Integration of trigeneration and CO refrigeration systems ... · COP LT refrigeration capacity...

School of Engineering and Design

Integration of trigeneration and CO2

refrigeration systems for energy conservation

in the food industry AFM 251

Savvas Tassou and INyoman Suamir

www.brunel.ac.uk/about/acad/sed

Savvas Tassou and INyoman SuamirOn behalf of AFM251 consortium

BRUNEL UNIVERSITY


Content of Presentation

• Background

• Aims and Objectives of Project and Partnership

• Test facilities and test results

• Test Supermarket


• Test Supermarket

• Energy analysis

• Results and Conclusions


Greenhouse Gas Emission Challenges for

Supermarkets

• Retail food outlets in the UK are responsible for 3% of

electrical Energy Consumption and 1% of CO2e

Emissions

• Energy consumption of 10 largest retail food chains


• Energy consumption of 10 largest retail food chains

(electricity and gas) responsible for 5 MtCO2e per year

• Significant pressures to reduce GHG emissions whilst

maintaining or improving sales and profitability

• Carbon Reduction Commitment (CRC) amongst others


Percentage emissions from the distribution

and retail phase of two food products*

Refrigerated warehouse

0%

Transport3%

Refrigerated display cabinets

42%Refrigerant leakage

Lighting3%

HVAC2%

Plastic shopping bags

2%

Food waste including

transportation2%

Refrigerated warehouse

0%

Transport1%

Refrigerated display Refrigerant leakage

34%

Lighting3%

HVAC2% Plastic shopping bags

1%Food waste including

transportation1%

Fresh packed meat Frozen peas


42%

Walk-in coolers&freezers

including refrigerant leakage

1%

Refrigerant leakage45%

Refrigerated display cabinets

57%

Walk-in coolers&freezers

including refrigerant leakage

1%

34%

*Tassou et.al. (2011) Applied Thermal Engineering 31 (2011) 147-156

Defra project (FO405)

477 gCO2e/kg 1000 gCO2e/kg


Reduction of direct emissions per kg of

temperature controlled (refrigerated) product

� ~ 50% of carbon footprint of refrigerated product in

supermarket from direct emissions - refrigerant leakage

(R404A and 15% leakage)

Approaches to reduce direct emissions


• Reduce leakage (F-Gas regulations)

• Use refrigerants with low GWP

• Use natural refrigerants (CO2, HCs, Ammonia in

cascade arrangement)


Reduction of indirect emissions per kg of

temperature controlled (refrigerated) product

� ~ 50% of carbon footprint from indirect emissions –

electrical energy consumption of refrigeration

equipment

Approaches to reduce indirect emissions

• Buy ‘green’ electricity – expensive and in short supply


• Buy ‘green’ electricity – expensive and in short supply

• Efficiency improvements

• Local Power Generation

– Natural gas as the fuel

– Biomass (wood chips)

– Biofuels (biodiesel, digester gas etc)


AFM 251- Integration of CO2 Refrigeration

and Trigeneration Systems

Why?

1. CO2 is a natural refrigerant with negligible GWP

2. Trigeneration- Local power generation using natural gas or

renewable fuels and simultaneous production of heat and

cooling


cooling

3. Use cooling/refrigeration from sorption system to

maximise efficiency of CO2 refrigeration system.

4. Significantly reduce both direct and indirect emissions


AFM 251- Partnership

Defra LINK funded programme

1. Brunel University (Academic/Research lead partner)

2. Retailers (Tesco Stores and Somerfield)

3. Consultants (CSA-Emerson; ACDP; Doug Marriott

Associates; CRT)


Associates; CRT)

4. Equipment manufacturers and Suppliers: Danfoss; Bock

Compressors; Cogenco; Bowman Power; George Barker

(Epta group); Bond Retail Services Ltd; Apex Air

Conditioning; A&N Shilliday&CO;


