Air conditioning

Air conditioning is a system for generating and maintaining a uniform indoor climate. The term air conditioning system used in Germany, in the sense that in a room temperature, humidity and air quality can be generated and maintained. In contrast, in the air conditioning foreign often only a space cooling ( air conditioning ) understood.

Air conditioning systems provide a defined space climate. For machinery spaces and data centers the necessary environmental conditions for plant and machinery are manufactured. A pleasant indoor environment for the human has a temperature of about 22 ° C and 50 % relative humidity.

• 9.1 Vehicles
• 9.2 ships
• 9.3 Railway
• 9.4 aircraft

Classification

An air conditioner is to condition a room using the air supply and the air guide the task. The classification is based on the controlled thermodynamic functions for the supply air.

Classification of ventilation, partial air conditioning and air conditioning systems according to DIN EN 13779

Legend: X is governed by the partial air conditioning. (x ) is influenced in part c, but not regulated. Furthermore, the air conditioners are also marked by the ventilation function. If outside air is supplied, it is an air conditioning system with ventilation function. Contrast, only convection is driven, the air conditioning is without ventilation function.

Pros and cons of air conditioning

The impact of air conditioning on productivity at work are controversial and influenced by many individual factors.

Pro:

• Fresh air, is supplied to the working spaces. This is in accordance with occupational health and safety, such as in Germany after the Workshop Guidelines ventilation (ASR 5) reached when the air quality is essentially the outdoor air quality is. In addition to CO2, odors and pollutants such as solvents from building materials or carpets, ozone from laser printers, dusts, gases and vapors evolved from manufacturing processes, etc.. Scale is the maximum workplace concentration (MAK).
• At about 20 ° C, the man is 100% efficient. At 28 ° C, the efficiency is lowered to 70% and at 33 ° C to 50%. According Workshop Guidelines room temperature ( ASR 6), the temperature at office workplaces do not exceed 26 ° C.

Cons:

• A survey of the AOK revealed that feel affected by poor ventilation and air conditioning systems for almost 40 % of respondents. Poorly maintained systems can not dissipate or even spread bacteria, mold and other microorganisms pollutants.
• Although consume modern, efficient air conditioners less energy than older devices, but a power loss -free operation is impossible in principle. The noticeably affected the power supply networks, particularly in urban areas.
• If refrigerant (eg R410A with a GWP of 1725 ) released into the environment, then transmits it in by the global warming potential for global warming. Operators of larger chillers are therefore bound by the Chemicals Climate Protection Ordinance to allow check the tightness of the system regularly. Modern refrigerants have no ozone -depleting effect more.
• The room temperature can also be set too cold by the user. Colds in the summer is partly attributed to a " cold shock " when entering a refrigerated space. It is, therefore, the room temperature is not recommended colder than 6 ° C of the set ambient temperature. Modern control systems with sliding adjustment of the room temperature to the outside temperature fulfill this automatically.

Central Air Conditioners

Air flow, filtration, temperature control, humidification and dehumidification - - For central air conditioning systems the necessary ventilation basic functions of the thermodynamic air treatment can be performed in a central supply air and exhaust air in a central unit. When the temperature of the Wärme-/Kältebedarf the supplied outdoor air and possibly the transmission heat / cooling for the rooms to be provided. Of the two devices off air ducts distribute the individual rooms.

Central air conditioners are divided into combined Luft-/Wasser-Anlagen and air-only systems.

• Luft-/Wasser-Anlagen

• Air-only systems

Central air conditioners are considered to be proven. The demands for comfort in space with respect to air quality, volume, humidity, freedom from drafts and temperature can be met. The spatial concentration of essential structural components offers economic advantages in terms of energy efficiency, maintenance, hygiene and land use.

Central ventilation systems allow a comprehensive and energy efficient processing of the required air. Regardless of the orientation of facade is mostly wind-/regengeschützt on the side of the building facing away from traffic near the ground in winter relatively warm and introduced relatively cool outside air into the building in the summer. The sizes allow for consistent use of components with high efficiencies, such as fans, heat recovery, sound attenuation. To increase energy efficiency, powerful multifunctional heat recovery systems can use that also in the summer " by-product " with indirect adiabatic evaporative cooling self-generated cold ready. Thus, the heating system is relieved by a portion of the thermal air conditioning, and large current- consuming refrigeration systems including their cooling plants are avoided. In addition, architectural ways to avoid transmission heat losses, such as double facade or passive house can be fully exploited.

