Views: 0 Author: Site Editor Publish Time: 2026-11-03 Origin: Site
A refrigeration contractor requests quotations for a new frozen food storage facility.
The specification calls for industrial evaporators with a cooling capacity of 100 kW per unit.
Three manufacturers respond.
The first offers a relatively compact evaporator with four axial fans. The second proposes a larger coil with three fans. The third provides a different tube arrangement, a different fin spacing, and a noticeably lower price.
All three quotations state approximately 100 kW.
At first glance, the decision appears straightforward. The buyer can compare dimensions, electrical consumption, delivery time, and price.
But there is a problem.
The three capacity figures may not represent the same operating conditions or even the same definition of cooling capacity.
One manufacturer may have calculated performance using a larger temperature difference. Another may use different refrigerant-side assumptions. A third may report coil capacity without clearly explaining how fan heat has been treated.
None of these differences necessarily means that a manufacturer is providing incorrect information.
However, unless the rating basis is understood, comparing the published capacities can lead to the wrong equipment selection.
For industrial refrigeration projects, a meaningful comparison requires more than matching the kilowatt figures printed on quotation sheets.
An industrial evaporator does not produce a constant cooling capacity under all conditions.
Its performance depends on the interaction between the heat exchanger, refrigerant, air, and operating environment.
Among the most important variables are:
Entering air temperature
Evaporating temperature or secondary-fluid temperatures
Refrigerant type and operating conditions
Airflow rate and fan operating point
Coil geometry and heat transfer surface
Refrigerant circuit design
Frost and moisture conditions
The method used to calculate or report capacity
This is fundamentally different from comparing two pieces of equipment by a simple physical dimension.
A 3,000 mm-long evaporator is 3,000 mm long regardless of where it operates.
A 100 kW evaporator, however, may deliver a different capacity when its operating conditions change.
Therefore, the first question when comparing evaporator manufacturers should be:
Under exactly what conditions was this capacity calculated or measured?
Without that information, the rating is incomplete.
One of the most influential variables in industrial evaporator ratings is the temperature difference between the air and the refrigerant.
For a conventional direct-expansion evaporator, the relationship is often discussed using TD.
However, manufacturers and rating standards may define the relevant temperature difference differently, particularly when refrigerant glide, changing air temperature, or secondary fluids are involved.
This makes it essential to establish a common definition before comparing figures.
Consider two hypothetical evaporator quotations.
Parameter | Manufacturer A | Manufacturer B |
|---|---|---|
Room air temperature | −25°C | −25°C |
Reference evaporating temperature | −35°C | −32°C |
Nominal TD | 10 K | 7 K |
Quoted cooling capacity | 100 kW | 100 kW |
Both suppliers quote 100 kW.
But Manufacturer A is using a larger nominal temperature difference.
Under otherwise comparable conditions, a larger temperature difference provides a stronger driving force for heat transfer.
This can allow a smaller heat exchanger to achieve a similar quoted capacity.
Manufacturer B, working with a smaller TD, may require more heat transfer surface or a different coil configuration.
The two products should not be judged by their capacity numbers alone.
Nor should Manufacturer A's 100 kW figure be assumed to remain valid if the project requires operation at the smaller TD.
A refrigeration system operating at a higher evaporating temperature can often achieve better compressor efficiency, assuming other relevant conditions remain comparable.
Consequently, a larger evaporator designed for a smaller TD may offer a system-level energy benefit in some applications.
That benefit must be weighed against the additional heat exchanger cost, fan power, pressure losses, and operating requirements.
The correct comparison is therefore not simply:
Which evaporator provides 100 kW at the lowest purchase price?
It is:
Which evaporator provides the required capacity at the intended system operating conditions, with an appropriate balance of capital and operating costs?
Refrigerant selection affects much more than the name printed on the equipment specification.
Ammonia, CO₂, HFC and HFO refrigerants, and secondary fluids such as glycol have different thermophysical properties.
These differences influence heat transfer, pressure drop, circuit arrangement, and fluid distribution.
For example, an industrial evaporator designed for pumped ammonia may use a different internal circuit arrangement from a direct-expansion unit operating with an HFC refrigerant.
A glycol air cooler introduces another set of variables, including fluid concentration, viscosity, inlet temperature, outlet temperature, and flow rate.
Suppose two quotations specify a room temperature of −20°C.
That does not establish equivalent rating conditions.
For a direct-expansion evaporator, the refrigerant-side calculation may depend on evaporating pressure, saturation temperature, refrigerant glide, superheat, and pressure drop.
For a glycol unit, the calculation depends on the actual fluid temperature profile through the coil.
A statement such as “100 kW at −20°C room temperature” is therefore insufficient for a technically reliable comparison.
For zeotropic refrigerant blends, saturation temperature can change during evaporation at a given pressure.
