Air conditioning of vehicles
The air conditioning of vehicles can be achieved by several measures: introduction of airstream, ventilation systems , vehicle heating and / or air conditioning systems .
Motor vehicles
General
Air conditioning systems should bring or keep the air in the vehicle interior within a comfortable temperature and humidity range. For this purpose, outside air can be filtered on the way into the vehicle interior, mixed with inside air, cooled and heated. The last two stages can be used to remove moisture , which helps prevent windows from fogging up from the inside , especially in the cooler seasons . In addition to convenience, this function provides a better view and thus road safety . Often only the "cooling" function is assigned to the air conditioning system. If a system cannot actively cool, it is referred to as heating in the vehicle .
The first fully functional air conditioning system based on today's principle is said to have been invented by WH Carrier in 1911. In the area of automobile air conditioning , these were first installed by Nash in 1938 and by Studebaker in the same year . The basic structure has remained essentially unchanged since then, but the control and characteristics have been continuously improved. In the upper-class segment , large numbers of air conditioning systems have been found since the late 1960s, today they are often part of the basic equipment of many vehicles or are available as an equipment option.
Air conditioning systems
Buyers can usually choose between two air conditioning systems: the manually adjustable air conditioning and the self-regulating automatic air conditioning.
- With the manual variant, the system only cools in the set level. If the vehicle interior cools down too much during operation, it must be readjusted manually. Changing environmental conditions (e.g. driving through a tunnel or changing solar radiation) can also make it necessary to adjust the cooling level manually.
- With automatic air conditioning, on the other hand, the operator sets the desired temperature and the technology ensures that this temperature is reached and maintained (e.g. with the help of temperature sensors in the interior) by automatically regulating the cooling capacity. If sensors detect a deviation from the set temperature, the cooling capacity is automatically adjusted.
Due to the type of function, an automatic air conditioning system usually works more efficiently, which leads to a reduction in fuel consumption: the system only calls up the power required in each case, avoiding (often) unnecessary continuous operation.
In addition to the interior temperature, modern air conditioning systems also regulate the amount of air (by automatically selecting the blower level) and the air distribution (by controlling the various air outlets in the foot area, pedestrian airflow or the window pane). Some systems use a sun position sensor (also: solar sensor) for improved control. This determines the direction and strength of the solar radiation and causes the affected side of the vehicle or the entire vehicle interior to cool down in order to compensate for the heat input from the sun. Some vehicles have an automatic air recirculation function that is activated when the outside air is poor, or when reverse gear is engaged, they temporarily switch to air recirculation mode in order to avoid sucking in their own exhaust gases.
The multi-zone air conditioning system is an extended variant, especially in higher-end vehicles: It enables separate settings for the driver and front passenger, and with some, separate settings can also be made for the rear area.
function
A compression air conditioning system works like a refrigerator : an evaporating liquid creates evaporative cooling (similar to evaporative cooling) or an expanding gas creates expansion cooling . With this continuously generated cooling process, the secondary medium indoor air is cooled via a heat exchanger. In everyday use, this effect can be experienced, for example, when an aerosol can is emptied, with the evaporation cold of the propellant extracting heat from the aerosol can and thereby cooling it. This effect is continuously generated in the air conditioning system with the help of a refrigerant (within a closed system). The then gaseous or expanded refrigerant must be recompressed and liquefied in the circuit, creating heat (more than the cooling capacity in the interior; see heat pump ). This heat is kept away from the interior and given off to the outside air.
Refrigeration cycle
The liquid refrigerant, which is in a closed circuit and under high pressure, is expanded through an expansion valve (Fig. Refrigeration circuit (diagram) , 2.) into a room with lower pressure (blue part of the circuit). The liquid refrigerant is injected into the evaporator (3), it can expand and change its physical state to gaseous. This heat exchanger is usually installed in the blower box behind the instrument panel. The expansion valve is therefore the point at which the refrigerant expands in the evaporator and cools it down.
