A field comparison of traditional mechanical fans to new electric fan technology.
In the late 1970s, electric fan technology for engine cooling was introduced to the automotive racing and performance industries. Compared to traditional belt-driven fans, the benefits of electric fans for cooling performance and efficiency became evident. They were quickly adopted as the standard across the entire automotive industry. Unfortunately, the medium/heavy-duty truck market has not been able to change as quickly due to a lack of durable fan technology. Cab-over refuse truck chassis have generally come standard with mechanically-driven fans for their primary engine cooling because no electric fan has been able to meet the intense cooling needs of these vehicles. That has recently changed as new technology has allowed durable, highly efficient, multi-fan electric systems to become available to the market with great results.
To better understand the true difference between mechanical and electric fan systems, within refuse specifically, an ongoing study is being conducted by a team of engineers.1 They have been investigating how electric fan system technology could eliminate many of the problems associated with mechanical fans. Starting in 2015, the study has included multiple refuse properties across the U.S. and logged more than 50,000 hours of field operation. The results seen throughout testing have proven that refuse fleets can benefit from adopting electric engine cooling, even more so than the automotive world. Haulers and OEMs are becoming aware of this and, in the coming years, electric engine cooling can be expected to become more prevalent.
Mechanical Versus Electric Basics
Traditionally, mechanical fans have drive systems that include pneumatic or viscus clutches, and hydraulic drives powering a single large fan. Most are coupled to engine speed as on/off devices without the capability of reversal or variable speed operation. Engine manufacturers require that cooling systems are designed to cool an engine in a worst case scenario of continuous peak power with outdoor temperatures in excess of 100°F. For an on/off mechanical fan, this means an engine is getting “all-or-nothing” cooling, and any time the fan is engaged it is cooling as if the vehicle is climbing a long grade while fully loaded in the Southwestern desert. In the vast majority of day-to-day operations only a very small fraction of this cooling is required. Using far more power than needed creates a parasitic draw from the engine, resulting in reduced horsepower, poor fuel economy and increased maintenance among other issues.
With an array of four to seven smaller durable fans, electric engine cooling systems are able to control fan speed variably and independently from the engine (see Figure 1). Each fan is individually controlled by a system controller. They respond to coolant and intake manifold temperatures from the vehicle’s J1939 communication link and AC system pressure. The fans will only run as fast as necessary to maintain control inputs at optimized temperatures, and are able to respond individually to those inputs. For example, if two fans are covering the AC condenser, only those two fans will run when elevated AC system pressure requires airflow through the condenser.
While engaged, a mechanical fan bogs down a truck’s engine, consuming around 20 to 30+ hp at peak power. Even when a mechanical fan is not in use, it still pulls 1 or more hp due to the drag of the clutch system and belt coupling it to the engine. Using this power on cooling when it is not necessary pulls performance from other places it could be used during normal routes.
Electric fan systems offer significant improvements to this thanks to variable speed and individual fan control. If a route requires minimal cooling then it will only use what is needed. When an electric system is off, it is completely off, drawing zero hp. An instance of this was recorded when two Peterbilt 520 cab-over trucks (with PACCAR MX-11 engines) in Phoenix, AZ were tracked in the hot summer months. The results were surprising. In day-to-day duty cycles, the electric cooling fans consumed less than 1 hp for 85 percent of operation and only drew 5 hp at peak. It is a significant improvement compared to the peak power usage that is typically consumed by mechanical systems.
Fuel consumption is a significant expense that comes from the unnecessary power usage of a mechanical fan. When more power is being used than needed, it creates excess fuel usage that can potentially cost fleets thousands of dollars each year on a single truck.
The reduced power consumption from electric fans results in easily measurable improvements in fuel economy. In a controlled side-by-side test of day-to-day operation, six refuse vehicles were outfitted with electric engine cooling to compare their performance to traditional mechanical cooling. Measured fuel economy improvements ranged from 5 to 18 percent with an average of 8 percent savings. This translates to roughly 600 gallons of fuel saved annually per vehicle.
Fan noise is also seen as an issue with mechanical systems, particularly for residential pickup when the air conditioning is running. The AC condenser needs airflow, but if a truck stops there is no ram air. Therefore, the mechanical fan needs to engage. When the truck starts moving again, the engine speed ramps up and so does the fan. This is the tell-tale ‘roar’ that many people are used to when they hear a refuse truck moving from stop to stop.
