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19 pages, 6997 KiB

Open AccessArticle

Analysis of Wind Pressure Coefficients for Single-Span Arched Plastic Greenhouses Located in a Valley Region Using CFD

by Zongmin Liang, Guifeng He, Yanfeng Li, Zixuan Gao, Xiaoying Ren, Qinan Wu, Shumei Zhao and Jing Xu

Agronomy 2023, 13(2), 553; https://doi.org/10.3390/agronomy13020553 - 15 Feb 2023

Cited by 1 | Viewed by 1427

Abstract

The wind pressure coefficient is essential for calculating the wind loads on greenhouses. The wind pressure on single-span arched greenhouses built in valleys differs from those in plain regions. To promote our understanding of wind characteristics and ensure the structural safety of greenhouses [...] Read more.

The wind pressure coefficient is essential for calculating the wind loads on greenhouses. The wind pressure on single-span arched greenhouses built in valleys differs from those in plain regions. To promote our understanding of wind characteristics and ensure the structural safety of greenhouses in valley areas, an analysis of the distribution law of wind pressure on greenhouses is required. Firstly, we carried out a survey on greenhouse distribution and undulate terrain distribution near greenhouses in Tibet and measured the air density in Lhasa, Tibet. Then, employing the validated realizable k-ε turbulence model and the verification of grid independence, the wind pressure on greenhouses with different greenhouse azimuths was investigated. According to the survey results, values, such as the distance between the greenhouse and the mountain in addition to the greenhouse azimuth, were also obtained for calculating the wind pressure on greenhouses placed in valleys. A calculation model considering the relationship between the mountain distance and the wind pressure coefficient is proposed, whose results fit well with the results from computational fluid dynamics. The relative errors between the two different results are within 15%. Research shows that there is a canyon wind effect in the valley area, and its effect on wind pressure should be considered in greenhouse design. This research is valuable for the design of plastic greenhouses built in Tibet or other valley regions. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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25 pages, 9133 KiB

Open AccessArticle

CFD Simulation and Uniformity Optimization of the Airflow Field in Chinese Solar Greenhouses Using the Multifunctional Fan–Coil Unit System

by Jiarui Lu, He Li, Xueying He, Chengji Zong, Weitang Song and Shumei Zhao

Agronomy 2023, 13(1), 197; https://doi.org/10.3390/agronomy13010197 - 8 Jan 2023

Cited by 2 | Viewed by 2576

Abstract

Supplying homogenous and suitable airflow schemes were explored in Chinese solar greenhouses, which had a positive impact on the crop yield and quality. This paper provided a multifunctional fan–coil unit system (FCU) to assist in circulating air. This system could collect the surplus [...] Read more.

Supplying homogenous and suitable airflow schemes were explored in Chinese solar greenhouses, which had a positive impact on the crop yield and quality. This paper provided a multifunctional fan–coil unit system (FCU) to assist in circulating air. This system could collect the surplus heat of daytime air and release it to heat the greenhouse at nighttime. However, the main problem to be faced was the nonuniform airflow distributions. Thus, this paper aimed to optimize and analyze the placement strategy of the FCU system for a Chinese solar greenhouse using the numerical methodology. The computational fluid dynamics model was constructed to evaluate the effect of the FCU system on the airflow field and to uphold its validation. The complex structure of the FCU system was simplified to a fan model by fitting the pressure jump and the air velocity to enhance the practicality of the simulation model. Finally, the coefficient of variation was used to optimize four parameters: the tilt angle, swing angle, height above the ground, and shape of the outlet baffle. The effective disturbance velocity percentage was proposed as the evaluation index to improve the turbulence characteristics. The mean absolute error (MAE) between the measured and simulated values of the air velocity for the two planes was 0.06 m/s and 0.09 m/s, and the root mean square error (RMSE) was 0.08 m/s and 0.11 m/s. The simulated results showed that the coefficient of variation before optimization was 0.76, and the effective disturbance velocity percentages of the planes at 0.7 m and 1.0 m from the ground were 42.73% and 41.02%, respectively. After optimization, the coefficient of variation was reduced to 0.33, and the effective disturbance velocity percentages of the two planes increased to 58.68% and 43.73%, respectively. These results significantly improved the uniformity of the interior airflow field. This paper provides a reference for the design and installation of the FCU system. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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14 pages, 6547 KiB

