Low grade heat driven adsorption system for cooling and power generation using advanced adsorbent materials

Highlights: • Adsorption system based on water and advanced physical adsorbents has the potential of producing cooling and power. • Adding an expander to physisorption system enhances efficiency by up to 11%. • MIL101Cr MOF can produce 95 W/kg and 1357 W/kg of specific power and cooling. • AQSOA Z02 can produce 73 W/kg and 640 W/kg of specific power and cooling. - Abstract: Globally there is abundance of low grade heat sources (around 150 °C) from renewables like solar energy or from industrial waste heat. The exploitation of such low grade heat sources will reduce fossil fuel consumption and CO₂ emissions. Adsorption technology offers the potential of using such low grade heat to generate cooling and power. In this work, the effect of using advanced adsorbent materials like AQSOA-Z02 (SAPO-34) zeolite and MIL101Cr Metal Organic Framework (MOF) at various operating conditions on power and cooling performance compared to that of commonly used silica-gel was investigated using water as refrigerant. A mathematical model for a two bed adsorption cooling cycle has been developed with the cycle modified to produce power by incorporating an expander between the desorber and the condenser. Results show that it is possible to produce power and cooling at the same time without affecting the cooling output. Results also show that for all adsorbents used as the heat source temperature increases, the cooling effect and power generated increase. As for increasing the cold bed temperature, this will decrease the cooling effect and power output except for SAPO-34 which shows slightly increasing trend of cooling and power output. As the condenser cooling temperature increases, the cooling effect and power output will decrease while for the chilled water temperature, the cooling load and power generated increased as the temperature increased. The maximum values of average specific power generation (SP), specific cooling power (SCP) and cycle efficiency are 73 W/kg_ads, 681 W/kg_ads (using SAPO-34) and 67% (using Silica-gel) respectively. However, MIL101Cr can generate SP and SCP of 95 W/kg_ads and 1367 W/kg_ads respectively, but this case cannot consider to be practical operating conditions, because of using relatively low cooling source temperature, but this material still offers potential of generating power.