Conference Agenda

The advantage of the diffusion absorption refrigerators (DAR) is that they can be thermally driven by waste heat or solar energy, without electricity consumption. This allows cooling at low carbon footprint, reduced to the embodied energy and carbon dioxide at the production, maintenance and recycling of the installations. For the solar cooling, the heat required for boiling and movement of the binary solution in DAR, is obtained by converting the solar energy in solar collectors. The change of the solar irradiation during the day is resulting in a variable power input in the generator and subsequent changeable cooling capacity of DAR. An experimental analysis of a laboratory DAR at variable heat supply was carried out to analyze the limits of these changes. The variation of the cooling capacity and the coefficient of performance of the refrigerator with the energy input have been established. On this basis, the possibilities for cooling by a DAR based solar system in Sofia were investigated.

This work proposes an experimental assessment of R448A as a lower-GWP alternative to R404A in the high-temperature stage of a R404A/R23 ULT two-stage cascade refrigeration system. Furthermore, the use of capillary tubes and electronic expansion valves is compared. First, the pull-down performance starting from three ambient temperatures (15, 20, and 25 °C) down to –80 °C is analysed. Then, the hysteresis operation with set freezer temperatures of –80, –70, –60, and –50 °C is studied. The pull-down time was higher (38 to 55 min slower) using the capillary tubes compared to the electronic expansion valves. Also, the energy consumption of the hysteresis operation was higher (up to 32.3% higher) using the capillary tubes. A comparable energy consumption and cooling capacity were obtained with R404A/R23 and R448A/R23 using the electronic expansion valves. The highest COP was achieved by R448A/R23 (up to 10.2% higher than R404A/R23). Therefore, the suitability of R448A as a replacement for R404A in ULT refrigeration is confirmed.

Containerised refrigeration systems are designed to operate across a broad ambient temperature spectrum ranging from as low as -30 °C to as high as 50 °C in accordance with design requirements of ISO1496-2:2018. Whilst the majority of shipments are at well within this range, operation at 50 °C in container holds is relatively common. Vessels holds are cooled either by ambient air or seawater. With tens or hundreds of 40’ containers, each with their own refrigeration system, operating in the holds, temperatures of 50°C and above are easily achieved.

The HFC refrigerants currently used by the marine industry, HFC-134a and HFC-404A, operate somewhat differently once the temperature goes beyond the design specification. A marine CO2 system is offered by one manufacturer therefore CO2 operation shall also be discussed.

It is found that operation in high ambients – even beyond 50 °C - is possible however it comes with coefficient of performance (CoP) losses.