Open AccessArticle

Closed-Loop Optimal Control of Greenhouse Cultivation Based on Two-Time-Scale Decomposition: A Simulation Study in Lhasa

by Dan Xu, Yanfeng Li, Anguo Dai, Shumei Zhao and Weitang Song

Agronomy 2023, 13(1), 102; https://doi.org/10.3390/agronomy13010102 - 28 Dec 2022

Cited by 3 | Viewed by 1623

Abstract

Due to the heavy computation load of closed-loop simulations, optimal control of greenhouse climate is usually simulated in an open-loop form to produce control strategies and profit indicators. Open-loop simulations assume the model, measurements, and predictions to be perfect, resulting in too-idealistic indicators. [...] Read more.

Due to the heavy computation load of closed-loop simulations, optimal control of greenhouse climate is usually simulated in an open-loop form to produce control strategies and profit indicators. Open-loop simulations assume the model, measurements, and predictions to be perfect, resulting in too-idealistic indicators. The method of two-time-scale decomposition reduces the computation load, thus facilitating the online implementation of optimal control algorithms. However, the computation time of nonlinear dynamic programming is seldom considered in closed-loop simulations. This paper develops a two-time-scale decomposed closed-loop optimal control algorithm that involves the computation time. The obtained simulation results are closer to reality since it considers the time delay in the implementation. With this algorithm, optimal control of Venlo greenhouse lettuce cultivation is investigated in Lhasa. Results show that compared with open-loop simulations, the corrections in yield and profit indicators can be up to 2.38 kg m⁻² and 11.01 CNY m⁻², respectively, through closed-loop simulations without considering the computation time. When involving the time delay caused by the computation time, further corrections in yield and profit indicators can be up to 0.1 kg m⁻² and 0.87 CNY m⁻², respectively. These conservative indicators help investors make wiser decisions before cultivation. Moreover, control inputs and greenhouse climate states are within their bounds most of the time during closed-loop simulations. This verifies that the developed algorithm can be implemented in real time. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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18 pages, 3349 KiB

Open AccessArticle

Autonomous Mobile Robot with Attached Multispectral Camera to Monitor the Development of Crops and Detect Nutrient and Water Deficiencies in Vertical Farms

by Dafni Despoina Avgoustaki, Ioannis Avgoustakis, Carlos Corchado Miralles, Jonas Sohn and George Xydis

Agronomy 2022, 12(11), 2691; https://doi.org/10.3390/agronomy12112691 - 29 Oct 2022

Cited by 9 | Viewed by 3663

Abstract

This study demonstrates the potential of using low-altitude multispectral imagery data to assess irrigation and fertilization techniques and the relative degree of plant water and nutrient stress. This study aims to create a methodology that can be widely used by vertical farms. Techniques [...] Read more.

This study demonstrates the potential of using low-altitude multispectral imagery data to assess irrigation and fertilization techniques and the relative degree of plant water and nutrient stress. This study aims to create a methodology that can be widely used by vertical farms. Techniques were used for early water and nitrogen stress detection using multispectral reflectance systems in an indoor environment with artificial lighting. The methodology focuses on irrigation and nutrition, that sets schedules, and automatically updates a decision-making system based on crop reflectance data and simplified reflectance indices. The experimental process took place on the premises of CphFarmHouse in Denmark. The results showed that crop reflectance increased due to water and nitrogen deficiencies. The detected reflectance increase was significant on the third day of the experiment when irrigation and fertilization were not applied. It should be noted that during the experimental period, the researchers did not detect water or nitrogen deficiencies visible to the naked eye. More specifically, the Normalized Difference Vegetation Index (NDVI) and the Photochemical Reflectance Index (PRI) showed statistically significant differences between the control treatment and the two stress treatments with limited water and nitrogen. Additionally, based on the reflectance measurements and the measured physiological crop parameters, significant correlations (p < 0.01) were observed mainly between the PRI and the chlorophyll content, the photosynthetic efficiency and the stomatal conductance (r = 0.84/0.90, 0.73/0.66, 0.61/0.66 among the nitrogen and water treatments). The research provides data analysis results on sensors and approaches for crop reflectance measurements as well as spectral indices for remote water and nitrogen detection. Finally, the results provide a feasibility analysis, suggesting that multispectral images could be used as a rapid tool to estimate the physiological status of plants, which is indicative of the spatial variation in the vertical farm. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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27 pages, 5504 KiB

