Performance Analysis of a Greenhouse Fan-Pad Cooling System: Gradients of Horizontal Temperature and Relative Humidity

Abstract

An experimental study was conducted to determine the performance parameters of system, as well as gradients of temperature and humidity along greenhouse when opening fan-ped cooling system. Measurements related with greenhouse environment were carried out by using seven sensors for different locations, as well as portable instruments. For this purpose, the five digital temperature and humidity sensors and two pyranometers were used during experiments. Among them, two were located outside greenhouse for external measurements. The rest one pyranometer above the crop canopy, four temperature and humidity sensors were mounted within the crop canopy along the greenhouse. Four sensors were placed according to positions defined between pad and fan. According to the experiment results, the non-uniform temperature changes, but approximately uniform humidity changes due to the crop transpiration were observed along greenhouse from pad panels to exhaust fans.

When the cooling system closed, hourly mean temperature and relative humidity from pad to fan inside greenhouse changed between 30–33°C and 30–47%, respectively, at outside climate conditions of 32°C and 25%. After providing stabile cooling by opening fan-pad system, hourly mean temperature and relative humidity along greenhouse from pad to fan ranged between 20 – 27°C, and 50 – 68%, respectively. The air temperature entering to greenhouse with air velocity of 0.8–0.9 ms^-1 through pad was approximately 12–13ºC lower than the outside air temperature. The air temperature from pad to fan increased approximately by 7 ºC.

The method of psychrometric calculations was employed to determine the cooling efficiency 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 temperature of 31.4 ºC. The hourly mean cooling effect and cooling efficiency calculated for fan-pad system were determined to be 6.96ºC and 76.8%, respectively.

Keywords

• Greenhouse; Fan-pad cooling system; Temperature and relative humidity; Psychrometric calculation; Cooling efficiency

Sera Fan-Pad Soğutma Sisteminin Performans Analizi: Yatay Sıcaklık ve Bağıl Nem Değişimleri

Öz

Fan-Pad soğutma sistemi çalışırken sera boyunca oluşan sıcaklık ve bağıl nem değişimleri ve soğutma sistemi performans parametrelerini saptamak için deneysel bir çalışma yapılmıştır. Çalışmada ölçümler yedi farklı noktaya yerleştirilen sensörler ve taşınabilir ölçüm cihazları kullanılarak gerçekleştirilmiştir. Bu amaçla, beş dijital sıcaklık-nem sensörü ve 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 arasında tanımlanmış konumlara göre yapılmıştır. Elde edilen deney sonuçlarına göre, Pad tarafından fan tarafına sera boyunca homojen olmayan sıcaklık değişimleri, ancak transpirasyon nedeniyle yaklaşık homojen kalan bağıl nem değişimleri gözlemlenmiştir. Soğutma sistemi kapalı olduğu zaman, havanın 32 °C ve % 25 olduğu koşullarda, sera içinde Pad tarafından fan tarafına saatlik ortalama sıcaklık ve bağıl nem değerleri sırasıyla 30–33 °C ve % 30–% 47 arasında değişmiştir. Fan-Pad sistemi çalıştırılıp kararlı soğutma sağlandıktan sonra, sera boyunca saatlik ortalama sıcaklık ve bağıl nem değerleri sırasıyla 20 – 27 °C ve % 50 –% 68, arasında değişmiştir. Islak Pad yüzeyini geçerek yaklaşık 0.8–0.9 m s-1 hava hızla seraya giren hava sıcaklığı dış hava sıcaklığından 12–13 ºC daha düşük olmuştur. Pad tarafından fan tarafına sera boyunca hava sıcaklığı yaklaşık 7 ºC yükselmiştir. Buharlaşmalı Fan-Pad sisteminin soğutma etkinliğini hesaplamak 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 olduğu belirlenmiştir. Fan-Pad sistemi için hesaplanan saatlik ortalama soğutma etkisi ve soğutma etkinliği değerleri sırasıyla 6.96 ºC ve % 76.8 olarak saptanmıştır

Anahtar Kelimeler

• Soğutma etkinliği, Fan-Pad soğutma sistemi, Sera, Psikrometrik hesaplama, Sıcaklık ve bağıl nem

References

1. 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
2. ASABE (2008). Heating, ventilating and cooling greenhouses. ASABE standards. ANSI /ASAE EP406.4 JAN2003 (R2008). St. Joseph, American Society of Agricultural and Biological Engineers
3. ASHRAE (2005). Psychrometrics, Ch 6: 6.1-6.17, In: American Society for Heating, Refrigeration, and Air Conditioning Engineers Fundamentals. SI ed. Atlanta
4. Bailey B (2006). Natural and Mechanical Greenhouse Climate Control. Acta Horticulture 710: 43-54
5. 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
6. Franco A, Valera D L, Madueno A, Pena A (2010). Influence of water and air flow on the performance of cellulose evaporative cooling pads used in Mediterranean greenhouses. Transactions of the ASABE 53(2): 565-576
7. Franco A, Valera D L, Pena A (2014). Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads. Energies 7: 1427-1447
8. Fuchs M, Dayan E & Presnov E (2006). Evaporative cooling of a ventilated greenhouse rose crop. Agriculture and Forest Meteorology 138: 203–215

9. Jain, D & Tiwari G N (2002). Modeling and optimal design of evaporative cooling system in controlled environment greenhouse. Energy Conversion and Management 43(1): 2235–2250
10. Kittas C, Bartzanas T & Jaffarin A (2001). Greenhouse evaporative cooling: measurement and data analysis. Transactions of the ASAE 44(3): 683–689
11. Kittas C, Bartzanas T, & Jaffarin A (2003). Temperature Gradients in a Partially Shaded Large Greenhouse equipped with Evaporative Cooling Pads. Biosystems Engineering 85(1): 87–94
12. 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: 1269–1275
13. Li S & Willits D H (2008). An experimental evaluation of thermal stratification in a fan-ventilated greenhouse. Transactions of the ASABE 51(4): 1443-1448
14. Lopez A, Valera D L, Molina-Aiz F D & Peña A (2012). Sonic anemometry to evaluate airflow characteristics and temperature distribution in empty Mediterranean greenhouses equipped with pad-fan and fog systems. Biosystems Engineering 113(4): 334-350
15. Malli A, Seyf H R, Layeghi M, Sharifian S & Behravesh H (2011). Investigating the performance of cellulosic evaporative cooling pads. Energy Conversion and Management 52(7): 2598-2603
16. 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
17. Sethi V P & Sharma S K (2007). Survey of cooling technologies for worldwide agricultural greenhouse applications. Solar Energy 81(12): 1447-1459
18. 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
19. Teitel M, Atias M & Barak M (2010). Gradients of temperature, humidity and CO2 along a fan-ventilated greenhouse. Biosystems Engineering 106(2): 166–174
20. Zabeltitz C (2011). Integrated Greenhouse Systems for Mild Climates Climate Conditions, Design, Construction, Maintenance, Climate Control. Springer, Hannover
21. Willits D H (2003). Cooling fan-ventilated greenhouses: a modelling study. Biosystems Engineering 84(3): 315-329