Stainless Steel Fan Coil Tube — HVAC Dry-Condition Application Series
Product Overview
The Stainless Steel Fan Coil Tube (Coil Tube) is a precision-engineered tubular heat exchanger component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for integration into Fan Coil Units (FCUs) operating under dry-condition (dehumidification-free) regimes, this product series addresses the critical engineering challenges associated with latent heat avoidance, low-velocity airside heat transfer, and long-term corrosion resistance in indoor air distribution systems.
Unlike conventional coil tubes that may suffer from condensation-related issues such as microbial growth, corrosion under deposit (CUD), and energy penalties from latent cooling loads, the Stainless Steel Fan Coil Tube is engineered to maintain optimal Surface Temperature (Ts) above the Dew Point Temperature (Tdp) of the incoming airstream, thereby ensuring fully sensible heat exchange. This design philosophy is rooted in the principles discussed in the technical literature "Discussion on Several Issues of Fan Coil Unit Dry-Condition Operation", which highlights the importance of material selection, geometric configuration, and hydraulic performance in achieving reliable dry-bulb-only cooling.
Material & Properties
The coil tube is fabricated from AISI 304 Stainless Steel (UNS S30400) or AISI 316L Stainless Steel (UNS S31603) depending on the application environment and corrosion resistance requirements. The material selection is governed by the following criteria:
- Corrosion Resistance: The chromium (Cr: 18–20%) and nickel (Ni: 8–10.5%) alloying elements in AISI 304 provide a passive oxide layer that resists atmospheric and condensate-induced corrosion. For aggressive environments (e.g., coastal, industrial), AISI 316L adds molybdenum (Mo: 2–3%) for enhanced pitting and crevice corrosion resistance.
- Thermal Conductivity: Approximately 16.3 W/(m·K) for AISI 304, providing adequate heat transfer performance while maintaining structural integrity at elevated temperatures.
- Wettability and Surface Finish: The stainless steel surface exhibits moderate wettability, which aids in the uniform distribution of antifouling coatings and reduces scale adhesion under dry-condition operation.
- Mechanical Properties: Yield strength ≥ 205 MPa (annealed), tensile strength ≥ 515 MPa, ensuring resistance to mechanical vibration and thermal cycling fatigue inherent in HVAC systems.
- Hygienic Performance: The non-porous surface prevents biofilm formation, a critical advantage in dry-condition operation where condensation is minimized but not entirely eliminated during transient conditions.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Fan Coil Tube (Coil Tube) | — |
| Material Grade | AISI 304 / AISI 316L | ASTM A270 / ASTM A213 |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2") | ASME B36.19M |
| Wall Thickness | 0.50 mm – 1.50 mm | Manufacturer tolerance ±0.05 mm |
| Coil Pitch (Row Spacing) | 12.7 mm – 25.4 mm | Customizable per HVAC design |
| Tube Length | 300 mm – 1500 mm | ASME B36.19M |
| Surface Treatment | Polished (Ra ≤ 0.8 μm) / Electropolished (Ra ≤ 0.4 μm) | ASTM A967 |
| Maximum Operating Temperature | −40 °C to +150 °C | — |
| Maximum Operating Pressure | 1.6 MPa (232 psi) | ASME BPVC Section VIII |
| Refrigerant / Fluid Media | Chilled Water, Glycol Solutions, R-410A, R-32 | ASHRAE Standard 34 |
| Application Mode | Dry-Condition Sensible Cooling / Heating | ASHRAE Standard 90.1 |
| Quality Standard | ISO 9001:2015, CE Marking, PED Directive 2014/68/EU | — |
Manufacturing Process
The production of the Stainless Steel Fan Coil Tube follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, surface integrity, and hydraulic reliability:
- Material Selection and Incoming Inspection: Stainless steel seamless or welded tube stock is sourced from certified mills. Each batch undergoes spectroscopic analysis (PMI — Positive Material Identification) and visual inspection for surface defects.
- Cold Drawing / Forming: The tube is cold-drawn to achieve precise outer diameter and wall thickness tolerances. This process also enhances mechanical strength through work hardening.
- Coil Bending: Precision CNC-controlled bending machinery forms the tube into the required serpentine or spiral coil geometry. The bend radius is calculated to minimize internal flow resistance and prevent tube wall thinning at bend apexes.
- Fin Attachment (if applicable): Aluminum or copper fins are mechanically or brazed onto the coil tube to increase the effective heat transfer surface area. Fin density is optimized for dry-condition operation to avoid excessive pressure drop.
- Surface Finishing: The coil tube undergoes polishing or electropolishing to achieve the specified surface roughness. This step is critical for minimizing fouling resistance and ensuring hygienic performance.
- Hydrostatic Pressure Testing: Each coil assembly is pressure-tested at 1.5× the maximum operating pressure (2.4 MPa) to verify leak-tightness and structural integrity.
- Final Quality Assurance: Comprehensive dimensional measurement, visual inspection, and material certification documentation are compiled for each production lot.
Applications
The Stainless Steel Fan Coil Tube is engineered for the following primary applications:
- Commercial HVAC Systems: Fan Coil Units in office buildings, hospitals, hotels, and retail spaces where dry-condition operation is mandated to maintain indoor relative humidity control and occupant comfort.
- Precision Climate Control: Server rooms, data centers, and cleanrooms where condensation must be strictly avoided to prevent equipment damage and microbial contamination.
- Food and Pharmaceutical Processing: Environments requiring hygienic-grade heat exchangers that comply with sanitary standards and resist corrosion from cleaning agents.
- Renewable Energy Integration: Heat pump systems and district cooling networks where the coil tube serves as the terminal heat exchanger interface.
- Residential High-End HVAC: Premium residential systems where long service life, low maintenance, and energy efficiency are prioritized.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality and compliance certifications for its Stainless Steel Fan Coil Tube product line:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control throughout the manufacturing lifecycle.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European Union directives, including the Pressure Equipment Directive (PED 2014/68/EU) for pressure-rated components.
- SGS Testing Reports — Independent third-party material and performance verification including tensile testing, hardness testing, and corrosion resistance assessment.
- Material Test Reports (MTR) — Full traceability documentation for each production batch, including mill certificates, chemical composition analysis, and mechanical property verification.
Unique Selling Points
1. Dry-Condition Optimization: The coil tube geometry and material properties are specifically engineered to maintain surface temperatures above the dew point, eliminating latent heat transfer and associated energy penalties. This directly addresses the technical issues identified in the literature on fan coil unit dry-condition operation.
2. Superior Corrosion Resistance: AISI 316L grade options provide exceptional resistance to chloride-induced pitting and crevice corrosion, extending service life in harsh indoor environments.
3. Hygienic Surface Finish: Electropolished surfaces (Ra ≤ 0.4 μm) prevent biofilm adhesion and facilitate easy cleaning, meeting the stringent hygiene requirements of healthcare and food processing facilities.
4. Precision Manufacturing: CNC-controlled bending and cold-drawing processes ensure dimensional accuracy and consistent coil geometry, resulting in uniform airflow distribution and optimized heat transfer performance.
5. Customization Capability: Flexible design parameters including tube diameter, wall thickness, coil pitch, and fin density allow the product to be tailored to specific HVAC system requirements and performance targets.