Anis Rabiu

The implementation of renewable energy systems (RESs) in the agricultural sector has significant potential to mitigate the negative effects of fossil fuel-based products on the global climate, reduce operational costs, and enhance crop production. However, the intermittent nature of RESs poses a major challenge to realizing these benefits. To address this, thermal energy storage (TES) and hybrid heat pump (HHP) systems are integrated with RESs to balance the mismatch between thermal energy production and demand. In pursuit of clean energy solutions in the agricultural sector, a 3942 m² greenhouse in Yeoju-si, South Korea, is equipped with 231 solar thermal (ST) collectors, 117 photovoltaic thermal (PVT) collectors, four HHPs, two ground-source heat pumps (GSHPs), a 28,500 m³ borehole TES (BTES) unit, a 1040 m³ tank TES (TTES) unit, and three short-term TES units with capacities of 150 m³, 30 m³, and 30 m³. This study evaluates the long-term performance of the integrated hybrid renewable energy and thermal energy storage systems (HRETESSs) in meeting the greenhouse’s heating and cooling demands. Results indicate that the annual system performance efficiencies range from 25.3% to 68.5% for ST collectors and 31.9% to 72.2% for PVT collectors. The coefficient of performance (COP) during the heating season is 3.3 for GSHPs, 2.5 for HHPs using BTES as a source, and 3.6 for HHPs using TTES as a source. During the cooling season, the COP ranges from 5.3 to 5.7 for GSHPs and 1.84 to 2.83 for ASHPs. Notably, the HRETESS supplied 3.4% of its total heating energy directly from solar energy, 89.3% indirectly via heat pump utilization, and 7.3% is provided by auxiliary heating. This study provides valuable insights into the integration of HRETESSs to maximize greenhouse energy efficiency and supports the development of sustainable agricultural energy solutions, contributing to reduced greenhouse gas emissions and operational costs.

The energy demand in greenhouses is enormous, and high-performance covering materials and thermal screens with varying radiometric properties are used to optimise the energy demand in building energy simulations (BES). Transient System Simulation (TRNSYS) software is a common BES tool used to model the thermal performance of buildings. The calculation of the greenhouse internal temperature and heating demand in TRNSYS involves the solution of the transient heat transfer processes. This study modelled the temperature and heating demand of two multi-span glass greenhouses with concave (farm A) and convex (farm B) shapes. This study aims to investigate the influence of the different BES longwave radiation modes on greenhouse internal temperature in different zones and the heating demand of a conditioned zone. The standard hourly simulation results were compared with the experimental data. The results showed that the standard and detailed modes accurately predicted greenhouse internal temperature (the Nash–Sutcliffe efficiency coefficient (NSE) > 0.7 for all three zones separated by thermal screens) and heating demand (NSE > 0.8) for farms A and B. The monthly heating demand predicted by the simple and standard radiation modes for farm A matched the experimental measurements with deviations within 27.7% and 7.6%, respectively. The monthly heating demand predicted by the simple, standard, and detailed radiation modes for farm B were similar to the experimental measurements with deviations within 10.5%, 6.7%, and 2.9%, respectively. In the order of decreasing accuracy, the results showed that the preferred radiation modes for the heating demand were standard and simple for farm A, and detailed, standard, and simple for farm B.

