energy efficient supermarkets of tomorrow -...

Energy Efficient Supermarkets of Tomorrow

Mazyar Karampour

Effsys Expand Fosrkardagar 2016, Tranås, Sweden17th May 2016

Outline

• Introduction• Supermarkets – facts & figures • CO2 in supermarket refrigeration systems

• Project overview and objectives• Main studies and findings• Ongoing and future research plans

2

• IntroductionSupermarkets – facts & figures

•IntroductionSupermarkets – facts & figures CO2 in supermarket refrigeration systems

•Project overview and objectives•Main studies and findings•Ongoing and future research plans

Supermarkets Rapid Growth

• Supermarkets have become one of the vital service facilities of our modern society.

• The total area (m2) of supermarkets are increasing in developed and developing countries.

• Main driving forces (Trail, 2006):

– Rapid growth example: frozen food global market is estimated to grow in sale value by 30% comparing predicted 2020 sales with 2014 values. (Persistence market research, 2014).

4

Rapid urbanization

Emerging middle class

Globalization and taste convergence

More female labour in market

Openness to inward foreign investment

Photos ref.: National geographic

Supermarkets Energy use (I)

• Share of national energy use of electricity• Sweden: 3% (Sjöberg, 1997), USA: 4% (Orphelin, 1997), UK: 3% (Tassou, 2011), France: 4%

(Orphelin, 1997), and Denmark: 4% (Reinholdt and Madsen, 2010)

• Supermarkets: largest consumer of energy; more than any other commercial building in Sweden and other industrialized countries.

5

Swed

enNorway

USA

Singapore

Ref.: (STIL2, 2010), (Energy star, 2012), (Enova, 2007), (BCA, 2014)

Supermarkets Energy use (I)

• Supermarkets refrigeration system: consumer of about 50% of electricity in supermarkets

6

Swed

en (I)

Swed

en (II)

Germany

USA

Ref.: (Arias, 2005), (STIL2, 2010),

(Kauffeld, 2007), (EPA, 2014)

Supermarkets Refrigeration

• Supermarkets are largest consumers of HFC gases in Europe.

7

Europe

Ref.: SKM Enviros, 2012

• Supermarkets are largest emitters of HFC gases in the world.

– Hundreds of Kgs of refrigerant charge– High leakage rate

World

3‐22%

Ref.: IPCC, 2005

Supermarkets Conventional refrigeration system in Sweden

• Indirect at medium temperature leveland direct expansion at low temperaturelevel, Typical refrigerant: R404A(GWP=3900)

• 2300‐2400 supermarkets in Sweden

8

R404A

R404A brine

ICA49%

COOP25%

AXFOOD10%

Bergendahl7%

Lidl5%

Netto4%

Ref.: (DELFI, 2015), (ICA, 2014), (COOP, 2014)

F‐gas regulation

9

R404

R404 brine

Not a long‐term solution!

Ref.: (Emesron, 2015)

• IntroductionCO2 in supermarket refrigeration systems



CO2 as refrigerant

11

Properties:• GWP=1 , ODP=0• Good safety: non‐flammable, non‐toxic• High cooling effect: compact system ‐

smaller pipe sizes than conventionalsystems

• High operating pressure• Low critical temperature 31°C @ Pc=73

[bar]

Sub‐critical

Trans‐critical

CO2 in supermarket refrigeration systems:CO2 trans‐critical booster system

12

10

1

3

2

89

11

4

1

3

2 56

789

10 11

12

4

5

6

712

13

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CO2 in supermarket refrigeration systemsmarket trends (2016)

13

CO2 in supermarket refrigeration systemsmarket trends (2013 & 2015)

14Ref.: Shecco guides, 2014 & 2015

Cascade(2013)

Booster(2013)

Booster(2015)

• Project overview and objectives:Supermarket refrigeration and heat recovery systems

using CO2 as the refrigerant



Research Project overview

16

‐ KTH research on “supermarket refrigeration” has been ongoing for more than 15 years.

