P3: Heat pump systems with CO2 as working fluid

Transcription

1 P3: Heat pump systems with CO2 as working fluid Experimental Investigation of the Performance of a Carbon Dioxide Heat Pump Yang Chen & Per Lundqvist Div. of Applied Thermodynamics and Refrigeration Dept. of Energy Technology Royal Institute of Technology Sweden

2 Contents General info. about Sanyo Eco-cute Tests and results Heat pump performance System performance Defrosting Tank performance Comments References

3 General info. about Sanyo Eco-cute The first CO2 heat pump for the Swedish market,which was released by Ahlsell on July 10th, 2005 Capacity-controlled by a variable-speed control (inverter). An air source heat pump provides both space heating and domestic hot water (DHW) heating. It is claimed to deliver 4.5 kw heat power down to an outdoor air temperature of -15 C and to be able to heat the water up to +70 C.

4 Transcritical cycle 100 Carbon DioxideTranscritical Cycle c 0, T [ C] e d 0, bar 90 bar 55 bar 0,01 0,063 m3/kg 0 f 35 bar 40 Bar a b 0,2 0,4 0,6 0, s [kj/kg-k]

5 Testing of system performance

6 Measuring points

7 Pre-test

8 Performance Testing (COP) 3.5 COP vs. Water inlet temp. to GC COP C 7 C -5 C -10 C Water inlet temperature to the gas cooler

9 COP comparison with manual Manual: 30/50 C water inlet and outlet gas cooler 7 C outdoor temperature: 30.1 / 59.2 C COP C outdoor temperature: 30.4 / 51.6 C COP

10 System testing condition Including the tank and radiator system in analysis Defined load cases at different T amb : 4,7 kw 8K deltat; 0,50m 3 /h 3,0 kw 8K deltat; 0,33m 3 /h 2,9 kw 5K deltat; 0,50m 3 /h 1,9 kw 5K deltat; 0,33m 3 /h heating load as funcion of deltat for different mass flow rates[m3/h] Stable condition is maintained for ca. 30 mins. before the averaged values are taken power output [kw] mass flow rates [m3/h] 0,2 0,25 0,3 0,35 0,4 0,45 0,5 deltat [degreec]

11 0 C ambient temperature

12 -5 C ambient temperature

13 -12 C ambient temperature

14 Frosting/defrosting tests - layout Pos. 1/2 represent the boiler position Position 1: strong moisture condition Position 2: normal condition

15 Test restult at pos.1 at -2 C Frosting-defrosting periods at -2 degreec T amb and 3,4kW heating load problem in data logging 6 5 evap. air in evap. air out CO2 compr. In water gas cooler in water gas cooler out temperature [C] temperature approach before defrosting st 2nd time[s] heating capacity [kw]; flow [-]; COP [-]; power [kw] CO2 Exp.-valve in CO2 compr. Out Comp normalized flow [x/0,239] heating capacity COP defrosting periods

16 Detail view at -2 C of frosting / defrosting Frosting-defrosting periods at -2 degreec T amb and 3,4 kw heating load detail of first two cycles CO2 compr. out, CO2 Exp.-valve in, water gas cooler in[ C] time[s] 20 17, ,5 10 7,5 5 2,5 0-2,5-5 -7, , ,5-20 Tevap bottom/mid, CO2 compr. in, evap. air in/out [ C]; COP[-]; flow[-]; water gas cooler in CO2 Exp.- valve in CO2 compr. Out evap. air in evap. air out CO2 compr. In normalized flow [x/0,239] COP Tevap bottom Tevap mid

17 Ice formation before defrosting -2 C

18 Development of Freezing Protection Stop the ice from building up at the bottom of the evaporator Warm CO 2 after the gas cooler is leaded to the bottom of the evaporator No electrical-heater needed Evaporator Pipe thickness 0.6 mm Air flow Warm CO 2 Pipe thickness 0.9 mm Freezing protection circuit

19 Water tank performance Tank behaviour is important for the heat pump performance Good temperature stratification can ensure better heat pump performance T1 T2 T3 T4 T5 T6 Thermocouple position in figure

20 Charging freshly filled tank tank charging with electric heater at -2 C Tamb el. heater stops Flow [m3/h]; power [kw]; COP [-] temperature [ C] T_top T1 T2 T3 T T T water gas cooler out water gas cooler in deltat_strat 5 1 compr. power Flow scaled 10 [m3/h] COP time [s]

21 Charging freshly filled tank tank charging with no electric heater at -2 C Flow [m3/h]; power [kw]; COP [-] temperature [ C] T_top T1 T2 T3 T4 T time [s] T6 water gas co in water gas co out deltat_strat compr. Powe flow scaled 1 [m3/h] COP

22 Comments The testing of heat pump performance shows that the European heat pump testing standard EN14511 can not give a fair comparison between CO2 heat pump and traditional heat pump. a high water inlet temperature a small temperature lift The heat pump COP testing shows simimlar results as the values specified in the user manual

23 Comments During the system testing, the heat pump system achieves a lower system COP than conventional heat pumps, which is mainly due to the reason that the water tank delivers water to the CO2 heat pump at an unfavorable high temperature The defrosting test shows that the start point of defrosting mode is controlled by the temperature difference between the evaporator air inlet temperature and evaporator temperature, which can indicate the ice blocking up the air flow path through the fins

24 Comments The testing results show that the tank is a critical component to improve the system performance Several mesurements can be done to iimprove stratification in the tank: Sensor position in the tank Connecting tubes position

25 Possible tank layout

26 Project reference: Poster Conference paper Reference Eco-cute testing reference Experimental Investigation of the Performance of a Carbon Dioxide Heat Pump Leonie Brachert Heat pump testing report André Alves Testing of a CO 2 heat pump sold in Swedish market (Sanyo-Ecocute) Yang Chen

27 Thank you for your attention