Strawberry cultivation depends on environmental factors, making its cultivation in the greenhouse a challenge in the winter. This study investigated the most appropriate greenhouse cladding material and thermal screen configuration for strawberry production in the winter by considering greenhouse air temperature, relative humidity (RH, vapor pressure deficit (VPD, and solar radiation (SR). Two gothic greenhouses with different cladding materials and thermal screen configurations, namely, the single-layer greenhouse and double-layer greenhouse, were used for strawberry cultivation. The greenhouse microclimate was controlled by natural ventilation aided with circulating fans and boilers. Strawberries were planted on 5 greenhouse benches, 660 stands per greenhouse. Daily environmental parameters were recorded and processed into daytime and nighttime. The impacts of cladding material-thermal screen configurations on temperature, RH, VPD, and SR, and the subsequent effect on strawberry yield in both greenhouse systems, were evaluated. Comparing the environmental parameters recorded in the single-layer and double-layer greenhouse showed that VPD and SR were significantly different in the daytime, whereas RH and VPD were significantly different in the nighttime. The post hoc test further showed that RH, VPD, and SR in both greenhouses were significantly different. The significant difference in RH and VPD can be attributed to the inner layer of polyethene in the double-layer greenhouse, which sealed up the pores of the thermal screen, resulting in humidity buildup, causing a lower VPD than in the single-layer greenhouse. The single-layer greenhouse yield was 14% greater than the double-layer greenhouse yield and can be attributed to the higher daytime VPD and lower RH achieved in the single-layer greenhouse at night. The study established that though the single-layer greenhouse system was cost-effective regarding construction, the operating cost of the single-layer greenhouse was higher than that of the double-layer greenhouse.

Recently, heat and mass distributions within a greenhouse were assumed to be homogeneous. Heat is gained or lost in absolute terms, and crop contribution in a greenhouse or its effect is not considered. In this study, statistical analyses were conducted to establish the significance of heat and mass variation at sensor nodes in two single-span and multi-span greenhouses. Three greenhouses were used in this study, 168 m² floor area a single-layered (SLG), double-layered (DLG) single-span gothic roof type greenhouses, and 7572.6 m² floor area multi-span greenhouse (MSG). The microclimatic parameters investigated were temperature (T), relative humidity (RH), solar radiation (SR), carbon dioxide (CO₂), and vapor pressure deficit (VPD). To check their horizontal distribution, all microclimate data collected from each sensor node in each greenhouse were subjected to descriptive statistics and Tukey honestly significant difference (HSD) test. The lowest minimum temperatures of 2.93 °C, 3.33 °C and 10.50 °C were recorded at sensor points in SLG, DLG, and MSG, respectively, whereas the highest maximum temperatures of 29.17 °C, 29.07 °C and 27.20 °C were recorded at sensor point, in SLG, DLG, and MSG, respectively. The difference between the center and the side into the single-span was approximately 0.88–1.0 °C and in the MSG was approximately 1.03 °C. Significant variation was observed in the horizontal distribution of T, RH, SR, and VPD within SLG, DLG, and MSG. Also significant was CO₂ in the MSG. Estimating the energy demand of greenhouses should be done based on the distribution rather than assuming microclimatic parameters homogeneity, especially for T, with VPD as a control parameter. Such estimation should also be done using a crop model that considers instant changes in air and crop temperature.

Strawberry cultivation is highly dependent on environmental parameters and energy during the winter. Two gothic greenhouses with different glazing material combinations, polyolefin–thermal screen (PoTS) and polyolefin–thermal screen–polyethylene (PoTSPe), were used for strawberry cultivation. The energy-saving capabilities of the two configurations and their impact on the microclimates of the greenhouses were investigated. The temperature, relative humidity, vapor pressure deficit, leaf temperature, carbon dioxide concentration and solar radiation over the experimental period in the PoTS greenhouse were 13.0 ± 2.3°C, 75.8 ± 6.5%, 0.4 ± 0.1 kPa, 13.6 ± 1.7 °C, and 168.8 ± 82.3W/m2, respectively, whereas those of the PoTSPe condition were 13.1 ± 2.3 °C, 80.0 ± 5.7%, 0.3 ± 0.1 kPa, 13.5 ± 1.6 °C, and 183.1 ± 90.5 W/m2. The mean fuel consumption by the PoTS and PoTSPe greenhouses were 5.5 and 3.5 L, respectively. The performance analysis shows that both greenhouses were able to maintain the environmental parameters and leaf temperature within the recommended ranges, although more energy was consumed in the PoTS. More yield was obtained in the PoTS greenhouse, however, not significantly different from PoTSPe yield.