Seasonal Performance Evaluation of an Earth-to-Air Heat Exchanger for Greenhouse Cooling under Humid Tropical Conditions

Öz

This study evaluates the seasonal performance of an earth-to-air heat exchanger (EAHE) system for greenhouse cooling under humid tropical conditions in Ibadan, Nigeria. Experiments were conducted at two burial depths (1 m and 2 m) during the dry and rainy seasons. The EAHE comprised a 14.24 m polyvinyl chloride (PVC) pipe (inner diameter 101.6 mm) with a mass flow rate of 0.012 kg/s driven by a 0.25 m³/s inline centrifugal blower rated at 0.006 kW. Inlet and outlet temperatures were recorded every five minutes between 9:00 am and 5:00 pm using K-type thermocouples (range: −50°C to +180°C; accuracy: ±1.5°C). Data were analysed to determine the coefficient of performance and degree of cooling achieved. Results showed consistent cooling throughout operation, with maximum temperature reductions of 3.1°C (dry season, 2 m) and 1.9°C (rainy season, 1 m). Paired sample t-tests confirmed statistically significant differences between inlet and outlet air temperatures at both depths in both seasons (p < 0.05). COP values were higher in the dry season (4.5 at 1 m; 5.3 at 2 m) than in the rainy season (2.4 at 1 m; 3.9 at 2 m), representing a 46–53% seasonal reduction. The 2 m installation consistently outperformed the 1 m installation (COP gain: +18% dry season; +62% rainy season); however, the additional excavation required for 2 m depth entails a higher initial cost, suggesting a trade-off between installation expenditure and long-term cooling efficiency that practitioners must weigh against local economic constraints. EAHE systems are effective for passive greenhouse cooling in humid tropical climates, with deeper installation offering superior seasonal resilience.

Anahtar Kelimeler

• Earth-Air heat Exchanger
• greenhouse cooling
• controlled environment agriculture

Nemli Tropikal Koşullar Altında Sera Soğutması İçin Bir Toprak-Hava Isı Eşanjörünün Mevsimsel Performans Değerlendirmesi

Öz

Bu çalışma, Nijerya, Ibadan'daki nemli tropikal koşullar altında bir seranın soğutulması için toprak-hava ısı değiştirici (EAHE) sisteminin mevsimsel performansını değerlendirmektedir. Deneyler, kuru ve yağışlı mevsimlerde iki gömme derinliğinde (1 m ve 2 m) gerçekleştirilmiştir. EAHE, 0,012 kg/s kütle akış hızına sahip, 14,24 m uzunluğunda polivinil klorür (PVC) borudan (iç çap 101,6 mm) oluşmakta olup, hava akışı, 0,006 kW gücünde 0,25 m³/s'lik bir hat içi santrifüj fan tarafından sağlanmıştır. Giriş ve çıkış sıcaklıkları, sabah 9:00 ile akşam 5:00 arasında her beş dakikada bir, K tipi termokupllar (aralık: -50°C ila +180°C; doğruluk: ±1,5°C) kullanılarak kaydedilmiştir. Veriler, performans katsayısını (COP) ve elde edilen soğutma derecesini belirlemek için analiz edilmiştir. Sonuçlar, tüm çalışma boyunca tutarlı soğutma olduğunu ve maksimum sıcaklık düşüşlerinin 3,1°C (kuru mevsim, 2 m) ve 1,9°C (yağışlı mevsim, 1 m) olduğunu göstermiştir. Eşleştirilmiş örneklem t-testleri, her iki derinlikte ve her iki mevsimde giriş ve çıkış hava sıcaklıkları arasında istatistiksel olarak anlamlı farklar olduğunu doğrulamıştır (p < 0,05). COP değerleri, kuru mevsimde (1 m'de 4,5; 2 m'de 5,3) yağışlı mevsime göre (1 m'de 2,4; 2 m'de 3,9) daha yüksek bulunmuş olup, bu %46-53 oranında mevsimsel bir azalmayı temsil etmektedir. 2 m'lik tesisat, 1 m'lik tesisata kıyasla tutarlı bir şekilde daha iyi performans göstermiştir (COP kazancı: kuru mevsimde +%18; yağışlı mevsimde +%62); bununla birlikte, 2 m derinlik için gerekli olan ek kazı, daha yüksek bir ilk yatırım maliyeti gerektirmekte olup, bu durum, uygulayıcıların yerel ekonomik kısıtlamaları göz önünde bulundurarak tesisat harcamaları ile uzun vadeli soğutma verimliliği arasında bir denge kurmaları gerektiğini işaret etmektedir. EAHE sistemleri, nemli tropikal iklimlerde pasif sera soğutması için etkilidir ve daha derin tesisat üstün mevsimsel direnç sunmaktadır.

Anahtar Kelimeler

• Toprak-Hava Isı Değiştiricisi
• Sera soğutması
• Kontrollü çevre tarımı

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