An air conditioner is a system of air and air conditioning systems for generating and maintaining a pleasant or required air -quality ( temperature , moisture , purity and CO 2 moiety) regardless of weather , heat and human and technical issues . An air conditioning system has the task of bringing the air in a room to a certain state and keeping it (“conditioning”). Often, however, an air conditioning system is only understood to mean room air cooling.
The functions of an air conditioning system are therefore:
- Change in air temperature (heating or cooling),
- Change in humidity (humidify or dry),
- Removal of air components (filter or replace),
- Changing the local air speed.
Smaller air conditioning systems often do not master all of these functions; mostly, however, one only speaks of an air conditioning system if at least the cooling function is available.
Air conditioning systems create the necessary environmental conditions for technical systems or a room climate that is comfortable for people in industrial, work and living spaces as well as in ships, trains and other means of transport, usually with a temperature of around 22 ° C and a relative humidity of around 50%. Is accepted.
Definition of terms and classification
According to EnEV 2009, DIN EN 15603 (withdrawn), Part 1 of DIN EN ISO 52000, DIN EN 12792 and the European directive on the overall energy efficiency of buildings (Energy Performance of Buildings Directive, EPBD) , air conditioning or an air conditioning system is required as "a combination of all components that are necessary to provide a form of air treatment in which the temperature, possibly in combination with ventilation, air humidity and air purity, is defined".
This definition is controversial among experts. One point of criticism here is that ventilation systems with simple air heaters or any form of heat recovery can also be described as air conditioning. Since every heating system always has an influence on the temperature of the room air, these systems would also fall under the umbrella term air conditioning. The 79th edition of the "Recknagel": pocket book for heating and air conditioning technology as a standard work in the field of HVAC technology states that the term "air conditioning system", although it is diverse in room conditioning, in vehicle technology, in legal Regulations and the rules of technology (standards and guidelines) are used, has not yet been clearly defined. Furthermore, it is shown in the work that the understanding of the terms and the associated classification of the RLT systems (air conditioning systems) has changed in some cases significantly in recent years. For this purpose, for example, the classification of air conditioning systems according to Part 7 of DIN V 18599 is compared with the classification of air conditioning systems (air conditioning systems) as contained in the 70th edition of the company's own work.
Sheet 1 of VDI 4700 defines the term air conditioning as "RLT system with ventilation function and with four thermodynamic air treatment functions". The definitions of the terms air conditioning , air conditioning unit and air conditioning contained in the draft of DIN 4749 go in the same direction. This standard also distinguishes between full and partial air conditioning. Regarding the latter it says: "If both thermodynamic functions of temperature and humidity are not regulated or controlled, it is a question of partial air conditioning."
A more differentiated, possible definition can be found in the table contained in DIN SPEC 13779 (withdrawn), which was published in December 2009 as a national annex to DIN EN 13779 “Ventilation of non-residential buildings” (withdrawn).
Classification of ventilation, partial air conditioning and air conditioning systems according to DIN SPEC 13779
The classification of DIN SPEC 13779 (withdrawn) was based on the thermodynamic influence that the system has on the supply air .
|category||regulated functions||Plant designation|
|THM-C0||Simple ventilation system|
|THM-C1||Ventilation system with heating function or air heating system|
|THM-C2||Partial air conditioning with humidification function|
|THM-C3||Partial air conditioning with cooling function|
|THM-C4||Partial air conditioning with cooling and humidification function|
|THM-C5||Air conditioning with all functions (or colloquially full air conditioning )|
- - Is regulated in the partial air conditioning
- - Is influenced in the partial air conditioning system, but not regulated.
Furthermore, the air conditioning systems are also marked according to the ventilation function . If outside air is supplied, it is an air conditioning system with a ventilation function . If, on the other hand, only circulating air is used , this is an air conditioning system without a ventilation function .
