Abstract
To utilize the energy in the thermal effluent, many attempts have been made to use the thermal effluent for agricultural facilities such as greenhouses. As the first step, it is important to estimate the energy loads of the greenhouse for deciding a suitable scale for the heating and cooling. Then, it is available to estimate the energy efficiency of the thermal effluent heat pump system installed in the greenhouse. Therefore, the main objectives of this study were to design and validate an energy model of the experimental greenhouse growing Irwin mangoes and to estimate the annual and maximum energy loads using building energy simulation (BES). Field experiments were conducted in a multi-span plastic-covered greenhouse growing Irwin mangoes to measure the internal environments of the greenhouse and crop characteristics. The energy exchange model of the greenhouse considering crop, cladding, heat pump was developed using BES. The BES model was validated using the data measured at field experiments. The designed model was found to be able to provide satisfactory estimates of the changes of the internal air temperature of the greenhouse (R2 = 0.94 and d = 0.97). The hourly energy loads computed by using the validated model were used to analyse the periodic and maximum energy loads according to the growth stage of the cultivated crops. Finally, the energy costs were compared according to the type of energy source based on the calculated annual energy loads. The average energy cost when using the thermal effluent—heat pump system was found to be 68.21% lower than that when a kerosene boiler was used.
Highlights
A comparative analysis of the energy costs was conducted according to an energy source as an essential prerequisite for the utilization of the thermal energy of the thermal effluent
An energy exchange model of the experimental greenhouse was designed in four parts: a model of the greenhouse structure, a model for generating the operational signals of the thermal screens, heat pumps, and vent openings, an energy exchange model of the crops, and a model of the thermal effluent–heat pump
To design the energy exchange model, field experiments were conducted to measure the structural characteristics of the greenhouse and the crop characteristics and the working schedule of the thermal screens, heat pumps, and vent openings in the greenhouse
Summary
As South Korea has four distinct seasons, it is difficult to produce crops via field culture throughout the year. Greenhouses can control the growing environment of crops and produce high-quality crops all through the year. The greenhouse cultivation in South Korea increased from 23,669 ha in 1990 to 51,226 ha in 2018. To maintain optimum growing environments for the crops, approximately 30% of all greenhouses utilized cooling and heating systems. Approximately 85% of all greenhouse farmers used fossil fuel as an energy source [1]. The heating cost of the greenhouse have been a large percentage of the total production cost because of four distinctive seasons in South Korea. Farmers have been burdened with production costs such as energy costs
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