Book - School of Science and Technology

Refrigerating media 535Table 19.1 Properties of refrigerantsRefrigerantProperties Ammonia R11 R12 R22 R123 R134a R407CGauge pressure (kPa)condenser (30 C) ‡1060 ‡24:8 ‡642 ‡1100 ‡8:2 ‡670 1160evaporator ( 15 C) ‡155 80:6 ‡81:2 ‡195 85:4 ‡62:6 189evaporator ( 5 C) ‡404 52:5 ‡254 ‡427 60:5 ‡249 321Boiling point ( C)(standard pressure) 33:3 ‡23:8 29:8 40:8 ‡27:8 26:1 43:8Critical temperature ( C) 1333 198 111 96 184 101 87.3Volume of vapourat 15 C(m 3 /kg) 0.509 0.766 0.093 0.078 0.873 0.121 0.09Latent heat of evaporationat 15 C (kJ/kg) 1320 198 162 218 175 187 212Theoretical energy inputper unit energy output(kW/kW) 0.211 0.200 0.213 0.216 0.203 0.217 ±Coefficient of performance(27 Cto 15 C) 4.75 5.00 4.69 4.65 4.93 4.61 ±Ozone depleting potential(ODP) 0 1.0 1.0 0.05 0.014 0 0Global warming potential(GWP) 0 1500 4500 510 29 1600 1980Occupational exposure limit(OEL) b (ppm) 25 1000 1000 1000 10 a 1000 a 1000CharacteristicsStrong irritantCan form anexplosive mixture incertain conditionsOdourlessNon-irritantNon-inflammableCentrifugal (1) (2) (1) (1) (2) (1) (1) (2)Usage Screw (2) (4) (4) (2) (3)Scroll (3) (3) (4)Reciprocation (4)(piston)Notesa Provisional recommendation by refrigerant manufacturers.b Health and Safety Executive. Occupational Exposure Limits. EH40/93.indices of common refrigerants are given in Table 19.1 together with those for ammoniaas a comparison.In addition, the table gives values for the occupational exposure limit (OEL), in partsper million, which reflect the toxicity level of the various refrigerants. In the knowledge ofthese allowable concentration levels in occupied areas, it is necessary that adequate ratesof ventilation be provided in plant rooms and recommended that refrigerant leakdetectionbe installed.It is clearly desirable to limit the discharge of any refrigerant to atmosphere and, inconsequence, provision should be made for pump-down (removal) from machines duringmaintenance activities. In addition, consideration should be given to limiting the volume