DIN SPEC 13779 also stated that, in accordance with Section 12 of the EnEV, regular energetic inspections must be carried out on all air conditioning systems of the THM-C3 to THM-C5 versions if the cooling capacity for air cooling is greater than 12 kW.
Advantages and disadvantages of air conditioning
The effects of air conditioning on the living atmosphere and productivity at work are controversial and influenced by many individual factors.
- Fresh air supply. This is according to occupational safety , z. B. in Germany according to the workplace directive ventilation (ASR 5) then necessary if the air quality does not essentially correspond to the outside air quality. In addition to CO 2 , smells and pollutants such as solvents from building materials or carpets, ozone from laser printers, dusts, gases and vapors from manufacturing processes, etc. are also removed when fresh air is supplied. The occupational health and safety ordinances use “MAK” values ( maximum workplace concentration ) as a standard .
- At around 20 ° C, people are 100% efficient. At 28 ° C the performance drops to 70% and at 33 ° C to 50%. According to the workplace guideline for room temperature (ASR A3.5), the temperature at office workplaces should not exceed 26 ° C.
Other sources give different values, but agree in the basic statement that the performance decreases at temperatures above 22 ° - 25 ° C.
- A survey by the AOK showed that almost 40% of those questioned feel impaired by poor ventilation and air conditioning. Badly maintained systems cannot remove pollutants or even spread bacteria , mold and other microorganisms .
- Energy consumption, waste heat and operating noise, even in efficient air conditioning systems, pose a problem, especially in urban areas.
- If refrigerant (e.g. R-410A ) gets into the environment, it can contribute to global warming and ozone depletion at high altitudes. Operators of larger refrigeration machines are therefore obliged by the Chemicals Climate Protection Ordinance to have the system checked for leaks on a regular basis. Modern refrigerants no longer have an ozone-depleting effect, but refrigerants that damage the ozone layer are still produced and used.
- The room temperature may be set too cold. It is recommended not to set the room temperature colder than 6 ° C below the outside temperature, which can also be achieved by automatically adjusting the room temperature to the outside temperature.
Central building air conditioning systems
In central air conditioning systems, the air treatment functions - air delivery, filtering, temperature control, humidification and dehumidification - are carried out in a central supply air - exhaust air device. Air ducts are distributed from the device to the individual rooms.
In central air conditioning systems, a distinction is made between combined air / water systems and air-only systems .
- Air / water systems
- With this type of construction, part of the temperature control takes place via water-based surface heating or cooling systems (radiators, cooling ceilings , etc.), while the temperature control of the outside air supplied, air flow, filtering, humidification and dehumidification remain in the central unit. This construction allows a strong cooling / heating of the room even with moderate air flow.
- Air-only systems
- With this type of construction, the entire room is conditioned exclusively with the air supplied. Air-only systems are used when, for special reasons, water-based surface heating or cooling systems are to be avoided in the room or when larger rooms, such as halls, auditoriums, theaters, assembly rooms, etc. have to be air-conditioned.
Central air conditioning systems are considered tried and tested. The requirements for air quality, quiet operation, humidity, freedom from drafts and temperature can be met. The spatial concentration of essential building components offers economic advantages in terms of energy efficiency, maintenance, hygiene and space utilization.
Central ventilation systems allow comprehensive and energy-efficient treatment of the room air. Regardless of the orientation of the facade, relatively warm outside air is usually brought into the building on the side of the building facing away from traffic, close to the ground, protected from wind / rain in winter and relatively cool outside air in summer. The sizes enable the use of components with a high degree of efficiency, such as B. Fan , heat recovery, sound absorption. To increase energy efficiency , powerful heat recovery systems can be used that also provide self-generated cold as a by-product with indirect adiabatic evaporative cooling in summer . This relieves the heating center of part of the thermal air treatment, and large, power-consuming refrigeration systems including their recooling systems are avoided.