Depending on the refrigerant and the applicable rating convention, dew-point, bubble-point, or mean evaporating temperature may be relevant.
Using different temperature references can create apparent performance differences even when the underlying equipment is similar.
A fair comparison should identify the refrigerant and the precise temperature basis used in the calculation.
Two manufacturers may use similar heat exchanger dimensions but select different fans.
One offers higher airflow.
The other uses lower airflow with a different fan arrangement.
The higher-airflow unit may show greater clean-coil heat transfer capacity under certain rating conditions.
However, that does not automatically make it the better selection.
Higher airflow may also increase:
Fan electrical consumption
Air velocity near stored products
Noise
Air-side pressure losses
Product dehydration risk in sensitive applications
Furthermore, fan performance depends on the resistance of the complete air path.
The fan's nominal free-air volume is not necessarily the airflow it delivers when installed against the evaporator coil, guards, casing, and other restrictions.
A large coil with moderate airflow may have a lower face velocity than a smaller coil with the same total airflow.
That difference can affect air-side heat transfer, pressure drop, frost behavior, and fan operating conditions.
For this reason, airflow figures should be evaluated together with the effective coil face area and fan characteristics.
A comparison that includes only cubic meters per hour is incomplete.
Engineer's Note
When reviewing competing evaporator quotations, request both the calculated airflow and the fan electrical input at the stated operating point.
For projects where air distribution is critical, the expected air throw and installation arrangement should also be reviewed.
This is one of the less obvious sources of confusion in evaporator quotations.
An evaporator absorbs heat from the surrounding air, but the fans and associated electrical components may also introduce heat into the refrigerated space.
Depending on the equipment arrangement and the rating convention, a manufacturer may report a gross heat exchanger capacity or a net cooling capacity after accounting for specified electrical heat inputs.
The distinction can be significant for equipment with high fan power.
Suppose an evaporator has:
Gross coil cooling capacity: 100 kW
Fan electrical input: 6 kW
If the full 6 kW of fan electrical input becomes heat within the refrigerated space, the net cooling effect available to offset other room loads would be approximately:
100 − 6 = 94 kW
This simplified example assumes the stated gross capacity and electrical input are defined consistently, and that the fan heat is not already included elsewhere in the calculation.
In a real installation, the result depends on motor location, electrical losses, fan energy transfer, and the applicable rating method.
The important point is not that every manufacturer should automatically subtract a particular percentage.
It is that gross and net capacities must not be mixed in the same comparison.
If one supplier reports gross coil capacity and another reports net unit capacity, the figures may look comparable while representing different performance quantities.
Industrial evaporators are not designed around one universal heat exchanger geometry.
Manufacturers can vary:
Tube diameter
Tube pitch
Number of tube rows
Number of tubes per row
Fin spacing
Fin geometry
Coil depth
Circuit arrangement
Effective heat transfer area
Different combinations can produce similar calculated capacities.
For example, a deeper coil may provide additional heat transfer surface within a relatively compact frontal area.
But increasing coil depth can also raise air-side pressure drop.
Similarly, reducing fin spacing can increase fin surface area, but the resulting design may be less suitable for severe frost conditions.
Heat transfer area is important, but its effectiveness depends on how the coil is operated.
A larger coil with poor refrigerant distribution may not perform as expected.
A densely finned coil with inadequate fan pressure capability may suffer reduced airflow.
A compact coil with an optimized circuit and appropriate fan selection may perform effectively under the intended conditions.
Therefore, physical size alone cannot establish which manufacturer has the better design.
The useful question is whether the coil geometry is appropriate for the required capacity, refrigerant, airflow, frost conditions, and installation constraints.
Evaporator pressure drop is sometimes treated as a secondary specification.
In industrial refrigeration, it can be important to system performance.
Excessive refrigerant-side pressure drop can reduce the effective evaporating pressure available through the heat exchanger and may affect system efficiency.
However, pressure drop cannot be evaluated independently of refrigerant velocity and distribution.
A design with very low pressure drop is not automatically superior if the resulting velocities or flow distribution are unsuitable.
For direct-expansion evaporators, the circuit must support appropriate refrigerant distribution and operating stability.
For pumped-liquid systems, circulation conditions and return flow behavior must be considered.
For glycol air coolers, fluid-side pressure drop directly affects pumping requirements.
One manufacturer may use fewer parallel circuits with higher refrigerant velocity.
Another may use more circuits with lower velocity.
Both designs may achieve similar thermal capacity, but their pressure drops and operating characteristics can differ.
The correct solution depends on the refrigeration system.
A meaningful quotation comparison should therefore include the calculated refrigerant-side or fluid-side pressure drop at the stated design conditions.
Low-temperature evaporators present an additional challenge: frost accumulation.
