A correctly configured double-wall enclosure may contribute to better thermoregulation, safety, and operational lifetime of a battery cabinet. The principle is to provide a controlled ventilation flow between the walls which would allow to dissipate heat from important elements without direct exposure of the battery system to the external environment. In case when battery cabinets are utilized outdoors, such design will provide extra protection against water, dust, solar radiation, and mechanical damage. Contact us for custom-designed battery cabinet enclosures.

What Is a Double Wall Battery Cabinet?

Double-wall battery cabinet includes an inner and outer enclosures where the volume between them forms an air cavity or thermal channel.

The inner wall is responsible for protecting the batteries, electrical parts, and controllers. Outer wall serves as an external environmental shield. Depending on specific application requirements, air cavity may be either natural or artificial ventilated.

Such approach is highly beneficial for outdoor energy storage systems where the cabinet has to work under conditions of internal heat production and fluctuations in external temperature.

How Ventilation Channel Works

The concept is fairly simple. The air enters the opening at the lower part of the outer enclosure, passes through the channel, takes the heat from the outer surface of the inner enclosure, and leaves through the upper opening.

It forms a steady airflow system.

The most common features of the passive ventilation system are as follows:

• Air intake opening at the bottom
• Ventilation channel itself
• Surface for heat transfer
• Opening for air at the top
• Protective louvers or screen
• Sealing and drainage devices

As the air in the channel becomes warmer, its density gets reduced and the air naturally flows up. It forms the chimney effect and enables to dissipate heat without using the fan.

Yet, the natural ventilation efficiency highly depends on the cabinet geometry, temperature difference, opening size, and air resistance.

Important Design Factors

1. Channel Width for Ventilation

The space between the inner and outer walls needs to be wide enough for constant flow of air but should not be too wide.

A narrow channel might result in high resistance to air flow. An excessively wide space will make the cabinet size larger and increase the amount of material used without providing more thermal benefits.

Thus, an ideal channel width should be chosen based on the following criteria:

• Size of the cabinet
• Amount of heat generated by the batteries
• Desired temperature range
• Direction of the air flow
• Ambient outdoor temperature
• Ventilation system used (forced/ passive)

2. Air Intake and Exhaust Opening Location

The location of ventilation holes affects the system performance greatly.

In case of natural ventilation, the intake hole is usually placed near the bottom part, whereas the exhaust opening is located closer to the top of the enclosure. It enables the rising heated air to flow up the vertical ventilation channel.

Ventilation openings must be made in a way which minimizes the chance for the rain to get inside the cabinet.

Louvers may be tilted downwards or installed behind protective constructions, while drainage routes must be provided so that the rainwater which gets into the outer ventilation area cannot get to the battery compartment.

3. Minimizing the Risk of Short Circuit Airflow

Another frequent mistake during design is that incoming air flows straight into the exhaust without flowing past the heat transfer surfaces.

The ventilation channel must promote the airflow over the cooled elements.

It may be achieved by placing internal partitions, guide plates, and appropriately placed holes.

From the engineering point of view, ventilation holes alone will not suffice – the whole airflow passage needs to be designed.

Passive Ventilation vs Forced Ventilation

There can be either passive ventilation or forced ventilation in double wall battery cabinets.

Passive ventilation has relatively simple construction and no need for fans and power. This option is appropriate for applications with moderate heat load and temperatures that are in acceptable range.

Forced ventilation implies the usage of fans. This type of ventilation gives more control and may be applicable to higher power battery systems.

However, forced ventilation has additional challenges connected with fans, such as:

• Fan breakdowns
• Dust collection
• Noise
• Energy consumption
• Maintenance
• IP rating

Hybrid solution may be applied to some battery systems. Double wall construction gives basic level of thermal protection while fans start operating when the internal temperature becomes equal to the set value.

Double Wall Construction and Outdoor Protection

Heat management is not the only motivation for using a double-wall enclosure.

An outer wall may also help shield the internal cabinet from the effects of sunlight directly. In intense sunlight conditions, the exterior metal surface may get much warmer than the surrounding atmosphere. The ventilation gap between walls ensures that the heat does not get passed directly into the battery bay.

A double-wall structure may also be utilized to provide protection against:

• Rain
• Dust
• UV radiation
• Windborne particles
• Impact
• Corrosion

The level of protection provided will depend on the construction of the cabinet as a whole.

Materials and Structure

The outer and inner walls can be constructed from materials like galvanized steel, stainless steel, or aluminum depending on the application.

In the case of outdoor battery enclosures, the surface treatment of these structures is crucial as well. Using powder coating, anti-corrosive treatment, and proper sealants will increase the lifespan of the enclosure.

The structure must have enough mechanical resistance while providing necessary ventilation.

Cable connections, doors, hinges, locking system, and ventilation points must be taken into account from the early stage of designing. The inclusion of ventilation points after the structure has been established may lead to some compromise points.

Customized Design for Battery Cabinet Enclosure

Battery cabinets are not necessarily standardized products. There will be diverse requirements on the structure of the enclosure for different types of battery cells, BMS design, PCS equipment, cooling system, and environments.

At HighJoule, custom design for battery cabinet enclosures can be provided based on the needs of the project. This includes the size of the cabinet, double walls, ventilation channel design, inlet and outlet locations of air, internal mounting structure, doors, cable entry, and exterior finishing.