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Advances in Energy Research
  Volume 4, Number 1, March 2016 , pages 87-106

Hybrid thermal seasonal storage and solar assisted geothermal heat pump systems for greenhouses
Abtin Ataei, Hoofar Hemmatabady and Seyed Yahya Nobakht

    In this research, optimum design of the combined solar collector, geothermal heat pump and thermal seasonal storage system for heating and cooling a sample greenhouse is studied. In order to optimize the system from technical point of view some new control strategies and functions resulting from important TRNSYS output diagrams are presented. Temperatures of ground, rock bed storage, outlet ground heat exchanger fluid and entering fluid to the evaporator specify our strategies. Optimal heat storage is done with maximum efficiency and minimum loss. Mean seasonal heating and cooling COPs of 4.92 and 7.14 are achieved in series mode as there is no need to start the heat pump sometimes. Furthermore, optimal parallel operation of the storage and the heat pump is studied by applying the same control strategies. Although the aforementioned system has higher mean seasonal heating and cooling COPs (4.96 and 7.18 respectively) and lower initial cost, it requires higher amounts of auxiliary energy either. Soil temperature around ground heat exchanger will also increase up to 1.5oC after 2 years of operation as a result of seasonal storage. At the end, the optimum combined system is chosen by trade-off between technical and economic issues.
Key Words
    heating COP; cooling COP; thermal storage; TRNSYS; heat pump; control strategies; parallel; series
Abtin Ataei, Hoofar Hemmatabady and Seyed Yahya Nobakht: Department of Energy Engineering, Graduate School of the Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran

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