The two latest projects:‐ Effsys+ (2011‐2014): A comprehensive evaluation of refrigeration and heating systems in supermarkets based on field measurements and modelling‐ Effsys expand (2015‐2017): Energy efficient supermarkets of tomorrow

‐ Focus of both projects: Supermarket refrigeration and heat recovery systems using CO2as the refrigerant

‐ Partners:

Objectives

17

‐ Evaluate the present supermarket refrigeration systems: focus on CO2 systemsComputer modelling• Analyse CO2 systems and components • Compare different system solutions• Heating and air conditioning integration Field measurements analysis• Performance of CO2 systems in Swedish supermarkets• Guidelines for instrumentation, field measurements and systems evaluation

‐ Evaluate & propose the “state‐of‐the‐art” supermarket refrigeration system in Sweden; computer simulation + field measurements analysis

• key features of a modern refrigeration system• Definition of a state‐of‐the‐art system, case studies• Compare with emerging alternative system solutions• Perform economic and environmental analysis of the suggested system

• Main studies and findings



Main studies and findings:publications (Effsys Plus 2012‐2014)

19

References Title AuthorsConference/Journal/Repo

rt

(Karampour et al., 2013)Field measurements and performance evaluation of CO2 supermarket refrigeration systems

Karampour, M., Sawalha, S., Rogstam, J.

2nd IIR International Conference on Sustainability and the Cold Chain. IIF/IIR, Paris, France

(Karampour and Sawalha, 2014)

Performance and control strategies analysis of a CO2 trans‐critical booster system

Karampour, M., Sawalha, S.

3rd IIR International Conference on Sustainability and the Cold Chain, IIF/IIR, London, UK


Investigation of using Internal Heat Exchangers in CO2 Trans‐critical Booster System


11th IIR Gustav Lorentzen Conference on Natural Refrigerants. IIF/IIR, Hangzhou, China

(Abdi et al., 2014)Heat recovery investigation of a supermarket refrigeration system using carbon dioxide as refrigerant

Abdi, A., Sawalha, S., Karampour, M.

11th IIR Gustav Lorentzen Conference on Natural Refrigerants. IIF/IIR, Hangzhou, China


Supermarket refrigeration and heat recovery using CO2 as refrigerant: A comprehensive evaluation based on field measurements and modelling


Effsys plus final report, Stockholm, Sweden

Main studies and findings:publications (Effsys Expand 2015‐2017)

20

References Title AuthorsConference/Journal/Repor

t

(Karampour et al., 2015)Review of supermarket refrigeration and heat recovery research at KTH

Karampour, M., Sawalha, S., Abdi, A., Arias, J., Rogstam, J.

6th IIR Conference: Ammonia and CO2 Refrigeration Technologies. IIF/IIR, Ohrid, Macedonia

(Sawalha et al., 2015)Field measurements of supermarket refrigeration systems. Part I: Analysis of CO2 trans‐critical refrigeration systems

Sawalha, S., Karampour, M., Rogstam, J.

Appl. Therm. Eng. 87, 633–647


Theoretical analysis of CO2 trans‐critical system with parallel compression for heat recovery and air conditioning in supermarkets


24th IIR Refrigeration Congress of Refrigeration. IIF/IIR, Yokohama, Japan


Integration of Heating and Air Conditioning into aCO2 Trans‐Critical Booster System with Parallel CompressionPart I: Evaluation of key operating parameters using field measurements


12th IIR Gustav Lorentzen Conference on Natural Refrigerants. IIF/IIR, Edinburgh, Scotland


Integration of Heating and Air Conditioning into aCO2 Trans‐Critical Booster System with Parallel CompressionPart II: Performance analysis based on field measurements


11th IIR Gustav Lorentzen Conference on Natural Refrigerants. IIF/IIR,Edinburgh, Scotland

Main Studies

21

Studies Computer modeling Field measurements analysis Project

Study 1: Refrigeration

Effsys PlusStudy 2: Refrigeration + heat recovery (HR)

Study 3: Refrigeration + HR + Internal HEX

Study 4: Refrigeration + HR + AC + Parallel compression

Effsys Expand


Study 6: Refrigeration + Ejector


Study 1

Q: How energy‐efficient is a CO2 supermarket refrigeration system comparing with a

conventional R404A system?

Field measurement analysis(Part of an earlier project)

• 8 supermarkets in Sweden have been compared.• 3 HFC systems• 5 CO2 systems

23

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

10,0 12,5 15,0 17,5 20,0 22,5 25,0 27,5 30,0

CO

P T

otal

-L

R3

[-]

Condensing temperature [°C]

TR1

TR2

TR4

TR5

RS123

[-9/-34]

[-10/-35]

[-8/-33]

[-7/-31]

[-7/-32]

[-11/-31]

R404

Old CO2

New CO2

New CO2

Old CO2

Conclusion: CO2 systems have COPs higher or comparablewith advanced HFC conventional systems.

