The need for reliable engine-off cabin cooling in off-highway machinery

  • 13-May-2016 01:47 EDT
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Polar Cab TS engine-off cabin cooling system features a patented storage core with a series of aluminum micro-channels routing liquid refrigerant around a graphite honeycomb substrate that is impregnated with water, and is capable of storing cold energy at an extremely high efficiency.

Increasingly stringent anti-idling laws continue to exert pressure on the off-highway industry to minimize the release of CO2 emissions and diesel particulate matter into the environment. However, in the face of tightening regulations, the evolution of larger loading and transport machinery with bigger payload capacities presents challenges to emissions-reduction goals.

Larger equipment results in longer loading cycle intervals, often requiring machines to sit and wait for extended periods of time. Large-capacity equipment in cue for both loading and weighing can create an environment where machines are idling their engines during the heat of the day, and additional prolonged engine idling periods such as lunch breaks most often occur when the sun is at its apex.

When not in use, equipment cabins and their internal surfaces can heat up quickly, creating uncomfortable conditions for the operator. Cabs on construction and mining equipment are designed for maximum visibility and utility, incorporating large glass surfaces and metal with low insulation ratings.

According to a “Study of Excessive Temperatures in Enclosed Vehicles” conducted by the Department of Geosciences at San Francisco State University, temperatures can rise quickly in an enclosed vehicle. Study author Jan Null found that the average temperature rise in an enclosed vehicle on a cloud-free day was 10.6°C (19°F) in the first 10 min. After 20 min the average rise was 16.1°C (29°F). At the 30-min mark the average rise was 18.3°C (33°F). The average rise after 60 min was 24.6°C (44°F). Null’s study shows that interior vehicle temperatures can exceed 50°C (122°F).

NASA conducted touch temperature tests with heated aluminum plates and concluded that pain onset occurred at a temperature of 45°C (113°F).

To avoid pain and injury, operators often employ makeshift methods to protect their skin from exposure to high-temperature surfaces, such as wearing long sleeves even in summer, or by draping fabric over hot surfaces. Full-sun load conditions can lead to operator discomfort, affecting operator safety and productivity until cabin and surface temperatures cool to acceptable temperatures.

Cabin cooling is a short duration proposition

Field testing has shown that cabin cooling intervals ranging from 5 to 30 min address the majority of periodic cooling situations encountered in off-highway applications. Assuming a machine’s air-conditioning system has been cooling the cabin during operation, any engine-off cooling system should be primarily designed to maintain a comfortable temperature within the cabin for relatively short durations of time and only until the operator restarts the engine.

Advanced cold energy storage and battery-driven technologies present the off-highway equipment industry with two reliable, economic, effective and environmentally friendly alternatives for cabin cooling.

Webasto has developed two different cabin-cooling technologies for the off-highway industry. Although the Polar Cab TS engine-off cabin cooling system and the Polar Cab ES engine-off battery-driven electric cooling system utilize distinctly separate technologies, both efficiently achieve engine-off cabin cooling. Due to the physical dimensions of the Polar Cab TS, it is favored for machines greater than 400 hp (298 kW), while the Polar Cab ES is well suited for a much broader range of machines and power classes.

In designing both its engine-off cooling technologies, Webasto had to overcome engineering challenges including finding the right balance between performance and size/volume of the system. Engineers committed to provide the marketplace with solutions that are highly adaptable and easy to install on a variety of machine platforms.

Polar Cab TS and ES systems

Webasto’s Polar Cab TS engine-off cabin cooling system is designed for larger equipment and has a cooling capacity of 1.3 kW (4450 BTU/h). The system features a patented storage core with a series of aluminum micro-channels routing liquid refrigerant around a graphite honeycomb substrate that is impregnated with water. The system’s graphite substrate is capable of storing cold energy at an extremely high efficiency.

During engine-off intervals, the system’s cold energy is transferred to the cab for on-demand cooling via a compact air handler. Use of the Polar Cab TS will result in enhanced operator comfort, fuel savings and a significant reduction in non-productive engine hours via reduced engine idling.

The system can be fully charged in 3 h and efficiently maintains cold stored energy with a very low static discharge rate of 10% per 8-h period at 54.4°C (130°F) ambient temperature. Field testing and climate chamber tests have substantiated 90 min of engine-off cooling performance at 43.3°C (110°F) ambient temperature, under full sun load.

Webasto offers the Polar Cab TS as an aftermarket kit that includes the thermo storage core, electrical compressor (24V), condenser with fan, air handler, wire harness and installation hardware. The Polar Cab TS does not require additional batteries, which reduces the long-term cost of ownership.

The Polar Cab ES battery-driven electric cooling system is suitable for all machines with an enclosed cab. The system offers a cooling capacity of up to 7000 BTU/h, consumes less than 40 A of battery power during normal use cycles and includes a compact 24-V variable-speed electric compressor, with no additional batteries required in most applications. The Polar Cab ES can be installed with one of two different aftermarket kit configurations. The Oakland kit is designed for ceiling-mounted evaporator applications, while the Osaka kit is engineered for floor-mounted evaporator applications.

Both Oakland and Osaka kits include refrigerant lines and fittings, mounting hardware, control unit and wiring harness. Additional batteries or upgrade of existing batteries may be required based on duty cycle requirements. A low voltage disconnect set at 24.1 protects battery levels from deep discharge.

R&D aimed at future performance and returns

Prior to its initial release in 2015, Polar Cab TS technology underwent more than two years of development and testing. The process included extensive customer field-testing under extreme climatic conditions of high humidity, high heat, dust and dirt. Testing was performed on machines in the southern regions of CA, AZ, TX, MS, NC, MI and AL. Webasto has been selling the BlueCool brand version of its thermal storage technology to the on-highway truck market for more than 10 years.

System benefits for both the Polar Cab TS engine-off cabin cooling system and the Polar Cab ES engine-off battery driven electric cooling system include decreased frequency of service and maintenance intervals and increased DPF (diesel particulate filter) longevity. Both engine-off cabin cooling systems can help maximize warranties, reduce lease rates and increase machine resale values.

Don Kanneth, Director of Off-Highway, Webasto Thermo & Comfort North America, Inc., wrote this article for Off-Highway Engineering as part of the annual Executive Viewpoints series appearing in the June 2016 issue.

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