The benefits of the hydraulically driven fan depend heavily on the ambient temperature where the machine operates. "The cooler the ambient temperature, the more benefit the hydraulically driven fan provides," says Hindman.
Sean McCurdy, cooling system engineer for large wheel loaders, Caterpillar, explains, "Technically, a hydraulic fan is less efficient at the same fan speed than a mechanically driven one. The fuel savings come because a hydraulic fan can be controlled to a lower speed when full fan speed is not required for cooling. Although cooling performance is directly proportional to fan speed, the fan power draw is cubic. Thus, being able to slow the fan down quickly saves a significant amount of fuel."
"The variable fan can reduce fan power consumption more than 90%, depending on the fan speed and fluid temperatures," adds Lucas Knapp, performance controls engineer for large wheel loaders, Caterpillar. "This translates to an overall machine power reduction of 7.7% at rated speed. At max fan speed, the fan uses slightly more power than the belt-driven fan. So over the life of the machine, a typical customer might see a 1% to 6% fuel savings with a hydraulic fan."
A hydraulic fan also reduces noise levels, prevents over cooling in cold weather and provides adequate cooling at high altitudes.
The cooler layout can play a role in cooling system efficiency, as well. For instance, John Deere designed its Quad-Cool system so that minimal recirculated air (warm air previously exhausted by the fan) finds its way back through the cooling package. "Continuously pulling in fresh, cool air through the cooling package keeps the fan speed lower and reduces fuel burn," says Hindman.
Self-cleaning capability also enhances operation. "Doosan has maximized efficiency of our cooler package by its design, with more efficient material and a self-cleaning feature (reversible fan)," says Ellis. "A well-maintained cooler group is key to efficiency."
But fuel economy is only one consideration when designing the cooling system. "In general, cooling design is a balance between three desires: cost, fan sound/power and system size. One can trade off any factor to improve another," says McCurdy.
"As for size/fan speed, we have strived for a balance that provides the operator the best visibility as compared to cooling package size," he continues. "Cat utilizes advanced software to study the air flow paths through the cooling package to minimize inefficient recirculation effects that would necessitate higher fan speed."
Beyond fuel costs
Of course, fuel efficiency is only a part of the equation. You also need to compare overall operating costs of the machine.
"Design of the wheel loader is key, but there must be a balance between fuel efficiency and performance," Ellis emphasizes. "A less fuel-efficient machine... may have higher production, so lower operating costs."