Field measurement analysis

24

051015202530354045

10 15 20 25 30

COP_

tot, LR3Increase [%

]

T_cond [C]

By‐pass Comp. Total Eff. T_evaporation

Int. Superheat Ext. Superheat

• Some of the main reasons for 35‐40% improvement in the newer CO2 systems performance have been found/discussed.

10 15 20 25 300

1

2

3

4

5

Tcond [C]

CO

P tot

;LR

3 [-]

COPold;field

COPold;model

COPnew;field

COPnew;model

Conclusion: main factors• System: Receiver + Flash gas by‐pass• Component: More energy‐efficient cabinets, compressors, …

Study 2

Q: How about integrating heating into the refrigeration system?

Is CO2 system an energy‐efficient system regarding heat recovery?

CO2 Trans‐criticalBooster System with heat recovery

26

• By increasing the discharge pressureand switching from sub‐critical to trans‐critical, the amount of available heat increases considerably.

Heat recovery

Heat recovery control strategy

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STEP 1STEP 2

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Heat recovery

• The following example shows the CO2 system operation in winter based on the suggested control strategy.

150

kW

185

kW

3535

Tamb11°C

P56

Tamb10°C

150

145

3535

4040 P58

29

150

90

4545

Tamb0°C

105

P78

150

140

5050

Tamb‐10C

6060 P88.4

150

230

8080

Tamb‐28C

P88.4

150

190

7070

Tamb‐20C

3030

P88.4

Standard CO2 Trans‐critical Booster Systemwinter & summer control strategy

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Winter1. Gas cooler full capacity‐

Pdischarge regulation2. Fixed max optimum Pdischarge

Poptimum = 2.7 TDSH,exit – 6.1

2.1 Fans slowed‐down 2.2 Fans off2.3 Gas cooler bypass

Summer1. Sub‐critical operation:

floating condensing

2. Trans‐critical operation Poptimum = 2.7 Tgas cooler exit – 6.1

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Summer and winter operation

0102030405060708090100

0123456789

10

-25 -20 -15 -10 -5 0 5 10 15 20 25 30 35

Pres

sure

[bar

]-T

empe

ratu

re[°

C]

CO

P [-

]Ambient Temperature [°C]

COP_HR T_gce [°C] P_disch [bar]Floating condensingHeat recovery

Floating condensingHeat recovery

gPdischargeCOPHR

Tgas cooler exitTgas cooler exitCOPHR = QHR / (EHS – EHS,fc )

Annual energy use and SPF (seasonal performance factor)

0

10

20

30

40

50

60

70

-150

-100

-50

0

50

100

150

200

January(-1.1°C)

February(-1.7°C)

March(0.9°C)

April (6.3°C)

May (11.4°C)

June (15.4°C)

July (18.7°C)

August(17.7°C)

September(12.7°C)

October(7.7°C)

November(3.5°C)

December(0.7°C)

Ele

ctri

city

use

[MW

h]

Coo

ling-

heat

ing

load

s [M

Wh]

Month-Average ambient temperature

Q_gascooler[MWh] Q_HR[MWh] Q_LT[MWh] Q_MT[MWh] E_HS[MWh] E_LS[MWh] E_fan[MWh]

SPF = ∑ QHR / ∑ (EHS – EHS,fc )

SPF= 417 MWh / 104 MWh = 4

Heating demand: 40‐190 kW for ambient temperatures 10 to ‐20°C

Conclusion: Heat recovery by CO2 trans‐critical booster system has high and comparable SPF to other commercial size heat pumps.

Avoiding the cost of new heating system installation is another advantage of heat recovery from CO2 system.

32Ref.: (Miara et al., 2011)

Average = 3.88

Study 3

Q: how about modifying the system design? What is the effect of using internal heat exchangerin CO2 “refrigeration + heat recovery” system?