At normal pressure, the refrigerant has a rather low boiling point (approx. −23 ° C) and evaporates here at low temperatures. The air to be cooled for the cabin, which mainly consists of cooled circulating air and only a little warm outside air to save fuel, is now routed outside the fins of the evaporator in the blower box. The heat required for the evaporation process of the refrigerant in the evaporator is extracted from the air flowing past and cools it down. At the same time, the air can also release moisture through condensation, since cold air can bind less moisture than warm air. The condensation water that forms on the fins of the evaporator is directed to the outside through a hose. This explains puddles of condensation under parked vehicles. The cooled air becomes drier when it is subsequently heated and is directed into the vehicle interior via the vent.
The refrigerant that has become gaseous through evaporation in the evaporator is now passed on to the compressor (4). This also takes care of the transport of the refrigerant in the system. The compressor, which is usually driven by the vehicle engine through a belt drive , sucks in the gaseous refrigerant and compresses it strongly in the red part of the circuit (approx. 15 bar). The temperature of the refrigerant rises to approx. 56 ° C.
The compressed, gaseous and hot refrigerant gas is then cooled in a downstream condenser (1). The refrigerant falls below the dew point , which is well above −23 ° C due to the high pressure , so that it (again) liquefies. The condensation heat that is additionally generated is released to the outside air, usually similar to that of the engine cooler. Therefore, the condenser is usually installed in the front of the body in front of the engine cooler in the airstream and is similar in appearance and size. As a rule, this is supplemented by a fan, for. B. to ensure the necessary heat dissipation in traffic jams.
Before the refrigerant gets back into the evaporator, any water and impurities (e.g. abrasion parts from the compressor) that may have been brought in from the refrigerant are removed from the refrigerant in a filter dryer (not shown). The cleaned and liquefied refrigerant is now returned to the expansion valve. Here the liquid refrigerant is injected into the evaporator. This closes the cycle of evaporation and compression.
Climate control
Today, vehicles with automatic air conditioning usually also have an outside temperature display with a frost warning. The temperature sensor, which is decoupled from the wind, engine heat and direct sunlight, also supplies the air conditioning control with the outside temperature. The difference between the adjustable setpoint cabin temperature (usually +16 ° C to +30 ° C) and the measured outside temperature is used to automatically switch between heating and cooling mode, and the required heating and cooling capacity is also determined.
power consumption
As long as the air conditioning control requires little or no cooling, suitable means are used to ensure that the compressor can build up less pressure, thus running with less resistance via the belt drive, putting less load on the combustion engine and thus also using less or no additional fuel. This function is often taken over by the expansion valve, which then no longer closes completely, but remains open accordingly. This is why this valve is also called a throttle . The mechanical power requirement of the car air conditioning compressor is around 4 kW ( BMW E28 ), but it can increase to up to 11 kW at high speeds.
Modern vehicles often also have what is known as intelligent energy management . In addition to the main function of “needs-based battery recharging”, highly developed specimens fulfill another function: As soon as additional consumers such as alternators and compressors do not require maximum power, their operation is postponed from expensive times to those in which energy is available much cheaper. This is cheapest when the engine brake is operating . Here energy is available as a waste product, so to speak. The engine should be braked to the maximum without causing workshop costs for brake wear or even bringing the brake fluid to a boil. Instead, the battery is recharged with the excess energy and the evaporator heat sink is "charged with cold" with reduced fan power. The second cheapest is energy at a low engine speed and high torque decrease, since the efficiency of internal combustion engines is at its maximum here . The second most expensive is energy at a high engine speed and the most expensive during idling, since the only thing that matters here is maintaining the internal combustion engine running independently with minimal fuel consumption. Here, the energy consumption of additional consumers is reduced or completely prevented in favor of the total consumption. Additional consumers require a certain delay time to adapt them to this change in operating modes.
