A cabinet can have enough physical space for every component and still lack a defensible thermal design. The quotation may list an enclosure size and a cooling-unit wattage without stating component losses, ambient conditions, operating combinations or the temperature that matters at each device. Purchasing then compares numbers that describe different systems.
Direct answer: build the RFQ around a thermal budget for the complete enclosure. Record heat generated inside the defined boundary, environmental heat exchange, the permitted operating conditions of the installed equipment and cooling performance at the actual proposed conditions. Request a calculation or verification package tied to the final layout and bill of materials. A cooling unit's headline capacity alone does not establish that the assembled cabinet is suitable.
This guide addresses whole-enclosure heat accounting and evidence for cooling selection. Use the enclosure condensation-control guide for moisture-management questions and the DC circuit-breaker enclosure-temperature guide for device-specific derating. Those reviews remain separate inputs to the assembly decision.
Official source pages were checked on 10 October 2026. The calculation examples below use hypothetical procurement inputs; the separately identified manufacturer figures are document-reading examples. Neither establishes an enclosure design approval, an installation instruction or a promise of SINAWATTS engineering, testing or supply capability. Actual products, verification scope, commercial terms and responsibilities require written agreement.
Set a boundary and define the operating scenarios
Start with a drawing that identifies what is inside the enclosure, what crosses its boundary and where heat is rejected. Include partitions, attached cooling equipment, adjacent cabinets and external equipment powered from the cabinet. This boundary prevents a common accounting error: treating all electrical power passing through a cabinet as heat generated inside it.
An internal converter supplying an external load contributes its own internal losses to the enclosure budget. Its exported output power is not automatically an internal heat load. Conversely, power supplied to internal electronics may ultimately become heat inside the enclosure. Trace the actual destination and avoid adding the same dissipation twice.
Define realistic operating scenarios before asking for a total. Examples can include normal production, maximum continuous output, charging, standby and a specified restart sequence. Record which components operate together, their loads and the duration of temporary conditions. A component inventory without simultaneous-operation assumptions is incomplete.
Ask the responsible designer to identify the governing thermal scenarios. Maximum ambient and maximum internal load may coincide, or the approved operating sequence may constrain that combination. Any claimed constraint needs evidence and ownership. A verbal expectation that “everything rarely runs together” should not silently reduce the quoted cooling requirement.
Build the component loss schedule
Request dissipation information for the actual operating point, not just a component's rated output. For conversion equipment, distinguish useful output, electrical input and heat loss. For switching and distribution components, ask for loss data tied to the applicable current, configuration and temperature basis. Do not invent a universal percentage for every device.
Where efficiency is used to estimate loss, preserve its basis. A hypothetical supply delivering 480 W at 96% efficiency has 500 W input and 20 W conversion loss because 480 / 0.96 = 500. That calculation applies only under the assumed conditions. It does not establish the efficiency at another load or the heat produced by equipment receiving the output.
Use a schedule that remains useful after the first quotation:
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| Schedule field | Required entry | Why the buyer needs it |
|---|---|---|
| Component identity | Model, revision and quantity | Connects losses to the offered BOM |
| Operating condition | Current, output or relevant duty | Prevents misuse of a nominal value |
| Loss evidence | Manufacturer data, measurement or justified estimate | Makes confidence visible |
| Heat destination | Inside, outside or documented split | Prevents boundary errors |
| Scenario participation | Concurrent operation and duration | Establishes the assessed combination |
| Data status | Confirmed, provisional or unresolved | Shows what must be closed before acceptance |
Include internal control electronics, power conversion, switching devices, conductors and other relevant sources where their losses belong inside the boundary. Identify auxiliary equipment and cooling-system contributions according to the chosen manufacturer's rating basis. Ask the technical reviewer to reconcile exclusions rather than assuming that small or unfamiliar items can be ignored.
Separate installed power, loss power and future allowance
Installed electrical capacity is useful for describing a cabinet, but it is not the same as thermal dissipation. A high-power feed may transfer most energy to external loads. A lower-power cabinet can still concentrate losses around temperature-sensitive equipment. Keep the electrical rating schedule and heat-loss schedule related but distinct.
Likewise, free mounting space does not prove thermal expansion capacity. An unused rail or spare circuit position may provide room for future devices while leaving no verified cooling allowance. If future expansion is part of the purchase, define its assumed loss contribution, location and operating scenario separately.
Avoid an unexplained multiplier called “safety factor.” Ask what each allowance covers: uncertain component losses, planned expansion, a named service condition or another documented assumption. Some uncertainties overlap, so simply adding several supplier percentages can obscure the actual design basis. The reviewer should record the reason and arithmetic for the selected allowances.
