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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