INCORPORATING COLD CHAIN
FEATURE
Development of R290 transport refrigeration
Daniel Colbourne presented the following paper at last year’ s Gustav Lorentzen Natural Working Fluids Conference in Edinburgh, Scotland, elaborating on the groundbreaking R290 project currently being trialled locally by Transfrig in association with the GIZ.
Transport refrigeration systems for small and large trucks have been developed in South Africa using R290. They are electrically driven via a diesel engine and an alternator and include a variable speed drive for capacity control. For the design of the systems, the main aspects addressed were circuit optimisation and integration of safety measures. Circuit optimisation comprised system simulations to select compressors and redesign of heat exchangers in order to achieve the same cooling capacities as R404A, whilst maximising improvement in coefficient of performance( COP) and reducing refrigerant charge as much as possible.
Subsequent to this, measurements were carried out to validate the performance with R290. To mitigate the flammability risk of using R290, several aspects were addressed. In terms of the equipment redesign, other than charge size reduction, the main changes were to remove potential sources of ignition or apply preventilation to remove any build-up of potentially flammable mixtures.
Additionally, a leak identification feature was integrated into the system controls whereby a suspected substantial leak would result in a shutdown of the system and a warning signal to ensure no additional refrigerant can leak into the refrigerated space.
Extensive leak simulation tests were carried out to characterise the development of potentially flammable concentrations around the condensing unit and surrounding area, within the refrigerated and adjacent spaces. Conformity to the relevant parts of EN 378 and the essential health and safety requirements of the Atex( equipment) directive were confirmed.
The team with the R290 prototype. From left: Peter Solomon( MD, Transfrig), Daniel Colbourne( technical advisor, Heat International), Michael Schuster( advisor, GIZ), Bill Wilson( director, Transfrig), and Leon de Swart( R290 project engineer, Transfrig).
Downloading the truck’ s data at the Transfrig offices. The R290 prototype up close.
Why do we need an alternative?
Transport refrigeration includes intermodal containers, refrigerated ships, refrigerated train carriages, air cargo containers, and refrigerated road vehicles, including vans, trucks and trailers. The emissions of refrigerant from this sector accounts for about 5 % of the total( as tCO 2
-eq) although it varies by country. Due to their widespread use, refrigerated road vehicles( RRVs) represent the largest portion of direct emissions.
Typically, annual leakage is high compared to other subsectors, with values ranging around 15 % to 50 % of the system charge per year depending upon region, manufacturer and local conditions. Currently, the majority of RRVs use R404A and R22, with a smaller percentage on R134a and R410A. Although, recently some RRV system manufacturers announced their intention to use other alternative refrigerants, including R452A as well as R744.
In parallel to conventional vapour compression systems, several manufacturers are supplying open cryogenic systems with R728, where the refrigerant is vented to atmosphere. To date, there have been limited trials
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