Auxiliary heating
Parking heaters are used to heat the passenger compartment of all types of vehicles without having to rely on the heat output of the running engine . They are generally operated directly from the tank with the fuel of the respective vehicle and can either heat the air in the interior or be integrated into the heating circuit via the vehicle's cooling water circuit.
In addition, the heating can also be done electrically; Due to the nature of the system, this works where there is a power connection ( commonly known as a socket). Vehicles with a purely electric drive or hybrid vehicles can also operate the auxiliary heating electrically if necessary.
Fuel-operated parking heaters
principle
Fuel is burned in a burner; the exhaust gases give off their heat via the boiler wall to the surrounding medium (water or air). The principle is the same as that of a boiler in a home heating system. In contrast to an oil burner , however, an auxiliary heater does not work with a high-pressure pump for the fuel.
Combustion chamber
The combustion air fan blows the air tangentially into the combustion chamber. This creates an air vortex similar to a tornado. A small part of the air is diverted into a secondary chamber. In this there is a glow plug surrounded by metal gauze .
The chamber is preheated by the glow plug and the fan is set to a minimum. As soon as the temperature of the chamber is sufficient, fuel is pumped into it. This ignites and the flame reaches the actual combustion chamber (into the main air flow) via a duct. As soon as the flame has stabilized (the combustion chamber is sufficiently warm), the glow plug is switched off. The fuel then evaporates in the secondary chamber and reaches the combustion chamber in gaseous form, where it ignites (cf. the combustion chamber of a jet engine). This design has the advantage of not requiring a high-pressure pump to atomize the fuel, as is necessary in oil burners, for example. The disadvantage is that the metal gauze ("burner fleece") is susceptible to contamination from residues in the fuel. Diesel heating systems in particular can easily coke .
The continuously burning flame allows almost ideal combustion with very low exhaust gas values. As with heating burners, the combustion produces a relatively loud noise. Parking heaters are therefore usually supplied with silencers, which should be used.
The burner starts without any problems at temperatures as low as −40 ° C; after about 30 seconds it delivers its full output of 4 to 6 kilowatts , with bus heating even up to 35 kilowatts in the cooling water (or - depending on the model - 2.5 to 5 kilowatts directly into the air in the interior).
Feeding the fuel
In a first variant, the fuel required for the combustion is conveyed to the heater via a separately installed fuel pump. The disadvantage of this option was that this fuel pump was often prone to failure. A second variant was therefore developed that integrates the heater directly into the return of the vehicle's fuel circuit. These heaters have their own small fuel storage tank ; an additional pump is not necessary. Vehicles that do not have a fuel return can also integrate the heater into the flow (petrol line or diesel line). If the additional tank is empty, the heating does not run (the engine must run again after one use; continuous operation is not possible).
Models with their own fuel tank have the advantage that only limited fuel is available in the event of a malfunction (if the device does not switch itself off in the event of a malfunction, operation ends when the fuel supply is exhausted).
Diesel devices must not be operated with biodiesel (RME), as this leads to a lot of smoke. In addition, RME leads to long-term deposits in the combustion chamber (coking); the proportion of 5 to 7% contained in diesel is sufficient for this. Newer models have modified combustion chambers to prevent this.
Air heating
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The air-based parking heater [ LH ] are mostly installed in the cabin interior and directly heat the cabin air, which is sucked in via a fan . The response behavior takes place almost without delay, as the internal flame does not first have to heat a water circuit. Modern devices are very quiet and are preferably used, for example, to keep the driver's cabs of trucks at a comfortable temperature even when the vehicle is stationary (overnight).
In order to avoid endangering the occupants, a strict separation of the combustion air and cabin air circuit is ensured. Combustion chambers must therefore also be exchanged at defined intervals.
Water heating
The water-based parking heaters are more compact and can be installed almost anywhere in the engine compartment and under the vehicle. That is why their domain is passenger cars , the interior of which does not allow any additional installations. The very compact design (see picture) also allows installations in the engine compartment or behind the bumper of small cars and micro cars .
The water heater transfers the heat generated by the burner to the vehicle's cooling water. An (additional) electric circulation pump ensures that the heat is distributed even when the engine is switched off. The interior fan is also activated, everything works as in normal heating mode. In the case of devices with high performance, due to the design, the energy generated during combustion is only given off via heat exchangers surrounded by water.
