P3: Heat pump systems with CO2 as working fluid

Presentationsmaterial EFFSYS 2 dagen 2008-11-11

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 RefrigerationDept. of Energy Technology

Royal Institute of TechnologySweden


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

-1.75 -1.50 -1.25 -1.00 -0.75 -0.50-25

0

25

50

75

100

s [kJ/kg-K]

T [°

C]

135 bar

90 bar

55 bar

35 bar

0,2 0,4 0,6 0,8

0,0

017

0,0

057

0,0

1

0,0

63 m

3/kg

a40 Bar

b

c

d

e

f

Carbon DioxideTranscritical Cycle


Testing of system performance


Measuring points


Pre-test


Performance Testing (COP)COP vs. Water inlet temp. to GC

1

1.5

2

2.5

3

3.5

10 15 20 25 30 35 40 45

Water inlet temperature to the gas cooler

CO

P

0 °C 7 °C -5 °C -10 °C


COP comparison with manualManual: 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 Tamb:

– 4,7 kW – 8K deltaT; 0,50m3/h– 3,0 kW – 8K deltaT; 0,33m3/h– 2,9 kW – 5K deltaT; 0,50m3/h– 1,9 kW – 5K deltaT; 0,33m3/h

• Stable condition is maintained for ca. 30 mins. before the averaged values are taken

heating load as funcion of deltaT for different mass flow rates[m3/h]

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7 8 9 10 11 12deltaT [degreeC]

pow

er o

utpu

t [kW

]

0,2 0,25 0,3 0,35

0,4 0,45 0,5

mass flow rates [m3/h]


0 °C ambient temperature


-5 °C ambient temperature


-12 °C ambient temperature


Frosting/defrosting tests - layout

• Pos. 1/2 represent theboiler position

• Position 1: strong moisture condition

• Position 2: normal condition


Test restult at pos.1 at -2°CFrosting-defrosting periods at -2 degreeC Tamb and 3,4kW heating load

2008-04-14

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

0 1800 3600 5400 7200 9000 10800 12600 14400 16200 18000 19800 21600 23400

time[s]

tem

pera

ture

[C]

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

heat

ing

capa

city

[kW

]; flo

w [-

]; CO

P [-]

; pow

er [k

W]

evap. air in

evap. air out

CO2 compr. In

water gas cooler in

water gas cooler out

CO2 Exp.-valve in

CO2 compr. Out

Comp

normalized flow[x/0,239]heating capacity

COP

problem in data logging

defrosting periods

temperature approach before defrosting

1st 2nd


Frosting-defrosting periods at -2 degreeC Tamb and 3,4 kW heating load 2008-04-14 - detail of first two cycles

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

1800 3600 5400 7200 9000

time[s]

CO

2 co

mpr

. out

, CO

2 Ex

p.-v

alve

in,

wat

er g

as c

oole

r in[

°C]

-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

Teva

p bo

ttom

/mid

, CO

2 co

mpr

. in,

eva

p. a

ir in

/out

[°C

];

CO

P[-]

; flo

w[-

];

water gascooler in

CO2 Exp.-valve in

CO2 compr.Out

evap. air in

evap. air out

CO2 compr.In

normalizedflow[x/0,239]COP

Tevapbottom

Tevap mid

Detail view at -2°C of frosting / defrosting


Ice formation before defrosting-2°C


Development of Freezing Protection•Stop the ice from building up at the bottom of the evaporator

EvaporatorPipe thickness 0.6 mm

Warm CO2Pipe thickness 0.9 mm

Freezing protection

circuit

•Warm CO2 after the gas cooler is leaded to the bottom of the evaporator

•No electrical-heater needed

Air flow


Water tank performance

• Tank behaviour is important for the heat pump performance

• Good temperature stratification can ensure better heat pump performance

• Thermocouple position in figure

T1

T2

T3

T4

T5

T6


Charging freshly filled tanktank charging with electric heater at -2°C Tamb - 2008-04-29

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 900 1800 2700 3600 4500 5400 6300 7200 8100 9000 9900 10800 11700

time [s]

tem

pera

ture

[°C

]

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Flow

[m3/

h]; p

ower

[kW

]; C

OP

[-]

T_top

T1

T2

T3

T4

T5

T6

water gascooler outwater gascooler indeltaT_strat

compr. power

Flow scaled 10[m3/h]COP

el. heater stops


Charging freshly filled tanktank charging with no electric heater at -2°C - 2008-05-01

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 900 1800 2700 3600 4500 5400 6300 7200 8100 9000 9900 10800 11700

time [s]

tem

pera

ture

[°C

]

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Flow

[m3/

h]; p

ower

[kW

]; C

OP

[-]

T_top

T1

T2

T3

T4

T5

T6

water gas coinwater gas cooutdeltaT_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


Reference• Project reference:

• Poster• Conference paper

• 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 CO2 heat pump sold in Swedish market

(Sanyo-Ecocute)-------- Yang Chen

PresentationsmaterialEFFSYS 2 dagen 2008-11-11

Thank you for your attention

Documents

P3: Heat pump systems with CO2 as working fluid