Internal Heat Exchanger (IHX)

• Internal heat exchanger or liquid‐suction heat exchanger main functions:

• Sub‐cooling the warm liquid flow • Superheating the suction flow

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Internal Heat Exchanger (IHX) Positioning

Example:AD ConfigurationWith By‐pass

(WBP)

• 36 cases are studied:• 9 IHX cases have been compared: NO IHX, A, B, C, D, AC, AD, BC, BD • 2 design alternatives: WBP: with by‐pass ‐WOBP: without by‐pass• (I) Refrigeration‐only function (II) Refrigeration + heat recovery function

35

Internal Heat Exchanger (IHX) Positioning@65 [bar]

• 36 cases are studied:• 9 IHX cases have been compared: NO IHX, A, B, C, D, AC, AD, BC, BD • 2 design alternatives: WBP: with by‐pass ‐WOBP: without by‐pass• (I) Refrigeration‐only function (II) Refrigeration + heat recovery function

36

70

80

90

100

110

120

2,1

2,2

2,3

2,4

2,5

2,6

A AC AD B BC BD C D No IHX

QHR[kW

]

COP r

efrig

eration[‐]

COP2‐WBP COP2‐WOBP QHR‐WBP QHR‐WOBP

• Conclusion: no significant impact in refrigeration‐only mode

• Example: QHR Normalization – reference: 85[kW]@ 65[bar]

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Internal Heat Exchanger (IHX) Positioning

QHR=85COPtot= 3.6 Pdischarge=65

NO IHX

• By using IHX AD, 3.8 bar decrease in discharge pressure, 11.8% increase in COP

QHR=85COPtot= 4 Pdischarge=61.2

IHX AD

• Example: QHR Normalization – reference: NO IHX‐WBP‐85[kW]@ 65[bar]

‐2

0

2

4

6

8

10

12

14

A AC AD B BC BD C D NO IHX

COP t

otincrease [%

]

COPtot‐WBP% COPtot‐WOBP%Up to 12% Up to

11%

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Internal Heat EXchanger positioning

Conclusion

IHX impact on COPtotincrease

Refrigeration [COPref] Refrigeration + heat recovery [COPref , COPtot]

Sub‐critical No impact Positive effect, up to 12%

Trans‐critical No impact No impact

Study 4

Q: How about modifying the system design and more system integration?

What is the effect of using parallel compression in CO2 “refrigeration + heat recovery + air

conditioning” system?

Parallel compression andair conditioning integration

40

Parallel compression (PC) vs Flash gas by‐pass expansion (FGBP) comparison in an integrated CO2 trans‐critical booster refrigeration system + heat recovery (HR) + air conditioning (AC)

Case 1: PC vs FGBP: summer case (floating condensing mode) – no air conditioningCase 2: PC vs FGBP: summer case (floating condensing mode) – with air conditioning Case 3: PC vs FGBP: winter case (heat recovery mode) – no air conditioning

COP increase% PC vs FGBPwithout AC (Summer)

COPtot = (QMT + QLT +QHR +QAC ) / (EHS + ELS+ EPC + Efan)Δprec = Prec ‐ PMT

0

5

10

15

20

15 20 25 30 35 40

CO

P tot

incr

ease

[%]

Ambient temperature [°C]

ΔP_rec= 3, No AC ΔP_rec= 8, No ACΔP_rec= 13, No AC

00,511,522,533,5

15 25 35

CO

P tot

[-]


COP_tot (PC), ΔP_rec=13 [bar]COP_tot (FGBP), ΔP_rec=3 [bar]

4%9%

12%

Increase in COPtot using PC compared to FGBP, summer with No AC case (left)Best cases comparison between PC‐ΔPrec=13 and FGBP‐ΔPrec=3 (right)

41

Conclusion: 5‐15 % increase

COP increase% PC vs FGBPwith HR (Winter)

• Conclusion: Up to 6% improvement, but in very low ambient temperatures

0

1

2

3

4

5

6

7

-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10

CO

Ptot

incr

ease

[%]


Increase in COPtot using PC instead of FGBP, winter No AC case with heat recovery

6%

42

Air conditioning comparison:Integrated CO2 vs Separate R410A

COPAC comparison of integrated CO2 and separate R410A air conditioning systems

COPAC = QAC / (Etot_AC – Etot_No AC )

0123456789

15 20 25 30 35 40

CO

P AC

[-]


COP_AC_R410A COP_AC_CO2

R410ACO2

43

Conclusion: High COPAC_CO2for Tamb < 25°C

Parallel compression:Annual energy saving

• Annual energy savings by using parallel compression instead of the standard flash gas by‐pass

44

0

2

4

6

8

10

Energy sa

ving

%

Annual energy savings % for 12 cities (DP=8 [bar])

Conclusion: 6‐9% annual savings

Field measurements studies 5, 6 & 7Supermarkets TR6, TR7 & TR8

45

Study 5

Q: How does the system perform in field?Field measurements analysisCO2 Integrated system TR6:

“refrigeration + heat recovery + air conditioning+parallel compression”