A useful quotation separates confirmed present load, unresolved estimates and an explicit expansion reservation. That structure helps the buyer compare a compact initial configuration against one with documented future capability. It also prevents later project changes from being approved merely because the first cooling unit appeared to have spare headline watts.
Define the temperature limits at the right locations
Outdoor weather temperature, room ambient, enclosure inlet air, internal bulk air and a component's local surrounding temperature can differ. Identify which quantity appears in each requirement and where it will be assessed. A controller display at one location does not automatically describe the hottest relevant area.
Obtain the operating conditions and temperature limitations applicable to each selected component. The responsible design reviewer should determine how those requirements apply to the assembled cabinet, including local conditions and any derating. Purchasing should not choose one convenient internal-air target and assume it establishes every component's suitability.
Record environmental scenarios with sufficient context: indoor or outdoor location, expected ambient range, solar exposure where relevant, nearby heat sources, elevation if relevant to the selected equipment, contamination and restrictions on air exchange. Ask which inputs are design requirements and which are preliminary assumptions.
Also distinguish normal operation from temporary conditions. A brief peak may require transient evaluation; a long operating period may require a steady-state assessment. Averages can conceal a limiting interval. Request the method used to decide which duration matters, without prescribing a universal test time or assuming that enclosure thermal mass makes every short peak acceptable.
Treat geometry and heat distribution as evidence inputs
An enclosure's dimensions do not fully describe its heat exchange. Which surfaces are exposed, which face another cabinet or wall, the material and construction, and the arrangement of partitions all affect the relevance of a proposed calculation. Request the actual configuration and its assumptions rather than relying on a generic family illustration.
The public scope of IEC TR 60890:2022 describes an air-temperature-rise calculation method for low-voltage switchgear and controlgear assemblies or similar products under their respective standards, primarily enclosed assemblies or sections without forced ventilation. Its revision summary includes guidance on uneven losses, solar effects, materials, ventilation, loss calculations and adjacent walls. This is a Technical Report; a quotation citing it still needs a documented applicability assessment and a calculation tied to the assembly.
That public scope does not supply every equation, limitation or acceptance requirement needed for a design. This guide has not treated the paid document as fully reviewed. The responsible technical party must use the applicable complete documents and assembly requirements when deciding the verification route.
Avoid a universal watts-per-square-meter capacity for every enclosure. A surface-area figure without temperature difference, exposure, construction and method can create false confidence. Ask the supplier to show the inputs and resulting temperature assessment for the exact configuration, including the limitations of the method.
Choose a cooling concept by its operating conditions
The first decision is the available heat-rejection path. Ordinary passive heat transfer through enclosure surfaces depends on the temperature relationship and the relevant enclosure conditions. A filter fan exchanges enclosure air with surrounding air. An air-to-air exchanger transfers heat between separated air paths. Refrigeration and liquid-based systems introduce different heat-rejection conditions and utility requirements.
Rittal's climate-control overview states that ambient-air cooling depends on surrounding air being below the required internal temperature and identifies environmental cleanliness as a selection consideration. For procurement, this supports checking the temperature relationship and environment before accepting an ambient-air cooling proposal.
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| Proposed approach | Evidence the RFQ should request | Limitation to resolve |
|---|---|---|
| Passive enclosure heat transfer | Configuration-specific calculation and operating conditions | Relevant surfaces, temperature rise and local hot areas |
| Filter fan or ventilation | Installed airflow basis, filter and environment | Available temperature difference and contamination |
| Air-to-air exchanger | Capacity under stated internal/external conditions | Heat-rejection temperature relationship |
| Refrigeration cooling unit | Capacity map, limits, supply and control basis | Performance at the proposed operating point |
| Air-to-water exchanger | Water and air conditions, flow and capacity | Availability and specification of the cooling-water system |
This table is an evidence checklist, not permission to install a particular method. The assembly designer must reconcile environmental protection, temperature, electrical requirements and manufacturer instructions for the final configuration.
Compare cooling capacity at the actual rating point
A catalog cooling category is not a constant available output under every condition. Compare capacity at the proposed internal and external temperatures, electrical supply and other declared conditions. Ask the manufacturer to identify the meaning of each rating label and provide a supported selection where the project's operating point differs from the tabulated points.
A concrete document example is Rittal's official SK 3328110 product page. Its table headed total cooling output to DIN EN 14511 lists 2,000 W at L35 L35/50 Hz and 1,450 W at L35 L50/50 Hz. Both figures are specifically 50 Hz ratings. It also lists electrical power consumption separately. The example demonstrates condition-dependent capacity and distinct quantities; it does not recommend that product, establish its suitability here or imply SINAWATTS availability. Retain the manufacturer's rating-point notation in the comparison and request its definitions and applicable performance curve for the proposed conditions. Two published points do not authorize an assumed linear interpolation or an extrapolation outside the documented range.
