Fleet Maintenance - 14

"Carrier Transicold's ComfortPro APU platform
includes both diesel and electric models," says
Ryan Rubly, product manager, alternative power,
truck/trailer/rail, Carrier Transicold. "With fully
featured ComfortPro diesel APUs, a small engine
runs a generator that provides power for cab air
conditioning and heating, hotel power, and truck
battery charging. The APU also provides truck
engine pre-heating to avoid cold starts, and it
offers optional shore power capability, enabling the
system to be plugged into a 110/120V source when
parked, bypassing the need to use the APU engine."
Carrier Transicold is an international producer of sustainable transport refrigeration systems
for trucks, containers, and controlled atmosphere
refrigerated transport.
Thermo King also offers both diesel and electric
APUs through their TriPac product line.
"With an APU, we're essentially putting on some
type of power source," Thermo King's Flaherty
says. "It's a fully secondary system for cooling
and heating for the tractor. We're delivering
power in a different way from the tractor engine
and powering the HVAC. On the diesel systems,
we obviously need to pull fuel from the truck's
system. And on electric systems, we're utilizing
the tractor batteries and of course adding additional batteries. Apart from that, the actual HVAC
side of the system is completely independent from
the tractor. This is true independent operation."
Flaherty explains that the TriPac APU is 'rightsizing' power for the needs of the driver when the
vehicle is stopped.
"The best way to think of it is we're scaling the
power delivery and power generation to only
needing it for HVAC and battery recharging rather
than having to move a 50' trailer down the road,"
he says.
The smaller engine of an APU provides more
efficient fuel consumption compared to the tractor
engine when powering the same vehicle systems.
"When you're idling that tractor, you're burning one gallon of fuel per hour," Flaherty says. "If
you use our diesel [APU] product, you're burning
about 0.18 gallons per hour. So, we're getting an 80
percent reduction in fuel consumption, but you're
still getting all the benefits that you need."
To recharge batteries on the truck, the Thermo
King TriPac APU utilizes a 120A alternator rather
than the larger 240A or 300A alternator on the
tractor engine, further contributing to the efficiency offered through an APU.
APUs are usually specified onto new vehicles and
installed through dealer networks, although retrofitting APUs onto used vehicles is also an option.
"Typically, APUs are mounted on the side rail
of the truck, so when spec'ing a new truck, it is
important to allow enough room to accommodate an APU," Rubly says. "Installation complexity will vary based on the type of system and
options included. For example, installation of a
basic electric APU air conditioning system can
be done in significantly less time than a fully
featured diesel-powered APU, or even an electric
APU with options such as a fuel-fired heater and
an inverter for hotel power."
One determination a fleet will need to make when
deciding to specify an APU is whether to utilize an
electric APU or a diesel APU. Currently, the industry

14 Fleet Maintenance | July 2020

»The smaller motor of an auxiliary power
unit provides more efficient fuel consumption
compared to the tractor engine when
powering the same vehicle systems.
Photo courtesy of Thermo King

predominantly specifies diesel APUs over electric.
This is largely due to the fact that diesel APUs have
been available for a longer period of time and are
therefore more thoroughly proven, Flaherty says.
Both Thermo King and Carrier Transicold offer cost
calculators on their respective websites for fleets to
evaluate the cost savings offered through implementing an APU into the fleet.
The major differences between diesel and electric APUs revolve around run-time, cooling power,
and emissions/fuel consumption.
"With diesel, you have unlimited run-time and
more powerful cooling," Flaherty says. "And with
electric, you're going to have a finite amount of
battery and slightly less cooling power. You can
always get more power by adding more batteries,
but the fact is [the batteries] weigh a ton, [and]
fleets don't want to add more weight."
Depending on the electric APU model, typical
run-times on a full charge range between seven
and 11 hours, whereas with a diesel APU, average
run-time is only limited by the amount of fuel in
the tank.
"Battery-powered APUs provide a lower cost
entry point, and their simpler configuration
means less maintenance than systems driven by
a diesel motor," Rubly says.
As mentioned before, diesel APUs significantly
reduce fuel consumption and emissions. However,
electric APUs reduce those factors even further,
and also produce less noise pollution.
Maintenance requirements for diesel APUs are
similar to that of any engine maintenance requirements. This will include changing the oil and oil
filter, replacing the air filter, changing the fuel filter,
as well as inspecting hoses and connection points.
Electric APUs require a different set of priorities when it comes to maintenance, particularly

the battery system, its connection points, and the
replacement of batteries. With advancements in
the technologies of APUs, service intervals have
increased to around 2,000 hours of run-time for
both diesel and electric APUs. Integrating APU
service intervals into a fleet's PM schedule is
crucial to maintain the performance of the APUs,
as well as capturing the most out of the benefits
offered through their performance.
Similar to APUs, Eberspaecher offers air
and water heaters through their Airtronic and
Hydronic product lines, respectively. These products are designed to provide in-cab and engine
temperature control while limiting the consumption of the vehicle's diesel fuel. The air heater
operates through the use of a small amount of
fuel from the truck's fuel tank, as well as some
battery voltage to start the unit. An internal
combustion-air fan motor and fuel metering pump
deliver fuel to an atomizer screen. With the heat
exchanger ignited, the combustion air fan moves
air through the heat exchanger and provides heat
to the truck's cab. The Airtronic heater operates
without the truck's engine running, offering
climate control without an idling engine.
Stencil mentions that maintenance procedures and service intervals for the air heaters
are straightforward.
"You do not have to remove the heater from the
bunk to do the maintenance on an Eberspaecher
Airtronic air heater," he says. "The items that will
be replaced will be the atomizer screen and the
fuel filter, which is internal to the fuel metering
pump. When servicing an Eberspaecher heater,
you can visit our webpage where we have an
extensive library of videos that show how to do
maintenance procedures."
A maintenance recommendation Stencil offers
is that fleets run the heater for at least 15 minutes
per month, every month of the year.
"This keeps the fuel system primed, keeps the
internal parts of the fuel metering pump from
varnishing up by cycling out stale fuel, it helps
burn off any accumulated carbon in the combus-

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