If the cooling requirement is calculated when planning a permanently installed air conditioning system, incorrect dimensions can be avoided. The cooling load calculation is based on VDI2078. It is often sufficient to record the data from the relevant existing documents (U-value of the building materials, floor plans, etc.).
Decentralized building air conditioning systems
Analogous to the central air conditioning systems, decentralized air conditioning systems can also be divided into air / water systems and air-only systems .
Decentralized air conditioning systems arose from window cooling units, as they have long been used in the hot regions of Asia and America, by adding a ventilation and heating function. Decentralized air conditioning systems are preferably intended for subsequent installation in individual rooms. In terms of comfort requirements, compromises may have to be made in terms of air quality, volume, humidity, freedom from drafts and hygiene. This can be due, for example, to the fact that, in the case of facades facing traffic, contaminated outside air is led into the room, that exhaust air blown out through the facade is sucked in again, that in addition to the fan noise through the facade openings also compressor and traffic noise penetrate into the room, that no loading and unloading Dehumidification takes place so that the wind pressure has an influence on the air balance of the building or soaked filters become contaminated due to the lack of filter preheating.
Decentralized air conditioning units are mainly installed under the floor or in the parapet. This reduces central air distribution in the building and the designation of technical areas in the basement or on the roof. Installation in the parapet offers the possibility of lower storey heights, but in return the effective room floor area is reduced by the protrusion of the parapet. It should be noted that rooms in the building core or in the basement can hardly be air-conditioned.
In order to avoid exhaust air suction through the facade and thus also limit the transmission of fire and smoke, decentralized air conditioning systems are now increasingly being implemented as hybrid designs. The exhaust air from the room in the building is combined and discharged via a central exhaust air device via the roof, while the outside air is drawn in from the individual rooms via the facade.
When it comes to achieving good energy efficiency, compromises have to be made in larger systems. This is because the advantage of avoiding air distribution does not outweigh the disadvantages of thermal air treatment.
Due to the limited installation situation, the individual components are kept small, which increases the achievable efficiency z. B. reduced with the fan, heat recovery or silencer. If the device is not protected against rain and wind, it can happen during the heating season that the supply air (facade outside air) is colder than at a central air conditioning system supply air location, and the air therefore has to be warmed up more and then with a higher air heating requirement is to be expected. Due to the sun's rays, the outside air in the facade also requires a higher cooling capacity in summer. Since indirect adiabatic evaporative cooling can usually not be used with the simply structured devices, the cooling capacity has to be generated via refrigeration machines and recooling units, which require additional technical areas and cause high power consumption. In the maintenance of decentralized components, it has been shown that the time and transport expenditure for long distances and renewed set-up times on site result in higher costs. Maintenance work in the room can also obstruct the workflow of the people present there.
Decentralized air conditioning systems allow their own concept for flexible use of space and cost accounting. The coefficient of performance of such small heat pumps is around 3. For 900 to 1000 watts of electrical power (consumption), 2700 to 3000 watts of thermal power are available.
In the case of a decentralized air conditioning system in the form of a split unit, the refrigerant is compressed outdoors, while the air treatment (air supply, filtering and temperature control) is carried out in the room to be cooled. With many small appliances, only the room air is circulated and cooled in the process. With some devices, a small proportion of air is sucked in in front of the facade, regardless of the direction of the sky of the building, brought into the room and usually the same amount of exhaust air is extracted. Many such devices allow a "reversal of operation": They can take over the function of a heat pump heater in winter .
Here all components are in a single housing that is located in the room to be cooled. It has at least one exhaust air hose through which it usually blows out hot air through an (otherwise sealed) window gap. In order to equalize the pressure, it is then necessary that the room to be cooled has enough cracks and gaps so that air can be drawn in again. This drawn in warm air reduces the efficiency of the device.
The compressor in the room represents a significant source of noise in the interior compared to a split device.
