Development of R290 transport refrigeration system.

Transport refrigeration systems for small and large trucks have been developed using R290. They are electrically driven via a diesel engine and 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 in order to select compressors and redesign of heat exchangers in order to achieve the same cooling capacities as R404A, whilst maximising improvement in COP and reducing refrigerant charge as much as possible. Subsequent to this, measurements were carried out to validate the performance with R290. In order 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 pre-ventilation 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 shut-down 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.