Performance Considerations in Adopting Zero-ODP and Low-GWP Refrigerants

8/16/2019 Performance Considerations in Adopting Zero-ODP and Low-GWP Refrigerants

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Performance considerations in adoptingzero-ODP and low-GWP refrigerants

Eiji Hihara

The University of Tokyo


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Contents

• Introduction

• Performance of natural working fluids

• Performance of low-GWP refrigerants

• Conclusion

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Background1. R-1234yf is developed for mobile AC.

2. For residential and commercial AC, R-32, R-1234yf, mixture with R-1234yf are considered as candidates of next refrigerant.

3. The new refrigerant/refrigerant mixture must balance the systemefficiency, GWP, and safety.

Annual shipment inJapan

Current refrigerant Low-GWP refrigerant

Domestic refrigerator 4.3 million isobutane isobutane

Mobile air-conditioner 4.75million R-134a R-1234yf

Residential air-conditioner

7.75million R-410A ?

Commercial air-conditioner

7.44million R-410A ?

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Thermodynamic properties of low-GWPrefrigerants

R-410A R-32 R-1234yf

Chemical formula R32/R125(50%/50%)

CH2F2 CF3CF=CH2

Boiling temperature -51.6ºC -51.7ºC -29ºC

Critical temperature 72.5ºC 78.1ºC 95ºC

GWP(100years) 2088 650 4

Toxicity ASHRAE A ASHRAE A ASHRAE A

Flammability - ASHRAE 2L ASHRAE 2LLifetime in the air - 5.6 yeas 11 days

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Latent heat

Refrigerant Latent heatkJ/kg@25ºC

R410A 186.5R32 270.9

R1234yf 145.4

R22 182.7

Propane 335.7

Small latent heat of R-1234yf causes a large mass flow rate and alarge pressure drop.

25ºC

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Trade-off problem

Changing refrigerant is an important option to solveenvironmental problem.

Current refrigerant R-410A ： GWP=2088

New low-GWP refrigerant R-1234yf: GWP=4

But the COP is very low for residential use.

Low GWP

Small latent heat

Large mass flow rate

Large pressure drop

Low COP

Trade-off

problem

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Contents

• Introduction


•

Performance of low-GWP refrigerants• Conclusion

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Fundamental heat pump cycle

1

23

4

P

ｈ

subcooling : 5ºC

superheat : 5ºC

Temperature

Cooling conditionsEvaporating temp.: Teva

9ºC

Cooling conditions

Condensing temp.: Tcond 45ºCHeating conditionsEvaporating temp.: Teva

-3ºC

Heating conditionsCondensing temp.: Tcond

30ºC

Subcooling 5ºC

Superheat 5ºC

Compressor efficiency 1.0

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Performance of Heat Pump Cycles(direct-expansion fundamental cycle)

0 1 2 3 4 5 6 7 8 9

ammonia

propane

CO2

R22

R410A

R407C

COP

heating

cooling

0 5000 10000 15000 20000

ammonia

propane

CO2

R22

R410A

R407C

Capacity per suction vapor volume, kJ/m3

heating

cooling

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Revised heat pump cycles for ammonia,

propane, and carbon dioxide

Refrigerant Problem Revised cycle

Ammonia • Flammability• High temperature

of discharge gas

Liquid injection and

secondary refrigerantcycle

Propane • Flammability Secondary refrigerantcycle

Carbon dioxide • Low COP Internal heatexchange cycle

R22, R410A,R407C

Non Fundamental cycle

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Secondary Refrigerant Cycle

Fundamental cycle Secondary

refrigerant cycle

Cooling conditionsEvaporating temp.: Teva 9ºC 4ºC

Cooling conditionsCondensing temp.: Tcond

45ºC 45ºC

Heating conditionsEvaporating temp.: Teva

-3ºC -3ºC

Heating conditionsCondensing temp.: Tcond

30ºC 35ºC

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Transcritical Cycle

with Internal Heat Exchanger for CO2

1

23

4

P

h

heat exchange

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Liquid Injection Cycle for Ammonia

• In order to decrease the

discharge gas temperature, smallamount of liquid ammonia isinjected to the compressionprocess at the intermediatepressure.

•

5

1

23

4

67

1

x

x +1P

h216 P P P

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Brief summary

The performance of basic cycle of natural working fluids was comparedwith conventional refrigerants.

1. R22 has the highest COP.

2. Concerning ammonia, two-stage compression with liquid injection

cycle improves the COP and decreases the compressor dischargetemperature. But due to the flammability, the secondary refrigerantsystem reduces the COP.

3. For propane the potential performance is similar to R22, but thesecondary refrigerant system reduces the COP.

4. The COP of carbon dioxide is very low.

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Contents

• Introduction


• Performance of low-GWP refrigerants

• Conclusion

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ObjectiveCalculate cooling and heating COP using three pure

refrigerants and a mixture; R-410A, R-32, R-1234yf andR-32/R-1234yf(50%/50%).

