Alternative cooling methods
In the search to find a "natural" refrigerant that is sustainable and meets demands.
Do "familiar friends" follow R134a? Ammonia and some hydrocarbons had been approved for a long time before they have been replaced gradually by CFCs in the middle of the 20th century. Today they have a renaissance as "natural" refrigerants in different fields of cooling technology. The reason is that they are an interesting alternative to CFCs that are harmful to ozone and climate. These refrigerants are available for the complete temperature range of compression refrigeration machines (-120 °C to +20°C), do not have any ozone depletion potential and no or only a minor global worming potential.
Are ammonia and hydrocarbons like propane or isobutene conceivable as refrigerants?
Each of these refrigerants has advantages and disadvantages. All have a favourable environmental effect. You should not forget one thing: A cold-climate sector that can fall 2/3 below the expected contribution to global warming in the medium term, could be able to end the pertinacious debate on the environmental effect of their refrigerants that lasts over decades.
Ammonia
Ammonia is a natural substance and thanks to its physical features the most efficient refrigerant of all. Due to its efficiency and its environmental behaviour it is an optimum substitute for R 134a. Unfortunately there are also negative aspects that considerably limit wide use in industry and require expensive technical solutions that have to be partly newly developed. The necessary measures considerably increase the expenditure for ammonia systems, especially in the field of medium and small outputs. For this reason efforts are undertaken worldwide in order to develop simpler systems that can be used in industry.
Hydrocarbons
Hydrocarbons are also efficient refrigerants. R 290 (propane) is especially suitable as a substitute. Pressure and cooling output are similar to R22 and the temperature behaviour is as favourable as R12 and R502. Cooling units have been operated worldwide with propane for years, primarily in industry. It is a proven refrigerant. Moreover, there is an increasing trend to use it in industrial cooling units and liquid cooling systems. A disadvantage of the hydrocarbons is that they can generate explosive mixtures in air. The filling quantity that is usually used in industry makes a design according to explosion protection regulations necessary.
"Outer values" are important for cooling units as well
A directed air routing must not only be ensured in the enclosure interior - the "outward effect" is also decisive for the cooling output. Cooling units must be able to dissipate their heat losses to the ambient unhindered. For this reason optimum air routing must be ensured in the interior and exterior circuit of enclosure cooling units.
The following example shows very clearly the negative impact of insufficient air routing in the exterior circuit. The warm exhaust air of the wall-mounted cooling unit of a competitor is dissipated out of the unit at the sides at the left- and right-hand top. Thus the enclosure surface is directly charged with radiated heat. Via convection it returns into the enclosure and leads inevitably to a lasting increase in the enclosure internal temperature and finally in heat loss to be dissipated. This again means the use of units with great cooling output. A kind of duct is generated between the two units in which hot air is blown in from both units. Here you can observe extreme temperature patterns.
The warm exhaust air of units with optimum air routing does not negatively affect the enclosure surface. The lower thermographic photo shows this impressively.
Green light for CO2 in motor vehicles
The EU ban against the R 134a refrigerant also includes the automotive field. The sub-suppliers must adjust themselves to the refrigerant CO2 for vehicle air-conditioning units and thus to a more expensive technology. Air-conditioning units in vehicles are only approx. 5% of the harmful emissions caused by traffic, but this share is too much: As of January 1st, 2007 only those substances are allowed whose GWP (Global Warming Potential - see Rittal Klima-Lexikon July 2004) reach a value of maximum 150 - as of 2011 this value will fall on 50. A long-term alternative is CO2, for the figures speak for themselves: Over a period of 100 years 1300 kg CO2 have the same effect on our earth climate as 1 kg of R134a.