Stainless Steel Coil Tube for HVAC Fan Coil Unit Heat Exchangers

Product Overview

The Stainless Steel Coil Tube (Model Reference: No. 462) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for integration into HVAC (Heating, Ventilation, and Air Conditioning) fan coil unit (FCU) heat exchanger assemblies. This product serves as a critical heat transfer medium within hydronic air handling systems, facilitating efficient thermal exchange between the circulating refrigerant or heating medium and the ambient air stream drawn through the unit by an axial or centrifugal fan.

The coil tube is fabricated from high-grade austenitic stainless steel, offering superior corrosion resistance, mechanical integrity, and thermal conductivity. It is formed into continuous serpentine or helical configurations to maximize surface area within a compact footprint, thereby optimizing the coefficient of performance (COP) of the overall thermal management system. This product represents a fundamental component in the architecture of modern commercial and residential climate control infrastructure.

Material & Properties

The coil tube is manufactured using austenitic stainless steel grades selected for their exceptional performance characteristics in HVAC thermal exchange applications:

Specifications

Parameter Specification Unit
Tube Outer Diameter (OD) 6.35 / 9.53 / 12.70 mm
Wall Thickness 0.50 / 0.65 / 0.80 / 1.00 mm
Inner Diameter (ID) 5.35 – 11.70 mm
Tube Length (per coil) 2,000 – 15,000 mm
Coil Bend Radius (minimum) ≥ 3 × OD —
Coil Pitch (row spacing) 10 – 25 mm
Number of Rows 2 / 4 / 6 / 8 —
Fin Material Aluminum (Al) or Stainless Steel (SS) —
Fin Density 10 – 14 fin/inch
Operating Pressure (design) ≤ 1.6 MPa
Hydrostatic Test Pressure 2.4 MPa
Heat Transfer Coefficient ≥ 50 W/(m²·K)
Applicable Refrigerants R-22, R-410A, R-32, R-134a, H₂O (hydronic) —
Standards Compliance ASTM A269, ASTM A270, EN 10217-7, GB/T 12771 —

Manufacturing Process

The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and long-term operational reliability:

  1. Material Preparation: Stainless steel strip or seamless tubing is sourced from certified mills and subjected to incoming inspection for chemical composition (via OES spectroscopy) and mechanical properties. Material is stored under controlled humidity conditions to prevent surface contamination.
  2. Precision Cutting: Raw tubing is cut to specified lengths using high-speed pneumatic or hydraulic shearing equipment with tolerances of ±0.5 mm. Cut edges are deburred and chamfered to prevent flow turbulence at inlet/outlet ports.
  3. Coil Forming: Tubes are cold-formed into serpentine or helical configurations using CNC-controlled forming dies. The bending process is executed at controlled speeds to prevent work hardening, micro-cracking, or ovalization. Minimum bend radius is maintained at ≥ 3 × OD to preserve cross-sectional geometry.
  4. Welding: Where continuous tube runs are required, joints are fabricated using orbital TIG (Tungsten Inert Gas) welding under argon shielding atmosphere. Weld beads are inspected via visual examination (VT) and periodic radiographic testing (RT) per ASME Section IX qualification procedures.
  5. Finning: Aluminum or stainless steel fins are mechanically attached to the formed tubes using a double-stack fin insertion method, ensuring uniform fin-to-tube contact resistance. Fin integrity is verified by ultrasonic testing at sampled intervals.
  6. Pressure Testing: Each coil assembly undergoes a hydrostatic pressure test at 1.5 × design pressure for a minimum dwell time of 10 minutes. Zero leakage tolerance is enforced. Electronic pressure gauges with ±0.5% accuracy are used throughout.
  7. Surface Treatment: Optional passivation treatment (per ASTM A967) is applied to remove free iron contamination and enhance passive film formation. Electropolishing may be applied to interior surfaces for critical hygienic applications.
  8. Final Inspection & Packaging: Dimensional verification is performed using calibrated calipers, micrometers, and coordinate measuring machines (CMM). Products are packaged in moisture-proof, VCI (Vapor Corrosion Inhibitor) treated cartons with protective end caps.

Applications

The stainless steel coil tube is integral to the operation of HVAC fan coil units, which are modular air handling devices deployed across a wide spectrum of commercial, industrial, and institutional buildings. The following control forms and application scenarios define the operational context of this product:

2-Way Valve Control

In the simplest control configuration, a 2-way control valve modulates the flow rate of the heating or cooling medium through the coil tube. A thermostat or building automation system (BAS) controller adjusts the valve position in response to room temperature deviation. The coil tube's uniform heat transfer characteristics ensure proportional thermal output, minimizing temperature overshoot and maintaining occupant comfort. This configuration is prevalent in residential and small commercial installations where independent zone control is required.

3-Way Valve Control

The 3-way valve configuration enables both flow modulation and flow bypass, providing enhanced control authority over the coil tube's thermal output. In heating mode, the 3-way valve mixes return water with supply water to modulate inlet temperature; in cooling mode, it regulates flow to prevent coil freezing. The stainless steel coil tube's resistance to thermal cycling and low-temperature operation makes it particularly suited for this application, where frequent temperature transients can cause fatigue failure in inferior materials.

Variable Speed Drive (VSD) Fan Control

In energy-efficient installations, the fan motor driving air across the coil tube is equipped with a Variable Speed Drive (VSD) or Variable Frequency Drive (VFD). The VSD adjusts fan speed in response to cooling/heating load, reducing parasitic energy consumption. The coil tube's aerodynamic design—optimized tube spacing and fin geometry—minimizes pressure drop across the heat exchanger, allowing the VSD to operate at reduced speeds while maintaining adequate heat transfer rates. This synergy between coil design and variable-speed control yields energy savings of 20–40% compared to fixed-speed systems.

Modulating Control with Building Automation Systems (BAS)

In large-scale commercial facilities, the coil tube operates under the centralized control of a BAS (e.g., BACnet, Modbus, or LonWorks protocols). The BAS integrates inputs from room thermostats, outdoor air temperature sensors, humidity sensors, and CO₂ monitors to dynamically modulate both the 2-way/3-way valve and the fan speed. The stainless steel coil tube's corrosion resistance ensures long-term reliability under continuous automated cycling, which can involve thousands of start-stop cycles annually.

Key Application Sectors

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:

Wenzhou Jixing Metal Materials Co., Ltd. — With a legacy of precision metal fabrication, the company delivers coil tube products that embody the convergence of metallurgical excellence, process engineering rigor, and application-specific design optimization. The stainless steel coil tube is not merely a passive heat transfer element; it is a dynamically engineered component whose performance directly determines the energy efficiency, service life, and reliability of the entire HVAC system. Every coil tube produced undergoes multi-stage quality gates from raw material verification through final pressure testing, ensuring that each unit performs to specification throughout its operational lifespan.