Is calculated the cooling load when planning a permanently installed air- conditioning, is incorrect dimensions can be avoided. The cooling load calculation is based on the VDI2078. Often receiving the data from the relevant existing documents shall be sufficient (U - value of building materials, floor plans, etc.).

Decentralized air conditioning

In decentralized air conditioning air treatment air promotion, filtering and tempering are carried out directly in the room. Regardless of the sky orientation of the building room by room is sucked in the air needed on the facade and incorporated into the building. The exhaust air is also discharged back room by room over the facade to the outside.

Analogous to the central air conditioning systems is decentralized air conditioning can also be divided into Luft-/Wasser-Anlagen and air-only systems. However, here the air-only systems confined to relatively small areas, such as office space on the facade.

Decentralized air conditioners are the result of window cooling units, as they have long been used in the hot regions of Asia and America, by a ventilation and heating function has been added. Decentralized air conditioners are preferably provided for retrofitting into individual rooms. At the comfort requirements offs must be made under circumstances when air quality, volume, humidity, draft-free and hygienic. This can for example be because loaded with traffic- facing facades, outside air is led into the room that over the facade blown exhaust air is sucked in again, that in addition to the fan noise on the façade openings and traffic noise in the room gets across that no humidification and dehumidification takes place, that the wind pressure has influence on the air balance of the building or become contaminated soaked filter due to lack of Filtervorerwärmung.

Decentralized air conditioners are mainly installed under the floor or in the parapet. This reduces central air distributions in buildings and the expulsion of some technology areas in the basement or on the roof. The incorporation into the sill has the potential lower floor heights, but the effective floor area is thereby in turn reduced by the projection of the parapet. It should be noted that facilities can not be air-conditioned building core or basements.

In achieving good energy efficiencies smears are able to make larger systems. This is because that the air distribution is not avoided advantage outweighs the disadvantages of the thermal air treatment. Due to the limited mounting situations, the individual components are kept small, which reduces the achievable efficiencies eg in fan, heat recovery or silencer. Not against rain and wind protection but it can happen during the heating season, the colder facade outside air must be warmed up more and then be expected with a higher Luftheizbedarf. Due to the thermal radiation and also the facade outside air in the summer requires higher cooling capacity. Since no indirect adiabatic evaporative cooling is available, the cooling performance on chillers and cooling towers must be generated that require additional technology areas and cause high power consumption. During maintenance of distributed components has shown that time and transportation costs for long distances and re- set-up times on the spot draw consistently increased costs. Maintenance work in the room can cause disabilities in the workflow of the people present there. Decentralized air conditioners allow their own concept for the flexible use of space and cost accounting.

To avoid Fortluftansaugungen over the façade and thus also reduce fire and smoke transmission, one introduces decentralized air conditioning systems now increasingly as hybrid versions of. The exhaust air is summarized in the building and removed via a central exhaust air unit on the roof, while the Außenluftansaugungen the individual rooms still take place on the facade.

Control and comparison process

The interconnection of the various units for air conditioning require special control algorithms. They have a direct influence on the economy, the consumption of resources and the environmental impact of air conditioning. The different control methods may be assessed, although with annual simulations for their efficiency, but it does not allow testimony regarding their actual, absolute quality article. For this reason, comparison of air conditioning processes have been developed. They are based on an optimization strategy ( dynamic optimization with variable temperature and humidity) with a variable -defined objective function.

Sick Building Syndrome

The Sick Building Syndrome is wrongly associated only with air conditioning. As the word syndrome indicates, but must have been several criteria to trigger symptoms. The well-being in air conditioned rooms is dependent on six main factors, of which only the first two of the following main factors can be influenced by air conditioners, however. Only when all criteria are met, it does not come to Sick Building Syndrome.

Ecological consideration

From the proliferation of air conditioning equipment, new and stressful problems such as very high energy costs, congestion of energy suppliers and local climate changes arise. For this reason, for example, people call in the Tokyo area their territory, which lies approximately at the latitude of Los Angeles, already " heat island ".

