An air conditioner cools a space by transferring heat from one place to another. It is based on the principle
that when a fluid evaporates into a gaseous state it absorbs heat, and when it condenses from a gas back to
a fluid state it releases heat.
The air conditioner uses a refrigerant – basically a chemical with a low evaporation temperature – which
flows around a closed loop, driven and pressurized by a compressor. As the refrigerant flows through the
evaporator coil it absorbs heat from the inside of the truck. The refrigerant is then pumped to the condenser,
where the heat is released into the outside air.
As a part of the cooling process, the air conditioner also removes moisture from the inside air, which makes
it feel more comfortable and keeps the interior dry and mildew-free.
A belt-driven compressor on the truck’s engine supplies air conditioning when you are driving or idling.
To keep you comfortable when the engine is shut down, it is necessary to have a separate auxiliary air
conditioning system that uses an alternative source of power.
To that end, Dometic has developed an engine-off air conditioning system that pulls 12V DC power from a
bank of batteries and inverts it to 115V AC, which drives the air conditioner. The batteries are recharged by
a high-capacity alternator, which replaces the truck’s standard alternator. When 115V AC shore power is
available, it can be connected directly to the air conditioner.
When looking at a battery-based HVAC solution, you should think of it as an engineered, integrated
system comprised of several components, which have been carefully chosen and tested to ensure reliable
performance.
• Heavy-duty batteries capable of numerous cycles of deep discharge and rapid recharge without
damaging the batteries
• High-capacity 270-320 amp alternator replacing the standard engine-mounted alternator
• Inverter capable of operating up to 16 hours with a continuous 100-amp DC load
• 7,000- or 10,000-BTU/hr air conditioning system with associated grills, electrical power supply and
controls
On the next page we’ll take a closer look at these components and how they work together to power your air
conditioning system.
BATTERIES
Traditionally, truck batteries are designed to provide sufficient power to start the engine and operate lights,
blower motors, electrical sensing circuits and other “hotel” loads like a refrigerator or TV. It takes much
more sustained power to run an air conditioner for ten hours or more (required to meet the HOS) without
recharging. For this purpose, we require batteries that have the following characteristics:
• They can be deeply discharged without damage to the batteries.
• They can be rapidly recharged without damage to the batteries.
• They can do this over many cycles to give two years or more of service.
This is why Dometic specifies absorbed glass mat (AGM) batteries. These batteries use a proven technology
and are readily available across North America. The batteries specified by Dometic have up to 500 cycles
in them, providing up to two years of service before replacing. The number of batteries will depend on the
capacity of the air conditioner, size of the sleeper and the use profile of the truck (see page 9).
ALTERNATOR
To provide the rapid recharging needed for the system, your standard 145- or 165-amp alternator will be
replaced by a higher-capacity alternator, typically 270 or 320 amps, depending on the number of batteries
and capacity of the HVAC system. In general, the alternator will be sized to recharge the batteries in a
specific timeframe based on the truck’s usage profile.
• Sleeper - recharge in 5 to 6 hours for long-haul trucks.
• Day cab - recharge in 20 minutes for route driving, 60 minutes for terminal-to-terminal operations.
See page 8 for specific guidelines on sizing the alternator.
INVERTER
Off-the-shelf inverters are generally designed for relatively light intermittent loads, such as TVs, microwaves,
computers and coffee pots. Dometic’s air conditioning systems draw a minimum of 70 DC amps when the
compressor is running. They are also subject to spikes when the compressor cycles on. We have worked
closely with an experienced inverter firm to develop a unit that can handle the requirements of an air
conditioning system as well as the normal house loads. It is offered in two versions:
• Inverter only
• Combination inverter/charger
All of the inverters have a low-voltage cutout to protect the truck’s battery system and ensure restarting.
Dometic’s specified systems have never failed to start a truck.
SHOREPOWER
Although there are relatively few electrified parking places at truck stops, rest stops and terminals, these will
become more readily available in the future. Dometic’s all-electric system is designed to run on an external
115V power source when available. If the combination inverter/charger is installed, the truck’s batteries can
be recharged from shorepower as well.
Air Conditioning System
Dometic offers a range of models and capacities designed to meet each truck’s load requirements, space
constraints and usage patterns. We will look at these choices on the next page.
Inverter or
inverter/charger
Batteries Group 31
AGM deep cycle
High capacity
alternator
Air conditioner
115
VAC
12
VDC
12 VDC
12
VDC
How to Select, Specify, Install, Operate & Maintain Dometic Battery-Based HVAC Systems
4
3
Содержание ACCD7
Страница 1: ...C A R B C O M P L I A N T...
