Custom Fin-and-Tube Coil RFQ Guide for Industrial Refrigeration OEMs

A custom fin-and-tube coil RFQ should describe more than cooling capacity and overall dimensions. For industrial refrigeration OEMs, the quotation must also reflect the refrigerant, operating conditions, airflow, circuit arrangement, installation interfaces, testing requirements, and production quantities.

Two coils with the same nominal capacity may have different pressure drops, refrigerant distributions, dimensions, and manufacturing requirements. Without a common technical basis, their quotations cannot be compared reliably.

This guide explains what OEM engineers and procurement teams should specify before ordering custom fin-and-tube evaporator, condenser, or secondary-fluid coils. It also provides an RFQ checklist, drawing review procedure, and supplier comparison framework.

1. Identify the Coil's Function Before Requesting a Quote

Finned tube heat exchangers typically consist of tubes that carry refrigerant or other heat transfer fluids and extended fins that improve heat transfer efficiency on the air side.

In this guide, the term primarily refers to a circular tube-plate finned heat exchanger assembly. It should not be automatically considered the same as spiral-wound or freestanding finned tube heat exchangers used in other industrial applications.

1.1 Direct-Expansion Evaporator Coils

A direct-expansion (DX) evaporator absorbs heat from air as refrigerant evaporates inside the tubes.

An RFQ should identify the refrigerant, evaporating condition, expansion-device arrangement, superheat requirement, expected capacity, and air conditions.

For low-temperature applications, frost formation and defrost arrangements are essential design inputs.

1.2 Air-Cooled Condenser Coils

An air-cooled condenser dissipates heat from the refrigerant into the surrounding air.

The buyer should specify the total heat dissipation, rather than assuming it equals the evaporator's cooling capacity.

Important input parameters include ambient design temperature, condensing conditions, refrigerant mass flow rate (if known), subcooling requirements, airflow rate, and allowable pressure drop.

For transcritical R744 systems, the gas cooler must be identified separately because its high-pressure side operation is not a traditional condensation process.

1.3 Water and Glycol Cooling Coils

Some industrial refrigeration OEMs use fin-and-tube coils carrying water, glycol, or another approved secondary fluid rather than refrigerant.

For these coils, the RFQ should provide fluid composition, concentration, flow rate, entering and leaving temperatures, and allowable liquid-side pressure drop.

The fluid should never be described simply as "water" if additives or antifreeze are present.

2. Establish the Thermal Design Basis

A useful custom-coil quotation begins with a clearly defined operating point and the range of conditions the coil must accommodate.

2.1 Define Capacity and Rating Conditions

Please specify whether this capacity refers to the evaporator cooling load, the condenser's total heat dissipation, or other heat exchange load.

Please specify the unit (e.g., kilowatts) and describe the operating conditions requiring this capacity.

Do not request a coil solely as a "30 kW evaporator" or "50 kW condenser" without supplying the temperatures, fluid conditions, and airflow that define those ratings.

2.2 Specify the Air-Side Conditions

For each applicable operating point, provide:

• Entering air dry-bulb temperature

• Entering wet-bulb temperature or humidity where relevant

• Required leaving air condition, if specified

• Air volume flow rate and its measurement basis

• Allowable air-side pressure drop

• Airflow direction and available face area

• Installation altitude, where relevant

For wet cooling coils, the impact of dehumidification on rated load must be considered.

For low-temperature evaporators, frosting and defrosting requirements must be considered separately from the performance of clean and dry coils.

2.3 Specify Refrigerant-Side Conditions

For refrigerant coils, provide:

• Refrigerant designation

• Evaporating or condensing condition, as applicable

• Relevant refrigerant inlet and outlet states

• Superheat or subcooling requirements, where applicable

• Refrigerant mass flow rate, if available

• Allowable refrigerant-side pressure drop

• Operating and design pressures

• Intended refrigerant feed or distribution method

For refrigerant mixtures with temperature glide characteristics, a suitable bubble point or dew point temperature reference should be determined.

For R744 gas coolers, actual high-pressure side pressures and gas cooling conditions should be included, rather than using conventional condensation temperature specifications.

2.4 Check the Heat-Transfer Calculation Basis

For a single-phase secondary fluid, the sensible heat-transfer rate can be estimated as:

Q = m × Cp × ΔT

Where Q is heat-transfer duty (kW), m is mass flow rate (kg/s), Cp is specific heat capacity (kJ/kg·K), and ΔT is the fluid temperature change (K).

