Project Overview

A client in Türkiye ordered three types of customised positive-pressure containers from TLS: PDU, workshop and office units. TLS supplied the container structures and specified pressurisation and safety systems, detectors, piping and Ex electrical components. The customer was responsible for installing the operational equipment inside.

The project requirements included Zone 2 protection, A60 fire protection and an operating temperature range of −20°C to +60°C. Preparation and production took approximately five months, followed by the customer’s final video inspection before delivery.

Read the original project report

1. Engineering Focus: How CPFG Coordinates Pressurisation and Safety Functions

A positive-pressure container is an engineered enclosure, not simply a container fitted with a ventilation fan.

Its protective function depends on maintaining the specified pressure conditions and coordinating monitoring, alarms and protective actions. For this project type, the Combined Pressurisation, Fire and Gas (CPFG) system is a key part of that arrangement.

A typical CPFG configuration may incorporate:

• Differential-pressure switches and airflow monitoring.
• Combustible-gas, smoke and heat detectors, according to the specified scope.
• A pressurisation fan and associated air-control components.
• An explosion-protected CPFG control cabinet.
• Audible and visual alarms, emergency-stop functions and defined electrical shutdown interfaces.

How the protection sequence works

Step 1 — Purging and pressurisation

The pressurisation system supplies air to purge the enclosure and establish the required internal pressure conditions. The required purge duration and pressure setpoint depend on the approved design.

Step 2 — Verification before energisation

The control system checks whether the specified conditions for safe operation have been achieved. Where the approved design requires it, the relevant non-Ex electrical circuits remain isolated until the required conditions are satisfied.

Step 3 — Continuous monitoring

During operation, pressure and other specified safety parameters are monitored. A loss of required pressure, gas detection or another abnormal condition may initiate alarms and protective actions according to the approved cause-and-effect logic.

Step 4 — Protective response

If the required conditions cannot be restored within the specified period, the system may isolate designated non-Ex electrical equipment. The actual response depends on the approved control philosophy and the equipment connected to the system.

This sequence is important because positive pressure is only one part of the protection concept. Monitoring, electrical isolation and the response to abnormal conditions must also be considered.

For PDU, workshop and office containers, the internal equipment and operational requirements may differ. The enclosure and its protection systems therefore need to be coordinated with the customer's intended installation rather than designed around an assumed standard equipment package.

For further technical background, see TLS's published guide, What Is CPFG and How Does It Work?.

2. Engineering Focus: What Does Factory Acceptance Testing Verify?

Factory Acceptance Testing (FAT) provides a structured way to check the supplied systems against the approved drawings, functional requirements and agreed acceptance criteria before shipment.

For a positive-pressure container, the test scope should cover both the physical installation and the behaviour of the protection system.

Key inspection and test areas

One important distinction is that achieving the normal pressure target does not, by itself, demonstrate that the complete protection sequence works correctly.

The FAT should also verify the specified responses to conditions such as pressure loss or sensor disconnection. The test procedure should define the relevant thresholds, timing requirements, expected actions and acceptance criteria.

TLS's published FAT guide for PDU and workshop pressurised containers describes visual inspection, CPFG checks, sensor-integrity testing and emergency-shutdown testing as part of the testing methodology.

These are examples of the checks that may be required by a project. The exact tests completed on the Turkish units, and their individual results, should be stated only where supported by the relevant project records.

Applicable Standards and Certification Scope

The standards applicable to this project were determined by the specified operating conditions, hazardous-area classification and contractual requirements. Individual certification claims should be based on the relevant project certificates and approved documentation.

• IEC 60079-13: Addresses the design, construction, assessment, verification and marking of rooms protected by pressurisation or artificial ventilation, within the applicable scope and edition.
• DNV-ST-E271 (DNV 2.7-1): Covers the design, approval, testing and certification of offshore containers and associated lifting sets, where applicable.
• A60 fire protection: Specifies a fire-resistance performance classification. Compliance should be supported by the applicable design, test and approval documentation.
• Hazardous-area electrical equipment: Explosion-protected electrical components and instrumentation must meet the requirements applicable to their intended installation, with certification verified against the actual equipment supplied.

The applicable standards, editions and certification scope must be confirmed against the approved project documents and relevant certificates. References to these standards should not be interpreted as confirmation that every container, component or customer-installed item is independently certified to all of them.

See the TLS pressurised-container technical overview for the published range of design options and applicable requirements.

4. Inspection and Delivery

The published Turkish project account reports quality checks covering structural fabrication, welding, lifting, coating thickness, positive-pressure performance and watertightness. It also records the customer's final video inspection before delivery.

These checks address different aspects of the finished product. Structural and lifting inspections concern the container's physical integrity and handling requirements, while pressure and functional tests address the performance of the specified protection system.

