• Technical Description
• Non-Technical Description

Technical Description

Internal combustion engines are notoriously inefficient converters of the total usable energy available in the fuel they burn. Typically, less than half is convertible into torque or horsepower to do mechanical work such as turning wheels. The diesel fuel engine is somewhat more efficient than its gasoline fueled, spark ignited cousin.

Where does the rest of the energy go? Some is converted into heat, overcoming the friction and inertial losses of the moving machinery that constitutes the reciprocating and rubbing components of an internal combustion engine. The rest is wasted in the form of excess combustion heat that is not converted into torque or horsepower during the combustion process. This excess heat is transferred to cooling water that surrounds the engine keeping it from overheating. This excess heat is dissipated to the exterior air via the vehicle radiator that is part of the engine cooling system.

The vehicle cab heater is also part of this system and, therefore, has available to it a very large source of energy. Normally, when the engine is off, this energy is dissipated to the vehicle exterior where it does little good.

Whenever a vehicle engine is "idled" to keep the interior cab warm, the operator is using a large, 200 to 500 horsepower engine to circulate 3 gallons or less of water to the vehicle heater. This works well while the vehicle is being driven, but is extremely inefficient when used in a parked vehicle. The inefficiency is thousands of times greater than what is necessary and can be realized using the AUTOTHERM® Energy Recovery System (ERS).

The AUTOTHERM® ERS utilizes a small, 1/100th horsepower, magnetically coupled, electric pump to automatically circulate all the hot water required to keep a truck cab warm in the coldest winter weather without needing to idle the truck's engine. The heat energy comes from all the hot water stored in the engine and radiator after the vehicle has been driven in normal use.

An earlier version of this ERS has been used in law enforcement vehicles for years. In V-8 powered police cars, the ERS keeps the interior of the vehicle warm for up to 1 ½ hours when the external temperature is at the freezing point (32° F, 0° C). These small gasoline engined vehicles have 12 to 16 quarts of coolant. Truck coolant capacities are 3 to 5 times greater, meaning the AUTOTHERM® ERS will deliver heat for much longer time periods. Tests in Class 6 and up trucks show heating times exceeding 3 to 4 hours when external temperatures are at freezing.

1. Vehicle coolant capacity
2. Maximum temperature at which cooling system is designed to operate
3. Outdoor ambient air temperature
4. Wind
5. Sun

Outdoor ambient air temperature is the third most important determinant of heating times, with freezing temperature used as the baseline comparison point. Ambient temperature as low as 0° F can reduce heating times to one-half of those available at 32° F. Conversely, an ambient temperature increase to 45° F can increase heating time by 50%.

In cold weather, wind plays an important role in how long the ERS will run, especially if the radiator/engine compartment is pointed into the wind. Parking out of the wind or diagonal to it can lessen the wind effect. Contrarily, the sun can contribute significantly to available heating times.

It is important to note that the AUTOTHERM® ERS automatically terminates operation when coolant temperatures decline to approximately 95 F. This means that the system will not circulate increasingly cooler air into the vehicle cab as the engine continues to cool to outside temperature levels.

In simple terms, the Energy Recovery System systematically dissipates heat to the interior cab that would otherwise be lost to external dissipation. The vehicle operator benefits from increased comfort and safety, significant reduction in fuel consumption, reduced maintenance and increased engine life.

And environmentally conscious operators can feel good about conserving a diminishing natural resource and contributing to significant reductions in air pollution, both of which come from using the AUTOTHERM® Energy Recovery System.