For the offered cooling unit, request useful or net cooling capacity as defined by its manufacturer and identify included auxiliary effects. Do not silently relabel a published total capacity as net capacity; require the supplier to reconcile the terminology and calculation basis in a controlled selection record. Keep cooling output separate from electrical input and from airflow. A larger electrical input is not evidence of a larger useful cooling benefit.
Also ask how the proposed control settings relate to the capacity selection. A unit's permitted operating range, achievable internal temperature under load and thermostat setting are different pieces of information. Avoid assuming that a selectable temperature is guaranteed at every heat load and ambient condition.
Send your enclosure loss schedule and operating conditions for an RFQ with the draft layout and required verification deliverables. Mark unresolved inputs so the quotation can address them explicitly.
Use a heat-accounting example with visible assumptions
Assume a hypothetical cabinet has the following internal dissipation during one agreed continuous operating scenario. The figures are invented solely to demonstrate arithmetic and document structure; they are not product specifications or recommended design values.
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| Assumed heat source | Quantity basis | Internal heat |
|---|---|---|
| Conversion equipment | Two units, each 35 W loss | 70 W |
| Controls and communications | Confirmed internal consumption for this example | 18 W |
| Switching and distribution components | Combined stated loss | 12 W |
| Conductors and connections | Separately assessed loss | 10 W |
| Total existing internal dissipation | Sum of the four rows | 110 W |
Now assume the project expressly reserves another 30 W of internal loss for a defined future addition. The scenario total becomes 140 W. Assume, separately, that a qualified project calculation determines 45 W of net environmental heat gain under the selected hot condition. The heat to be removed under those simplified steady-state assumptions is 185 W before any other documented additions or adjustments.
The 45 W value is an assumed calculation result, not a solar rule, surface coefficient or universal allowance. It already represents net environmental exchange for that scenario. Do not subtract the same passive wall heat rejection again if it was included in deriving this net figure. Under a cooler scenario the enclosure may instead reject some heat passively. Keep the sign convention clear: heat entering the enclosure increases the removal duty; validated passive rejection can reduce the active duty within that scenario.
Do not select a unit simply because its brochure says more than 185 W. Its supported capacity at the actual conditions, the rating basis, local temperature behavior, uncertainty allowances and complete verification remain to be assessed. The example gives the buyer an auditable subtotal, not a finished thermal design.
Ask for installed airflow and heat-rejection evidence
For a fan proposal, a free-air flow figure is not automatically the airflow through the completed cabinet. Request the manufacturer's selection basis including the proposed filters, grilles and other relevant restrictions. Ask how the supplier has accounted for the actual arrangement and the specified condition of service.
For an air-to-air or air-to-water exchanger, request the conditions associated with the capacity figure. For a liquid system, identify who supplies the fluid conditions and who confirms availability across the required scenarios. A capacity stated at one water condition cannot silently become a promise at another.
For refrigeration equipment, ask where rejected heat goes and whether the surrounding space can support the proposed operation. Multiple cabinets discharging into a common area can change the external conditions used in selection. Assign responsibility for that interface rather than allowing the enclosure supplier and site team to assume that the other has checked it.
nVent HOFFMAN's enclosure climate-control page separates air conditioners, fans and heat exchangers and directs selection through application inputs. This manufacturer resource supports requesting an application-specific selection record. Its product portfolio and company services do not establish the performance or services of another supplier.
Resolve missing loss data before ranking the offers
Use an explicit open-items register when a component has no supported loss value. Record the missing condition, the person responsible for obtaining it and the affected operating scenarios. The technical reviewer can choose an appropriately justified provisional estimate, request a measurement or hold the affected comparison. An empty cell must not be interpreted as zero dissipation.
When new evidence arrives, update the scenario subtotal and check whether it changes the selected cooling concept, capacity or layout. Preserve the previous assumption so reviewers can understand the change. This makes clarification work actionable and prevents a quotation with more missing data from appearing thermally superior.
Define verification before placing the order
Require the supplier to state how the final assembly will be assessed: calculation, relevant existing evidence, physical testing or a justified combination. Identify the evidence owner, reviewer and acceptance authority. The buyer needs a reviewable package, not an unsupported statement that the cabinet “has been thermally designed.”
For a calculation, request the method and version, input schedule, layout, environmental cases, assumptions, results and applicability limitations. A report should allow the reviewer to trace a changed component to its effect on the result. An unexplained final temperature with no input table is difficult to evaluate or maintain.
For physical verification, request an agreed plan prepared by the responsible technical party. It should identify the representative configuration, operating scenario, environmental conditions, measurement locations, instrumentation basis, stabilization or transient criteria and applicable acceptance limits. This guide does not prescribe sensor positions, electrical procedures or pass temperatures.