Two evaporators may achieve the same clean-coil capacity but behave differently after several hours of operation.
Consider a freezer where the evaporators operate at a temperature well below the freezing point of water.
Moisture entering the room can deposit on the heat exchanger.
As frost develops, the coil experiences increasing resistance to airflow and heat transfer.
The rate of deterioration depends on factors including:
Moisture load
Fin spacing
Coil geometry
Air velocity
Operating temperatures
Defrost frequency
Room usage
A closely spaced fin arrangement may offer attractive clean-coil performance while requiring more frequent defrost under demanding moisture conditions.
A more open coil arrangement may have different initial capacity characteristics but retain airflow more effectively during certain operating cycles.
Neither design is universally better.
The appropriate choice depends on the application.
For applications with significant frost formation, buyers should ask how the evaporator is expected to perform over the intended operating cycle.
This may require reviewing frost allowance, defrost intervals, air pressure drop development, and practical operating experience.
A single clean-coil rating cannot answer all these questions.
Recognized performance standards are useful because they establish common terminology, test methods, or rating conditions.
In the European market, the EN 328 standard is particularly relevant to forced-convection unit air coolers for refrigeration.
Its scope and applicable provisions should be checked against the equipment type and the edition being used.
In North America, relevant AHRI standards and certification programs may also be encountered, depending on the product category and application.
However, the presence of a standard reference does not eliminate the need to review the actual quotation conditions.
A manufacturer may provide performance data calculated using proprietary selection software.
Another may provide certified ratings for a defined product range.
A third may offer a custom industrial evaporator outside a particular certification program.
These situations should not automatically be treated as equivalent.
Nor does a reference to a standard necessarily mean that an individual product has been independently certified.
Ask the supplier to identify:
The applicable rating or test standard, if any
The edition or rating convention used
The actual operating conditions
Whether the capacity is measured or calculated
Whether the capacity is gross or net
Whether the specific equipment is covered by an independent certification program
This makes the comparison more transparent without unfairly excluding customized equipment that may be technically suitable.
Consider a hypothetical cold storage project requiring approximately 100 kW of evaporator capacity at a defined design point.
Three suppliers submit the following initial quotations.
Parameter | Supplier A | Supplier B | Supplier C |
|---|---|---|---|
Quoted capacity | 100 kW | 100 kW | 100 kW |
Room temperature | −25°C | −25°C | −25°C |
Reference evaporating temperature | −35°C | −32°C | −33°C |
Nominal TD | 10 K | 7 K | 8 K |
Airflow | 42,000 m³/h | 36,000 m³/h | 39,000 m³/h |
Fan electrical input | 6.0 kW | 4.5 kW | 5.2 kW |
Capacity definition | Gross | Gross | Not specified |
All figures are illustrative and do not represent actual STELX or competitor products.
At first glance, Supplier A appears attractive because it offers the highest airflow with the same nominal capacity.
Supplier B appears to have the lowest fan electrical consumption.
Supplier C may look like a compromise.
But these conclusions would be premature.
The capacity ratings use different evaporating temperatures.
The quoted airflow figures do not reveal coil pressure drop or air distribution performance.
The fan electrical inputs have not been evaluated against the same capacity basis.
Supplier C has not even identified whether its rating is gross or net.
Request that all three manufacturers calculate performance at the same project design point.
For example:
Room temperature: −25°C
Refrigerant: same specified type
Reference evaporating temperature: −33°C
Same applicable superheat and refrigerant-side assumptions
Same capacity definition
The resulting capacities may differ from the original quotations.
Supplier A's published 100 kW rating at a larger TD cannot simply be carried over unchanged.
Supplier B may retain more capacity relative to its original rating because its original temperature difference was smaller.
The exact revised capacities require manufacturer calculations; they cannot be established reliably from the table alone.
Once the thermal conditions are aligned, review airflow, fan power, coil air resistance, and room air distribution.
A higher airflow rate is not automatically better.
The appropriate airflow depends on the room geometry, product requirements, and coil design.
Review pressure drop, refrigerant distribution, circuit arrangement, and connection requirements.
A quotation that appears thermally acceptable may still require changes to the system piping or refrigerant supply arrangement.
If the room has frequent door openings or substantial moisture infiltration, frost performance becomes important.
If installation height is restricted, casing dimensions may be decisive.
If energy consumption is a major project priority, fan power and the evaporator's effect on the overall refrigeration system should be evaluated together.
Only after these factors are understood does a meaningful price comparison become possible.
Industrial evaporators are often compared using a simple metric:
Equipment price ÷ nominal cooling capacity
This can be useful for preliminary screening when the equipment and rating conditions are genuinely comparable.
But it becomes misleading when the quoted capacities are based on different assumptions.
