Research on CO 2 Heat Pumps and Other CO 2 Novel Systems at The Energy Department of KTH

Transcription

1 Research on CO 2 Heat Pumps and Other CO 2 Novel Systems at The Energy Department of KTH Yang Chen (KTH) Per Lundqvist (KTH) 1

2 Content Research on CO2 heat pump systems (Effsys 2 project) Thermal properties of Supercritical CO2 and their influences on heat exchanger performance Research on other CO2 novel systems 2

3 Current Research Project on Carbon Dioxide Heat Pump Systems (EffSYS 2) Companies involved in the project (more than 12 industrial companies involved) Ahlsell Alfalaval AB Climate Check Climate well Dorin (Italy) Danfoss (Danmark) Güntner (Germany) IVT NIBE RANOTOR SRM Thermia Värme Green and Cool EffSYS 2 is a Swedish governmental energy research program on efficient refrigeration and heat pump systems. 3

4 Research Contents of Current Effsys 2 project Testing the performance of a commercial CO2 heat pump sold in Sweden (Sanyo. Eco-cute) Building up a permanent testing center at the Energy Department of KTH for CO2 heat pump system research Heat exchanger design (temperature profile) System performance (optimization) Control strategy Component testing 4

5 A transcritical refrigeration/heat pump cycle Carbon dioxide has a low critical temperautre but high critical pressure (31.1 C, 73.8 bar), thus a carbon dioxide refrigeration/heat pump system works as a transcritical cycle). 5

6 Problems with Heat Exchanger Design in Supercritical Region C P of Supercritical Carbon Dioxide Thermophysical properties of CO 2 have rapid changes near the critical point, which create many new phenomena for heat exchanger design. CP(KJ/kg K) P=8.0 Mpa P=9.0 Mpa P=10.0 Mpa P=11.0 Mpa P=12.0 Mpa Temperature (ºC) Cp (kj/kg k) e 6 3 a IHX GC d b g CO 2 transcritical refrigeration cycle integrated heat exchanger's Cp h chart H (KJ/kg K) Supercritical carbon dioxide Low pressure side carbon dioxide in IHX Gas cooler cooling air c h Temperature (ºC) e a 0 IHX GC g d b CO 2 transcritical refrigeration cycle integrated heat exchanger's T h chart Low pressure side carbon dioxide in IHX Gas cooler's cooling air Supercritical carbon dioxide H (KJ/kg K) c h 6

7 Research on other CO2 novel system System research CO2 power system in low-grade heat source utilization CO2 double loop system Dynamic simulation Employing EES+TRNSYS to develop a dynamic system model for yearly performance simulation 7

8 The advantages of CO2 power system in utilizing low-grade heat source Supercritical CO 2 s temperature profile can match better to the heat source than other working fluids (organic working fluid, fluid mixtures, etc.) Schematic illustration of the heat transfer between the low-grade heat source and the working fluid in a counter flow heat exchanger. (1a) pure fluid; (1b) zeotropic fluid mixtures; (1c) carbon dioxide 8

9 Reverse CO2 Refrigeration Cycle for Power Production Carbon Dioxide Transcritical Power Cycle d 0.01 T [ C] bar bar 220 bar 160 bar 100 bar f e 0.019m3/kg b c a 60 bar 40 bar s [kj/kg-k] 200 Carbon Dioxide Brayton Cycle d A bottoming cycle with carbon dioxide as a working media Approx.12% efficiency with 150 C expansion inlet temp. T [ C] a b 0, bar 300 bar 250 bar 200 bar c 150 bar 0,2 0,4 0,6 0,8 100 bar s [kj/kg-k] 0,0057 f e 0,01 0,063 m3/kg 0,034 9

10 Solar Driven Carbon Dioxide Power System 30 m bar Controller controls the temperature Turbine efficiency: 0.85 CO 2 mass flow:540 kg/hr Pump efficiency: bar No IHX Cooing water mass flow:720kg/hr. Inlet temperature: 15 C 10

11 Simulation Methodology Weather data Type66c Collectors Collectors TRNSYS Ees.lnk 11

12 Daily Performance Daily performance of solar driven carbon dioxide power system under a randomly selected Swedish summer day (15th of July) in stockholm (at 120 bar gas heating pressure) Temperature ( C) Tsc_out P_turbine P_pump P_net 09:30 10:30 11:30 12:30 13:30 14:30 15:30 Time Power (kw) 12

13 Annual Simulation of Daily Net Energy Production (kwh s) Daily net energy production (kwh s) of a solar driven carbon dioxide power system in one year (at 120 bar gas heating pressure) Net power prodution (kwh's) January February March April May June July Auguest September October November December 13

14 Annual Simulation of Monthly Net Power Production (kwh s) Monthly net power production (kwh s) of a solar-driven carbon dioxide power system in one year (at 120 bar gas heating pressure) Net power production (kwh's) January February March April May June July Auguest September October November December 14

15 CO 2 Double Loop System Pump Expansion valve e c g a Heat Source Gas heater c b Gas Cooler f e d Internal Heat Exchanger f c f h a b Internal Heat Exchanger d M Expansion machine Compressor The system has two subsystems running in parallel: one carbon dioxide power subsystem and one carbon dioxide transcritical refrigeration/heat pump sub-system. It is also possible to take advantage of temperature glide of the both sub-systems. The system will to provide cooling (and heating) in a more efficient way. h Evaporator g 15

16 Corresponding Cycles 150 Carbon Dioxide Double Loop Cycle 150 Carbon Dioxide Double Loop Cycle T [ C] bar bar 140 bar 120 bar 80 bar 100 bar s [kj/kg-k] Supercritical power cycle double loop m3/kg T [ C] bar 140 bar 60 bar 120 bar s [kj/kg-k] 100 bar 80 bar Transcritical power cycle double loop m3/kg 16

17 Basic system analysis Turbine efficiency: 0.85 Pump efficiency: 0.8 Effectiveness: 0.9 Compressor efficiency: 0.75 Gas cooler efficiency: 0.85 Superheat: 5 C 17

18 Basic system analysis popt = ( te) tc + (0.381te 9.34) Liao et al.(2000) Gas heater pressure: 120 bar Expan. Inlet temp.: 120 C C.W. mass flow rate: 540 kg/h Gas cooler pressure: 83 bar GC outlet temp.: 35 C C.W. inlet temp.: 15 C Evaporator pressure: 40 bar Refrig. Mass flow: 290 kg/h 18

19 Simulation results Basic refrigeration system COP Double loop system COP double Water outlet temperature System cooling capacity Performance Parameters Double loop power part thermal efficiency (without IHX) Double loop power part thermal efficiency (with IHX) Power of hot water production Value 4.77% 7.48% Unit C kw kw 19

20 Carbon Dioxide Cooling and Power Combined System Carbon Dioxide Cooling and Power Combined Cycle T-S Chart f Such a system under a typical working condition can achieve COP = 3.18 for the cooling part η= 12.6% for the power part After transferring the energy gained from the cycle to the compressor, New COP = 4.45 The improvement of COP will be around 40% -1,50-1,25-1,00-0,75-0,50-0,25 T [ C] k 0, bar 300 bar 250 bar 150 bar 100 bar 40 bar a 0,2 0,4 0,6 0,8 j b c d S [kj/kg k] i Waste heat 0,0057 e 0,01 0,019 h 0,034 g 0,063 m3/kg 20

21 Thanks for your attention! 21