S R C C Alternatives to H F s in the efrigeration and Air Conditioning Sector ection 01 27 becomes necessary to make a risk assessment to ensure that risks are acceptable. On most markets hydrocarbons are rarely introduced in existing equipment as electrical systems and controls are often not suitable and need to be redesigned. There are systems that after careful evaluation can be modified to be safe but the challenges are much bigger than in new systems designed for a flammable refrigerant. Extensive presentation of hydrocarbons as an option in RAC systems can be found in (gtzgtz-Proklima, 2008). The hydrocarbons most commonly used in traditional HCFC applications are: Propane (R-290) having characteristics similar to those of R-22 has been introduced in a wide range of commercial and air conditioning applications. The cooling capacity is typically significantly lower than R-22 and performance (COP) in the range of -2 to +6% relative to R-22 [Bitzer, 2008]. Propane has been introduced in a wide range of applications and when proper consideration of high solubility in oils has been taken good operating experiences are reported. Propylene (R-1270) has higher cooling capacity and lower boiling temperature than propane and is the preferred option by some manufacturers. The higher pressures and discharge temperatures need to be taken into consideration especially for use in hot climates. Hydrocarbons are often claimed to be compatible with all commonly used oil (mineral, alkyl benzene and ester oils). This statement is very questionable as not all oils will give a reliable function with hydrocarbons. Use of hydrocarbons with traditional oils without changing oil viscosity and/or making system design modifications has in many cases resulted in high failure rates caused by the extreme miscibility between oils and hydrocarbons resulting in increased wear in compressor. Besides redesign or relocation of electrical systems and controls, it is often advisable to also increase the viscosity of the oil and ensure sufficient superheat through a suction gas heat exchanger [Bitzer, 2008]. TEC HNICAL INFORMATION For an unventilated area the allowed refrigerant charge in kilograms to avoid flammability is: mmax = 0.25 x LFL x A x 2.2 [T. JABBOUR, D. CLODIC] W here LFL is the Lower Flammability Limit in kg/m3 and A is room area in m2. For propane (R-290) LFL = 0.038 kg/m3 For Isobutane (R-600a) LFL = 0.043 kg/m3 The safety limit of 0.25 is used to compensate for the differences in density resulting in an increased concentration near the floor. For example, in a room that is 3x4 meters the maximum allowed charge of R-290 is 250.8 grams, not taking into account the increased safety measures according to standard IEC 60335-2-40 [IEC, 2005]. 1.4.3 CarbCarbon dioxide (COCO2) Su mmary CarbCarbon Dioxide Carbon dioxide technology is currently the most innovative area in refrigeration. CO2 is not a new technology, but it has been widely used in the RAC sector for a long time because there have been easier and lower cost competing technologies. However, with an increased movement to reduce the use of HFCs and the search for non-flammable, non-toxic refrigerants, CO2 has become an interesting alternative with zero ODP and insignificant GWGWP. The two main challenges involved are the high system pressure at normal operating temperatures and the low energy efficiency (COP) for a standard refrigeration cycle. It is possible to design new equipment to make it suitable for higher pressures and more and more manufacturers