Mehmet Ali DAYIOĞLU, Hasan Hüseyin SİLLELİ

Performance analysis of a greenhouse fan-pad cooling system: Gradients of horizontal temperature and relative humidity

Fan-Pad soğutma sistemi çalışırken sera boyunca oluşan sıcaklık ve bağıl nem değişimleri ve soğutma sistemi performansparametrelerini saptamak için deneysel bir çalışma yapılmıştır. Çalışmada ölçümler yedi farklı noktaya yerleştirilensensörler ve taşınabilir ölçüm cihazları kullanılarak gerçekleştirilmiştir. Bu amaçla, beş dijital sıcaklık-nem sensörüve iki güneş ışınım sensörü kullanılmıştır. Sensörlerden ikisi sera dışına, bir güneş ışınım sensörü bitki örtüsü üstüne,dört sıcaklık-nem sensörü sera boyunca bitki örtüsü içine yerleştirilmiştir. Dört sensörün yerleşimi Pad ve Fan arasındatanımlanmış konumlara göre yapılmıştır. Elde edilen deney sonuçlarına göre, Pad tarafından fan tarafına sera boyuncahomojen olmayan sıcaklık değişimleri, ancak transpirasyon nedeniyle yaklaşık homojen kalan bağıl nem değişimlerigözlemlenmiştir. Soğutma sistemi kapalı olduğu zaman, havanın 32 °C ve % 25 olduğu koşullarda, sera içinde Padtarafından fan tarafına saatlik ortalama sıcaklık ve bağıl nem değerleri sırasıyla 30 33 °C ve % 30 % 47 arasındadeğişmiştir. Fan-Pad sistemi çalıştırılıp kararlı soğutma sağlandıktan sonra, sera boyunca saatlik ortalama sıcaklık vebağıl nem değerleri sırasıyla 2027 °C ve % 50 % 68, arasında değişmiştir. Islak Pad yüzeyini geçerek yaklaşık0.8 0.9 m s-1 hava hızla seraya giren hava sıcaklığı dış hava sıcaklığından 12 13 ºC daha düşük olmuştur. Pad tarafındanfan tarafına sera boyunca hava sıcaklığı yaklaşık 7 ºC yükselmiştir. Buharlaşmalı Fan-Pad sisteminin soğutma etkinliğinihesaplamak için psikrometrik hesaplama yöntemi kullanılmıştır. Hesaplama sonucuna göre, dış hava sıcaklığının 31.4 ºC olduğu koşullarda kararlı soğutma sağlandıktan sonra sera içindeki ortalama sıcaklığın 24.5 ºC olduğubelirlenmiştir. Fan-Pad sistemi için hesaplanan saatlik ortalama soğutma etkisi ve soğutma etkinliği değerleri sırasıyla6.96 ºC ve % 76.8 olarak saptanmıştır.

Sera fan-pad soğutma sisteminin performans analizi: Yatay sıcaklık ve bağıl nem değişimleri

An experimental study is conducted to determine the performance parameters of system, as well as gradients oftemperature and humidity along greenhouse when opening Fan-Pad cooling system. Measurements in the study werecarried out by using seven sensors for different locations, as well as portable instruments. For this purpose, the fvedigital temperature and humidity sensors and two pyranometers were used during experiments. Among them, twowere located outside greenhouse for external measurements. The rest one pyranometer above the crop canopy, fourtemperature and humidity sensors were mounted within the crop canopy along the greenhouse. Four sensors were placedaccording to positions defned between pad and fan. According to the experiment results, the non-uniform temperaturechanges, but approximately uniform humidity changes due to the crop transpiration were observed along greenhousefrom pad panels to exhaust fans. When the cooling system closed, hourly mean temperature and relative humidity fromPad to Fan inside greenhouse changed between 30 33 °C and 30 47%, respectively, at outside climate conditions of32 °C and 25%. After providing stabile cooling by opening Fan-Pad system, hourly mean temperature and relativehumidity along greenhouse from pad to fan ranged between 2027 °C, and 5068%, respectively. The air temperatureentering to greenhouse with air velocity of 0.8 0.9 ms -1 through pad was approximately 12 13 ºC lower than the outsideair temperature. The air temperature from Pad to Fan increased approximately by 7 ºC. The method of psychrometriccalculations was employed to determine the cooling effciency of Fan-Pad system. According to the calculation result,the average of air temperatures inside greenhouse was 24.5 ºC after achieving stable cooling for outside air temperatureof 31.4 ºC. The hourly mean cooling effect and cooling effciency calculated for Fan-Pad system were determined to be6.96 ºC and 76.8%, respectively.

