Adsorption chilling driven by low temperature heat: New adsorbent and cycle optimization

This paper aims to present a new composite sorbent, specifically developed at BIC-RAS to operate at low regeneration temperature (<70 °C), and its testing by a lab-scale adsorption chiller installed at ITAE-CNR. Adsorption equilibrium measurements demonstrated that the new composite, LiNO3/vermiculite, named SWS-9V, exchanges app. 0.4 g H2O/g in an exceptionally narrow temperature range, 33–36 °C (adsorption at 12.6 mbar) and 62–65 °C (desorption at 56.2 mbar), corresponding to a remarkable heat storage capacity (0.9 MJ/kg). The new sorbent, embedded into an adsorber, was tested at ITAE with the aim to optimize the cycle taking into account both the thermodynamic and kinetic properties of SWS-9V. The results demonstrated that the optimal cycle performance, for given operating conditions, are strongly dependent on the cycle time (τ) and the relative duration (R) of the isobaric adsorption and desorption steps. Indeed, at Tc = 35 °C, Te = 10 °C and high driving temperature (Td = 90 °C), the system provided the best performance at τ = 20 min delivering about 230 W/kg of specific cooling power (SCP) with a coefficient of performance (COP) equal to 0.66 when the adsorption duration is 7 times longer than the desorption one (R = 7). Differently, at low driving temperature (Td = 68 °C), the best performance (COP = 0.59 and SCP = 96 W/kg) were obtained at τ = 30 min, protracting the duration of the desorption step at the expenses of the adsorption one (R = 0.75).