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.