI (Air-Conditioning, Heating, and Refrigeration Institute) Standard 440/460 to validate heat exchange capacity, pressure drop, and flow distribution characteristics under design conditions.
- Final Inspection and Packaging: Dimensional verification, surface quality assessment, and traceability documentation are completed prior to protective packaging and dispatch.
Process Quality Control Points
| Stage | Inspection Method | Acceptance Criteria | Standard |
|---|---|---|---|
| Material Verification | OES Spectroscopy | Composition within ASTM A213 limits | ASTM E415 |
| Dimensional Check | Laser Micrometer / CMM | OD, wall thickness within ±0.10 mm | ISO 286 |
| Weld Integrity | Dye Penetrant Testing | No indications of cracks or porosity | ASTM E707 |
| Pressure Test | Hydrostatic Gauge Monitoring | No pressure drop over 30 min | ASME BPV Section VIII |
| Thermal Performance | Calorimetric Test Rig | U-value ≥ 450 W/(m²·K) | AHRI 440/460 |
Applications
Primary Application Domain: Fan Coil Unit (FCU) Air Conditioning Systems
The stainless steel coil tube is the core heat exchange element within Fan Coil Unit (FCU) systems. In design-condition verification calculations, the coil tube's performance parameters are critical for determining:
- Cooling Capacity: Total cooling load (sensible + latent) delivered by the FCU under design indoor and outdoor conditions. The coil tube's geometry (row count, fin density, tube diameter) directly influences the air-side and water-side heat transfer coefficients.
- Heating Capacity: Hot water coil performance for space heating, including minimum flow temperature requirements to prevent freezing and maintain surface temperatures above dew point to avoid condensation.
- Pressure Drop Verification: Both air-side static pressure drop across the coil (impacting fan power consumption) and water-side pressure drop (impacting pump selection and system hydraulics) are calculated based on coil tube geometry and flow characteristics.
- Part Load Performance: Evaluation of coil effectiveness at reduced flow rates and part-load conditions, which determines the system's seasonal energy efficiency ratio (SEER).
- Condensate Management: Coil surface temperature relative to air dew point determines condensate formation rate, influencing drain pan sizing and condensate pump capacity in design calculations.
Secondary Applications
- Commercial HVAC Systems: Office buildings, hotels, hospitals, and retail facilities requiring precise temperature and humidity control.
- Industrial Process Cooling: Precision temperature control in pharmaceutical manufacturing, food processing, and electronics fabrication.
- Data Center Cooling: High-density thermal management for server rooms and IT infrastructure.
- Marine and Offshore Applications: AISI 316L grade coil tubes for saltwater-resistant HVAC systems on vessels and offshore platforms.
- Cleanroom Environments: Electropolished coil tubes for pharmaceutical and semiconductor manufacturing facilities requiring ultra-low particulate emissions.
- Geothermal Heat Exchange: Integration into ground-source heat pump systems for sustainable building energy management.
Quality Certifications
International Standards Compliance
- ISO 9001:2015 — Quality Management Systems (QMS) certification ensuring consistent product quality and process control throughout manufacturing.
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices and waste minimization.
- ASME BPV Section VIII — Pressure Vessel and Piping code compliance for pressure-containing heat exchange components.
- EN 10216-5 — European Standard for heat exchangers and refrigeration equipment — metallic tubes — austenitic stainless steel tubes.
- EN 12163 — European Standard for air conditioning and heat pump equipment — rating and testing.
- AHRI Standard 440/460 — Rating and performance testing for air-to-water fluid coolers and heat exchangers.
- ASTM A213/A269 — Standard specifications for austenitic stainless steel seamless and welded tubes.
- CE Marking (EU 2014/68/EU) — Pressure Equipment Directive compliance for products operating above 0.5 bar gauge pressure.
Product-Specific Certifications
| Certification | Scope | Validity |
|---|---|---|
| Mill Test Certificate (MTC) — EN 10204 3.1 | Material composition and mechanical property verification per batch | Per production lot |
| Hydrostatic Test Report | Pressure integrity verification for each coil assembly | Per unit |
| Non-Destructive Testing (NDT) Report | Weld quality and structural integrity documentation | Per unit |
| Third-Party Performance Test Report | AHRI/EN-compliant thermal performance validation | Per product type |
| Material Traceability Certificate | Full supply chain traceability from raw material to finished product | Per production lot |
Unique Selling Points
1. Design-Condition Verified Performance: Unlike generic coil tube