Regulation and comparison process
The interconnection of the various units for air treatment requires special control algorithms. They have a direct influence on the economy, the consumption of resources and the environmental compatibility of the air conditioning system. The various control procedures can be assessed for their efficiency with annual simulations, but they do not allow any statement to be made regarding their actual, absolute quality level. For this reason, comparison processes for air conditioning technology were developed. They are based on an optimization strategy (dynamic optimization with the variables temperature and humidity) with a variably definable target function.
Environmental and health related problems
Air conditioning systems are potential sources of emissions for bioaerosols . The prevailing milieu promotes the growth of microorganisms such as Legionella pneumophila and actinomycetes . However, the prerequisites for growth niches for these bacteria are only found in poorly maintained cooling towers , whose freedom from bacteria is usually guaranteed by chlorination as part of routine maintenance.
Sick building syndrome
An inadequately designed or poorly maintained air conditioning system can encourage the occurrence of symptoms of sick building syndrome . The release of strongly smelling or irritating substances from walls, floors, ceilings, furniture and appliances or moisture damage to the building are possible causes. Differentiating it from other workload factors can be very difficult.
The use of chlorofluorocarbons (CFCs) as refrigerants in air conditioning systems was widespread well into the 21st century. Above all, the coolants R-11 and R-12 ("Freon-12") were preferred because of their good properties in the areas of stability and safety. However, when these gases escape from damaged or poorly maintained devices, they reach the atmosphere, where they act as catalysts in a chain reaction under the influence of UV light, promoting the homolytic breakdown of ozone (see: CFCs - environmental impact ). In 1994 the use of R-12 was changed to R-134a , which has no ozone depletion potential. However, due to the high global warming potential , this agent has no longer been permitted in cars in the EU since 2017. Possible successors are CO 2 and R1234yf .
R410a is predominantly used in household appliances, rarely R32, R407C or R134a. These refrigerants are all very harmful to the climate when they are released (several hundred times more harmful than CO 2 ). The hardly climate-damaging R290 (about three times as harmful as CO 2 ) has so far (as of summer 2018) only been used in a few monoblock devices, so split devices are only expected from 2019. In March 2018, a split device from Midea was awarded the Blue Angel as the first split air conditioning device , as it works with the R290 in a very environmentally friendly and at the same time energy-efficient and quiet way. However, it is not yet available (status: 06/2019).
However, the increasing spread of air conditioning units also results in new problems such as higher electrical energy consumption, climate changes due to the associated higher carbon dioxide emissions and changes in the ozone layer due to escaping refrigerants. Therefore, alternatives to conventional compressor air conditioning systems are being sought. Since the mid-1980s, so-called adiabatic cooling has also been used more and more in building air conditioning in Germany. The necessary cold is generated by evaporative cooling . The evaporation of water in the air creates a cooling potential that is always below the ambient temperature. The achievable sub-temperature depends on the relative humidity of the air. Apart from the transport of air and water, no mechanical or electrical energy is required for cooling. However, only small temperature differences can be achieved. There are three procedures:
- Evaporative cooling of the supply air (limit: high room humidity)
- Evaporative cooling of the exhaust air with a heat exchanger for the supply air
- Drying of the supply air before evaporative cooling (additional effort)
For example, the German Federal Chancellery has an adiabatic cooling system: With 1 m³ of water (around € 5), a good 1000 m² of office space can be cooled per day. Another example of adiabatic cooling was the 1992 EXPO in Seville. There, the outside air temperature on the EXPO site was reduced from sometimes 42 ° C to 36 ° C through evaporation. In the vicinity of power plant cooling towers, it can be statistically proven that their adiabatic cooling leads to increased precipitation in the vicinity (see also industrial snow ).
Cooling systems for office buildings are also installed on the basis of geothermal cooling (including well water or surface water). For example, 4 ° C cold water is taken from a nearby lake from a sufficient depth and distributed in buildings through a kind of local cooling network , then the water is returned to the lake. However, changing temperatures can have an impact on the ecological system (fish population, water quality, etc.).