PDF

___

Al-Helal I, Al-Abbadi, N M & Al-Ibrahim A (2006). A study of evaporative cooling pad performance for a photovoltaic powered greenhouse. Acta Horticulture 710 :153-164
ASABE (2008). Heating, ventilating and cooling greenhouses. ASABE standards. ANSI /ASAE EP406.4 JAN2003 (R2008). St. Joseph, American Society of Agricultural and Biological Engineers
ASHRAE (2005). Psychrometrics, Ch 6: 6.1-6.17, In: American Society for Heating, Refrigeration, and Air Conditioning Engineers Fundamentals. SI ed. Atlanta
Bailey B (2006). Natural and Mechanical Greenhouse Climate Control. Acta Horticulture 710 : 43-54
Bartzanas Th & Kittas C (2005). Heat and Mass Transfer in a Large Evaporative Cooled Greenhouse Equipped with a Progressive Shading. Acta Horticulture 691 : 625-631
Franco A, Valera D L, Madueno A, Pena A (2010). Infuence of water and air fow on the performance of cellulose evaporative cooling pads used in Mediterranean greenhouses. Transactions of the ASABE 53 (2): 565-576
Franco A, Valera D L, Pena A (2014). Energy Effciency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads. Energies 7 : 1427-1447
Fuchs M, Dayan E & Presnov E (2006). Evaporative cooling of a ventilated greenhouse rose crop. Agriculture and Forest Meteorology 138 : 203215
Jain, D & Tiwari G N (2002). Modeling and optimal design of evaporative cooling system in controlled environment greenhouse. Energy Conversion and Management 43 (1): 22352250
Kittas C, Bartzanas T & Jaffarin A (2001). Greenhouse evaporative cooling: measurement and data analysis. Transactions of the ASAE 44 (3): 683689
Kittas C, Bartzanas T, & Jaffarin A (2003). Temperature Gradients in a Partially Shaded Large Greenhouse equipped with Evaporative Cooling Pads. Biosystems Engineering 85 (1): 8794
Kumar K S, Tiwari K N & Madan K Jha (2009). Design and technology for greenhouse cooling in tropical and subtropical regions: A review. Energy and Buildings 41 : 12691275
Li S & Willits D H (2008). An experimental evaluation of thermal stratifcation in a fan-ventilated greenhouse. Transactions of the ASABE 51 (4): 1443-1448
Lopez A, Valera D L, Molina-Aiz F D & Peña A (2012). Sonic anemometry to evaluate airfow characteristics and temperature distribution in empty Mediterranean greenhouses equipped with pad-fan and fog systems. Biosystems Engineering 113 (4): 334-350
Malli A, Seyf H R, Layeghi M, Sharifan S & Behravesh H (2011). Investigating the performance of cellulosic evaporative cooling pads. Energy Conversion and Management 52 (7): 2598-2603
Sabeh N C, Giacomelli G A & Kubota C (2006). Water Use for Pad and Fan Evaporative Cooling of a Greenhouse in a Semi-Arid Climate. Acta Horticulture 719 : 409-416
Sethi V P & Sharma S K (2007). Survey of cooling technologies for worldwide agricultural greenhouse applications. Solar Energy 81 (12): 1447-1459
Tashoo K, Thepa S, Pairintra R, Namprakai P (2014). Reducing the Air Temperature Inside the Simple Structure Greenhouse Using Roof Angle Variation. Tarım Bilimleri Dergisi-Journal of Agricultural Sciences 20 (2): 136-151
Teitel M, Atias M & Barak M (2010). Gradients of temperature, humidity and CO 2 along a fan-ventilated greenhouse. Biosystems Engineering106 (2): 166174
Zabeltitz C (2011). Integrated Greenhouse Systems for Mild Climates Climate Conditions, Design, Construction, Maintenance, Climate Control. Springer, Hannover
Willits D H (2003). Cooling fan-ventilated greenhouses: a modelling study. Biosystems Engineering84(3): 315-329