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Refrigeration systems & heat pumps with co2
1. REFRIGERATION AND HEAT PUMP
SYSTEMS WITH CO2
AS A REFRIGERANT
S. Girotto
Enex S.r.l., Italy
sergio.girotto@enex-ref.com
2. INDEX
WHY NATURAL REFRIGERANT CO2
ENVIRONMENTAL IMPACT OF CO2 / R404A
EXAMPLE – TYPICAL “COLD CLIMATE”
INVESTMENT & OPERATING COST
EFFICIENCY
FLASH VAPOR RECOMPRESSION
COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS
HEAT PUMPS FOR HOT WATER
3. 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 ->
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)
5. 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
80000
70000
60000 refrigerant
50000 pipi ng/ins.
€ 40000 condenser
30000
elec.panel
20000
compr.unit
10000
0
CO2 HFC R404A
6. INVESTMENT & OPERATING COST (2)
In a proper economical analysis other factors must be considered:
a) cost for refilling of refrigerant during the lifetime of the system
b) cost for inspections due to leak emission control (F-GAS Directive)
c) unforeaseeable cost increase and unavailable of synthetic refrigerant
d) disposal cost
7. EFFICIENCY (1)
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
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.
8. 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 recovery
2) extremely low condensing pressure in winter time when no Heat Recovery is
required
3) LPR design – standard solution for some heat pumps and single compressor units
4) 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
10. FLASH VAPOR RECOMPRESSION (2)
SIMULATION FOR BARCELLONA CLIMATE
Temperature profile July Temperature profile September
40 40
Te m pe rature [°C]
Tem perature [°C]
30 30
average
20
20
max_daily average
10
10
0
0
0 5 10 15 20
0 5 10 15 20
hour
hour
14. COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 1
“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
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.
15. COMMERCIALLY AVAILABLE REFRIGERATION SYSTEMS - 2
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° eva poration for large
C
cold rooms, hypermarkets, water and brine chilling
-2-stage internal compound up to 100 kW at -35°C evaporation for deep
freezing (cold rooms, hypermarkets)
- Cascade for LT (supermarkets, freezing tunnels,…)
19. HEAT PUMPS FOR HOT WATER
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° up to 90°
C 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
20. HEAT PUMPS – FOR HOT WATER
AIR HEAT 25
Best applications:
- Hotels
- Hospitals
- Laundries – Elderly people houses
- Wheneven hot water is needed in large amounts
