Abstract
The refrigerants and electricity consumption of existing air conditioning systems create significant greenhouse gas (GHG) emissions. This work describes a new air conditioning cycle that uses a lower critical solution temperature (LCST) liquid mixture to provide dehumidification and cooling. The cycle uses no refrigerants and is driven by low-grade heat. Upon heating, the LCST mixture phase separates into a water-rich phase and a water-scarce phase. After cooling both phases to ambient temperature, the water-scarce phase absorbs moisture from humid air (providing dehumidification), while the water-rich phase desorbs water to the outdoor air (providing evaporative cooling). In this work, we theoretically develop and experimentally demonstrate this cycle for the first time, using three different LCST mixtures. A ternary mixture of oleic acid, lidocaine, and water showed the best performance by dehumidifying air to ∼86% relative humidity, while the other LCST mixtures we investigated were only able to dehumidify to ∼98% relative humidity. While a relative humidity of 86% is still too high for thermal comfort, this first investigation of a new cycle motivates further investigation into other LCST mixtures. Future discoveries could lead to new mixtures that can reach lower humidities. To this end, we derive the thermodynamic equations that govern LCST liquid mixtures and determine the enthalpy and entropy of mixing that these hypothetical future LCST mixtures would possess.
