Dynamic evaluation of sorption working pairs and hybrid configurations for waste heat - to- cool solutions

Adsorption chillers and heat pumps have been often considered for waste heat utilization, e.g. from engines. The vessels are a very attractive application case for the adsorption cooling because of : a) Availability of waste heat in large quantities and good quality b) Large cooling demand, especially on passenger vessels such as ferries and cruise ships. c) Availability of a heat sink with high heat capacity at beneficial temperature levels (sea water). In contrary to onshore applications, where ambient air usually serves as the heat sink, dissipation of heat to water does not require the use of fans, which significantly reduces the consumption of electrical energy by the overall cooling system. d) Benefits for the vessel operator and the environment are significant. The lower the electrical energy consumption of the HVAC system, the lower the fuel consumption and the longer range of the ship. In addition, the reduced fuel consumption directly leads to lower emissions of CO2, sulphur, and nitrogen oxides. The activity presented in the current paper has the ultimate goal to design and manufacture a sorption chiller for installation on a ferry that moves on the Crete-Athens route within the H2020 project ENGIMMONIA. To this aim, a first screening was carried out on several sorption working pairs using data from experimental measurements carried out at CNR, in terms of sorption capacity and specific heat. The measurements were performed for AlPO 18, SAPO 34, Siogel and SWS. Results from the measurements were used within a thermodynamic model developed by CNR to estimate the Coefficient of Performance (COP) and Specific Cooling Effect (SCE) for the various materials. Results indicated that SAPO has a more stable performance with varying conditions and allows up to 3 times higher cooling effect than Siogel for the same amount of material. Finally, starting from design parameters from Fahrenheit and previous models available at CNR, dynamic evaluation in Dymola/Modelica environment was carried out at CNR, considering both the use of a single working pair or a hybrid configuration with both silica gel (Siogel) and zeolite (SAPO-34) modules. Regarding the cooling capacity, the SAPO module showed much higher performances if compared with the SIOGEL one. Indeed, the SAPO cooling capacity is almost double than that of Siogel. However, the performance derating when passing from LT=16°C to LT=10°C is more visible in the SAPO module, thus making SIOGEL more performant at 16°C. As can be expected from the shape of the adsorption curves, the behaviour of the Siogel module is linear with varying evaporation and condensation temperature, whereas the effect of the increased temperature lift between condenser and evaporator is more marked in the case of the zeolite module. Such a result indicates that the zeolite module, in a hybrid configuration, might work better if the Siogel module is used with a pre-cooling function. Starting from such results, dynamic simulations for two hybrid configurations were carried out: o Pre-cooling configuration with a parallel connection of the modules on the MT side and a series connection on the LT side for LTin=16°C. 100 Barcelona, 2022 o Series connection on both MT and LT, with the Siogel unit as the topping one. Results of the dynamic simulations show that the average cooling power achievable with the pre-cooling configuration is about 15% higher, with a significant effect on the evaporator outlet temperature, that is about 1.5°C lower than in the series configuration. It is also possible to notice that, whereas there is not a significant difference at 25°C, the pre-cooling configuration guarantees a more stable cooling power also with increasing condensation temperature. Such results will be validated in the next months through experimental activity at CNR.