For a refrigerant undergoing a phase change, heat transfer can be evaluated from refrigerant mass flow and the relevant inlet-to-outlet enthalpy difference:

Q = m × Δh

The applicable inlet and outlet states must be clearly defined.

These equations support the thermal-duty specification; they do not replace a detailed coil selection or refrigerant circuit calculation.

3. Define the Coil Geometry and Refrigerant Circuiting

A custom coil must fit the OEM equipment and connect correctly to its refrigeration system.

3.1 Physical Envelope and Mounting

Provide dimensioned drawings showing:

• Maximum overall length, height, and depth

• Finned length and height

• Maximum allowable coil weight, if relevant

• Frame and mounting-hole locations

• Connection side, orientation, and clearance

• Airflow direction

• Space for service access and condensate drainage

Distinguish the finned core dimensions from overall dimensions including headers, return bends, and connections.

3.2 Tube and Fin Specifications

If the design is finalized, please provide the tube outer diameter, wall thickness, tube material, fin material, fin spacing, fin thickness, number of tube rows, and tube bundle arrangement.

If these details are not yet finalized, please specify the performance requirements and allow the supplier to propose configuration options for review.

Fin spacing must take into account factors such as airflow resistance, scaling, cleaning, and frost buildup (if applicable).

3.3 Refrigerant Circuiting and Distribution

The circuit layout affects refrigerant distribution, flow rate, pressure drop, and the coil's ability to operate within the required load range.

The original equipment manufacturer (OEM) should specify the applicable expansion or refrigerant supply scheme, connection locations, and system limitations. The coil supplier should describe the proposed circuit layout and any assumptions requiring approval.

3.3.1 Review the Integration Drawing

The drawing should show the coil core, tube connections, headers, distributor connections where applicable, mounting interfaces, and airflow direction.

Critical Interface Review

Before approving the drawing, check dimensions against the OEM cabinet, pipework, expansion devices, fan arrangement, and service access requirements.

Production Release Check: Freeze the Approved Interfaces

Production shall not commence until both parties reach an agreement on drawing modifications, critical dimensions, connection directions, material specifications, and acceptance criteria.

Any proposed replacements or dimensional changes must be approved in writing before production begins.

4. Account for Refrigeration Operating Risks

4.1 Frost, Defrost, and Condensate

Low-temperature evaporator coils may require special consideration of frost accumulation, fin spacing, defrost method, drainage, and fan operation.

The RFQ should identify whether defrost equipment is included in the supplier's scope or provided by the OEM.

4.2 Materials and Refrigerant Compatibility

Material selection must take into account the refrigerant, operating pressure, connection method, and external environment.

For example, in traditional refrigeration applications, ammonia (R717) is incompatible with copper and brass. Do not assume that copper tubing coils are suitable for ammonia refrigeration systems.

For coastal, chemical, or flushing environments, exposure conditions and any required protective coatings should be clearly specified; a general-purpose corrosion-resistant coating cannot be assumed to be sufficient.

4.3 Applicable Standards and Safety Requirements

Confirm the performance rating standards and safety or pressure equipment requirements relevant to the actual equipment.

AHRI 410 covers specified forced-circulation air-cooled and air-heated coils, but excludes certain refrigeration applications, such as defrost operation and certain refrigerant evaporator and condenser coils.

AHRI 420/421 are for coolers in defined factory-manufactured refrigeration units. AHRI 460 covers specified remote mechanical-ventilated air-cooled refrigerant condensers.

These standards are not interchangeable, and their applicability must be verified based on the type of equipment and the scope specified.

Also, agreement should be reached on applicable refrigeration safety standards, pressure equipment rules, inspection requirements, and regional regulations.

5. Custom Fin-and-Tube Coil RFQ Checklist

The following checklist can be used to prepare a technical inquiry.

Unknown values should be marked "To Be Confirmed" rather than silently replaced with supplier assumptions.

6. How OEM Buyers Should Compare Supplier Quotations

A lower quoted price is not necessarily a better technical or commercial offer.

Request comparable proposals using the same design conditions and clearly identify deviations.

Ask suppliers to state exclusions, unresolved inputs, and assumptions separately from confirmed specifications.