The published account does not provide detailed pressure-test readings, complete signed FAT records or unit-by-unit test results. Those details should not be inferred from the reported successful inspection and delivery.

Conclusion

A positive-pressure container must be designed around the intended application, the equipment that will be installed and the required safety functions.

For PDU, workshop and office applications, the enclosure, pressurisation system, CPFG controls, detection devices and specified explosion-protected electrical components form part of a coordinated design. Clearly defining the supply boundary and verifying the agreed functions before shipment helps establish a sound basis for subsequent equipment installation and commissioning.

TLS provides customised positive-pressure containers for industrial and offshore applications, with the configuration and supply scope defined according to project requirements.

Short Summary

A transformer needs a purpose-built container when the project requires protection, integration, relocation or operating access that a suitable outdoor transformer installation cannot adequately provide. The decision must account for heat rejection, electrical clearances, fire strategy and maintenance. Putting an outdoor transformer inside a box can reduce its usable capacity.

The Direct Answer

Choose a purpose-built transformer container when a coordinated enclosure solves a defined site or operational requirement: protecting sensitive equipment from contamination, integrating electrical systems, enabling factory assembly, or supporting relocation. An appropriately rated outdoor transformer can remain the better choice when it meets the environmental, safety and maintenance requirements directly.

The useful comparison is between two complete installations. Compare the outdoor unit, fencing, foundations, cable arrangements and any separate electrical room with the containerized package, its auxiliaries and its site works. Both options need safe access, suitable protection and a workable replacement route.

When an Outdoor Installation Is Enough

An outdoor-rated transformer may suit a permanent site with adequate space, acceptable exposure and direct maintenance access. Confirm the manufacturer's service conditions, including ambient temperature, altitude, contamination and installation clearances.

Outdoor suitability is specific to the transformer and its accessories. A weather-resistant transformer tank does not establish that adjacent switchgear, terminations or controls can tolerate the same environment. Schneider Electric's installation instructions illustrate the need to follow the selected transformer's ventilation and installation requirements. Transformer installation guidance

Where only the controls need protection, a separate electrical enclosure may be more practical than enclosing the transformer as well. Keep the scope proportional to the actual exposure and operating requirement.

When a Purpose Built Container Adds Value

A container becomes useful when the project needs equipment and interfaces assembled as a coordinated module. Transformer connections, switchgear, metering, auxiliaries and controls can then be laid out together, with an agreed division between factory and site work.

Remote projects may benefit when site assembly resources are limited. Relocatable facilities may also need a transportable structure with documented lifting arrangements and equipment restraints. Neither benefit removes the need to check shipping mass, route restrictions, foundations and commissioning after transport.

Dust, wind-driven rain, coastal exposure or security requirements can justify additional protection. The enclosure design must address the particular hazard. A general description such as weatherproof does not define dust filtration, corrosion protection, flood resistance or access control.

TLS's published power-infrastructure scope includes configurable electrical enclosures and project-defined integration of equipment such as dry-type transformers and switchgear. The specific transformer type and integration boundary must be agreed for the project. TLS power infrastructure scope

Heat Rejection Often Determines the Decision

A transformer enclosure must remove the heat produced by the installed equipment while keeping its cooling environment within the manufacturer's limits. Ventilation must accommodate the transformer's losses; restricted airflow can cause overheating. Schneider Electric ventilation guidance

Use supplier loss data for the intended duty, including no-load losses, load losses and any additional effects associated with the load. Add heat from other installed equipment and relevant environmental gains. The MVA rating is electrical capacity, not the enclosure cooling load.

Natural ventilation may work where the geometry and environment permit it. Fans add controllable airflow but introduce maintenance and auxiliary-power dependencies. Mechanical cooling may be appropriate for some compartments, especially controls, but its capacity and failure response need calculation.

Filters, acoustic treatment and weather louvres create airflow resistance. Evaluate the complete air path, including dirty-filter conditions and hot-air recirculation. Closing ventilation openings to improve environmental protection can undermine transformer cooling.

Before approving the arrangement, request a thermal calculation and an agreed verification method. Establish whether the quoted transformer rating remains available inside the proposed enclosure at the design site conditions.

Electrical and Fire Requirements Must Shape the Layout

Define cable entry, termination space, bending radii, operating aisles, isolation points and earthing before fixing the container dimensions. A transformer that physically fits may still leave inadequate room for cable work or safe maintenance.

Dry-type and liquid-immersed transformers require different assessments. Dry-type equipment still needs cooling and a fire-risk review. A liquid-immersed design also requires consideration of leaks, fluid containment, pressure relief and the applicable fire-separation strategy. An outdoor arrangement may be preferable if enclosure requirements become impractical.

