Test Drive: Kenworth Clean Power

Kenworth's Clean Power System is designed to provide managed comfort when the driver needs it.

March 2008, - Test Drives

by Steve Sturgess, Executive Editor

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However, I had no such difficulty with the climate control overnight in the T660. The simple control panel in the sleeper requires that you tell the system whether you'll need heat or cold, and then you set the level with a rotary switch. 

If I were to be picky, I'd say a settable thermostat would be even simpler for the driver and make the overnight experience more like a very comfortable motel room, but the system does what is required. The important thing about the Clean Power climate control is that it is a managed system: It is designed to be managed so it can provide climate comfort for the time the driver needs it, and that can be up to 10.5 hours at an ambient 95 degrees.

The T660 is a very comfortable sleeper and, as part of the Clean Power option, the excellent overhead and reading lighting features LCD light sources to conserve battery power. Using the pull-out table and the 110-volt supply, I caught up on some work on the laptop, then read before turning in for a comfortable night. Because it was cool and I had minimal bedding I set the heating with the diesel furnace occasionally kicking in, maybe once every couple of hours, though I wasn't particularly aware of it.

The rest area is used by trucks loaded with apples from orchards that surround the region. They began to make their appearance in the small hours, idling alongside and showing what a intrusion idling trucks can be. I believe when we finally make the transition to a truck population that has similar climate systems to Clean Power, drivers will enjoy a much less disturbed sleep and better rest.

Day Two

The truck was due back in the Kenworth plant in Renton by midday, but the route back was only 165 miles, so an 8:30 a.m. start saw me jogging up scenic Route 243 along the Columbia River to pick up I-90 again and cross the Columbia at Vantage. Down through here, the air discs provided sure stopping even on longer grades.

The drive back in to the greater Seattle area was uneventful as the Clean Power system recharged what little of the resources I had used overnight. According to Kenworth, the 185-amp alternator that is part of the system, plus the a/c compressor and thermal storage will recharge in four or five hours from a totally discharged state.

I had not run any fuel economy figures, but Kenworth says the Clean Power system can potentially save as much as 8 percent over a truck with significant idling for driver comfort and hotel loads. That's a significant saving that the company says will pay back the option upcharge in months, not years.

I suspect a Clean Power truck will command a premium when it comes time to trade, as well.


There's no doubting the electric APU has a lot going for it. First and foremost, it complies with all current and likely pending anti-idling regulations. It is also quiet and - depending on how many starting batteries you save - likely lighter than a diesel-powered APU.

It does have a couple of downsides: The system is bulky, with batteries, compressor, condenser and fan all occupying real estate along the frame rails. That's not so bad, but there is significant intrusion into the under-bunk storage space. And the deep cycle batteries, while top of the line and among the best for longevity, may well have to be replaced over the life of the truck.

But the upside is just too good to pass up. Clean Power is a winner.

Cooling It

Clean Power is a complete, self-contained climate control system that has been developed in co-operation with climate control experts at Webasto. The target set by Kenworth was to be able to maintain the cab and sleeper at 72 degrees for 10.5 hours in an ambient of 95 degrees. This has been more than achieved, says John Duffy, Kenworth's advanced technology manager and the lead for the Clean Power program. 

In fact, the system also provides for hotel loads through an available 110-volt supply and the time target has been met - even using equipment like a microwave oven to prepare an evening meal and breakfast the next morning. Stretching the battery power to the limit, LED interior lighting is part of the overall package.

The system provides cooled air from a thermal storage unit for when it's hot, heated air from a diesel-fired furnace for when it's cold. An inverter provides 110 volts from the extra batteries carried on board and there's also a shorepower connection for when an external 110-volt supply is available.

Cooling is always the toughest task, and this system uses a refrigerant compressor separate from the vehicle a/c compressor. This circulates refrigerant through a box containing graphite in water. The containers are akin to the ice packs you chill in the home freezer to pop into a cooler. Driving down the road, the system is refrigerated and the water freezes, taking about five hours from totally depleted and storing (or extracting) approximately 21,000 BTU.

A pump circulates water through the iced compartment to a heat exchanger and a variable speed fan blows air across the cooled surfaces and then, chilled, out through ducting into the sleeper. Significantly, the chilled-air outlet is close to the bunk and, for double sleepers, a second outlet cools the upper bunk. This is one of the keys to the cooling performance where cooling of the people - not the whole space - is the primary concern.

The electrical load is handled by an additional battery pack of four Optima deep-cycle batteries, mounted to the driver's side frame rails right at the back-of-cab deckplate. Two conventional batteries handle starting and vehicle loads (so depending on the standard fleet spec, this could be a saving of one or two starting batteries).

For the 110-volt system, the inverter feeds household-type electrical outlets located in the sleeper.

Because the system can also run from shorepower, a driver can hook up where power is available and the climate control then has no time limit to its operation since it is fully self-contained. That also means a driver can plug the truck in at the terminal so it is fully charged when he returns several days later.

Controls are simple, with a heat/cool level set knob on the usual sleeper climate control panel.

By addressing driver comfort without the need for an auxiliary power unit, the Kenworth Clean Power solution sidesteps the new California laws. According to Duffy, it looks like other states may follow California's lead, particularly those in the Northeast. 

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