Room air-conditioners

Various types of equipment are grouped under the heading of room air-conditioners.

Depending on the type of unit, the air in the room may be cooled, dehumidified or heated. The great majority of units produced in Japan, for example, are “reversible” and hence suitable for heating as well. Known as “heat-pump air-conditioners”, these appliances must however be distinguished from the heat pumps commonly used for heating purposes in Germany (see Chapter 3.7).

A basic distinction can be made between units with an exhaust air hose (mobile room air-conditioners) and units with an external component (split units). Split units with an external component circulate the room air and use a refrigerant to extract the heat from it. Hose units remove the waste heat from the condenser to the outside via an exhaust hose and at the same time draw warm outside air into in the room to be cooled. The cooling effect of such units is therefore very low.

Mobile room air-conditioners are used where there is a need for fast and flexible solutions.

They are only suitable for short-term use (e.g. to bridge short periods of heat) and not for continuous use. Typical areas of application include living and work rooms [Stiebel Eltron 2003a]. The cooling capacity of these units ranges from 1 to 5 kW.

There are also compact air-conditioning units (window-mounted room air-conditioner) with a hermetically sealed compact refrigeration circuit in the range 1.5 to 9 kW, and split room air-conditioners – usually stationary – up to about 15 kW. The latter are systems consisting of a factory-made internal unit (evaporator) and a factory-made external unit (compressor-condenser unit) which are joined together on site to form a single system with connecting refrigerant pipes.

In an article in the magazine “test”, published by the consumer test foundation Stiftung Warentest, the authors say the following about the test results for several single-split and mobile air-conditioning units with a capacity of 2 to 4 kW: “From an environmental point of view, air-conditioners cannot be recommended because of their power consumption.

Intelligent heat protection with sources of shade is better.” And also: “Improve […] the building’s heat protection. If you prevent too much sunlight from entering the building in the first place, there is no risk of extreme overheating. In many cases an external roller blind can work wonders” [test 2008].

In capacity ranges up to about 50 kW (max. up to 100 kW) one finds stationary multi-split room air-conditioners consisting of several internal units connected to a single external unit [Daikin 2003]. Multi-split units are usually described as VRF units (VRF: variable refrigerant flow). By installing multiple VRF room air-conditioners it is also possible to serve larger buildings. This technology is then in competition with the centralised systems usually employed for air-conditioning of buildings. Centralised systems and the possibilities they offer for using halogen-free refrigerants are described in Chapter 3.3.5.2.

Stationary air-conditioners can be very quiet and are suitable for continuous operation. The internal and external parts of these systems are usually connected by copper pipes. The range of applications is broader than for mobile units: offices, living accommodation, technical rooms, wine cellars etc. [Stiebel Eltron 2003a].

Units with an internal and an external part (split units) can be implemented as mobile units. In this case the two parts are usually joined by a permanent “umbilical cord”, enabling the small external unit to be placed on the window-sill or balcony [Fachinstitut Gebäude-Klima 2003].

The great majority of units on the market in Germany are produced in Asia, and a few in other European countries [Daikin 2003].

In the past the refrigerants used were initially CFCs and HCFCs, most recently R 22 in particular, but these are now banned for new systems in the EU. The substitutes used are mainly HFC blends such as R 407C and R 410A, but also hydrocarbons (R 290/propane) [TÜV Süd 2003a; Daikin 2003; Delonghi 2009]. In the year 2000, units already produced using R 22 were converted to the HFC blend R 417A, because they were no longer allowed to be sold in Germany with R 22 [Rhodia 2000].

Split air-conditioners are also sold in department stores, building material/DIY stores and to some extent in supermarkets. This raises problems in connection with refrigerant emissions, especially in cases of improper use. Unlike “plug-in units” (mobile room air-conditioners), these units require expert installation. In many cases, however, this is not clear to the buyer, or only becomes clear after reading the instructions. Incorrectly installed units must be expected to cause increased refrigerant leaks, sometimes resulting in total loss.

HFC emissions in 2008 came to 321 t, or 64 times the figure for 2001 [Schwarz 2009b]. This is mainly due to the fact that since the final ban on R 22 in 2000, most of the appliances coming onto the market have used HFCs. The estimate of emission rates is based on the assumption that the units are installed correctly.

