Dynamic simulation of a novel liquid desiccant air-conditioning system for greenhouse cooling and water recovery

Abstract

We present dynamic, hour-by-hour modelling of a multi-stage nanofiltration regeneration system for liquid desiccant air-conditioning (NF-LDAC) of horticultural greenhouses in 17 locations covering four climate types. Four technologies are compared: fan ventilation, evaporative cooling (EvapC), conventional air-conditioning (AC), and NF-LDAC. The comparison is based on acceptable conditions for cultivation and coefficient of performance (COP). On average, fan ventilation and EvapC achieve acceptable conditions for 2 months per year, compared to 5.4 and 10.5 months for AC and NF-LDAC respectively. The highest COP value of 7.6 for NF-LDAC is reached at Colombo (Sri Lanka), followed by 5.3 at Mecca (Saudi Arabia). The permeate of the multi-stage regenerator can be recycled for irrigation, providing water savings. The highest water saving of 63% is at Mecca. These results are inferior but more realistic than those from an earlier idealised and steady-state model, which predicted a COP of 12.4 and water savings of 100% at Mecca. Nevertheless, in hot desert climates, NF-LDAC maintains acceptable conditions for year-round cultivation and saves water that is scarce in such climates. Future advances in nanofiltration membrane fabrication could increase the COP of NF-LDAC to 12.1 at Colombo and 7.4 at Mecca.