In electric and hybrid vehicles and vehicles with a pronounced automatic start-stop system, electrically driven compressors are generally used.
Additional fuel consumption
The compression of the refrigerant gas requires power. The operation of the air conditioning compressor therefore increases the working resistance of the engine and thus also the consumption . Around 10 to 15 Newton meters are often required for this. The additional consumption is largely independent of the speed and, if used properly and not in a consumption-optimized manner, is between 0.2 and 0.5 l per hour at outside temperatures customary in Germany. The calculated additional consumption per kilometer driven is therefore dependent on the time required, the percentage additional consumption also depends on the average consumption.
Various consumer protection organizations advocate showing the additional consumption due to the air conditioning system in the vehicle data.
Consumption-optimized use of vehicle air conditioning systems
Air conditioning systems cause operating costs for fuel and workshop costs for coolant replacement and compressor shaft wear. Use of the air conditioner should minimize these factors. Only the cooling requirement that is actually necessary should be generated and any waste avoided.
When parking, a place should be preferred that is in the shade for some time before the intended start of the journey. Once the heat has built up in the vehicle, it should first be released through open doors and windows. This can also be done by the air blower, integrated parking heaters also call this option "parking ventilation". Only then should the air conditioning be switched on. Modern automatic air conditioning can take over some of these steps automatically (flushing mode).
In summer, the air outlets should preferably be directed to where the coolness is first and most intensely perceived, i.e. (depending on health compatibility) preferably on the face, neck, armpits, arms or upper body of the occupants. If necessary, air outlets can be closed for unoccupied seats.
The target temperature should not be too low and should be a maximum of 5 ° C below the outside temperature, so that the air flow only appears slightly cool, but in no case unpleasantly cold or even frosty.
Of course, neither windows nor sunroofs or even the convertible top or hardtop should be open during operation, as otherwise warm “false air” would penetrate. As with the refrigerator, doors should be opened as rarely and only briefly as possible. It is preferable to get out of the car before unavoidable external conversations.
Recirculation mode reduces the clogging of the pollen filter, which means that it has to be cleaned or replaced less often. Inside air that has already been cooled can be cooled to the outlet temperature with less energy than warm outside air.
Incorrect operation due to incorrectly adjusted settings
If a very low target cabin temperature (e.g. 16 ° C) and only a weak air flow is set, not only the cabin but also the space behind the dashboard is cooled disproportionately. The evaporator in the blower box cools down significantly without this cold being adequately conveyed into the cabin. Instead, the cold acts through heat conduction and convection on the neighboring components, the engine compartment and outside. This setting leads to increased fuel consumption and bearing wear, despite only moderate cooling performance in the cabin.
Incorrect operation due to air conditioning that has been switched off for a long time
Many users believe that they can save operating costs with air conditioning that is constantly switched off (refrigeration from the compressor and engine from fuel). In the long term, non-use leads to damage to the system: Even when the system is switched off, the air conditioning compressor is driven by the combustion engine via a belt and is simply kept depressurized. If the system is never active, the bearings of the compressor shaft may not receive enough lubrication, which may result in long-term leaks and then constantly lose refrigerant. Subsequent sealing and topping up with coolant are very expensive. Even in winter, the air conditioning should therefore not be switched off all the time. Instead, we recommend setting a target temperature that is higher than the measured outside temperature. The control will initially not request any cooling either and let the compressor run idle without additional consumption. Since the system is not permanently shut down, the control system should take suitable countermeasures to keep the breakdown rate low, such as B. initiate a corresponding "pump kick". Cold is briefly requested at the required minimum intervals in order to lubricate the compressor shaft bearings.
In air conditioning compressors with magnetic coupling , the compressor is disconnected from the belt drive when the air conditioning system is not in use, so it does not run continuously, which reduces wear and tear and energy consumption. Long-term non-use of the air conditioning can lead to the embrittlement of membranes.