Evaluate the performance of heat pump considering the

effect of the connecting tube.

Estimate total equivalent CO2 emission by using LCCPmethod.

Performance of low-GWP refrigerants is compared with thatof conventional refrigerants.

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Calculation Conditions

†)Based on JIS C 9612:2005

Test conditionRated cooling

capacity

Half cooling

capacity

Rated heating

capacity

Indoor dry bulb temp. [ºC] 27 20

Indoor wet bulb temp.[ºC] 19 -

Indoor air flow rate [m3 /min] 3.0

Outdoor dry bulb temp. [ºC] 35 29 7

Outdoor wet bulb temp.[ºC] - - 6

Outdoor air flow rate [m3 /min] 12.0

Capacity[kW] 1.3 0.65 1.6

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Heat Pump ModelIndoor Heat Excahnger

Outdoor Heat Exchanger

Suction Tube

Length: 7.5[m] I.D.:5.5[mm]

Discharge Tube


Expansion Valve

CompressorFour way valve

Outdoor Unit

Indoor Heat Excahnger

Outdoor Heat ExchangerSuction Tube


Discharge Tube


Expansion ValveCompressor

Four way valve

Outdoor Unit

Cooling mode

Heating mode

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Heat exchanger modelIndoor heat exchanger Outdoor heat exchanger

Fin-tube HEX Air

Air

Row ColumnTotallength[m]

I.D.

[mm]

Finthickness[mm]

Finpitch[mm]

7/6 2 8.645 6.4 0.1 1.3

Row ColumnTotallength[m]

I.D.

[mm]

Finthickness[mm]

Finpitch[mm]

10 1 8.0 6.4 0.1 1.3

Fin-tube HEX

Refrigerant

Refrigerant

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1. On the rated cooling capacity condition, the COP of R-1234yf is about 60%of R-410A. The COP of R32 is the highest.

2. On the half cooling capacity condition, the difference becomes small.

3. The COP of R-32/R-1234yf mixture is better than that of R-1234yf.

COP on the rated & half coolingcapacity conditions

0

0.5

1

1.5

2

2.5

Rated coolingcapacity

Half coolingcapacity

C O P r

a t i o t o

R - 4 1 0 A

R-410AR-32

R-1234yfR32/R1234yf(50/50%)

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0.00.51.0

1.52.02.53.03.54.04.5

G[kg/s] ratio atrated capacity

Δ P[kPa] ratiothrough

evaporator atrated capacity

Δ P[kPa] ratiothrough suctiontube at rated

capacity

G[kg/s] ratio athalf capacity

Δ P[kPa] ratiothrough

evaporator athalf capacity

Δ P[kPa] ratiothrough suction

tube at halfcapacity

R

a t i o

t o

R 4 1 0 A R-410A

R-32R-1234yf R32/R1234yf(50/50%)

Mass flow rate and pressure drop incooling operation

• The COP of R-1234yf is very low due to its large pressure drop.

• The effect of pressure drop is not so large on the half capacity condition.

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LCCP Evaluation

Life Cycle Climate Performance

Climate impact is presented as an amount of equivalent CO2 emission.

LCCP is consists of two factors: direct impact and indirect impact.

Three different annual operation times for the heat pump areassumed.

normal: 1430h for cooling, 2889h for heating 1/2: 715h for cooling, 1445h for heating

1/3: 477h for cooling, 763h for heating

Direct Impact Indirect ImpactRegular emission of refrigerant duringoperation and end-of-life emissionsfrom the recovery of refrigerant at theend-of-life of the heat pumps.

Electricity consumption duringmanufacturing, operation andend-of-life of heat pumps.

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Comparison of total equivalent CO2 emission

• Direct impacts of R-1234yf and R-32 are negligibly small, because indirectimpact accounts for a substantial portion of total equivalent CO2 emission.

• R-32 and R-1234yf are better refrigerants than R-410A.

0

0.20.4

0.6

0.8

1

1.2

R - 4 1 0 A

R - 3 2

R

- 1 2 3 4 y f

R - 4 1 0 A

R - 3 2

R

- 1 2 3 4 y f

R - 4 1 0 A

R - 3 2

R

- 1 2 3 4 y f

Normal Time 1/2 Time 1/3

T o t a l e q u i v a l e n t C O 2 e m i s s

i o n

r a t i o

Indirect CO2 emission ratio of heating operation

Indirect CO2 emission ratio of cooling operation

Direct CO2 emission ratio

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Drop-in test of R-1234yf

APF

“Performance and Reliability Evaluation of a Room Air Conditioner with Low GWP Refrigerant,” TakashiOkazaki et al. Mitsubishi Electric Corporation

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Drop-in test of R32/R1234yf mixtures

“Experimental Study of Low GWP Refrigerants for Room Air-Conditioners ,” Hideki HARA et al. DAIKININDUSTRIES, LTD

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Thank you for your attention!

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Performance Considerations in Adopting Zero-ODP and Low-GWP Refrigerants

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