If switchgear is included, determine the applicable fault and internal-arc requirements for that equipment and installation. A general-purpose container shell does not establish an internal-arc classification. Any required pressure-relief path must be coordinated with personnel access and nearby equipment.

Noise control also affects layout. Specify where the noise limit applies and at what operating condition. Acoustic measures must be checked against ventilation performance and maintenance access.

Maintenance and Transport Can Change the Preferred Option

Show how technicians will inspect terminations, service cooling equipment and remove the largest replaceable component. Allow for doors, lifting equipment and the actual site access route.

Decide whether the transformer ships installed or separately. An installed unit needs structural and restraint checks for transport and lifting. Separate shipment needs a site installation method and space for positioning the equipment. Either arrangement requires inspection and agreed electrical checks before energization.

Procurement Inputs for Comparing Both Options

Provide:

• Single-line diagram, transformer type, rating, voltages, frequency and loading profile.
• Supplier losses, cooling method and permitted service conditions.
• Ambient temperature, altitude, dust, salt exposure, flood risk and noise criteria.
• Switchgear scope, fault levels, protection requirements and cable interfaces.
• Fire strategy, fluid-containment needs and governing installation requirements.
• Maintenance clearances, replacement route, transport limits and lifting constraints.
• Required drawings, tests, documentation and responsibilities for site works.

Request a comparison of installed cost, auxiliary demand, maintenance and downtime exposure. A smaller footprint does not necessarily produce a simpler installation.

Frequently Asked Questions

Does every transformer at a coastal site need a container?

No. Suitable outdoor equipment, corrosion protection and maintenance may meet the requirement. Compare that approach with an enclosure that also preserves cooling and access.

Can an existing shipping container become a transformer room?

Only after an engineering assessment of structure, ventilation, electrical clearances, access, fire requirements and equipment support. Physical space alone is insufficient.

Does containerization increase transformer capacity?

Containerization does not inherently increase capacity. Enclosure conditions can require derating unless the thermal design supports the required duty.

Does an integrated module arrive ready to energize?

Energization depends on the agreed supply boundary and completion of site connections, earthing, protection checks, transport inspections and commissioning.

Request a Defined Transformer Enclosure Scope From TLS

Send the single-line diagram, transformer datasheet, loss figures, site environment and transport constraints to sales@tls-containers.com. Ask TLS to review an enclosure or integrated power-module scope, including thermal duty, access, interfaces and testing. Confirm the proposed equipment, ratings and compliance requirements before procurement.

Further Reading

• TLS containerized power infrastructure
• Schneider Electric dry-type transformer installation instructions
• Schneider Electric transformer ventilation and heat dissipation guidance

Short Summary

A refrigerated container can regulate its internal air temperature within the selected system's operating limits. Depending on equipment, it may also manage fresh-air exchange, dehumidification or atmosphere. It cannot reverse damaged cargo, guarantee uniform product temperature despite blocked airflow, or replace a properly managed cold chain.

The Direct Answer

A refrigerated container controls the environment around cargo within a defined operating envelope. It can remove incoming and internally generated heat when the refrigeration system has sufficient capacity and airflow. Its ability to protect a shipment also depends on the product's starting condition, packaging, loading pattern, power supply and operating procedures.

The controller setpoint is a target for the refrigeration system. It is not proof that every product core is at that temperature. A complete specification defines the cargo requirement and how compliance will be measured.

Temperature Control Has a Defined Duty

The selected unit must suit the carrying temperature, outdoor conditions, cargo heat load and door-opening pattern. Insulation reduces heat transfer through the enclosure, while the refrigeration unit removes heat. Neither provides unlimited capacity.

Distinguish three temperatures: the controller setpoint, measured supply or return air, and the product itself. Their readings can differ during loading, defrost, recovery and changing operating conditions. Hapag-Lloyd explains the distinction between supply and return air and the factors that can affect reefer readings. Reefer monitoring guidance

Procurement should therefore state which measurement determines acceptance, where sensors are located, their required accuracy and how excursions are assessed. A display photograph gives much less evidence than a defined measurement and recording plan.

A Standard Reefer Is Primarily for Maintaining Prepared Cargo

Cargo should normally enter at the required carrying condition. A conventional transport reefer should not be assumed to function as a blast freezer or rapid product chiller. MSC's handling guidance calls for pre-cooled cargo and distinguishes airflow needs for chilled and frozen products. MSC reefer handling guidance

Warm cargo adds a product-cooling load that can take far longer to remove than cooling the surrounding air. Dense packaging can delay heat transfer from the core. Lowering the setpoint does not establish a safe or predictable cooling process and may expose outer products to unsuitable temperatures.

