Saving Energy with a Hybrid Heating System using an Air-to-air Heat Pump and Oil Heater in a Rose Greenhouse

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  • 空気熱源式ヒートポンプと燃焼式温風暖房機とのハイブリッド運転によるバラ栽培の暖房費削減効果
  • クウキ ネツゲンシキ ヒートポンプ ト ネンショウシキ オンプウ ダンボウキ ト ノ ハイブリッド ウンテン ニ ヨル バラ サイバイ ノ ダンボウヒ サクゲン コウカ

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Abstract

We compared the total cost of greenhouse heating between a conventional oil-fired air heater and a hybrid system comprising an electric heat pump (rated at 49.2 W m-2) and an oil-fired air heater (rated at 199.4 W m-2) in identical rose greenhouses in Iwata city, Shizuoka, Japan. The greenhouses had a heat load coefficient of 3.7 W m-2 K-1. The average nighttime temperature in the hybrid-system greenhouse during August and September was 2.2°C lower than that in the oil-heater greenhouse owing to nighttime cooling by the heat pump. To maintain a minimum temperature of 18°C required an annual consumption of heavy oil for heating of 12.61 L m-2 by the hybrid system and 33.49 L m-2 by the oil heater. The annual consumption of electricity was 14.91 MJ m-2 by the hybrid system and 1.13 MJ m-2 by the oil heater. The total energy input for heating was 43.77 MJ m-2 for the hybrid system and 81.62 MJ m-2 for the oil heater. Using 3.79 as the coefficient of performance of the heat pump gave an estimated energy use of 78.19 MJ m-2 for heating by the hybrid system, lower than the calculated value of 81.62 MJ m-2; that is, the rated COP was exceeded. At an oil price of 65.8 yen L-1, the annual running cost was 1645 yen m-2 in the hybrid-system greenhouse and 2162 yen m-2 in the oil-heater greenhouse. The annual cut rose production was 712.7 g per plant in the hybrid-system greenhouse and 643.2 g per plant in the oil-heater greenhouse. In particular, production in the hybrid system was 53% higher in August and September, when nighttime cooling was operated. Overall, the hybrid system resulted in savings of 46% of input energy and about 24% of energy costs.

Journal

  • Shokubutsu Kankyo Kogaku

    Shokubutsu Kankyo Kogaku 25 (1), 19-28, 2013

    Japanese Society of Agricultural, Biological and Environmental Engineers and Scientists

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