In principle, both the heating and cooling requirements can be met in the moderate latitudes without additional energy by using seasonal heat and cold storage.
Passive cooling through shading
There is also the option of not allowing the temperature inside buildings to rise too much in the first place. This happens in particular through the shading of windows and glass fronts, so that the solar radiation is reduced or blocked completely and the inside of the building cannot heat up as much. It is important to ensure that the appropriate devices are attached to the outside of the window so that the heat radiation does not even reach the inside of the building through the window. This is done for example by shutters , awnings , external blinds , shutters , awning and similar devices or by an architecture in which the cool air of the shadow in an atrium is used.
Compared to conventional heating and air purification systems , an air conditioning system can also cool, filter and dehumidify. For this purpose, it has a refrigeration machine , similar to that found in many refrigerators and all freezers. The filtering is often done using filter fleece . Condensation surfaces with water drains are used to dry the air. The heat is transported via the cooling circuit and then released on the other side. As a result, an air conditioning system always needs a medium (refrigerant) with which it can transport the heat. For this purpose, refrigerants R-410A , R407C , R134a , chlorodifluoromethane (R22), R290 , or R12 are usually used.
R12 is banned today. R-134a has been banned in new vehicles in the EU since 2017. Some refrigerants, such as B. R290, have an increased or high risk of fire.
An air conditioning system that generates cold air has a compressor refrigeration machine (see also under heat pump for principle ). In their refrigeration cycle , the relationship between pressure and temperature of the climate gas (refrigerant) is used: a gas that is compressed warms up; conversely, it cools down when you relax it (expand again). A cooling air conditioning system works as follows:
- The air conditioning gas is compressed outdoors with a compressor and liquefied in a subsequent heat exchanger. The resulting heat is dissipated to the environment. The refrigerant then has approximately (outside) ambient temperature.
- The liquid refrigerant is led into the interior, where it is allowed to expand again after a capillary in cooling fins (in the evaporator), cooling them below (interior) room temperature. It absorbs its specific heat of vaporization .
- Room air is blown past the cooling fins and gives off its heat to the cooling fins - and is clearly cooled and released back into the room.
- The evaporated climate gas, which is warmed up to almost room temperature again by the heat transfer from the room air, is led back outside to the compressor. The cycle starts all over again.
The energy consumption that air conditioning systems require for cooling or heating has been steadily reduced. Today's good air conditioners have a COP of 3.5 to 4.0. So they need for a cooling output of 4 kW only a driving power of about 1.1 kW.
In residential and car air conditioning systems, the energy consumption depends heavily on the difference between the indoor and outdoor temperatures. In the case of air conditioning systems for cooling data centers or machines, the primary consumption factor is the heat generated by the devices, which must be dissipated.
Air conditioning systems are also being used more and more for heating (i.e. reverse operation), as they take around 2/3 of the amount of heat given off from the outside air and only absorb 1/3 of the amount of heat given off electrically ( heat pump principle ). Modern devices achieve COPs of up to 5 in heating and up to 4 in cooling mode, i.e. H. only 20-25% of the required amount of energy is electrical consumption energy. Air conditioners with a heat pump function are therefore far more efficient than electric heaters despite the higher acquisition costs. Heat recovery systems are being built for larger properties, in which the waste heat in cooling mode can be used to heat domestic water. A combination with underfloor heating is also useful because it can lower the temperature level on the warm side.
When split units such air conditioners are referred to, which includes an outdoor unit ( condenser / compressor) and connected thereto via refrigerant lines indoor unit ( evaporator ), possibly also a plurality of indoor units (multi-split systems), are equipped.
Air conditioning systems with inverter or with inverter technology are those systems in which the output of the air conditioning compressor can be variably adapted to the cooling requirement. The central role in regulating the compressor is played by a frequency converter , also called an inverter - hence the name.
