**1. Introduction**

Worldwide, greenhouses are used to provide favorable climate conditions to crops, where outdoor weather conditions are not suitable for crop production [1]. In severe climatic conditions, to achieve the desired temperature condition inside the greenhouse for optimal crop growth, different heating and cooling systems are used. Although good crop yields can be obtained in well-controlled micro-environments within the greenhouse, such systems tend to increase operational costs [2]. The heating cost in South Korean greenhouses is 30–40% of total production costs, which makes the greenhouse sector one of the most energy-intensive [3]. Ahmed et al. [4] reported that the heating costs in Canadian greenhouses are 15–20% of total production costs [1]. Globally, various technologies, especially renewable energy technologies, have been utilized to fulfill the energy demands of buildings, including those in the agricultural sector [5]. In addition to using different energy sources, energy saving techniques can be helpful in reducing energy costs [6]. Hence, the reduction in the energy demand of greenhouses is very important. Having an energy-efficient greenhouse can contribute to reducing its energy demand. Therefore, the design parameters of the greenhouse significantly affect its the energy consumption [4].

Several studies [7–14] performed by different researchers considered single-span greenhouse design analyses, including varying the greenhouse's shape and orientation and evaluating the saving potentials of each. In our previous studies, Rasheed et al. [15] and Ahmed et al. [1] evaluated the design parameters of a single-span greenhouse with fully closed conditions including the shape, orientation, span, and width of the single-span greenhouse. The studies found that the single-span gothic shaped, east–west orientated greenhouse covered with double glazing of Polymethylmethacrylate (PMMA) is the most energy efficient greenhouse design parameter. Two studies conducted by Lee at al., [16] and Ha et al. [17] analyzed the heating and cooling loads of the Venlo type and wide-span greenhouse roof geometry under different weather conditions in different parts of South Korea. The outcomes of the studies show that the wide-span greenhouse required less energy when compared with the venlo type multi-span greenhouse. Lee et al. [18] designed a Building Energy Simulation (BES) model of the multi-span greenhouse to predict the annual and maximum heating load at six different locations of the greenhouse in South Korea and evaluated the performance of the heating system. On behave of the maximum heating load at each location feasibility of the heating system was evaluated.

The most feasible and practical approach to selecting energy-efficient greenhouses according to local weather conditions is through simulations. There are many types of Building Energy Simulation (BES) software such as Energy Plus, RETScreen, and the Transient System Simulation Program (TRNSYS)-18. Baglivo et al. [19] suggested that the TRNSYS program is more convenient and easier to use for this kind of simulation including energy modeling of greenhouse control strategies. For this specific study, TRNSYS-18 software, which is widely used for the estimation of building energy load and energy system performance, was selected. Moreover, in agricultural greenhouses, the software demonstrates a very high level of flexibility in terms of improving the structure of varying case studies as well as carrying out their energy analysis [20].

The specific objectives of this study are as follows:


The proposed BES model provides a tool for efficiently analyzing multi-span greenhouse design parameters while taking into account local weather conditions and crop needs. The proposed model allows the dynamic simulation of greenhouse systems and also enables the application of different control strategies.
