Conference Year
2016
Keywords
hydrocarbon, laboratory equipment, performance, optimization, conversion
Abstract
Platelet incubators provide temperature controlled environments for laboratories that preserve platelets in liquid form at close to ambient temperature. Quality and shelf life of the stored platelets strongly depend on the storage temperature uniformity and continuous movement of the platelets provided by an agitator to avoid coagulation. Incubator manufacturers usually provide assurance that temperature uniformity within +/-1°C from the set point can be attained. Tight temperature tolerances are achieved with a combined vapor compression cooling system and an electric resistance heating system integrated into the incubator. Standard refrigerants currently employed in refrigerated laboratory equipment are HFCs with high GWPs. In the future, HFCs could be gradually replaced mostly by flammable natural refrigerants of the ASHRAE A3 group such as R600a (isobutane), R290 (propane) and R170 (ethane) depending on the cooler size and application temperature. Flammable refrigerant charge is limited to 150g or less which in some cases requires complete redesign of the refrigeration circuit. The focus of this study was to convert the refrigeration system of an existing platelet incubator to hydrocarbon refrigerant. The selected incubator is able to store 32 apheresis bags and based on the required cooling capacity R600a refrigerant was identified as the most suitable replacement for R134a. The baseline R134a system performance was experimentally evaluated at a wide range of ambient temperatures between 15°C to 35°C specified by the manufacturer and at 3 different cabinet set points: 20°C, 22°C and 27°C. Attention was given to the energy consumption by distinguishing between contributions of individual components: compressor, fans, pulse heater, agitator, condensate tray heater and controller. Temperature uniformity was determined from measurements at 17 locations inside the cabinet over a 24 hour period. Subsequently, the refrigeration system was converted to R600a refrigerant and its performance was optimized by capillary tube size selection, refrigerant charge amount, evaporator fan speed and by replacing the electric condensate heater with a discharge gas loop. The redesigned machine required only 50g of R600a refrigerant charge and resulted on average in 20% lower energy consumption. Cabinet temperature uniformity was within the required +/-1°C for all tested conditions and uniformity of +/-0.5°C at 15°C and 25°C ambient temperatures was confirmed.