Post on 20-Apr-2020
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
School of Engineering and Design
Content of Presentation
• Background
• Aims and Objectives of Project and Partnership
• Test facilities and test results
• Test Supermarket
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• Test Supermarket
• Energy analysis
• Results and Conclusions
School of Engineering and Design
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
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• 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
School of Engineering and Design
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
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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
School of Engineering and Design
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
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• Reduce leakage (F-Gas regulations)
• Use refrigerants with low GWP
• Use natural refrigerants (CO2, HCs, Ammonia in
cascade arrangement)
School of Engineering and Design
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
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• 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)
School of Engineering and Design
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
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cooling
3. Use cooling/refrigeration from sorption system to
maximise efficiency of CO2 refrigeration system.
4. Significantly reduce both direct and indirect emissions
School of Engineering and Design
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)
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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;
School of Engineering and Design
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
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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
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Test facilities Pulse vessel and plate heat
exchanger
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Environmental test chamber
for CO2 work
LT compressor and pump
unit
CO2 Coil design process
School of Engineering and Design
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
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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
Te = -6 [C] Te = -8 [C] Te = -10 [C]Teva= -6oC Teva= -8oC Teva= -10oC
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]Teva= -6oC Teva= -8oC Teva= -10oC
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)
Te = -6 [C] Te = -8 [C] Te = -10 [C]Teva= -6oC Teva= -8oC Teva= -10oC
Performance of MT CO2 refrigeration system at different evaporating temperatures
School of Engineering and Design
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
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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
School of Engineering and Design
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)
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clerestory windows)
• CHP
• Doors on chilled food cabinets
• Mixed mode ventilation (wind
catchers)
• Fully automatically dimmable lights
School of Engineering and Design
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
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- 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
School of Engineering and Design
ACTUAL ELECTRICITY AND GAS DEMAND OF THE STORE
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Electricity:Annual demand: 2,731 MWh
Hourly annual average: 309.2 kW
Hourly peak demand: 463 kW
Electricity usage:
Gas: Annual demand: 874 MWh
School of Engineering and Design
ELECTRICAL ENERGY CONSUMPTION OF REFRIGERATION PACKS AND
CABINETS
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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
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HOURLY COOLING DEMAND
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Cooling demand:Annual demand: 202,247 kWh
Hourly annual average: 58 kW
Hourly peak demand: 210 kW
Average COP: 2.9
School of Engineering and Design
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
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Lighting, preparation, food,
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
School of Engineering and Design
FUEL UTILISATION RATIO OF SYSTEM 1 (CONVENTIONAL)
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49.60 % 19.00 % 2.07 % 7.29 % 21.23 %
Cooling
Annual average Fuel Utilisation Ratio (FUR)
ElectricalHeatingOverall Refrigeration
School of Engineering and Design
� System-2: Existing system with Cascade transcritical CO2 refrigeration,
biodiesel engine based CHP, electric chiller (R-407A), and gas boiler
assuming
Lighting, preparation, food,
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
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MT refrigeration demand
LT refrigeration demand
Domestic hot water demand
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
School of Engineering and Design
EXISTING CO2 REFRIGERATION SYSTEM IN THE STORE
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School of Engineering and Design
FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY
SYSTEM (SYSTEM - 2)
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Overall Electrical Cooling Heating Refrigeration
58.7% 24.1% 2.4% 9.4% 22.8%
Annual average Fuel Utilisation Ratio (FUR)
School of Engineering and Design
� 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
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LT pack HT pack
LT condenser
HT liquid receiver
trigeneration
From
other HT
packs
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FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY
SYSTEM (SYSTEM - 3)
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Overall Electrical Cooling Heating Refrigeration
60.7% 28.1% 2.4% 8.8% 21.5%
Annual average Fuel Utilisation Ratio (FUR)
School of Engineering and Design
Lighting, preparation, food,
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)
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MT refrigeration demand
LT refrigeration demand
Domestic hot water demand
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
School of Engineering and Design
*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
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MT display cabinets
LT Pack
LT display cabinets
MT Pack
Liquid receiver
IHX
IHX
Pump pack
CHP
ICMT
RV
EXV
School of Engineering and Design
FUEL UTILISATION RATIO OF THE INVESTIGATED ENERGY SYSTEM
(SYSTEM - 4)
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Overall Electrical Cooling Heating Refrigeration
64.3% 29.5% 2.6% 9.2% 23.0%
Annual average Fuel Utilisation Ratio (FUR)
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PLANT OPTIMISATION
OF THE PROPOSED ENERGY SYSTEM (SYSTEM - 4)
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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%
School of Engineering and Design
PLANT OPTIMISATION (Cont’d)
OF THE PROPOSED ENERGY SYSTEM (SYSTEM - 4)
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Optimum size of trigeneration in the range 320 to 340 kWe with
absorption chiller cooling capacity 310 kW
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VARIATION OF PAYBACK PERIOD OF THE PROPOSED ENERGY
SYSTEM (SYSTEM - 4) WITH SPARK RATIO
Proposed energy
system payback 3.2 years
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Trigeneration: 340 kWe and absorption chiller of 310 kW
School of Engineering and Design
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
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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
School of Engineering and Design
� 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
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� 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
School of Engineering and Design
� 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
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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