Water and Ethanol as Refrigerant Mixture Enabling Adsorption Cooling below 0 °C

Adsorption chillers can avoid two types of greenhouse gas emissions from conventional cooling technologies: energy-related emissions by utilizing waste heat and refrigerant leakage-related emissions by employing the natural refrigerant water. However, water restricts the minimal cooling temperature to its freezing point. To overcome this limitation, herein, a boiling antifreeze in adsorption chillers is proposed. For this purpose, a databank of over 12 000 molecules for suitable antifreezes is screened and ethanol is derived as the best candidate. Employing ethanol as antifreeze, the experimental feasibility in a lab-scale adsorption chiller is demonstrated: ethanol can prevent freezing at a cooling temperature of -5 degrees C and, thus, extend the operating range of the adsorption chiller. Thereby, the favorable properties of water can be partially retained. Furthermore, water-ethanol mixtures to pure water at a cooling temperature of 10 degrees C are compared: maximal coefficient of performance (COP) and specific cooling power (SCP) decrease by 45% and 42%, respectively, when 14 mol% ethanol is used instead of pure water. Herein, the influence of ethanol on the adsorbed mass and heat transfer during evaporation are crucial. In summary, boiling antifreezes can extend the operating range of water-based adsorption chillers below 0 degrees C.

Automated summary

Adsorption chillers can avoid greenhouse gas emissions by utilizing waste heat and a natural refrigerant. To overcome the limitation of water's freezing point, a boiling antifreeze using ethanol is proposed. Ethanol can prevent freezing at -5 degrees C and extend the operating range of the adsorption chiller, while retaining some of the favorable properties of water.