Ideal performance of a self-cooling greenhouse. (25th February 2019)

• Record Type: Journal Article
• Authors: Davies, Philip A.; Zaragoza, Guillermo
• Is Part Of: Applied thermal engineering. Volume 149(2019)
• Page Start: 502
• Page End: 511
• Publication Date: 2019-02-25
• Subjects: Solar refrigeration -- Greenhouse cooling -- Solar thermal -- Solar PV -- Thermodynamic limit -- Endoreversible; COP Coefficient of performance -- PV Photovoltaic; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2018.12.056
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: The self-cooling greenhouse intercepts a fraction of incident solar energy to maintain its internal climate below ambient. This fraction is constrained by basic thermodynamic considerations analysed here. Both solar thermal and solar-PV cases are covered. In a completely ideal system, the fraction intercepted could be as low as 0.056. Implications for development of real self-cooling greenhouses are outlined. Abstract: The self-cooling greenhouse is a concept to enable crop cultivation in adversely hot climates. It sacrifices a fraction γ of the incident solar energy to drive a refrigeration system, thus lowering the internal temperature below ambient. Heat is actively rejected to a stream of coolant such as air or water. To maintain availability of sunlight for photosynthesis, γ should be as small as possible. Nonetheless, the laws of thermodynamics dictate a minimum value of γ. Using the approach of endoreversible thermodynamics and the theory of selective blackbody absorbers, we determine ideal minimum values achievable for cases of both thermal and photovoltaic solar collection with and without solar concentration. To achieve an internal temperature 10 °C below that of the incoming coolant, a minimum γ = 0.056 is needed using multicolour absorption at maximum concentration C = 46300 – representing an absolute minimum for either type of solar collection. Without concentration ( C = 1) a selective thermal collector permits minimum γ = 0.089 and a single-junction PV solar collector permits minimum γ = 0.15. We discuss briefly implications for development of a real self-cooling greenhouse to approximate the performance of these ideal cases.