Ask how disagreement will be resolved when calculation and measurements differ. Preserve both records, investigate changed assumptions and obtain an authorized disposition. Do not alter the acceptance condition after a result is known simply to make the package appear compliant. Any revised scope or operating restriction should be explicit in the final documentation.
Compare lifetime obligations and control changes
Maintenance assumptions influence whether the selected solution continues to match its evidence. Request the proposed service requirements, replaceable items, access needs and the conditions used when rating expected performance. Avoid inventing a universal filter-change interval; the manufacturer and operating environment should inform the documented plan.
Separate normal cooling operation from specified abnormal or unavailable-utility scenarios. Ask the system designer which events need consideration, what monitoring or response is required and who owns those functions. Do not treat a purchase of two cooling devices as automatic redundancy without an approved operating and failure-response concept.
Compare commercial scope on the same basis. List enclosure, cooling equipment, controls, accessories, required evidence, any separately quoted testing, commissioning responsibility and service items. Obtain actual price, availability, quantity and schedule rather than assuming that every item in a conceptual solution is included.
After award, a different enclosure size, partition, component, filter, cooling unit or operating duty can change the evidence. Require a documented review of thermal implications before accepting substitutions. Preserve the approved loss schedule and layout as controlled records. The useful thermal budget is the one that continues to describe the cabinet actually supplied.
Buyer FAQ
1. Is the sum of component nameplate watts the enclosure heat load?
Not generally. Some ratings describe useful output or transferred power. Establish the heat generated inside the chosen boundary at the relevant operating condition. Trace exported power separately and check internal consuming loads so that the same energy is not counted twice.
2. Can the enclosure size tell us its cooling capacity?
Dimensions are only part of the evidence. Exposure, construction, temperature difference, nearby surfaces and internal distribution affect the assessment. Request a configuration-specific result with its method and limits. Do not substitute a generic surface-area rule for a documented assembly review.
3. Does a filter fan cool below outside-air temperature?
An ordinary filter-fan arrangement uses surrounding air as its cooling source; it is not refrigeration. The proposed solution needs an adequate temperature relationship and a supported installed-airflow assessment. If the required internal condition cannot be met that way, ask the responsible designer to evaluate another concept.
4. Is a cooling unit's power consumption its cooling output?
No. Electrical input and heat-removal capacity are different quantities. Compare the manufacturer's stated capacity at the relevant conditions and keep its input-power requirements in the electrical and operating-cost review. Ask how the stated useful capacity accounts for auxiliaries.
5. Does an IEC TR 60890 reference prove assembly compliance?
No. It identifies a possible calculation method with an applicability scope. The responsible party must explain its use for the exact assembly and the relationship to applicable product requirements. The public listing alone cannot establish a complete calculation or a conformity determination.
6. Can average duty replace the maximum operating scenario?
Only when the responsible technical assessment justifies that treatment for the actual time behavior and requirements. A short peak and a continuous load can need different evaluation. Require the scenario, duration and reasoning instead of accepting an undocumented average.
7. How much spare cooling should an RFQ request?
Define the intended future loss, uncertainty or service condition rather than using an unexplained universal percentage. Ask the supplier to identify the supported remaining capability at the stated conditions. Spare mounting space alone does not prove spare thermal capacity.
8. Are ambient-air heat exchangers and liquid heat exchangers interchangeable?
No. They reject heat through different interfaces and depend on different conditions. A liquid proposal needs a defined cooling-water supply and responsibility for it. An ambient-air proposal needs a suitable temperature relationship and environmental assessment. Compare complete supported applications.
9. Does a good bulk-air temperature rule out hot components?
No. The local conditions relevant to each device still need assessment. Request evidence that the layout and operating scenario satisfy the applicable component and assembly limits. One displayed temperature should not be treated as proof for every internal location.
10. Should condensation control be included in the same calculation?
It should be coordinated with the thermal design, but moisture control has its own conditions and evidence. Identify any heater or other device that adds heat and the scenarios in which it operates. Do not assume a successful cooling calculation resolves every humidity issue.
11. What should happen when the supplier changes a component?
Request an updated loss entry, applicable temperature information and a review of the thermal implications. The reviewer should decide whether the existing calculation or test evidence remains sufficient. Preserve the approved change and avoid relying only on a shared electrical rating.
12. What documents make the cooling quotation reviewable?
Provide the layout, component list, loss schedule, operating scenarios and environment. Request the selection record, capacity conditions, applicability assessment, verification plan and included commercial scope. Identify who must confirm unresolved inputs and what evidence is needed before accepting the assembly.
Send your complete enclosure thermal-budget checklist for an RFQ to organize the proposed configuration, cooling conditions and evidence responsibilities before comparing offers.