The basic concept

Chilled fluid pump

Absorption chiller

Exhaust gas

MT Display LT Display

CO2 liquid receiver

CO2 condenser

Electricity

Hot fluid pump

Three main subsystems

• CHP unit

• Sorption refrigeration

system

• CO2 refrigeration system


gas

CHP Plant

MT Display cabinet

LT Display cabinet

CO2 Compressor Bock HGX12P/60-4 CO2

CO2 Pump

IHX

Air

Fuel

Electricity

Boiler HX

Generator Set


Test facilities Pulse vessel and plate heat

exchanger


Environmental test chamber

for CO2 work

LT compressor and pump

unit

CO2 Coil design process


Some test results

0

2

4

6

8

10

12

14

2700 2880 3060 3240 3420 3600 3780 3960 4140 4320 4500 4680 4860

Time (20 seconds)

Refr

igera

tio

n c

ap

acit

y ,

or p

ow

er (

kW

)

0

1

2

3

4

5

6

7

CO

P

LT refrigeration capacity Compressor power COP

0 180 360 540 720 900 1080 1260 1440 1620 1800 1980 2160

Performance of CO2 LT

refrigeration system

(Investigated at Tc = -7

[C] and Te = -32 [C])

Performance of MT CO2 refrigeration system at different evaporating temperatures


0

10

20

30

40

50

60

70

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

CO

P

Te = -6 [C] Te = -8 [C] Te = -10 [C]Teva= -6oC Teva= -8oC Teva= -10oC

0

10

20

30

40

50

60

70

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

CO

P

Te = -6 [C] Te = -8 [C] Te = -10 [C]

0

10

20

30

40

50

60

70

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

CO

P


0

1

2

3

4

5

6

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

Ref

riger

ati

on

Ca

pa

city

(k

W)


0

1

2

3

4

5

6

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

Ref

riger

ati

on

Ca

pa

city

(k

W)

Te = -6 [C] Te = -8 [C] Te = -10 [C]

0

1

2

3

4

5

6

0.6 0.8 1 1.2 1.4 1.6 1.8 2

Circulation ratio

Ref

riger

ati

on

Ca

pa

city

(k

W)


Performance of MT CO2 refrigeration system at different evaporating temperatures


Some test results

Combined performance of MT and LT CO2 refrigeration system

20

30

40

50

60

CO

P-M

T

4

6

8

10

12

CO

P-L

T o

r O

vera

ll .

COP-MT COP-Overall COP-LT


CR =1.3, Tc = -7oC and Te = -32oC)

0

10

20

2700 2880 3060 3240 3420 3600 3780 3960 4140 4320 4500 4680 4860

Time (20 seconds)

CO

P-M

T

0

2

4

CO

P-L

T o

r O

vera

ll .

0 180 360 540 720 900 1080 1260 1440 1620 1800 1980 2160


Case Study – Application of system to a medium size

supermarket

• 50,000 ft2 net sales area store

• Timber frame and sustainable

cladding

• Daylighting (roof lights and

clerestory windows)


clerestory windows)

• CHP

• Doors on chilled food cabinets

• Mixed mode ventilation (wind

catchers)

• Fully automatically dimmable lights


CASE STUDY STORE

Energy system of the store:

� Electricity: supplied from National Grid and CHP/Trigeneration option

� Cooling for HVAC: Air cooled electric chiller installed (R-407A) 200 kW . Option for cooling to be supplied by Absorption chiller

� Refrigeration: Cascade transcritical CO2 refrigeration system with flash gas bypass

Design refrigeration-capacity:

- MT system 4 packs @ 55 kW


- MT system 4 packs @ 55 kW

- LT system @ 35 kW

� Heating: 2 gas boilers @ 200 kWth.

