Ideal performance of a self-cooling greenhouse

Philip A. Davies, Guillermo Zaragoza

Research output: Contribution to journalArticle

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.
Original languageEnglish
Pages (from-to)502-511
Number of pages10
JournalApplied Thermal Engineering
Volume149
Early online date13 Dec 2018
DOIs
Publication statusPublished - 25 Feb 2019

Keywords

  • Endoreversible
  • Greenhouse cooling
  • Solar PV
  • Solar refrigeration
  • Solar thermal
  • Thermodynamic limit

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