Investigation of the Performance of Trigeneration and CO 2 Refrigeration Systems in Supermarket Applications

Transcription

1 PRO-TEM Special Session on Power Generation and Polygeneration Systems Investigation of the Performance of Trigeneration and CO 2 Refrigeration Systems in Supermarket Applications Y.T. Ge, S.A. Tassou, I.N. Suamir Brunel University

2 Contents Background Supermarket Energy Control Systems Building and HVAC Refrigeration Trigeneration Model Prediction and Analysis Conclusions

3 Background A modern supermarket energy control system has a concurrent need for electricity, space heating and/or cooling and food refrigeration. The power supply to the supermarket is primarily from the national grid, which is less efficient due to the processes of energy conversion and transmission. The use of CHP can increase primary energy utilisation efficiency to over 60% and above 75% if space cooling or food refrigeration is provided from the CHP exhaust gas conversion (trigeneration). CO 2 refrigerant has attracted significant attention for application in supermarket refrigeration systems. A detailed performance analysis for the application of trigeneration in supermarket with all CO 2 refrigeration systems is therefore required.

4 Supermarket Energy Control System Building and HVAC Net sales area: 4536 m 2 Opening hours: 24 hrs weekdays until 22:00 on Saturday and 10:00-17:00 on Sunday Mechanical and electrical services of the store: Air Conditioning: 2 AHU Electric chiller with R-407A refrigerant for space cooling Heating system: 2 gas LPHW boilers and heating circuit Domestic hot water system Cold water service system CO 2 refrigeration CCHP (Trigeneration) with heating circuit and chilled water circuit.

5 Store Internal Space Temperature Controls Supply air duct HC Fresh air Sales area 18⁰C in winter 24⁰C in summer CC From compressors Return air Exhaust air Return air duct For supply and return air fan speeds: For fresh air damper: Where, f fan = percentage of fan speed(%) ; t sl = temperature of sales area ( C)

6 Refrigeration System 6 CV_HP 3 2 REC_HT EV_MT EV_LP Gas cooler/ Condenser BPV MT Evaporator LT Condenser COMP_HI_ 9LT REC_LT EV_LT 16 SHX LT Evaporator All CO 2 cascade system Compressor Isentropic efficiency COMP_LO P-h diagram of transcriticalcycle Constants a and b Refrigeration pack Compressor a b Dorin MT TCS362D Dorin TCS340D Bitzer 4EHC- LT 6K Bitzer 2EHC- 3K

7 Trigeneration System Feed Water Hot Water Boiler Hot Water Exhaust Gases Recuperator 3-way Valve 3ph Output Inlet Air Combustor Alternator Compressor Power Electronics & Controls Turbine Bowman MTG 80RC-G-R microturbine

8 Model Prediction and Analysis 90 Simulation-power Test-power Ambient temperature Ambient air temperature( temperature( C) Compressor power consumption in high cascade side (kw) Time (hour) Comparison of simulation and test results for hourly variation of compressor power consumption on high cascade side of CO2 refrigeration system

9 Simulation Test Compressor power consumption in medium temperature pack (kw) Time (hour) Comparison of simulation and test results for hourly variation of compressor power consumption of low cascade side of CO 2 refrigeration system

10 Air temperature ( C) Time (hour) Hourly variation of space air temperature in sales area

11 Heating/ /Cooling demand(kw) Heating demand Cooling demand Time (hour) Hourly variations of space heating and cooling demands of the sales area

12 200 Electrical or thermal energy(kw) Heat capacity from CHP exhaust Power generation Time (hour) Hourly variations of applicable heat capacity and power generation from one 80 kw CHP

13 Temperature( C) Time (hour) Hourly variation of flue gas temperature from one 80 kw CHP after meeting the heating and cooling demands of the sales area

14 Temperature( C) Time (hour) Hourly variation of flue temperature from two 80 kw CHPs after meeting the heating and cooling demands in sales area

15 Conclusions The application of 80 kw microturbine CHP systems to provide power, heating and cooling/refrigeration in a supermarket using cascade CO 2 refrigeration systems has been investigated. Due to the low ambient temperature and refrigeration cabinets, the heating demand dominates in the supermarket in the winter but there is also cooling demand in the summer. The use of two 80 kw CHP systems with heat recovered in the summer employed to drive a double effect Li-Br/H 2 O absorption refrigeration system has been found to be able to satisfy both the electrical demand of the CO 2 refrigeration systems as well as the space heating and cooling demands of the supermarket. Further investigations are necessary to include economic analysis for the application of trigeneration within supermarkets.