A STUDY OF EVAPORATIVE COOLING PAD PERFORMANCE FOR A PHOTOVOLTAIC POWERED GREENHOUSE

The performance of the fan and pad evaporative cooling system for a photovoltaic powered greenhouse was investigated under extreme summer conditions. Temperature, relative humidity and electricity consumed for cooling were studied in a Quonset greenhouse covered with a sheet of corrugated Fiberglass-Reinforced plastic producing cucumbers. Pads clogging due to salt buildup was found to reduce the cooling performance. Additionally pads clogging caused the cooling system to run at longer time, causing more power to be drawn from the photovoltaic system. As a result, the system tripped three times during the summer period for one to three days. During most of the daytime, the averages of inside air temperatures with clogged pads were between 30 and 51°C, and the inside relative humidity was between 8% and 30%. This adversely affected plant growth, and caused wilting to plants in the second half of the greenhouse especially when accompanied by high solar radiation levels (10:00 to 16:00). Shade reduced the stress on plants, but air temperatures and relative humidity were far from the suitable ranges for good production practice. On the average, temperatures with shade ranged from 40 to 47.5°C, and relative humidity ranged from 8 to 12%. Replacing pads clearly improved the greenhouse environment. Air temperature and relative humidity inside the greenhouse during daytime ranged from 28 to 32°C, and from 39.3 to 44%, respectively. The cooling efficiency for new pads was averaged 71%, with 8 to 17.3°C reductions in ambient temperature. Electricity consumption with new pads was found to be around 22% less than that with old pads. Results also showed that the electricity consumption increased non-linearly as the ambient temperature increased. The cooling system consumed the maximum level of electricity (2.7 and 3 kW) at ambient temperature of 37°C or higher suggesting that the cooling system was in full operation. Shade had very minimal effect on the electricity consumption for the greenhouse cooling system