Greenhouse water recovery system for crop production in semi-arid climate

The greenhouse is considered water use efficient compared to open-field production systems; nonetheless, conventional semi-arid greenhouses use large amounts of water, for both evaporative cooling and irrigation. The goal of this project is to examine the feasibility of installing a water recovery system for reducing semi-arid greenhouse water consumption. Specifically, we examined a water recovery system placed in the stream of the exhaust air of the greenhouse equipped with a fan and pad evaporative cooling system, where chilled water naturally generated and therefore this water can be used as an energy sink to recover the water via condensation. We monitored the dew point temperature of the greenhouse exhaust air (t _dp) and the temperature in the pad sump water (potential coolant for condenser) (t _fw1), in a commercial greenhouse (Willcox, AZ) to use the collected data in simulating amount of condensate water during the pre-monsoon (May-June, 2006) and the monsoon season (July-Sep, 2006). The energy balance model of condenser used in the simulation was validated by data obtained using a condenser unit placed under a semi-arid greenhouse condition. Comparing to water use in the plant canopy transpiration of 0.0036-0.0105 m ³ m ^-2 d ^-1 and 0.0033-0.0081 m ³ m ^-2 d ^-1 during the pre-monsoon day and monsoon day, respectively, our steady-state model simulated that, relative to minimum and maximum irrigation water use (min/max), 26.9%/9.2% and 15.1%/6.2% of water can be recovered in pre-monsoon day and monsoon day, respectively, when equipped even with the relatively inefficient (bypass factor =0.92) condenser units. If we improve the condenser efficiency to 50% (BF= 0.5), the proposed system could recover 100%/57.6% of irrigation water in pre-monsoon day and 94.3%/38.4% recovery in monsoon day. The result showed that integration of a water recovery system using the pad sump water as chilled water source into a pad and fan cooled semiarid greenhouse is technically feasible.