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REFRIGERATION AND HEAT PUMP SYSTEMS WITH CO2AS A REFRIGERANT
S. Girotto
Enex S.r.l., Italy
INDEX
� WHY NATURAL REFRIGERANT CO2
� ENVIRONMENTAL IMPACT OF CO2 / R404AEXAMPLE – TYPICAL “COLD CLIMATE”
� INVESTMENT & OPERATING COST
� EFFICIENCY� EFFICIENCY
� FLASH VAPOR RECOMPRESSION
� COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS
� HEAT PUMPS FOR HOT WATER
WHY NATURAL REFRIGERANT CO2
� Zero ODP / Zero GWP
� Non toxic / Non flammable
� No further changes of refrigerant in future (with synthetic refrigerants : R12, R502, R22 -> R404A/R507, R134a + tens of blends -> : R12, R502, R22 -> R404A/R507, R134a + tens of blends -> HF1234yf -> ?? what comes after?)
� CO2 is largely available all over the world as a by-product, low cost
� No subject to legislation constraints (F-Gas Directive in EC)
ENVIRONMENTAL IMPACT OF CO2 / R404AEXAMPLE – TYPICAL “COLD CLIMATE”
INVESTMENT & OPERATING COST (1)� For a refrigeration system of one supermarket energy cost during lifetime is
85% of the total running cost
� Due to above investment running cost must be considered together
� Comparison between a DX-CO2 and a conventional HFC system cost splitting for a reference system 100 kW MT / 30kW LT
0
10000
20000
30000
40000
50000
60000
70000
80000
€
CO2 HFC R404A
refrigerant
piping/ins .
condenser
elec.panel
compr.unit
� In a proper economical analysis other factors must be considered:a) cost for refilling of refrigerant during the lifetime of the systemb) cost for inspections due to leak emission control (F-GAS Directive)c) unforeaseeable cost increase and unavailable of synthetic refrigerantd) disposal cost
INVESTMENT & OPERATING COST (2)
� CO2 itself is not “more efficient” or “less efficient” than other fluids.
� Efficiency theoretically does not depend on the fluid used (Carnot’s law) but from the combination of plant design and refrigerant.
� Guideline should be: for a given refrigerant (operating fluid) to improve as
EFFICIENCY (1)
much as possible the design of the system so as to obtain maximum performance.
� Compared with other refrigerants CO2 has a lower critical temperature, which might require a modified cycle for some applications.
EFFICIENCY (2)� A simple comparison with HFC solution cannot enhance differences due to better
heat transfer characteristics or lower influence of pressure drop on efficiency
� Efficient CO2 – only systems use one or more of the following:1) maximum heat recovery2) extremely low condensing pressure in winter time when no Heat Recovery is required3) LPR design – standard solution for some heat pumps and single compressor units4) recompression of flash vapor in warm ambient conditions(air cooled systems)
� Not – in – kind solutions (like expander, ejector) do exist, but they are still under evaluation and/or laboratory test
FLASH VAPOR RECOMPRESSION (1)
FLASH VAPOR RECOMPRESSION (2)SIMULATION FOR BARCELLONA CLIMATE
Temperature profile July
10
20
30
40
Te
mp
era
ture
[°C
]
average
max_dai ly
Temperature profile September
10
20
30
40
Te
mp
era
ture
[°C
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average
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10
0 5 10 15 20
hour
Te
mp
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ture
[°C
]
0
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0 5 10 15 20
hour
Te
mp
era
ture
FLASH VAPOR RECOMPRESSION (3)Temperature profile July average
FLASH VAPOR RECOMPRESSION (4)
Temperature profile July max_daily
FLASH VAPOR RECOMPRESSION (5)
Temperature profile September average
� “New” CO2 systems are on the market since 2006, after a long development started in late ‘90s (first CO2 only installation : 1999 – Italy /first CO2–only multi-compressor rack : 2001 - Italy)Now there are standardized and proven design concepts
Example : booster system for supermarkets
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 1
� CO2 as a refrigerant was used in early 20th century (until ’50s) but the application was completely different, so a complete re-invention of technology was necessary.
Other concepts using only CO2 as a refrigerant are well proven and available on the market:
-Single stage, with a capacity up to 300 kW at -10°C eva poration for large cold rooms, hypermarkets, water and brine chilling
-2-stage internal compound up to 100 kW at -35°C evaporation for deep
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 2
-2-stage internal compound up to 100 kW at -35°C evaporation for deep freezing (cold rooms, hypermarkets)
- Cascade for LT (supermarkets, freezing tunnels,…)
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 3
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 4
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 5
For one specific applications CO2 transcritical concept has no rivals : sanitary water heat pumps.
The gliding temperature for an isobaric/non-isothermal heat rejection reduces thermodynamic losses bringing performances at a level that cannot be reached with any other existing commercial solution :- Water heating in one pass from 10°C up to 90°C-COP higher than 4,0 for air-source heat pump with air 7°C-50% R.H. and water in-out 10-65°C
HEAT PUMPS FOR HOT WATER
in-out 10-65°C
HEAT PUMPS – FOR HOT WATERAIR HEAT 25
Best applications:- Hotels- Hospitals- Laundries – Elderly people houses- Wheneven hot water is needed in large amounts
Many thanks for your attention
