A PILOT-SCALE STUDY FOR EVALUATING THE PERFORMANCE OF A FAN-PAD COOLING SYSTEM UNDER DIFFERENT CLIMATIC CONDITIONS OF SAUDI ARABIA

Al-Helal, Ibrahim M.

doi:10.21608/mjae.2020.110169

A PILOT-SCALE STUDY FOR EVALUATING THE PERFORMANCE OF A FAN-PAD COOLING SYSTEM UNDER DIFFERENT CLIMATIC CONDITIONS OF SAUDI ARABIA

Document Type : Original Article

Author

Ibrahim M. Al-Helal

Department of Ag. Eng., College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Kingdom of Saudi Arabia

10.21608/mjae.2020.110169

Abstract

In the present study, a special test setup was designed to evaluate the performance of a fan-pad evaporative cooling system under different climatic conditions in Saudi Arabia. Weather data for Riyadh representing arid climate, Jeddah representing humid climate and Abha representing moderate climate were analyzed. These data contained hourly readings for air temperature, relative humidity and solar radiation. An evaporative cooler consisting of a 10 cm thick cooling pad, suction fan and water pump was used. The cooling pad was installed in a 1080mm high, horizontal duct of square cross-section insulated by 50mm polyurethane. The duct cross-section measures 1000mm ×1000mm. A variable speed suction fan was fitted at one end and the pad was designed so that the inlet air passed through the wetted pads. Air temperature and relative humidity of the inlet air were changed to simulate dry, humid and moderate climatic conditions of Saudi Arabia. The inlet air was heated by two types of electrical heater. The heaters were fixed in a contraction-cone-profile that is mounted in the air duct. The inlet air temperature was controlled by a PID temperature controller. Electrical high pressure steam boiler was used to produce low pressure steam for heating and humidifying the inlet air stream. The boiler capacity is 57 kg/h steam at a pressure of 5.5 bar.

The weather data analyses showed that cooling of agricultural structures in Riyadh and Jeddah is very essential. The mean monthly temperature during summer in Riyadh area varies between 31.5^oC and 36^oC, and the relative humidity is between 14.4% and 20%. These conditions encourage the use of evaporative cooling.

In Jeddah, the mean monthly temperatures during summer vary between 30^oC and 33.5^oC, and the relative humidity is between 57% and 82%. Cooling of agricultural structures in Abha is not necessary, except greenhouses that act as solar collectors. The mean monthly temperatures in Abha during summer vary between 22^oC and 23.5^oC, and the relative humidity was between 35% and 70%.
Averages of monthly solar radiation levels during summer vary between 570 and 619 W/m², for Riyadh, between 503 and 580 W/m², for Jeddah, and between 477 and 591 W/m², for Abha. Experimental results showed that averages of cooling efficiency were 82.4%, 72.2% and 75% under arid, humid and moderate conditions, respectively.
The highest air temperature drop through the pad was observed under arid dry conditions with a range of 12-32.5^oC. Whereas air temperature drop was lowest under humid hot conditions with a range of 2.8-8.6^oC. The drop under moderate conditions ranged from 6 to 15.3^oC. The maximum cooling of 20612W was obtained for the arid climatic conditions compared to 11883W and 5992W for moderate and humid climatic conditions, respectively. Cooling water consumption rate increased by increasing both temperature of the inlet air and air speed through the pads. The consumption rates were 11.8 and 13.8 l/hr at inlet air temperatures of 40 and 45^oC, respectively, when air speed was 0.5 m/s. The rate increased from 8.8 l/hr at air speed of 0.25 m/s to 19.8 l/hr at air speed of 1 m/s when the air temperature at the inlet was 40^oC. The water consumption decreased as the relative humidity of the inlet air increased at the same temperature. The water consumption rate decreased from 13.8 l/hr to 5.8 l/hr by increasing relative humidity from 8% to 58%, respectively, at inlet air temperature of 35^oC.

Main Subjects

Agricultural Constructions Engineering

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