A lower purchase price may reflect:
A larger rating temperature difference
Less heat transfer surface
A different material specification
A simpler fan arrangement
Different defrost equipment
Different refrigerant circuit requirements
A different scope of supply
Some of these differences may be perfectly acceptable.
Others may create additional installation costs, operating costs, or performance risks.
For example, a quotation may exclude fan controls, drain pan heaters, or other components that another supplier includes.
The apparent price difference may therefore reflect differences in scope rather than manufacturing efficiency.
A fair comparison should use the same performance requirements and the same equipment scope.
This protects both the buyer and the manufacturer.
Standard catalogue products provide a convenient starting point for many refrigeration projects.
However, industrial applications often require equipment that does not fit neatly into standard selection tables.
A custom evaporator manufacturer can adjust the heat exchanger design to meet specific requirements.
At STELX, this may include adapting:
Tube and fin materials
Coil dimensions and geometry
Refrigerant circuit arrangement
Fin spacing
Fan brand and configuration
Casing construction
Defrost method
Installation and maintenance arrangements
This flexibility is particularly valuable when an application combines unusual dimensions, demanding operating temperatures, specific refrigerants, or challenging environmental conditions.
But customization should not be presented as a substitute for verified performance.
A well-designed custom evaporator should still be supported by clear operating assumptions, appropriate thermal calculations, and documented mechanical specifications.
The objective is not simply to produce a different design.
It is to produce a design that meets the actual project requirements.
Before approving an industrial evaporator quotation, verify the following information.
Comparison item | Required clarification |
|---|---|
Cooling capacity | Gross or net? At what conditions? |
Room temperature | Same entering air temperature for every supplier? |
Refrigerant | Same refrigerant and operating assumptions? |
Evaporating temperature | Same reference temperature and definition? |
Airflow | Calculated installed operating airflow or nominal fan airflow? |
Fan power | Electrical input at the quoted operating point? |
Coil design | Tube arrangement, fin spacing, and relevant dimensions? |
Refrigerant pressure drop | Calculated at the specified duty and conditions? |
Defrost | Same method, components, and operating assumptions? |
Materials | Same tube, fin, casing, and drain pan requirements? |
Rating method | Standard, calculation method, or certification identified? |
Scope of supply | Fans, controls, heaters, accessories, and packaging included? |
This information allows buyers to move from a superficial comparison to a technically defensible selection.
It also reduces the likelihood of disputes after equipment delivery.
They may use different tube arrangements, fin spacing, coil depths, fan configurations, or refrigerant circuits. Their capacity ratings may also be based on different operating conditions. Physical dimensions alone do not establish equivalent thermal performance.
Only if the rating conditions, capacity definitions, and relevant equipment specifications are sufficiently aligned. Otherwise, the comparison may be misleading.
Higher airflow can increase heat transfer under certain conditions, but the relationship depends on coil geometry, fan performance, air pressure drop, and the refrigeration operating point. Higher airflow can also increase electrical consumption and affect product conditions.
Gross capacity generally describes heat absorbed by the coil under the stated rating definition. Net capacity accounts for specified heat inputs associated with the unit, such as relevant fan heat. The exact definitions should be confirmed against the manufacturer's rating method.
No. A larger heat exchanger may permit operation at a smaller temperature difference, potentially improving refrigeration system efficiency. However, fan power, pressure drop, control strategy, and overall system conditions must also be considered.
Not inherently. Reliability depends on engineering design, manufacturing quality, material selection, operating conditions, and maintenance. Custom equipment should be evaluated using the same technical discipline as standard products.
Request performance at a common design point, the refrigerant and temperature assumptions, airflow, fan electrical input, pressure drop, coil specifications, defrost configuration, and a clearly defined scope of supply.
The purpose of an industrial evaporator quotation is not simply to provide a cooling capacity figure.
It should establish how the equipment is expected to perform under a specific set of operating conditions.
Two manufacturers can legitimately quote the same nominal capacity while offering very different equipment.
The difference may arise from rating assumptions, heat exchanger geometry, refrigerant circuit design, airflow, or included components.
For the buyer, the challenge is to distinguish meaningful engineering differences from differences in how the performance is presented.
The most reliable comparison is not between two nominal capacity figures. It is between two complete equipment selections evaluated at the same operating conditions.
That is the foundation of an informed purchasing decision.
If you are evaluating industrial evaporator quotations for a cold storage, food processing, or freezing project, STELX can review your technical requirements and develop a customized equipment selection.
Our industrial air coolers and evaporators can be configured for different refrigerants, operating temperatures, heat exchanger materials, fan arrangements, installation dimensions, and defrost methods.
Send us your operating conditions, required cooling capacity, refrigerant details, and project specifications. We can help you evaluate an appropriate evaporator configuration and provide a technical quotation based on clearly defined conditions.
Website: https://www.stelxtech.com