To prevent these problems, has been used since the mid-1980s in Germany more and more adiabatic cooling in air conditioning of buildings. The required cooling is produced by evaporative cooling. By evaporation of water to air results in a cooling potential that is always below the environmental temperature. The achievable lower temperature depends on the climatic conditions of the air and is located in Germany on average over 10 ° C. Except for the transport of air and water, no mechanical or electrical energy is required for cooling. Thus, the adiabatic cooling enhances summer in the premises of the German Federal Office for a pleasant climate. With one m³ of water ( about 5 € ) can be so on the day about 1000 sqm of office space cool. An extreme case for the adiabatic cooling was the EXPO in Seville in 1992. There, the outside air temperature was lowered to the EXPO site by evaporation on peak days of 42 ° C to 36 ° C significantly more pleasant. Also (for example, well water, surface water) be installed cooling systems for office buildings based on Erdkälte. In this example, a nearby lake is 4 ° C cold water taken from sufficient depth and distributed by a kind of " local cooling network " in certain buildings, then the water is returned to the lake. Condition is the environmental impact of such measures as they may have altered temperatures effects on the ecology system ( fish stocks, water quality, etc.) in the vicinity of power plant cooling towers can be statistically demonstrated that the adiabatic cooling leads to increased precipitation in the nearby area ( also " industrial snow ").

Mechanical cooling

Air conditioning can over conventional heating and air purification systems also cool, filter and dehumidify. For this purpose it has a cooling circuit, as is similarly to be found in many refrigerators. The filtering is often filter webs. Condensation surfaces with water outlets are used for air drying. Roughly speaking, heat is carried away by the refrigerant circuit and then released on the other side. Consequently, air conditioning always requires a medium with which they can transport the heat. This is usually done is modern refrigerant R410A, R407C; R134a; Chlorodifluoromethane (R22 ) or R290 ( for small systems because of fire ), and in vehicles as well as R-134a used in the older R12 now banned.

A cold air producing air conditioning has a heat pump in general. In the refrigeration cycle, the relationship is exploited between pressure and temperature of the greenhouse gas: a gas which is compressed, heats up; conversely, it cools down when you relax it ( expand again) leaves.

The energy consumption, the need of modern air conditioning systems for cooling or heating could be steadily reduced. Since they only pay for the transport of heat through the refrigerant circuit (compressor), today higher quality air conditioners with a capacity figure 3.5 and 4.0 are not uncommon. So this need in a modern, high quality air conditioner with a cooling capacity of 4 kW only a drive power of about 1.1 kW.

For home and car air conditioners, the consumption strongly depends on the difference between indoor and outdoor temperature. If air-conditioning for cooling of data centers or machines, the primary consumption factor is the heat generated by the devices, which must be dissipated.

Air conditioners are also increasingly used for heating (ie, a " reverse operation"), as they refer to around 2 /3 of the amount of heat emitted from the outdoor air and only 1/ 3 of the amount of heat emitted electrically record ( heat pump principle ). Modern devices achieve performance figures of up to 5 in heating and up to 4 in the cooling mode, ie only 20-25 % of the required amount of energy coming from the outlet. Higher-order split air conditioners with heat pump function are therefore far more efficient than electric heaters. It will be for larger buildings already built heat recovery systems, where the waste heat in cooling mode can be used for the heating of domestic hot water. A combination with floor heating is possible today.

As such split systems air conditioners are called that. Above an outdoor unit ( condenser / compressor) and connected thereto via refrigerant lines indoor unit ( evaporator) and optionally multiple indoor units ( multi-split systems) have, For technical understanding of the running cycle process in split units, see section " compression refrigeration systems " in the article chiller.

As air conditioners with inverter or inverter technology such facilities are referred to, in which the performance of the air-conditioning compressor can variably adjust the cooling demand. The central role in the regulation of the compressor in this case has a frequency converter, also known as inverters - hence the name.

In conventional air conditioning systems the compressor is running either on maximum power or is turned off. The adjustment of cooling capacity is through the exchange of different length periods of operation and standstill of the compressor. In inverter - controlled systems, the performance of the compressor is adapted to the cooling demand variable and fluid. The alternating current from the power network will be first converted by means of a rectifier to direct current, while the downstream inverter converts the current to an alternating current of different frequencies. Depending on the ac frequency, the motor of the compressor then turns faster or slower, thus changing the performance of the compressor.

Since in an intense start-stop operation, the mechanical components of the device due to greater use and also the power supply is charged inefficient due to abrupt changes in power consumption, are air conditioners with inverter technology in situations with frequently and continuously changing cooling (or heating ) needs more efficiently. In situations where a continuous operation is required on maximum power, the conventional devices are again at an advantage, since considerable energy losses caused by the conversion between AC and DC current at the inverter technology.

As with other appliances, the devices in energy efficiency classes from A ( good) to G ( worst) to be divided; this information is now mandatory.