Incorrect operation due to long-term deactivation of the ventilation
Constantly switched off ventilation can save operating costs (battery power from fuel via an alternator). In the long term, however, problems can arise: All air ducts in the blower box, including the evaporator fins, are then no longer flushed with air in the long term and are permanently subject to a temperature profile similar to that outside. As a result, a potential breeding ground with long available growth time for z. B. Fungal attack arise. Even with a single restart (possibly also by the subsequent owner), health risks can arise. Cleaning or replacing behind the dashboard, as well as reinstallation, are labor-intensive.
effect
Comfort and security
Formerly dismissed as a dispensable luxury, vehicle air conditioning systems in Germany experienced a real boom from the 1980s. This was also promoted by aerodynamically optimized bodywork and larger glazing: Inclined windshields and side windows lead to accelerated interior heating in solar radiation. An increased comfort is often perceived by air conditioning systems; the driver's concentration can also decrease significantly at high temperatures.
Small puddles of water under the vehicle when parking are due to the humidity in the form of water in the cooled air due to the lowering of the dew point and, if the evaporator is frozen, to the "defrosting" of the air conditioning evaporator.
Today, air conditioning in cars is often part of the standard equipment and ensures not only cool, but also clean air in the interior through a suitable filter. The air is cleaned using a cabin air filter , also known as a pollen or cabin filter . This protects passengers from pollen, diesel soot, fine dust, ozone and other irritant gases. In certain vehicle classes today, a lack of air conditioning in a used vehicle is considered to be severely impairing.
Colds from air conditioning
It is sometimes said that passengers believe that they have caught a cold by operating an air conditioning system in the vehicle . The traditional and still widespread assumption that colds are regularly caused by cold alone - in the scientific sense of heat deprivation as a pathophysiological mechanism - or that it causes or forms of cold such as drafts, moisture or hypothermia is incorrect. When operating an air conditioning system, moisture is usually extracted from the incoming air. Therefore, the mucous membranes in the ear, nose and throat tend to dry out. Bacteria, which can promote a viral infection, can settle more easily on the dried out mucous membranes . You should therefore ensure that you are hydrated in air-conditioned vehicles. In addition, regular disinfection and filter replacement as part of the maintenance of an air conditioning system is recommended.
Maintenance and retrofitting
Climate maintenance
Air conditioning systems in the car do not have to be maintenance-free. Refrigeration systems in motor vehicles have refrigerant losses that are caused by the installation of "open compressors". Usually the lifetime losses are too small and have no effect. The losses are primarily caused by leaking compressor shaft seals. Leaks are favored if the compressor is not switched on in winter and no oil is supplied to the shaft seal. In addition, there are possible leaks in detachable connections that can be caused by vibrations (engine and road). The system should be checked about every two to four years for any loss of refrigerant; at the latest, however, when the cooling capacity decreases. When opening the system, it is advisable to replace the dryer filter.
Coolant loss can also be used as an indicator of compressor shaft wear. Replaced refrigerant quantities should always be recorded in the service book. Exceeding the cumulative limit quantities suggests sealing before further refilling (usually relocation or replacement of the compressor).
Household refrigerators and freezers differ from vehicle air conditioning systems in the following points: The compressor runs without “winter idling”, ie regularly when there is a need for refrigeration. The individual components are compact and relatively easily accessible. They are not permanently connected to another expensive commodity (here: the vehicle). Since sealing and refilling the separate device are far more expensive than buying a new one, loss of coolant is considered an economic total loss.
Retrofitting
Air conditioning systems can also be retrofitted. However, the effort for this is often considerable, since the dashboard usually has to be removed in order to be able to install the evaporator. The use of CFC refrigerants such as R12 (Freon) has long been banned. State of the art is the use of the fluorinated hydrocarbon R134a . The mixture R413a , which only consists of 88% R134a, but in contrast to R134a, has similar flow and lubricating properties as R12, is suitable for replacing R12 in old air conditioning systems .
