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
Contents General info. about Sanyo Eco-cute Tests and results Heat pump performance System performance Defrosting Tank performance Comments References
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.
Transcritical cycle 100 Carbon DioxideTranscritical Cycle c 0,0057 75 T [ C] 50 25 e d 0,0017 135 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 0,8-25 -1.75-1.50-1.25-1.00-0.75-0.50 s [kj/kg-k]
Testing of system performance
Measuring points
Pre-test
Performance Testing (COP) 3.5 COP vs. Water inlet temp. to GC 3 2.5 COP 2 1.5 0 C 7 C -5 C -10 C 1 10 15 20 25 30 35 40 45 Water inlet temperature to the gas cooler
COP comparison with manual Manual: 30/50 C water inlet and outlet gas cooler 7 C outdoor temperature: 30.1 / 59.2 C COP 2.91 3.1 20 C outdoor temperature: 30.4 / 51.6 C COP 4.2 3.75
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] 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Stable condition is maintained for ca. 30 mins. before the averaged values are taken power output [kw] 7 6 5 4 3 2 1 mass flow rates [m3/h] 0,2 0,25 0,3 0,35 0,4 0,45 0,5 deltat [degreec]
0 C ambient temperature
-5 C ambient temperature
-12 C ambient temperature
Frosting/defrosting tests - layout Pos. 1/2 represent the boiler position Position 1: strong moisture condition Position 2: normal condition
Test restult at pos.1 at -2 C 160 150 Frosting-defrosting periods at -2 degreec T amb and 3,4kW heating load 2008-04-14 problem in data logging 6 5 evap. air in evap. air out CO2 compr. In 140 4 water gas cooler in 130 3 water gas cooler out temperature [C] 120 110 100 90 80 70 60 50 40 30 20 10 0-10 temperature approach before defrosting -20 0 1800 3600 5400 7200 9000 10800 12600 14400 16200 18000 19800 21600 23400 1st 2nd time[s] 2 1 0-1 -2-3 -4-5 -6-7 -8-9 -10-11 -12 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
Detail view at -2 C of frosting / defrosting Frosting-defrosting periods at -2 degreec T amb and 3,4 kw heating load 2008-04-14 - detail of first two cycles CO2 compr. out, CO2 Exp.-valve in, water gas cooler in[ C] 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 1800 3600 5400 7200 9000 time[s] 20 17,5 15 12,5 10 7,5 5 2,5 0-2,5-5 -7,5-10 -12,5-15 -17,5-20 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
Ice formation before defrosting -2 C
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
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
Charging freshly filled tank tank charging with electric heater at -2 C Tamb - 2008-04-29 70 65 60 55 50 45 el. heater stops 14 13 12 11 10 9 Flow [m3/h]; power [kw]; COP [-] temperature [ C] 40 35 30 8 7 6 T_top T1 T2 T3 T4 25 5 T5 20 4 T6 15 10 3 2 water gas cooler out water gas cooler in deltat_strat 5 1 compr. power 0 0 0 900 1800 2700 3600 4500 5400 6300 7200 8100 9000 9900 10800 11700 Flow scaled 10 [m3/h] COP time [s]
Charging freshly filled tank tank charging with no electric heater at -2 C - 2008-05-01 70 65 60 55 50 45 14 13 12 11 10 9 Flow [m3/h]; power [kw]; COP [-] temperature [ C] 40 35 30 25 8 7 6 5 T_top T1 T2 T3 T4 T5 20 4 15 3 10 2 5 1 0 0 0 900 1800 2700 3600 4500 5400 6300 7200 8100 9000 9900 10800 11700 time [s] T6 water gas co in water gas co out deltat_strat compr. Powe flow scaled 1 [m3/h] COP
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
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
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
Possible tank layout
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
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