In addition, to a lesser extent, gas heat pumps in use. These are operated by an internal combustion engine and take their energy from natural gas or LPG. Current is needed here only for control or for cold water machine for smaller pumps. A well-known manufacturers of this equipment is the company Aisin Seiki. Gas heat pumps have the advantage that they use primary energy directly as losses that are lost in the generation of electricity from gas and losses due to transport of electrical energy can be avoided. However, they have the disadvantage of increased cost and maintenance.

Application areas and types

The types of air conditioners are very different; there is a distinction between

• Direct evaporators and
• Indirect cooling via chilled water or brine cooler.

In small air conditioning systems such as space cooling devices, mobile air-conditioning systems, crane systems and air conditioning systems in trains, the air is cooled directly by the installation of an evaporator bundle into the air stream. Great plants for air conditioning in office buildings or even for cooling larger switchboards with a larger number of cooling junctions are cooled indirectly. The evaporator of the refrigeration system is a heat exchanger that cools water or brine. The brine consists of water, is added to the antifreeze. There is a closed cooling circuit operated with centrifugal pumps, in which an expansion vessel is mounted for receiving the thermal change in volume.

The performance of air conditioning systems ranging from 2 kW cooling capacity ( air conditioner ) to central refrigeration systems in coal mines with a cooling capacity up to 3000 kW per compressor unit.

For private use monoblock or split units are:

• Monoblock units have an exhaust hose to be permanently installed in a wall opening or to be hung from a window. These devices have the disadvantage that by the inevitable pressure compensation blown to the outside air is replaced immediately by warm and humid outside air flowing through the cracks in windows and doors. Thus, a large part of the effect of the air conditioner zunichtegemacht again. Furthermore, these devices are louder than split systems, since the compressor has to work inside the home. However, there are also devices having a monoblock second tube for suctioning outside air, so that no air pressure compensation is required. This dual-hose units are but so far not widespread.

• Split units are more efficient, as the condenser can be placed at a convenient location outside the space to be cooled. Condenser and evaporator are connected via hoses. The hose coupling is carried out with practically no dead space, so that after connecting the parts of the air conditioning system can be operated without intervention in the refrigerant circuit. Some split air conditioning units are now sold with a so-called heat pump circuit, which makes it possible to operate the air conditioner in the fall, winter and spring as an energy- saving additional heating up to an outside temperature of -15 ° C.

Known from the U.S. is also air conditioning on the size of a microwave oven that can be placed in a window frame, and delivers the heat directly to the outside. This, however, it is necessary to close the rest of the window frame against the exhaust otherwise reentrant. This is only feasible with the usual in the USA, windows that can be slid upwards.

Other areas of application

Rolling stock

Air conditioners are also used in aircraft and motor vehicles. Often this is spoken of climate control. The general difference is in the automatic control of an automatic climate in contrast to the simple control of a classic air-conditioning. This means, by constantly comparing the nominal / actual values ​​regulates automatic climate control independently after their own performance in order to maintain the desired temperature range. By contrast, the control of a conventional air conditioning is permanently available on the power set, so the user has to readjust itself constantly manually when the desired temperature range is no longer maintained. In addition, it is equipped with modern automatic climate control systems in vehicles even possible to adjust the temperature on the driver, front passenger and rear seats separately. Usually, the differential heating of the passenger compartment is compensated by sunlight, by the position of the sun over a Sun sensor (also: solar sensor ) is determined and accordingly the affected side of the vehicle cooled more.

Ships

The operation of an air conditioner is much easier and cheaper to ship, since the temperature drop can be delivered via the virtually unlimited available and relatively cold seawater. For this reason, much lower temperatures can be achieved. Examples of such as " chiller " designated air conditioners can be found eg on almost all vessels of the German Navy.

Railway

Nearly all modern rail vehicles such as unit trains, cars and the cabs of many locomotives are equipped with air conditioning. The units are either under the floor, but more often installed on the roof (especially with low-floor vehicles ). They are powered by the electrical system of the vehicle or via appropriate converter directly from the train line with energy. To prevent warm outside air can get into the car, the windows can not be opened when the air-conditioned trains. The units are designed mainly as compact units, rarer than split units.

Aircraft

History of development

The first fully functional air conditioning system according to the current principle to have been invented by WHCarrier 1911. In the area of car air conditioners, these were also built by Studebaker first in 1938 by Nash, and in the same year.

Abbreviations

• A / C ( " type air conditioning Carrier" ) = air conditioner according WHCarrier ( in vehicles. Conventional key)
• VRF ( "Variable Refrigerant Flow" ) = Variable refrigerant mass flow
• BTU ( "British thermal unit " ), 1000 BTU / h ≈ 293 W