7. Prototype Approval and Production Quality Requirements

7.1 Prototype Evaluation

For a new OEM design, an agreed prototype or first-article process can help identify integration issues before volume production.

Depending on the project, evaluation may include dimensional inspection, connection fit, pressure and leak testing, and thermal or airflow performance verification.

A pressure test alone does not establish the coil's thermal capacity.

7.2 Inspection and Documentation

Before placing your order, please review the documents accompanying the product.

These documents may include approved drawings, material records, inspection reports, pressure or leak test reports, identification labels, and packaging specifications.

The specific scope depends on the project and should not be considered part of the standard service.

7.3 Revision Control for Repeat Orders

OEM purchasing often involves repeat production of a previously approved coil.

All orders should specify the correct version of the drawings and the approved specifications.

Any changes to tubing, fin geometry, loop layout, connection methods, or testing requirements should be assessed for their impact on heat dissipation, mechanical integrity, and installation compatibility.

8. Example OEM RFQ Brief

Illustrative Example — Not an Aidear Product Specification

Project: Custom fin-and-tube evaporator coil for an industrial refrigeration OEM.

• Application: Industrial air-cooling equipment

• Refrigerant: To Be Confirmed

• Required cooling duty: To Be Confirmed

• Evaporating temperature and superheat: To Be Confirmed

• Air inlet temperature and humidity: To Be Confirmed

• Airflow and available fan pressure: To Be Confirmed

• Frost and defrost requirements: To Be Confirmed

• Available installation envelope: Drawing attached

• Connection locations: Drawing attached

• Required pressure and leak tests: To Be Confirmed

• Prototype quantity and annual production volume: To Be Confirmed

This example demonstrates the RFQ format, not a completed thermal design. Missing operating data must be resolved before a reliable selection can be finalized.

9. Frequently Asked Questions

9.1 Can a Custom Coil Be Quoted from Dimensions Alone?

Dimensions can support an initial replacement assessment, but they do not establish thermal capacity or refrigeration compatibility.

Provide the operating duty, air conditions, refrigerant or fluid data, and pressure requirements wherever possible.

9.2 Is Fin Pitch the Same as Fins Per Inch?

No. Fin pitch is the distance between adjacent fins, usually expressed in millimeters. Fins per inch (FPI) expresses the number of fins within one inch of fin-pack length.

The two are related, but the units and measurement convention must be clearly identified.

9.3 Should the OEM Specify Every Tube and Circuit Detail?

Not necessarily. The OEM should lock critical performance and integration requirements while identifying which geometric details the supplier may propose.

Supplier-designed circuiting still requires engineering review and approval.

9.4 What Is the Difference Between an Evaporator Coil and a Complete Air Cooler?

An evaporator coil is a heat-transfer component. A complete forced-air unit cooler may also include fans, casing, defrost equipment, drain pan, controls, and other components.

The RFQ must state the actual supply boundary.

9.5 What Should Be Approved Before Mass Production?

At minimum, the agreed drawing revision, critical materials, mechanical interfaces, inspection requirements, and commercial supply scope should be approved.

Prototype or performance testing should also be agreed where required.

10. Conclusion: A Better RFQ Creates a Better OEM Supply Process

A custom fin-and-tube coil RFQ should connect thermal requirements with the mechanical, manufacturing, and commercial details needed for repeatable OEM supply.

The most important information is not a long list of preferred features. It is a clear, verifiable design basis:

• Define the coil duty and operating conditions.

• Identify the refrigerant or secondary fluid.

• Specify air-side and fluid-side constraints.

• Confirm geometry, circuiting, materials, and connections.

• Agree on testing, documentation, and drawing revisions.

• Resolve open items before production release.

For broader refrigeration heat exchanger selection considerations, see How to Select a Heat Exchanger for Industrial Refrigeration Systems.

Request a Custom Fin-and-Tube Coil Quote from Aidear

Aidear offers tube-fin heat exchanger products and custom copper tube-and-fin heat exchanger options for relevant refrigeration and cooling applications.

Share your coil function, working fluid, required duty, air conditions, pressure limits, installation drawing, connection requirements, and expected order volume.

These details provide a practical starting point for reviewing a suitable coil configuration and confirming project-specific technical requirements.

Request a Custom Quote to discuss your OEM heat exchanger project.