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FEATURE
INCORPORATING COLD CHAIN using hydrocarbons, particularly R290 in Australia, Germany and the UK. However, they do not seem to have become commercialised on a wider scale.
This article describes the development of a prototype R290 system for use in a medium-sized RRV. The starting point for the development was a baseline R404A system and it involved a number of stages, as illustrated in Figure 1.
Since the primary concern is overcoming the flammability hazard of R290, the majority of the steps address risk minimisation. This involved reduction of refrigerant charge, development of a leak control and safety system, improving leak tightness, identification of potentially flammable zones and subsequently addressing potential sources of ignition within those zones.
If the failure modes and effects analysis( FMEA) and quantitative risk assessment( QRA) yield any concerns, prior steps are re-evaluated in order to help minimise the risk further; these steps are consistent with the approach given in EN 1127-1. When the risk is believed to be sufficiently low, final compliance against a safety standard is carried out followed by drafting of guidance for users and finally applying the prototypes for field trials. In addition to safety matters, performance( capacity and efficiency) is also important. Since these parameters are closely linked to the charge reduction process, they were carried out simultaneously.
Figure 1: Summary of the main stages in the development of an R290 transport refrigeration system.
Final remarks
A prototype refrigeration system for RRVs has been developed. Major aspects of the development were significantly reducing the refrigerant charge and adopting a special leak control and safety system. A risk assessment indicates that the level of flammability safety of the prototype should not present any concerns. Now that the prototype has been developed and tested, it is undergoing field trials, so far with favourable results.
The motivation behind the project is to reduce the emissions of greenhouse gases. An initial assessment of lifecycle emissions suggests about 16 % lower diesel consumption— which translates directly into reduction in‘ indirect’ emissions— and on account of the negligible GWP of R290 an elimination of‘ direct’ global warming emissions. Overall, the R290 model is expected to generate only 34 % of the global warming emissions( in terms of tCO 2
-eq) compared to the R404A baseline model.
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Acknowledgements
The authors would like to acknowledge the German Ministry for Environment, Nature Conservation, Building and Nuclear Safety and the Deutsche Gesellschaft für Internationale Zusammenarbeit( GIZ) GmbH and Transfrig Ltd for giving permission for publication.
Overall, the R290 model is expected to generate only 34 % of the global warming emissions
( in terms of tCO 2
-eq) compared to the R404A baseline model.
Checking in on the project
The field trial of the joint venture between Transfrig and GIZ on the R290 prototype successfully kicked off on 29 November last year at Transfrig’ s premises in Linbro Park, Johannesburg.
The next step is for Transfrig and GIZ to approach suitable customers for an extended field trial with 10 units. In January, Daniel Colbourne visited South Africa again to check up on the project and talk to various key role players in the industry about this research. CLA
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