Compared to air heaters, water-based parking heaters offer decisive advantages:
- A preheated engine starts more easily in the cold and thus puts significantly less strain on the car battery, which is already less powerful due to the cold.
- The pre-heated engine suffers from the mechanically stressful cold start only for a short period of time, as it quickly reaches operating temperature after the engine has started.
- Compared to a cold start, the preheated engine requires less fuel, which reduces pollutant emissions and costs.
- If the vehicle is parked for a short time, the internal combustion engine can be switched off without the vehicle heating system failing. The electric water pump continues to deliver the residual heat stored in the engine to the vehicle heater.
- Depending on the model, the auxiliary heating can be switched to ventilation mode in the warm season in order to bring the internal temperature of a vehicle parked in the sun close to the external temperature before driving off.
Compared to air heaters, however, indirect heating via the heating water circuit also has disadvantages:
- The start-up or integration time after switching on is usually several minutes, especially if the motor is also preheated.
- The efficiency drops because the water circuit is usually poorly insulated .
- Water heaters are often not regulated by a thermostat in the interior of the vehicle. Therefore and because of the high power consumption of the vehicle's fan motor, they are suitable for continuous operation, such as. B. overnight, unsuitable.
These first two disadvantages can be avoided if the water-based parking heater supplies the heating heat exchanger directly and exclusively without heating the engine (so-called island circuit).
Electric parking heaters
Electric heaters use different solutions. There are instantaneous water heaters that are looped into the coolant circuit like a fuel-operated heater, and variants in which immersion heater-like heating coils are used instead of the frost plugs in the engine. The latter system was combined with a fan heater in the interior. This saved the otherwise necessary water pump and electrical wiring for the vehicle heater fan.
Relatively often, only fan heaters are used in the interior, as they only require minor changes to the vehicle itself (socket, cabling). However, the engine's coolant circuit is not heated here. These fan heaters are specially designed for this purpose, fan heaters for household purposes have excessively high outlet temperatures and there is a risk of fire.
service
A parking heater can be activated either via a timer or a radio remote control . Newer models allow the temperature of the vehicle interior to be queried and the auxiliary heater to be switched on and off via mobile phone .
Timer
There are two types of timer control: one is used to set the switch-on time of the heating, and the other to set the expected departure time.
With the former, the driver has to estimate how long experience shows that the heating needs to bring the car to a comfortable temperature. In the latter case, the auxiliary heater uses a temperature sensor to determine the expected heating time and activates itself sufficiently before the planned departure.
In the meantime there are also radio-controlled time switches of the second type. (See below)
Radio remote control
There are two main types of radio remote control that can be distinguished according to the transmission technology used: GSM and standard radio technology .
GSM remote controls
The mobile phone remote control usually works via SMS . This has the disadvantage that an additional SIM card is installed in the associated module in the vehicle , which is associated with regular fees even with prepaid cards . The necessary SMS usually cost telephone charges. The basically unlimited range is to be seen as an advantage: In principle, such an auxiliary heater can be activated from anywhere in the world.
Some manufacturers expand an existing mobile phone, which makes it possible to offer this function particularly inexpensively. In any case, it should be ensured that it is not permitted within the EU and some other countries to use electrical vehicle accessories without approval, as otherwise the vehicle's operating license will expire (see E-marking ).
Sometimes there are also GSM remote controls for parking heaters that have a voice chip . The auxiliary heater is called and lists the various options. The answer is not given by voice, but via the telephone's multi-frequency selection .
Radio remote control
The usually built-in alternative is a common radio remote control, which has ranges of around 300 to 500 meters depending on the geographical conditions. A range of 1000 m is achieved under optimal conditions.
There are two principles in the area of radio remote controls: with and without feedback.
Without feedback (also unidirectional) means that the remote control does not show whether the radio command has been received. This procedure is still the standard.
With feedback (bidirectional) means that a receiver is also integrated in the remote control and a transmitter in the vehicle that confirms receipt of the message. Remote controls with feedback usually also allow a time preset analogous to the settings on the timer. With the new bidirectional remote controls, a diagnosis of the parking heater is sometimes also possible.
literature
- Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Vieweg & Sohn, Wiesbaden 2003, ISBN 3-528-23876-3 .