In conventional air conditioning systems, the compressor either runs at maximum power or is switched off. The cooling capacity is adjusted by changing periods of operation and standstill of the compressor of different lengths. In inverter-controlled systems, the performance of the compressor is constantly adapted to the cooling requirement. In the frequency converter, the alternating current from the power grid is first converted into direct current with the help of a rectifier , while the downstream inverter converts the current back into alternating current of different frequencies. Depending on the alternating current frequency, the compressor's asynchronous motor then turns faster or slower and thus changes the performance of the compressor.
Since the mechanical components of the devices are more stressed with frequent start-stop operation and the power grid is also disrupted by abrupt changes in power consumption, air conditioning systems with inverter technology are in situations with frequently and continuously changing cooling (or heating) requirements more efficient. In situations in which continuous operation at maximum power is required, the conventional devices again have an advantage, since with inverter technology, energy losses occur through the conversion.
As with other household appliances, the appliances are divided into energy efficiency classes from A (good) to G (bad); this information is now mandatory.
In addition, heat pumps operated by gas engines are used to a lesser extent. These obtain their energy from natural or liquid gas. Electricity is only required here for control or, in the case of chillers, for operating the cold water pumps. Gas-powered heat pumps have the advantage that losses in power generation and in the transport of electrical energy are avoided. They have higher acquisition costs and higher maintenance costs.
Areas of application and types
A distinction is made between air conditioning systems:
- Direct evaporator
- indirect cooling via cold water or brine circuits
In small air conditioning systems such as room cooling units, car air conditioning systems, crane systems and air conditioning systems in trains, the air is cooled directly by installing an evaporator bundle in the air flow. Large systems for the air conditioning of office buildings or for cooling larger electrical switchgear with a large number of cooling points are cooled indirectly. The evaporator of the refrigeration system is a heat exchanger that cools water or brine. The brine consists of water to which antifreeze has been added. A closed cooling circuit with centrifugal pumps is operated in which an expansion vessel is installed to absorb the thermal volume change.
The performance of the air conditioning systems range from 2 kW cooling capacity (room air conditioner) to central cooling systems in hard coal mining with a cooling capacity of up to 3 MW per compressor unit.
Monoblock or split devices are suitable for private use:
- Monoblock devices have an exhaust air hose that has to be permanently laid in a wall opening or hung from a window. These devices have the disadvantage that, due to the inevitable air pressure equalization, the exhaust air blown to the outside is immediately replaced by warm and moist outside air that flows in through the cracks in windows and doors. A large part of the effect of the air conditioning system is thus nullified again. Furthermore, these devices are louder than split devices because the compressor has to work inside the apartment. However, there are also monoblock devices with a second hose for drawing in outside air, so that air pressure compensation is no longer necessary. However, these two-hose devices are so far not very common.
- Split units are more efficient because the condenser can be placed in a convenient location outside of the room to be cooled. The condenser and evaporator are connected via hose lines. Nowadays, some split air-conditioning units have a so-called heat pump circuit , which enables the air-conditioning system to be operated as an energy-saving additional heating system in autumn, winter and spring even at an outside temperature of down to −15 ° C.
Also known from the USA is an air conditioning system the size of a microwave oven which can be placed in a window frame and emits waste heat directly to the outside. To do this, however, it is necessary to seal the rest of the window frame against the exhaust air that would otherwise re-enter. This is only practicable with the windows customary in the USA, which can be pushed open upwards.
Further areas of application
Air conditioning systems are also used in aircraft and automobiles . One often speaks of automatic air conditioning. The general difference lies in the automatic control of an automatic air conditioning system in contrast to the simple control of a classic air conditioning system. This means that by constantly comparing the target / actual values, an automatic air conditioning system automatically adjusts its own performance in order to maintain the desired temperature range. In contrast, the control of a conventional air conditioning system remains permanently at the set power, which means that the user has to readjust manually if the desired temperature range is no longer maintained. In addition, with modern automatic air conditioning systems in vehicles, it is even possible to set the temperature separately for the driver, front passenger and rear seat. Usually, the different heating of the passenger compartment due to solar radiation is compensated for by determining the position of the sun using a sun position sensor (also: solar sensor) and accordingly cooling the affected side of the vehicle more.