,

Net sales area: 51,190 ft2

Opening date: 12-01-2009

Opening hours: 8 a.m. to midnight

CHP/Trigeneration

Biofuel engine based CHP

� 200 kW electricity

� 350 kW heat

Water-LiBr absorption chiller

� 250 kW cooling capacitywith chilled water circuit


ACTUAL ELECTRICITY AND GAS DEMAND OF THE STORE


Electricity:Annual demand: 2,731 MWh

Hourly annual average: 309.2 kW

Hourly peak demand: 463 kW

Electricity usage:

Gas: Annual demand: 874 MWh


ELECTRICAL ENERGY CONSUMPTION OF REFRIGERATION PACKS AND

CABINETS


Total Refrigeration HT-Refrigeration LT Refrigeration Display cabinets

31.72

1,067,359 604,266 124,542 338,551Annual kWh

Hourly average (kW)

Hourly max (kW)

Percentage (%)

121.8 69.0 14.2

100 56.61 11.67

38.6

200.0 142.0 28.3 58.3


HOURLY COOLING DEMAND


Cooling demand:Annual demand: 202,247 kWh

Hourly annual average: 58 kW

Hourly peak demand: 210 kW

Average COP: 2.9


ENERGY SYSTEM ALTERNATIVES INVESTIGATED

� System-1: Conventional energy system with R-404A refrigeration,

electric chiller and gas boiler

Lighting, preparation, food,

SUPERMARKET ENERGY

DEMAND Mix fuel

E

National grid

Standby Generator NG

ima

ry F

ue

l

Ee-grid

Ee-SG

ηe-grid

ηe-SG



services, cabinets and others

MT refrigeration demand

LT refrigeration demand

Domestic hot water demand

Heating demand

Cooling demand HVAC

Gas fired boiler

NG

Ee-others

Ec Ee-chiller

ηth

R-407C Chiller

Ef-conv

Annual fuel

Eh

Er R-404A

Refrigeration

Pri

ma

ry F

ue

l

Ee-R404A

Ef-boiler


FUEL UTILISATION RATIO OF SYSTEM 1 (CONVENTIONAL)


49.60 % 19.00 % 2.07 % 7.29 % 21.23 %

Cooling

Annual average Fuel Utilisation Ratio (FUR)

ElectricalHeatingOverall Refrigeration


� System-2: Existing system with Cascade transcritical CO2 refrigeration,

biodiesel engine based CHP, electric chiller (R-407A), and gas boiler

assuming


services and others

FOOD RETAIL STORE

Biofuel Engine based CHP

Mix

Bio-fuel

R-407A Chiller

57.3%

42.7 %

202 MWh

National grid

Pri

ma

ry F

uel

ηe = 33%

ηe = 35%

Exported

electricity





Heating demand

Cooling demand HVAC

Absorption Chiller

Gas fired boiler

CASCADE TRANSCRITICAL CO2 REFRIGERATION

AND TRIGENERATION PLANT

Natural gas

Cascade CO2

Refrigeration

Display Cabinets

706 MWh

202 MWh Pri

ma

ry F

uel

ηth = 80.8%

1,328 MWh

432 MWh

MWh

Annual store’s fuel


EXISTING CO2 REFRIGERATION SYSTEM IN THE STORE



FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY

SYSTEM (SYSTEM - 2)


Overall Electrical Cooling Heating Refrigeration

58.7% 24.1% 2.4% 9.4% 22.8%



� System-3: Modification of existing system with transcritical CO2

refrigeration cooled by trigeneration, gas engine based CHP, electric

chiller for space cooling (R-407A), and gas boiler

MT display

cabinets

LT display

cabinets

Air cooled

gas cooler/

condenser

HT condenser

HT liquid

LT liquid

receiver Cooling from

trigeneration IHX

EXV

EXV

EXV

SV

SV

ICMT

ICM


LT pack HT pack

LT condenser

HT liquid receiver

trigeneration

From

other HT

packs


FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY

SYSTEM (SYSTEM - 3)



60.7% 28.1% 2.4% 8.8% 21.5%




services and others

FOOD RETAIL STORE

Gas Engine based CHP

Mix

Natural Gas

R-407A Chiller 202 MWh P

rim

ary

Fu

el

ηe = 33%

ηe = 36.6%

National grid

Exported

electricity

Energy Flow Diagram of the Proposed Energy System with

Integrated Volatile/DX CO2 Refrigeration (System-4)





