Since the signing of the Montreal protocol in 1987, many countries have carried out the study on the replacement of CFCs and HCFCs substances. In 1997, the CFCs and HCFCs refrigerants were studied in order to protect the ozone. However, the "Kyoto Protocol" after the signing, people turn to focus on ozone protection and reduce the greenhouse effect, requires that the OPD value of the refrigerant is not only smaller, GWP value is also smaller.
According to the "Montreal Protocol" CFCs in developed countries has been disabled, HCFCs because of the destruction of ozone is also about to be eliminated. Due to the higher GWP, the Kyoto Protocol will replace the CFCs and HFCs HCFCs substances included in the list of restricted substances, which requires developed countries to control HFCs emissions. All of these have a higher requirement for alternative refrigerants. Therefore, the ideal alternative refrigerants in addition to the lower ODP and GWP values, but also has good security, economy, good thermal properties and other advantages, to achieve both environmental protection and energy saving.
The new type of alternative refrigerants mainly consists of two kinds of artificial synthetic and natural type, which have two aspects, one is a single working medium and the other is mixed. The mixture can be divided into three kinds: one is the mixture, the other is the mixture of the other and the other is the mixture.
There are mainly the following aspects of the synthesis of refrigerants:
1.R-134a
ODP = 0, GWP = 420, R134a =, non flammable, non-toxic, tasteless, safe use, its thermal properties and R12 is very close, can be used to replace R12, used in automotive air conditioning and home refrigerators and other fields. However, the use of R134a, will increase the energy consumption, and with the CFC - 12 used in lubricating oil is not compatible with the material compatibility aspects are also different CFC-12. In addition, it is a kind of greenhouse effect gas, so it still has some defects.
2.R-152a
From materialization of aspect HFC-152a also with CFC-12 close, R152a substitutes for R12 after energy consumption can be reduced 3% to 7%, but the in the air content of 4.8% - 16.8% with combustible. Therefore, to promote the use of receive certain restriction. And it can be mixed with other substances, to form a non - boiling mixture to replace CFC-12.
3.R-410A
R410A is a nearly co boiling mixed refrigerant, which is composed of 50% R32 and 50% R125 by mass fraction. ODP = 0, mainly used to replace R22, the unit volume refrigeration capacity, heat transfer performance and flow performance is good, but the same temperature and pressure value is about 60% higher than R22.
4.R-407C
R407C is a non - co boiling mixed refrigerant, which is composed of 23% R134a, 25% R125 and 51% R32 by mass fraction, ODP = 0, and the unit volume refrigeration capacity is large, but the heat transfer performance is poor.
There are mainly natural refrigerants:
5 hydrocarbon [6]
At present, R600a is widely used in refrigerators in Europe and some developing countries, including GWP (R290), R600a, and ODP, which is in accord with the requirements of the Kyoto protocol. In addition R290 and R600a composition of the mixed refrigerant also has a certain development.
6 ammonia (R-717)
Ammonia has been used for 120 years and is still in use. The ODP=0, GWP=0, has excellent thermal properties, low price and easy to leak. But ammonia is toxic and flammable, it should be noticed, but more than a hundred years of use records show, ammonia accident rate is very low. In the future, we should find a safe way to better, such as reducing filling quantity, adopts the screw compressor, the introduction of plate heat exchanger and so on. However, the oil soluble, and some of the material is not high, the high exhaust temperature and other issues also need to be solved reasonably. It seems that the NH3 will have a greater market share.
7 carbon dioxide (R-744)
CO2 is the natural existence of natural substances, ODP = 0, GWP=1. Wide range of sources, low cost, CO2 safe, non-toxic, non flammable, adapted to a variety of commonly used mechanical parts and components of the oil, even in high temperature does not decompose harmful gases. CO2 of the latent heat of evaporation is larger, unit volume refrigerating capacity is very high, so the compressor and component sizes are smaller; adiabatic index is higher K=1.30 compressor pressure ratio is 2.5 to 3.0, lower than that of the other refrigeration system, volumetric efficiency is relatively large, close to in the best economic level, have great potential for development.
Filling method of air conditioning refrigerant