The operation of an air conditioning system on ships is much simpler and more cost-effective, since here the waste temperature can be given off via the practically unlimited availability of relatively cold seawater. For this reason, significantly lower temperatures can also be reached. Examples of such air conditioning units referred to as water chillers can be found e.g. B. on almost all ships of the German Navy .
Traveling on trains with an air-conditioned, air-filtered and pressure-protected environment offers a high level of passenger comfort. Measured variables and their target values for comfort are specified in a number of standards, in particular EN 13129. The essential variables are temperature, air humidity, thermal radiation (surface temperature and passage through windows), air speed in the train and the sound level. The place of use (geographical location) and the type of application (tram, subway, regional train or high-speed train) basically require different, adapted air conditioning systems. These are called HVAC systems (English: Heating, Ventilating and Air Conditioning or in German: Heating, ventilation, air conditioning (HLK)).
Almost all modern rail vehicles such as multiple units and passenger cars as well as the driver's cabs of many locomotives are equipped with air conditioning. The air conditioning units are either installed under the floor, but more often on the roof, mostly in low-floor vehicles. They are supplied with energy via the vehicle's on-board network or a corresponding converter directly from the train busbar . To prevent warm outside air from getting into the interior of the car, the windows of air-conditioned trains cannot be opened or only by the conductor . The air conditioning units are mainly designed as compact units, less often as split units.
The air conditioning system in the aircraft ( environmental control system (ECS) ) also includes the pressure supply. This often requires a different construction and energy source with significantly greater power requirements and increased safety requirements. Air conditioning is required in commercial aircraft in order to provide passengers with the necessary atmosphere in the cabin with sufficient air pressure , adequate oxygen supply and an appropriate ambient temperature at altitudes of up to 11,000 meters . In aircraft with jet engine (s), it is operated, among other things, with bleed air from these.
The first fully functional air conditioning system based on today's principle is said to have been invented by WHCarrier in 1911. In the area of car air-conditioning systems, these were first installed by Nash in 1938 and by Studebaker in the same year .
- A / C (" Aircondition type Carrier ") - air conditioning according to WH Carrier (button commonly used in vehicles)
- VRF (" Variable Refrigerant Flow ") - variable refrigerant mass flow
- VRV (" Variable Refrigerant Volume ") - variable refrigerant volume flow
- BTU (" British Thermal Unit ") - 1000 BTU / h ≈ 293 W.
- RLT system (ventilation system)
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- Chemicals in the environment: Freon 113
- Changing an A / C Compressor - What Year Did They Stop Using R12?
- Sophie Jankowski: EU directive on emissions from car air conditioning systems . In: Federal Environment Agency . July 18, 2013 ( Umweltbundesamt.de [accessed May 11, 2018]).
- Changes in Atmospheric Constituentsand in Radiative Forcing (PDF)
- R22 exit (Johnson Controls advertising brochure) ( Memento from November 14, 2014 in the Internet Archive )
Query at Geizhals.de regarding refrigerants, August 8, 2018:
- Monoblock: 1 * R134a, 11 * R290, 2 * R32, 2 * R407C, 57 * R410A, 23 * unknown
- Split units: 1 * R134A, 2 * R32, 43 * R410A, 20 * unknown
- press article ; exact device name blau-engel.de; accessed on August 8, 2018
- energieagentur.nrw (PDF)
- p. 75, Why do we heat our room? in: Michail W. Wolkenstein (Mikhail Vladimirovich Volkenstein), Entropy and Information