Reduction options

In the case of split units where the internal parts are in living or office areas, there is a direct connection to these rooms. This causes problems with the use of halogen-free refrigerants such as hydrocarbons [Daikin 2003].

Some European manufacturers nevertheless use hydrocarbons (R 290) as well, especially for mobile room air-conditioners (R 290) [TÜV Süd 2003a; Daikin 2003; Delonghi 2009]. There are also isolated cases on the market of split air-conditioners using hydrocarbons [Delonghi 2009]. These air-conditioners have a refrigerant charge of between < 500 g and 1,000 g [TÜV Süd 2003a]. As an approximation, one can generally work on the basis of 0.25 kg of refrigerant per kW of cooling capacity (or 0.15 kg per kW in the case of hydrocarbons) [UNEP 2003]. The German development aid agency (Gesellschaft für Technische Zusammenarbeit – GTZ), in cooperation with the Chinese manufacturer Gree, has developed a split air-conditioner using propane as refrigerant. This has a maximum charge of 330 g and a capacity of between 2.7 and 3.5 kW depending on the size of the unit. The units have a COP of at least 3.5, which is well in excess of the European requirements for energy efficiency class A. In the event of a leak the compressor stops running to avoid high temperatures, but the fan continues, thereby diluting the escaping refrigerant and preventing the formation of combustible concentrations. Acoustic and visual warnings indicate leaks. Series production is to start in 2010 [Hasse 2009]. Other manufacturers are also about to launch single-split systems using hydrocarbons [Hydrocarbons21 2010].

UNEP [UNEP 2003] reports that a number of organisations have made risk assessments which come to the conclusion that the use of hydrocarbons tends to reduce the fire or explosion risk. The risk is proportional to the refrigerant charge.

However, widespread use of hydrocarbons presupposes recognised standards and rules for their use even in cases of low risk. From an energy point of view, the use of hydrocarbons (propane) must be considered favourable [UNEP 2003; Calor 2002].

Although the use of CO₂ in the air-conditioning/comfort sector has so far been adjudged technically difficult and unfavourable from an energy point of view [Daikin 2003], the first prototype of a VRF air-conditioning system with CO₂ as refrigerant has recently been unveiled [Daikin 2009; CCI 2008]. This is designed so that it can be run with CO₂ or the HFC

and a new heat exchanger and valve technology were developed to achieve the high condensation pressures of up to 123 bar. However, delivery of the first series systems is not expected before 2012. In view of the heat pumps with CO₂ as refrigerant that have recently come onto the market (see Chapter 3.3.6), it can however be assumed that further advances will be achieved in future and a growing number of manufacturers will offer similar split systems.

Compared with compact units, the refrigerant charge in VRF units (greater cooling capacity) is large. In view of the design of these systems (one external unit and multiple internal units, resulting in numerous connections), the risk of refrigerant leaks is also greater, not least because of the total length of piping required, which may add up to a few hundred metres or as much as several kilometres [KI 2008b]. The leakage rate is around 5-15% [Jakob 2009]. In most cases it is possible to opt for alternative air-conditioning solutions with smaller refrigerant charges and lower refrigerant emissions. Possible examples include chillers with ammonia (see Chapter 3.3.5.2).

Another possibility for reducing emissions in this field of applications as well is technical and/or organisation measures. This includes ensuring installation by specialist personnel.

Conclusions

In the case of room air-conditioners, it is necessary to distinguish between mobile compact units and (usually stationary) split and multi-split (VRF) systems.

In mobile units where refrigerant charges can be kept below 500 g, it is possible to use halogen-free refrigerants (hydrocarbons) even having regard to safety aspects. Especially in the field of standardisation there is a need to establish better requirements/conditions for safe larger-scale use of hydrocarbons in appropriate areas.

Only in the case of split or multi-split systems is it still not possible to do without HFCs entirely. But there are also isolated (fairly small) split systems on the market which use propane. An alternative to installing multiple VRF air-conditioning units with large total HFC charges is the installation of a centralised air-conditioning system (see Chapter 3.3.5.2).

At present there is no reason to expect widespread use of CO2, although it remains to be seen how things develop in this field in future.

In the case of units intended for direct sale to final consumers, a clearly visible indication of the need for installation by a specialist enterprise should be provided where necessary.