Supermarket TR6CO2 integrated system

47


48

Supermarket TR6Field measurements analysis

49

Study the performance of an integrated CO2 trans‐critical booster refrigeration system + heat recovery (HR) + air conditioning (AC) + Parallel compression (PC) for:

• A warm month in summer• A cold month in winter

Supermarket TR6CO2 Integrated system: Results

refrigeration and AC temperatures

50


Heating temperatures

51


Cooling & Heating Loads

52

Supermarket TR6CO2 Integrated system: ResultsRefrigeration & total COPs

53


Heating & AC COPs

54

Supermarket TR6CO2 Integrated system

Conclusion

55

• The system can provide the entire refrigeration, air conditioning and a considerable share of heating demands.

• The system provides the required temperatures for:• Refrigeration: MT@‐7°C & LT @‐32°C• AC @7‐8°C• Space heating @35‐45°C• Tap water heating @60°C

• The system provides the demands with high or reasonable COP values.

Study 6

Q: How does the system perform in field?Field measurements analysis

CO2 “refrigeration + ejector” system TR7

Supermarket TR7Ejector in CO2 refrigeration system

57

Supermarket TR7CO2 refrigeration + ejector

58


59


Conclusion

60

System without ejector: KA1, system with ejector: KA2• The system with ejector (KA2) doesn’t show a significant performance increase

over the system without ejector (KA1). The main reason is very short opening time of ejector and not enough liquid CO2 feed. It is planned to convert the evaporators from DX to flooded in future and this will increase the operation time of ejector..

Study 7

Q: How does the system perform in field?Field measurements analysisCO2 Integrated system TR8:

“refrigeration + heat recovery + air conditioning+ parallel compression”


62


63

Supermarket TR8CO2 Integrated system

Conclusion

64

• System is able to provide the heating and air conditioning demands.• The required temperature demands has been fulfilled.• COP for air conditioning is comparable with conventional AC systems.

Summary of main findings (I) – Effsys Plus

65

Field measurements analysis of 8 supermarkets (continuation of a previous study at KTH)

• CO2 new systems have higher or equal energy‐efficiency compared with HFC systems.

• CO2 new systems are 35‐40% more efficient than the old ones. Main reasons:• Receiver + flash gas by‐pass• More efficient compressors and cabinets

CO2 booster system + heat recovery study• A suggested heat recovery control strategy has been used in an annual energy

use modelling.• CO2 booster system is able to provide the entire or a great share of supermarket

heating demands with high SPF and COP.

Summary of main findings (II) – Effsys Plus

66

IHX study• 36 cases have been evaluated to find the effect of IHX on COPtot increase.• Using some configurations in subcritical refrigeration + heat recovery mode

increase the COPtot by 11‐12%.

Parallel compression + Air conditioning study• Integration of air conditioning and parallel compression into standard CO2

booster system + heat recovery have been evaluated for summer and winter:• 5‐15% COPtot increase in summer case, up to 6% increase in very low

ambient temperatures of winter case • CO2 integrated air conditioning is more efficient than conventional AC

systems for ambient temperatures lower than 25°C.

• Using parallel compression instead of flash gas by‐pass have been evaluated in 12 European cities:

• 6‐9% annual electricity savings

• Ongoing and future research plans



68

Ongoing/future research plans (I)

• State‐of‐the‐art system features; computer modeling and field measurements analysis

• Heat recovery at multiple temperature levels• Parallel compression • Air conditioning integration• Ejector • Ground thermal storage• Internal heat exchanger (continuation of the previous study) • Control strategies for integrated CO2 trans‐critical booster system• Evaporative cooling on gas cooler / evaporative condenser• New emerging solutions?

69

An example for State‐of‐the‐art systemFeatures being studied/to be studied

1‐ tap water heating2‐ space heating3‐ parallel compression4‐ air conditioning5‐ ejector6‐ ground source coupling7‐ LT de‐superheating or heat recovery

1

3

2

4

5

6

7

6

70

Ongoing/future research plans (II)

• Comparative studies of different system solutions in different climatic conditions

• Energy efficiency comparison of (1) standard CO2 booster, (2) state‐of‐the‐art CO2 booster, (3) direct and indirect new HFC/HFO systems

• Environmental and economical aspects of the above‐mentioned systems• Most energy‐efficient system solutions for cold, mild and warm climates

• Defining and analysis of a “State‐of‐the‐art” system

Thank you!Questions?

[email protected]

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