Experimental study on advanced indirect evaporative cooling and desiccant dehumidification systems for agricultural greenhouses

The study aims to evaluate evaporative cooling and/or desiccant based solution(s) for energy-efficient control of greenhouse temperature (T) and relative humidity (RH). In this regard, a lab-scale greenhouse alongside experimental apparatus for three kinds of T/RH control systems (i.e. standalone M-cycle evaporative cooling, standalone desiccant air-conditioning (DAC), and M-cycle assisted DAC) are developed and thermodynamically evaluated. The standalone M-cycle evaporative cooling system showed potential to reduce ambient air T up to 13 °C, however, it was not able to maintain greenhouse humidity during humid conditions. The M-cycle assisted DAC system is outperformed for maintaining optimum greenhouse T and RH conditions as compared to standalone DAC with maximum moisture removal rate of 1.73 kg/h, cooling potential of 25.66 kJ/kg, and COP of 1.50 at regeneration T of 60 °C. The cooling potential and COP of the M-cycle assisted DAC system is ∼2 and ∼ 3.7 times higher as compared to standalone DAC system with maximum energy efficiency ratio of 3.52. Payback period and levelized cost of energy for M-cycle assisted DAC system is found 3.70 years and 0.07 USD/kWh, respectively. Moisture removal cost of solar PV operated M-cycle assisted DAC system is ∼2.6 times lower than grid electricity operated system. Integrating solar PV electricity into M-cycle assisted DAC system reduced CO₂ emissions to 7.98, 4.02, and 7.73 tons CO₂e/year than electricity from coal, natural gas, and oil, respectively. The study concludes that the M-cycle assisted DAC system has the potential to efficiently control greenhouse T/RH conditions.