Evaluation Efficiency Increase With CO2
Efficiency increase of CO2 refrigeration systems
Carbon dioxide has been used as a refrigerant since circa 1920, when the only refrigerants were some natural fluids.
Since the beginning of the application of CO2, many studies have been done to improve cycle efficiency under conditions of high temperature heat transfer. The low critical temperature penalizes this refrigerant in high temperature ambient conditions. This argument is interesting now due to high summer temperatures in Europe.
The modified cycles analyzed were, briefly, of this type:
a) 2-stage compression, for evaporation temperatures below -20°C
b) Voorhees
c) Plank (post-compression and cooling)
d) Auxiliary compression (flash recompression)
e) Energy recovery from expansion with turbine or expander
f) Post-gas cooler subcooling
g) Evaporative cooling of the gas cooler
Recently, ejectors for semi-flooded feeding of evaporators and flash gas pre-compression have been introduced.
I participated directly in the years 2011-2014 in the conception and development of concepts using ejectors, but also, previously, in the development of the 2-stage compressor, a), and in the recompression of the flash, d).
Separate considerations must be made for the Voorhees method, as I will say later. Apart from a) and d) the other solutions, specifically c), e) have not been proven technically and/or economically are not viable.
The subcooling, f), was the first thing that came to mind but the problem is the cost.
In fact, some devices proposed to improve performance have rather high payback times.
What else remains? At present, there is nothing else realistic.
I will come back with another blog on the Voorhees method.
To increase efficiency in the immediate future, all what remains is to work on apparently secondary aspects but whose benefits are obtained at low cost and, above all, produce effects all year round:
- Capacity control more precise
- to avoid or limit losses that are normally neglected, such as leakage and pressure drops
- to limit electrical losses (consumption of electrical panel and control equipment)
- to limit the consumption of “auxiliary” components, such as oil heaters, fans and more