Since electric systems are not tied to the engine, fans can maintain optimal speeds whether or not the vehicle is stopped, accelerating or decelerating. This means there are no power spikes making for much quieter operation. When fan noise comparisons have been done, electric fans systems are inaudible over engine noise 99 percent of the time.
Excessive dirt and debris get sucked into the radiator of mechanical systems regularly which requires frequent cleaning. As debris blocks the radiator, it takes more and more peak power for an equal amount of cooling. If regular cleaning is not done, the radiator can become so clogged that air cannot get through causing overheating, which can bring down a vehicle. This clogging is caused because mechanical fans pull debris with the air through the radiator like a giant vacuum. The frequent need for preventive maintenance on the radiator can add to maintenance costs and increase downtime.
Electric fan cooling addresses this by offering fully reversible fans to prevent radiator clogging. These systems come with a simple fan reversal button located in the cab that allows the driver to back flush the radiator several times per day, or when exiting an area known to be particularly dirty (i.e. landfills). In addition to the reversible fan benefits, reduced fan speed with electric systems lessens the amount of debris to the radiator in the first place. A Mack MRU in Milwaukee, WI with a history of overheating due to a plugged radiator was selected to study this concept. Prior to the system’s installation, the radiator was professionally boiled clean. After one year in the field only using the fan reversal feature of the electric system, the radiator was removed for inspection and found to be virtually free of debris (see Figures 2 and 3, page 34).
A mechanical fan’s on/off nature makes it impossible to control coolant temperature as precisely as a variable-speed system, which can cause accelerated engine wear due to extreme temperature spikes. These spikes, also known as thermal cycling, can potentially cause the need for more active DPF regeneration, as well as accelerate wear on hoses and the engine overall. Electric fan systems have the ability to maintain more precise engine temperatures, within plus or minus 3°F. This more precise control means that thermal cycling is significantly reduced, potentially reducing active regenerations and extending the life of the engine and its components.
Clutches used to drive a mechanical fan degrade over time and usually fail within the useful life of a vehicle. Clutch failures can cause extensive damage, possibly resulting in a destroyed radiator, fan and fan shroud, in addition to the clutch. When this happens in the field, the vehicle must be towed back to the depot and can be down for several days if all of the parts are not readily available.
In electric systems, using multiple fans creates a redundancy that solves this clutch issue. If an electric fan fails there is no damage and the remaining fans continue to operate normally, allowing the route to be completed. This was exemplified by a Peterbilt 320 in Miami, FL. An electrical failure caused two of the five fans to stop working. However, the vehicle continued to operate normally with the remaining three fans for several days until replacement parts arrived. The parts were replaced, restoring full functionality of the cooling system with zero down time for that vehicle.
Making Electric Engine Cooling the New Standard
As electric fan systems are being installed, tested and operated regularly, feedback from the field has continued to be positive and abundant. Maintenance managers appreciate the reduction in vehicle down time and preventive maintenance on the cooling system. Technicians enjoy the fact that they no longer need to disassemble a mechanical fan to simply replace a serpentine belt, and rave at the overall openness the electric cooling system provides in the engine compartment. Drivers comment on how they can easily feel more available power to the wheels when accelerating or going uphill. And lastly, fleet managers embrace the fuel economy savings that create a short return-on-investment.
Refuse, an industry traditionally plagued by overheating and vehicle down time, can now eliminate many of the problems caused by mechanical systems, and provide additional benefits. Because of this, the expectation is that more private haulers and municipalities will retrofit their current fleets. Some have already begun moving forward with specifying electric cooling as a requirement on their future chassis orders. Electric cooling has also caught the attention of OEMs who are working to offer it as early as 2019. With an average fuel savings of 8 percent, cleaner radiators eliminating preventative maintenance, and less down time, this new technology is motivating the refuse industry to make electric engine cooling the new standard. | WA
The content of this article was contributed and combined by project engineers with EMP’s Research & Development division based in Escanaba, MI. EMP is an engineering and manufacturing leader in advanced thermal management technologies for the heavy-duty market. It has been a manufacturing leader since 1991, and introduced electric cooling to the Transit market in 2006. Since then, EMP’s Mini-Hybrid system has become the standard among transit OEMs and aftermarket applications. This system is now being used among refuse properties with promising results. For more information, contact Todd Kangas at (906) 789-7497, e-mail firstname.lastname@example.org or visit www.emp-corp.com/refuse.
1. Study performed by EMP (Engineered Machined Products, Inc) Research and Development division