Testing the performance of EV batteries requires test chambers built to precise environmental conditions that can easily be changed and monitored. MAHLE Powertrain, an engineering and consultancy partner to the automotive industry, approached Ultra Refrigeration to design, build, and install three new environmental test chambers for testing EV batteries at their facility in Northampton. 

The finalised test chambers delivered a temperature range of -40°C to +60°C with the 100°C temperature change achieved in 30 minutes. The chambers use highly customised PLC software and precision controls that communicate with the existing building management system.

The Project

MAHLE Powertrain supports the development of EV technologies which includes the assembly and testing of battery modules and full-size battery packs. To add three new test chambers to their existing facility in Northampton, they approached Ultra Refrigeration who deliver specialised cooling solutions for advanced testing applications.

The three independently driven environmental test chambers had specific requirements to ensure accurate and reliable test conditions:

  • Utilising a low GWP refrigerant
  • A temperature range of -40 to +60°C
  • Temperature precision of at least +/-0.2°C
  • The option to change the temperature by 100°C within 30 minutes for rapid shock-tests
  • New control software to interface with MAHLE Powertrain’s control system
  • Pressure-tight conditions
The Solution 
Utilising a low GWP refrigerant

Due to the upcoming phase-out and environmental impact of f-gas refrigerants, MAHLE Powertrain specified the use of a refrigerant with a low global warming potential (GWP). CO2 was selected as the refrigerant in this case as it will be available for the foreseeable future.

Providing a temperature range of -40°C to +60°C

Selecting CO2 as the refrigerant ensured that the environmental impact of the system will be kept to a minimum. However, the specifications included enabling a temperature of -40°C which had the potential to cause issues in the system due to the CO2’s triple point of -56°C.

To enable temperatures of -40°C, CO2 needs to be evaporated near -50°C, which is edging very closely to its triple point. Strategically placed sensors and bespoke control software enabled precise pressure management to ensure a safe operation.

The bespoke control software was created using Resource Data Management’s (RDM’s) HVACR PLC controllers: Intuitive TDB. Intuitive TDB devices provide flexible control capabilities and feature RDM’s PLC software TDB. TDB software enables users to write customised PLC software to suit niche control requirements which would not be possible with standard controllers.

Apart from pressure management, safety measures were also built into the software to ensure the temperature does not sink to the triple point of CO2.

Each chamber has a refrigeration plant which consists of four reciprocating compressors. The compressors operate either in pairs at different temperature ranges or together as an externally compounded boost system to achieve -40°C with inter-stage cooling.

An electric heater bank, mounted close to the evaporator, supplies the heating for the chambers which needs to rise to 60°C. RDM’s Intuitive TDB devices control the heating elements via PWM outputs. These can quickly pulse the heaters on and off to provide almost stepless control. A defrost mechanism is not needed as the chambers use dehumidified air.

To accurately control the temperature at low load conditions, close to the compressors’ minimum speed capabilities, the compressors are run at a comfortable speed instead and heat is added using the heating elements. The heating and cooling are thereby ‘feathered’ with RDM’s Intuitive controllers maintaining temperature accuracy.

The airflow around the chamber is controlled using volumetric fan controls. These automatically adjust the AHU fan to overcome the air resistance of any object that might be in the test cell.

Temperature precision of at least +/-0.2°C

MAHLE Powertrain specified a temperature precision of at least +/-0.2°C. To achieve this accuracy, Ultra Refrigeration wrote new code using LUA software, a feature of RDM’s PLC software TDB, to control the speed of the compressors individually.

Changing the temperature by 100°C in 30 minutes

It is required to test EV batteries while simulating an extreme change in temperatures. The system of these newly built test chambers can change the temperature by 100°C in only 30 minutes. The warm air from the humidifiers is used to achieve this quick temperature change.

Connecting the new control system to the existing system

Having two separate control systems is not just impractical and time-consuming to maintain, it also restricts control functions and decreases the site’s efficiency. It was therefore important that the newly installed system can link to the existing one.

RDM’s controllers were selected for the new chambers as they are ideally suited for communicating with third-party systems because they are based on open protocols. The refrigeration, heating, and ventilation system of each of the three new chambers is controlled using RDM’s HVAC controller range, Intuitive.

The Intuitive controllers from each chamber are linked to RDM’s control and monitoring system front-end DMTouch. Both DMTouch and Intuitive controllers can communicate via open protocols such as BACnet, Modbus, LonWorks, XML, and Web Services.

The existing control system and the new one communicate via BACnet. This allows integrating the existing dehumidifier into the overall control strategy which helps changing the temperature by 100°C temperature in 30 minutes.

Pressure tight conditions

Due to the temperature range in the sealed chambers, Ultra Refrigeration designed the system to deal with internal pressure changes. Release valves can relieve high pressure while low pressure is counteracted with a more intricate system. The PLC algorithm communicates the demand for air from the on-site dehumidifier based on the low pressure in the chamber.


The finalised test chambers feature precision control to perfectly manage their internal temperatures to the required level of +/-0.2°C and allow quick temperature changes. RDM’s open protocol option enables the new and old HVAC and refrigeration control systems to communicate, creating a streamlined system with extensive capabilities. Utilising their years of experience, Ultra Refrigeration delivered an innovative solution that features highly customised control software that perfectly suits this project and an intricate design which together create a specialised solution for this advanced testing application.

Ultra Refrigeration 

Ultra Refrigeration offer the design and implementation of refrigeration solutions for special applications including ultra-low temperature, close control and humidity regulation. They provide services to many industries, including the catering, leisure and food retail trades.

“We were impressed with Ultra Refrigeration’s ability to deliver this complex and demanding project. Their ability to write bespoke software for the control system, their refrigeration expertise and their CAD design capabilities enabled a successful solution to be designed, built and installed. We particularly appreciated Ultra’s willingness to look at innovative ways of solving problems to deliver the precision temperature control we demanded.”

Derek Wise, Chief Engineer Build and Test, MAHLE Powertrain