Heating demand

Cooling demand HVAC

Absorption Chiller

Gas fired boiler

VOLATILE/DX CO2 REFRIGERATION

AND TRIGENERATION PLANT

Natural gas

Volatile/DX CO2

Refrigeration

Display Cabinets

706 MWhth

202 MWh Pri

ma

ry

Fu

el

ηth = 80.8%

1,328 MWh

432 MWh Annual store’s fuel

MWh


*System-4. Schematic diagram of proposed system - Integrated

Volatile/DX CO2 Refrigeration (System-4)

MT display

Hot water pump

Condenser

Cooling tower Sorption chiller

Cold water pump

Chilled water pump

Air cooled gas cooler

CHP

SV


MT display cabinets

LT Pack

LT display cabinets

MT Pack

Liquid receiver

IHX

IHX

Pump pack

CHP

ICMT

RV

EXV


FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY SYSTEM

(SYSTEM - 4)



64.3% 29.5% 2.6% 9.2% 23.0%



PLANT OPTIMISATION

OF THE PROPOSED ENERGY SYSTEM (SYSTEM - 4)


FSR and CO2 emission savings increase with trigeneration electrical

capacity up to 340 kW

FUR optimum in the range 280 to 340 kW at 65%


PLANT OPTIMISATION (Cont’d)

OF THE PROPOSED ENERGY SYSTEM (SYSTEM - 4)


Optimum size of trigeneration in the range 320 to 340 kWe with

absorption chiller cooling capacity 310 kW


VARIATION OF PAYBACK PERIOD OF THE PROPOSED ENERGY

SYSTEM (SYSTEM - 4) WITH SPARK RATIO

Proposed energy

system payback 3.2 years


Trigeneration: 340 kWe and absorption chiller of 310 kW


Supermarket’s energy systems

Energy

consumptionCO2 emissions Payback

kWh/year Saving kgCO2/year Saving Years

System-1: Conventional energy

system9,411,406 2,187,736

System-2: Existing system based

on 2009 data (absorption system 9,068,097 3.6% 1,428,014 34.7% No payback

SIMULATION RESULTS

Comparison of fuel consumption, CO2 emissions and payback

period


on 2009 data (absorption system

not in operation)

9,068,097 3.6% 1,428,014 34.7% No payback

System-3: Integration of cascade

transcritical CO2 refrigeration

system with trigeneration7,088,252 24.7% 1,327,358 39.3% 4.7

System-4: Proposed energy

system - Cascade subcritical (MT

volatile pumped CO2) with

trigeneration

6,654,630 29.3% 1,246,897 43.0% 3.2

2,758 MWh/year 941 tCO2/year


� Integration of CO2 refrigeration with trigeneration systems can offer energy savings

of 30% and CO2 emissions savings of the order of 43% compared to conventional

approaches.

� System can be applied to both MT pumped systems and all CO2 transcritical

cascade systems.

� A wide range of fuels can be employed such as natural gas, biogas or biodiesel.

� System design can be adapted to suit both adsorption and absorption (LiBr-Water

CONCLUSIONS


� System design can be adapted to suit both adsorption and absorption (LiBr-Water

and R717-Water) refrigeration systems.

� In the event of trigeneration system failure the CO2 refrigeration system can be

arranged to operate transcritically.

� Good payback periods can be achieved, of the order of 3.2 years.

� Further overall system optimisation is possible


� Energy system design for supermarkets that can lead to significant energy and

GHG emission savings.

� Modelling tools for design and analysis of CO2 refrigeration systems as well as

complete energy systems for supermarkets

� Unique facilities and expertise at Brunel for test and development of CO2

refrigeration components and systems (subcritical and transcritical) as well as

OUTPUTS AND BENEFITS FROM PROJECT


trigeneration systems.

� Exposure of participating companies to new technologies and opportunities for

the improvement of existing and/or development of new products.

� Wide dissemination of the results to the user community through dissemination

events and publications

Integration of trigeneration and CO refrigeration systems ... · COP LT refrigeration capacity...

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