Refrigerant
General
The selection of suitable refrigerants for vehicle air conditioning from the wide range available is relatively small. In extreme ambient conditions (up to approx. 90 ° C) the refrigerant must still be able to be safely liquefied, which requires a high specific heat capacity of the refrigerant. At the same time, the pressures should be at a low, manageable level and the refrigerant, like oil, should be compatible with most of the materials favored in automotive engineering. In addition, the vibration decoupling from the moving engine still requires flexible hose connections that must be impermeable to the refrigerant and are not attacked by it.
Refrigerants used in vehicles
Until the turn of the millennium, only the refrigerant R12 was used, but this was forbidden in all applications because of its high potential for destruction in relation to the ozone layer.
R134a was chosen as the successor. In 2006, the EU issued the MAC Directive (2006/40 / EG), which regulates the use of fluorocarbons with a global warming potential (GWP value) greater than 150 in air conditioning systems in newly registered vehicle types from December 31, 2011 and in all newly registered vehicles Prohibited from December 31, 2016 ( phase-out time window). R134a has a GWP of 1430.
Carbon dioxide (refrigerant designation R744) was initially discussed as a replacement . With a GWP value of 1, it has a much lower global warming potential than conventional refrigerants and does not contribute to the depletion of the ozone layer . In addition, in test drives it showed a higher energy efficiency than R134a in almost all cases. The decision for CO 2 (R744) was announced at the so-called “green” IAA 2007 by the President of the Association of the Automotive Industry ( VDA ), Matthias Wissmann, as a joint result. Some car manufacturers advertised the more dangerous 2,3,3,3-tetrafluoropropene - ASHRAE designation R1234yf - (trade name e.g. Solstice ), as this can also be used in previous air conditioning systems. In the further course of time, almost all manufacturers turned away from CO 2 as a refrigerant, since the new development of CO 2 -compatible air conditioning systems is significantly more expensive than switching to R1234yf. R1234yf is relatively climate-friendly (GWP value 4), but flammable and is only produced worldwide by US manufacturers ( DuPont and Honeywell ). Attempts to extinguish the fire after an accident can produce dangerous hydrofluoric acid . Despite the existing ban, the EU Commission issued an exemption that allowed the continued use of R134a in new vehicle types until December 31, 2012 at the latest. The reason for this was the blatant delivery delay by the two main manufacturers.
In October 2015, Daimler announced that it would be delivering models of the S-Class and E-Class as the first series vehicles with CO 2 air conditioning systems from the end of 2016 . As of January 1, 2017, the Group initially converted vehicles from the other model series to R1234yf, possibly taking additional safety measures into account, so that they comply with the law. The Mercedes-Benz S-Class coupe since the end of 2016 as the world's first production car with a R744 equipped -Air conditioning, more vehicles will follow the 2017th
Since January 1, 2017, refrigerants with a global warming potential of over 150 have been banned in all new vehicles in the European Union. R1234yf is currently used by almost all vehicle manufacturers.
The simply constructed Schukey motor works with air as the refrigerant .
Controversy over R1234yf and infringement proceedings against Germany
In September 2012, Mercedes announced that it would no longer use the R1234yf refrigerant due to its flammability. Vehicles already filled with it were called back to the workshops and the filling was exchanged for R134a. During accident tests, R1234yf ignited in hot spots in the engine compartment and set the test vehicles on fire. In the following years, new cars from Daimler AG and in some cases also from other manufacturers continued to be delivered with the old refrigerant R134a.
Following a pilot process lasting several months, the EU initiated infringement proceedings against Germany on January 23, 2014, because refilling a vehicle approved with the new R1234yf refrigerant with the old R134a refrigerant is just as illegal as adding new vehicles as an extension to old existing vehicle type approvals . The first step in the infringement proceedings is the result of Germany’s actions in connection with various vehicle type approvals from Daimler . Further cases in other member states (e.g. United Kingdom , Belgium and Luxembourg ) are also being investigated by the EU.
