A refrigeration system for supermarkets using natural refrigerant CO2

0 London South Bank University , 103 Borough Road, London, SE1 OAA 1 Tesco Stores Ltd , Shire Park, Welwyn Garden City This paper describes a refrigeration system using a natural refrigerant that has been developed to reduce significantly both direct and indirect greenhouse gas emissions. The new system uses both R-404A and CO2 (R-744) as refrigerants. The new system has very low global warming potential compared with conventional HFC systems which reduces significantly direct emissions. Indirect emissions are also much reduced as the system efficiency is much greater than achieved using conventional HFC refrigeration. The paper firstly describes an experimental system that has been used to demonstrate the new technology. It then compares the relative efficiency, operating cost and greenhouse gas emissions from the new system with that from a conventional system. It can be seen that emissions are approximately 66% of those from a conventional installation. Introduction R-744 (CO2) as a refrigerant Proposal to use CO2 as a refrigerant (Alexander Twining, British patent) The peak of utilizing CO2 as refrigerant Renewed interest in CO2 refrigeration technology. New system demonstrated in Kilmarnock Scotland Solid Solid Liquid Liquid -10 oC 26 Bar -28 oC 11Bar Liquid - vapour - 56,6 Deg.C Solid - Vapour - 78,4 Deg.C Enthalpy (kJ/kg) +31 Deg.C Supercritical Critical point Triple point Vapour R744 R404A R410A Temp-Pressure Comparison Power Steering 115 Bar Bar (g) CO2 15C Temperature Compressor CMO 28 at 1470 rpm Compressor CMO 28 at 1470 rpm Condensing temperature at 10C 45 Evaporating temperature (C) R744 CO2 150 kW 50.8 mm 2026.0 mm2 25.4 mm 506.0 mm2 Refrigerant Capacity Circuit Penalty Velocity Diameter Area Velocity Diameter Area 150 kW 1.4 K 11.3 m/s 101.6 mm 8107.0 mm2 38.1 mm 1140.0 mm2 150 kW 1.5 K 25.6 m/s 72.6 mm 4139.0 mm2 25.4 mm 506.0 mm2 Dry Suction Line LIquid Line 20.0 kW 15.0 kW 10.0 kW 5.0 kW 0.0 kW EVAPORATING TEMPERATURE Heat Transfer Comparison (same coil) [5]. R-744 systems Figure 8. Danish Supermarket Pack Installed at ISO Roskilde Denmark. Commissioning of test rig R744 COMPRESSOR R404a COMPRESSOR R404A CYCLE Expansion Device PULSE VESSEL PUMPED R744 10C R744 PUMP Expansion Device Expansion Device R744 L.T. CYCLE COPtotal = QeM.T. + QeL.T. P404A + Pcond fans + Ppump + PCO2 COPtotal = QeM.T. + QeL.T. P404A M.T. + Pcond fans + P404A L.T. + Pcond fansL.T. MT P404A sor kW Ppump = power input refrigerant pump kW, Pcond fans = power input condenser fans kW The COP of the test rig was better than expected by about 0.3, although this COP could be improved with a correctly sized pump and a more balanced system. These crude Table 1. Test Rig Performance Copeland ZB45KCE-TFD 2 Copeland ZB45KCE-TFD 2 Actual High Side Tc Te Qe Te Qe Ppump COPCO2 MT Te Qe Ptotal COPTotal L.T. Bitzer 2KC-3.2 K System 36C 15C 17.8 kW 7.0 kW 0.5 kW 24.8 kW 2.39 10C 4.7 kW 0.8 kW 5.7 Expected High Side Tc Te Qe Te Qe Ppump COPCO2 MT Te Qe Ptotal COPTotal L.T. Bitzer 2KC-3.2 K System 36C 10C 4.7 kW 1.0 kW 4.7 Figure 11. Cycle Prediction for Low Temperature System from Cool Pack Software [8]. Leakage Recovery losses Energy consumption Where High Side Copeland ZB45KCE-TFD 2 R404a/CO2 Cascade Tc Te Qe Te Qe Ppump Tc Te Qe Ptotal System STANDARD System Copeland ZB26KCE-TFD 1 Te Qe Tc Te Qe Ptotal L.T. Copeland ZF48K4E-TFD 1 36C 28C 10.1 kW System 36C 15C 17.8 kW 8.0 kW 1.7 kW 25.8 kW 1.83 10C 4.7 kW 0.2 kW 23.50 10C 28C 10.0 kW 1.5 kW 11.5kw 6.67 11.4 kW 1.29 Conclusion 9.0 kW 21.4 kW 1.5 kW 0.96 14.4 kW 1.06 Standard Method of Calculation Input Data Annual Energy Consumption Sectoral Factors Recovery Efficiency () CO2 Emission Factor Refrigerant Loss Operational Refrigerant Loss Retirement Total Lifetime Refrigerant Loss (L) CO2 Equivalent Indirect Effect TEWI Application Sector Refrigerant Fluid Refrigerant Charge (M) Power Input Ancillary System Operational Life Time (N) Refrigerant GWP L1 5 L2 0 Commercial R404A 70 107,844 0.00 smaller compressors smaller pipe work and valves smaller heat exchangers more energy efficiency environmentally more friendly reduction in greenhouse gas emissions cheaper refrigerant Acknowledgements TEWI Calculations for the R-744 Rig Standard Method of Calculation Input Data Application Sector Refrigerant Fluid Refrigerant Charge (M) Annual Energy Consumption Power Input Ancillary Sectoral Factors System Operational Life Time (N) Refrigerant GWP Recovery Efficiency (a) CO2 Emission Factor Input Data Application Sector Refrigerant Fluid Refrigerant Charge (M) Annual Energy Consumption Power Input Ancillary Sectoral Factors System Operational Life Time (N) Refrigerant GWP Recovery Efficiency () CO2 Emission Factor R404A CALCULATIONS Refrigerant Loss Operational (L) Refrigerant Loss Retirement Total Lifetime Refrigerant Loss CO2 Equivalent Indirect Effect TEWI R404A R744 CALCULATIONS Refrigerant Loss Operational Refrigerant Loss Retirement Total Lifetime Refrigerant Loss CO2 Equivalent Indirect Effect TEWI R744 TEWI TOTAL Commercial R404A 10.0 kg 4423.9 kWh 0.0 kWh Commercial R744 (CO2) 40.0 kg 725.3 kWh 0.0 kWh 10.00 1.00 25.00 0.00 30.00 7.00 37.00 138 750.00 19 022.73 157 772.73 110.00 0.00 110.00 110.00 3 118.88 3 228.88 161 001.60 (...truncated)