Powering fridge engines

Some operators are moving to a single-engine solution to power the vehicle and chill the load, finds Steve Banner

Gone are the days when donkey engines used to power fridge engines on temperature-controlled trailers could be run on cheap red diesel. Nowadays their tanks have to be filled with pricey white diesel instead, a change which is imposing an extra cost burden on hard-pressed transport fleets.

Nor is it winning them any green kudos. No matter what colour it is, burning diesel produces NOx, particulate and CO2 emissions; bad news for businesses seeking to minimise their environmental impact.

Furthermore, diesel engines are noisy and are unlikely to make operators popular with consumers if they are making out-of-hours deliveries to premises with homes and slumbering home-owners in the vicinity.

One option is to do away with the donkey engine completely and fit an all-electric fridge unit instead. However, scrapping a diesel-fired unit with many working hours left in it and shouldering the added cost of installing an electric package instead is unlikely to be an appealing option so far as fleets operating on tight profit margins are concerned.

There is another route to consider. Keep the donkey engine as a back-up, and use the tractor unit’s engine to drive the fridge instead.


It is an approach that has long been advocated by Swedish company Hultsteins which currently promotes it under the Ecogen CostSaver banner. “Opting for it can cut CO2 emissions by as much as 75% to 90% and virtually eliminate particulate and NOx emissions which would normally be pumped out by a trailer fridge because it does not have any filtration or particulate capture,” says Hultsteins’ UK managing director, Graham Usher.

“Bear in mind that a standard diesel trailer fridge unit is Euro II or thereabouts,” he adds.

Retrofittable, Ecogen uses a power take-off (PTO) from the truck’s engine to power a hydraulic pump used to drive a generator that delivers a constant three-phase 400V at 50Hz. Employing a five-pin plug, the generator can be connected to the motor of virtually every make of fridge unit with an electric stand-by.

If a trailer with a diesel-fired fridge is coupled to a tractor without Ecogen, then it can still function. All the operator needs to do is fill the diesel tank, and start the engine.

“Ecogen can also operate at 480V/60Hz which gives you a 10% to 12% increase in cooling capacity,” says Usher.

Ecogen is designed for a 12-year working life, he says. Maintenance requirements are modest, he adds, with only one service a year which mainly involves either a filter or an oil and filter change, and the capital cost of the unit is around £16,000.

Cutting emissions by fitting a purely electric fridge costs at least £45,000, he points out – and if a customer does not wish to purchase Ecogen outright, then it can be rented for around £13 a day.

Ecogen weighs from 190kg to 240kg, depending on the specifications, he says. “You can use it to run an electric fridge if you wish to,” Usher adds.


Run a fridge off a PTO and the truck will burn more fuel. The consumption penalty is minimal, however, he argues. “You’re typically talking about a 0.1mpg to 0.2mpg increase,” he says.

A 6x2 tractor covering 100,000 miles annually at an average 11mpg might consume an extra 572 litres, Hultsteins contends. Bear in mind though, it adds, that a diesel-powered fridge on a trailer operating for 2,500 hours annually can burn a whopping 7,500 litres of fuel and emit almost 20 tonnes of CO2 a year.

Ecogen does not run constantly, says Usher. It only kicks in when the fridge unit demands power in order to keep the trailer’s cargo at the required temperature.

Ecogen’s applications are not limited to diesel engines. In a repeat order, Southampton company Ferytrans has specified it on six new Scania tractor units that run on compressed natural gas.

Says managing director, Feri Lazar: “Fitting Ecogen means we’ve reduced our CO2 emissions by around 17 tonnes per vehicle combination per year.” Ferytrans bought its Ecogens, and Lazar anticipates a return on the investment in around 18 months.

Fitting a PTO costs approximately £1,200 and can be a challenge with some makes and models of tractor, Usher warns.

Scanias, Volvos and Renaults all have the necessary timing gear in their engines, he says, so a PTO can be bolted on easily. With other brands, a PTO may have to be specified when the truck is ordered new; retrofitting is likely to involve an extended workshop visit.


Hultsteins is not the only company to pursue this approach to fridge unit propulsion.

Carrier Transicold offers a rival PTO-powered electro-hydraulic three-phase package called Eco-Drive, starting at 400V/50Hz.

“It can be fitted by a Carrier technician in around a day and a half,” says Carrier Transicold managing director, UK and northern Europe, Scott Dargan.

Thermo King uses a different approach to achieve the same end. Its system features an alternator driven off the engine’s crankshaft plus an inverter coupled to a DC-DC transformer to deliver a constant three-phase voltage.

“The tractor’s fuel usage will increase slightly, perhaps by 1.5% to 2%, but you’re not using a separate diesel engine to run the fridge unit,” points out Thermo King’s UK sales manager, Stephen Williams. “We acquired this technology when we bought Frigoblock in 2016.”

Both air- and water-cooled alternators are available, with 400V or 500V power outputs.

Like everything else, the cost is volume related. An operator that wants to equip a fleet of 50 tractor units with what Thermo King has to offer might pay approximately £14,000 a vehicle.

A drawback of the aforementioned approaches is what happens if the tractor unit and laden trailer have to be parked up overnight in a location with no access to an electric standby.

In those circumstances the fridge unit’s diesel engine will have to be fired up to keep it running, or the tractor unit’s engine will have to be left on tick-over to provide the necessary power. Neither approach is environmentally friendly and results in more fuel being burned.

The alternative is to run the fridge off an onboard back-up battery, which Hultsteins does offer, but as this adds both cost and weight, anybody relying on an engine-driven system might be best advised to employ it on routes that do not require the driver to spend the night in a lay-by miles from the nearest stand-by.

“The technology doesn’t suit everybody,” Williams concludes.


Carrier Transicold’s PTO-driven Eco-Drive is offered with seven different options depending on the power required and the space available on the tractor unit.

Dargan says: “The most important advantage gained by connecting Eco-Drive to a PTO rather than relying on an alternator-driven power source is that the system operates totally independently of the truck’s engine speed, ensuring that 100% refrigeration capacity is always available,” he contends.

None of the truck’s power output is wasted, he says. “Thanks to Eco-Drive’s variable displacement pump, energy is harvested from wasted engine over-run, tick-over and braking,” he comments.

What if the tractor unit is battery-electric?

“We’ve developed a power box,” replies Dargan. “Functioning like an electronic power take-off, it takes energy from the vehicle’s driveline battery and converts it to the necessary AC and frequency required to power temperature-controlled systems.

“The power box is capable of delivering more than 95% efficiency when converting the energy required from the driveline, helping to ensure negligible impact on driving performance and range,” he says.

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