The RM1 CTMS represents Grayson’s most advanced and highest capacity thermal management solution for next-generation electric buses and coaches.

Built for high ambient conditions and designed to meet the latest TfL 2.6 specification, the RM1 manages passenger and drier climate comfort, battery thermal management, and power electronics and traction motor cooling in one intelligent, rooftop-mounted unit.

Delivering up to 40 kW of heating and cooling, it combines a reversible heat pump, active and passive battery cooling, integrated high-voltage PTC water heating, and waste-heat recovery to achieve superior efficiency and comfort.

Grayson’s proprietary CAN-based automatic thermal control system dynamically regulates multiple subsystems for precise temperature control, while liquid-to-air and air-to-air heat exchange ensures robust performance in real-world, high-demand environments.

With 900V DC compatibility, R407C or R454C refrigerant compatibility, and a modular design to suit different requirements for different markets, the RM1 is purpose-built to deliver high efficiency, reliability, and compliance for electric buses worldwide.

Our products include a range of features designed to support efficient operation and straightforward system integration.

• High-Capacity Thermal Management: Delivers up to 40 kW heating and cooling to maintain passenger and component comfort in hot and high-load environments.
• Complete Multi-Loop Integration: Combines battery thermal management, driver/passenger HVAC, and power electronics cooling within a single intelligent module.
• Reversible Heat Pump with Integrated Water Heating: Features an integrated high-voltage PTC water heater and liquid heat pump loop for efficient cabin and floor heating.
• TfL 2.6 Compliance: Designed and tested to meet the Transport for London 2.6 specification, ensuring readiness for regulatory and market requirements.
• Active and Passive Battery Cooling: Maintains battery pack temperature within safe limits, improving energy efficiency, safety, and service life.
• Grayson Intelligent Thermal Controller: Developed and validated by Grayson for precision regulation.
• CAN J1939 Communication: Seamless integration with pumps, heaters, and sensors.
• Dynamic Control Software: Continuously adjusts operation to match vehicle thermal demands.
• High-Voltage Compatibility: up to 900V DC, meeting the needs of next-generation electric platforms.
• Low-GWP Refrigerant Option: Compatible with R407C or R454C refrigerants, supporting reduced environmental impact while maintaining performance.
• Suitable for 8 m – 24 m Bus Lengths

Each technical component contributes to stable performance and dependable operation in service.

• Nominal Cooling Capacity: 36kW @ 40°C
• Maximum Cooling Capacity: 40kW @ 40°C
• Nominal Heating Capacity (Heat Pump): 30kW @ 0°C
• Maximum Heating Capacity (Heat Pump): 40kW
• Operating Temperature: -20°C to +45°C
• High Voltage Range: 540–900V DC (Nominal 800V)
• Low Voltage Range: 18–32V DC (Nominal 28V)
• Refrigerant: R407C / R454C
• Dimensions (L × W × H): 2800 × 2000 × 365 mm
• Weight: 340 kg
• Communication: CAN protocol: J1939
• Ingress protection: IP67 (controller box)