If product cooling is part of the duty, specify product mass, entry temperature, target core temperature and required time. Ask for a validated cooling process or equipment selected for that duty.

Pre-cooling the empty container is a separate operating decision. Coordinate it with the loading environment and carrier guidance: opening a cold container in warm, humid air can introduce moisture. Product preparation and loading procedures both matter.

Airflow Connects the Refrigeration Unit to the Cargo

The refrigeration machine can operate correctly while some cargo receives inadequate cooling. Packaging, pallet arrangement and loading height determine whether conditioned air reaches the load and returns to the unit.

For bottom-air delivery containers, keep the intended floor channels and return-air path clear and respect the marked loading limits. Follow commodity-specific loading instructions. Chilled produce may need air through ventilated packaging, while properly frozen loads use a different heat-removal strategy. MSC cargo loading guidance

For static storage with frequent picking, assess the actual usage pattern. Repeated door openings introduce heat and moisture, and partial loads can alter airflow. Discuss appropriate access arrangements and operating procedures as part of the design.

Humidity and Atmosphere Control Depend on the Equipment

Some refrigeration systems offer dehumidification, fresh-air adjustment or controlled-atmosphere functions. These capabilities must be specified and confirmed for the selected model. Carrier lists dehumidification, fresh-air exchange and remote monitoring among configurable refrigeration options. Carrier refrigeration options

Dehumidification does not imply the ability to add moisture or hold any requested relative humidity under all conditions. Fresh-air ventilation and controlled atmosphere are also different functions. Ventilation exchanges internal and outside air; controlled atmosphere requires equipment and procedures suited to specified gas conditions.

Mixed cargo needs particular care. Products may have incompatible temperature, moisture, odour or ventilation requirements. One setpoint cannot resolve those conflicts, and a single compartment should not be assumed to provide independent temperature zones.

A Reefer Cannot Reverse Damage or Replace Power Continuity

Refrigeration cannot restore freshness lost before loading, reverse freeze damage or remove contamination. Cargo acceptance should include its condition and relevant temperature history. Where an excursion occurs, the product owner needs an assessment appropriate to that product; returning the air to setpoint does not establish that the cargo is acceptable.

A reefer also requires a suitable energy supply. Define voltage, frequency, phase, connection, starting demand and available capacity. Include planned power interruptions during handling or transfer and arrange a backup strategy where the cargo requires it.

Insulation slows temperature change during an outage, but there is no universal safe holdover time. The outcome depends on the load, starting temperature, weather, door use and enclosure condition.

Remote monitoring can help identify alarms and operating changes. Its value depends on connectivity and someone acting on the information. Agree local recording, alarm recipients, escalation and recovery procedures. For cargo requiring formal qualification, define mapping, calibration and documentation separately from basic reefer operation.

Procurement Inputs for a Useful Reefer Enquiry

Provide:

• Product type, mass, packaging, pallet dimensions and compatibility requirements.
• Required carrying temperature, permitted excursions and acceptance measurement.
• Product entry temperature and any required product-cooling duty.
• Outdoor conditions, loading method, door-opening frequency and journey or storage duration.
• Available power, transfer interruptions and backup arrangements.
• Required ventilation, humidity or atmosphere functions.
• Monitoring, calibration, alarm response and qualification requirements.
• Dimensions, payload, handling method, destination and applicable certification needs.

Frequently Asked Questions

Does the displayed temperature prove my cargo is at setpoint?

No. Confirm what the sensor measures. Product temperatures require suitable probes or a validated relationship between the recorded air conditions and the load.

Can a reefer freeze warm goods quickly?

Do not assume it can. Product freezing requires a defined heat load and verified process. Standard transport service normally starts with cargo already prepared for carriage.

Does every refrigerated container control humidity?

No. Check the selected equipment, operating mode, adjustment range and cargo conditions. Dehumidification and humidification are different capabilities.

Can an offshore reefer certification prove cargo performance?

Structural and lifting certification addresses its stated scope. Cargo temperature performance requires separate refrigeration selection, operating procedures and agreed verification.

Discuss Your Refrigerated Container Duty With TLS

TLS supplies offshore refrigerated containers with project-specific refrigeration and container configurations. Its published range identifies refrigeration equipment from manufacturers including Daikin, Carrier and Thermo King. Confirm the selected unit, temperature duty, options and certification scope in the quotation. TLS reefer containers

Send your cargo details, entry and carrying temperatures, loading pattern, site conditions and power supply to sales@tls-containers.com. Ask for a proposal that states the operating envelope, included controls, monitoring scope and acceptance checks.

Further Reading

• TLS refrigerated container product scope
• MSC reefer cargo preparation and loading guidance
• Carrier configurable container refrigeration options
• Hapag-Lloyd reefer monitoring and air temperature guidance