On September 25, 2014, the EU initiated the second step in infringement proceedings against Germany.
On October 4, 2018, the European Court of Justice condemned Germany for negligent handling of the auto industry, but without imposing a penalty. According to the court, the federal government did not ensure in good time that the climate-damaging greenhouse gas R134a is phased out in over 133,000 vehicles made by Daimler. The Federal Motor Transport Authority ordered the retrofitting more than two years after the deadline.
Planes
Passenger planes have built in air conditioning as standard since jet planes existed . In the parking position, the air conditioning is provided externally by air conditioning vehicles, if necessary.
Railways
Modern passenger trains have air conditioning, older models partly with ventilation or windows that can be opened.
Ships
In larger vessels, wind scoops or Dorade fans and air conditioning systems are used.
See also
Individual evidence
- ↑ a b O.V .: How does an air conditioning system work? In: SPRINT - The Mitsubishi car magazine. 04/2007, p. 50.
- ↑ BMW AG (Ed.): Operating Instructions, Service Booklet 518, 520i, 525e, 525i, 528i, 535i, M535i, 524td . August 1985, p. 6–22 ( bmw-grouparchiv.de [accessed on February 20, 2017] archive signature AB-82-10).
- ↑ Richard van Basshuysen, Fred Schäfer (Ed.): Handbuch Internal Combustion Engine, 8th edition, Springer, Wiesbaden, 2017, ISBN 978-3-658-10901-1 . P. 516
- ↑ Dieter Schlenz, Dietmar Fischer: Car air conditioning: air conditioning concepts, control strategies and development methods for vehicles with significantly reduced fuel consumption expert verlag, 2000, ISBN 3-8169-1818-2 .
- ↑ Do air conditioning systems make you sick? In: autobild.de. August 6, 2003, accessed January 10, 2015 .
- ↑ Directive 2006/40 / EC of the European Parliament and of the Council (pdf) (PDF)
- ↑ Andreas Halbach, Christian Rohde: Danger in the car - dispute over new coolant, publication on AI cold, air, air conditioning. (No longer available online.) Frontal21, October 28, 2008, formerly in the original ; Retrieved February 20, 2011 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ The supply shortage of an essential component in mobile air conditioning systems and its impact to the application of Directive 2006/40 / EC in the automotive industry. ( Memento of February 22, 2014 in the Internet Archive ) at: ec.europa.eu
- ↑ Jürgen Pander: Refrigerant dispute: Mercedes equips cars with CO2 air conditioning systems. SpiegelOnline, October 21, 2015, accessed on October 21, 2015 .
- ↑ Christiane Köllner: On the way to CO2 air conditioning systems. Springer Professionell, November 28, 2016, accessed February 11, 2017 .
- ↑ EU directive on emissions from car air conditioning systems. Federal Environment Agency, June 10, 2015, accessed on October 22, 2015 .
- ↑ Jürgen Pander: Dispute over refrigerants: Daimler boycotts agreement on R1234yf. SpiegelOnline, September 25, 2012, accessed October 22, 2015 .
- ↑ Jürgen Pander: Controversial refrigerant R1234yf: The hot problem. SpiegelOnline, January 17, 2013, accessed October 22, 2015 .
- ↑ The European Directive on mobile air-conditioning systems (MACs) aims at reducing emissions of specific fluorinated greenhouse gases in the air-conditioning systems fitted to passenger cars (vehicles of category M1) and light commercial vehicles (category N1, class 1). ( Memento of April 28, 2013 in the Internet Archive ) at: ec.europa.eu
- ↑ Judges condemn Germany for being too lax with the auto industry. Spiegel Online, October 4, 2018, accessed October 4, 2018 .
- ↑ munich-airport.de ( Memento of the original from January 18, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