Open AccessArticle

Effects of Light Conversion Film on the Growth of Leafy Vegetables in Facilities under Haze Weather

by Jingjing Li, Lili Zhangzhong, Xin Zhang, Xiaoming Wei, Shirui Zhang, Lichun Wang and Wengang Zheng

Agronomy 2022, 12(10), 2391; https://doi.org/10.3390/agronomy12102391 - 3 Oct 2022

Cited by 4 | Viewed by 2298

Abstract

The light intensity is low in haze weather, and the facility is in a weak light environment for a long time. As a functional film, light conversion film (LCF) can improve the light conversion performance and is conducive to regulating the environment in [...] Read more.

The light intensity is low in haze weather, and the facility is in a weak light environment for a long time. As a functional film, light conversion film (LCF) can improve the light conversion performance and is conducive to regulating the environment in the facility to promote crop growth. It can be seen from the test that the light transmittance of LCF under visible light conditions (400–780 nm) is 8.67% higher than that of ordinary film (OF), with stronger light transmittance. In the red–orange light band (600–700 nm), the LCF is 1.3% higher than that of the OF. Through the detection of irradiance, it was found that the irradiance was outdoor environment > LCF > OF in any weather. A two-year greenhouse experiment was conducted to study the effect of LCF on the whole growth process of facility agriculture (environment-soil-crop) under weak light. It is found that LCF reduces the air humidity by 0.47~2.83%; it has an obvious warming effect on the surface soil of greenhouse, and it is linearly correlated with temperature. In terms of crop growth, LCF significantly (p < 0.05) increased the photosynthetic rate at heading stage, and finally increased the yield, total soluble sugar and reduction-type Vitamin C by 8.97–39.53%, 9.22–30.14%, and 1.41–21.09%, respectively. In addition, considering the frequent haze weather in North China, the use of LCF can improve air temperature, CO₂ concentration, photosynthetically active radiation (PAR), and soil temperature, and it can effectively deal with the challenge of weak light. In conclusion, LCF can improve the facility environment and improve crop yield and quality, indicating that the implementation of LCF has potential benefits in solving crop yield reduction and quality decline in haze weather. In addition, as the main component of LCF, rare earth materials are a new type of clean energy, which can effectively promote the sustainable development of the agricultural ecosystem. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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23 pages, 8749 KiB

Open AccessArticle

Study on the Natural Ventilation Characteristics of a Solar Greenhouse in a High-Altitude Area

by Bohua Liang, Shumei Zhao, Yanfeng Li, Pingzhi Wang, Zhiwei Liu, Jingfu Zhang and Tao Ding

Agronomy 2022, 12(10), 2387; https://doi.org/10.3390/agronomy12102387 - 2 Oct 2022

Cited by 6 | Viewed by 2025

Abstract

The ventilation rate of a greenhouse is one of the major factors to consider when assessing its ventilation performance. Compared with plain areas, high-altitude areas have lower air pressure, thinner air, and stronger solar radiation, which in turn affect the magnitude of the [...] Read more.

The ventilation rate of a greenhouse is one of the major factors to consider when assessing its ventilation performance. Compared with plain areas, high-altitude areas have lower air pressure, thinner air, and stronger solar radiation, which in turn affect the magnitude of the local greenhouse ventilation rate. This paper is based on the use of online monitoring and computational fluid dynamics (CFD) techniques for modeling and model validation. The average relative error (ARE), mean absolute error (MAE), root-mean-square error (RMSE), and determination coefficient (R²) of the temperature were 4.88%, 1.396 °C, 1.428 °C, and 0.9982, respectively. The ARE, MAE, RMSE, and R² of the velocity were 9.525%, 0.035 m/s, 0.049 m/s, and 0.9869, respectively. Then, the distributions of the wind pressure, Reynolds number (Re), thermal pressure, air density, air speed, and temperature in greenhouses in high-altitude and plain areas were researched to obtain the relevant factors affecting the ventilation rates of greenhouses in high-altitude areas. In addition, correlation analyses were conducted for five variables affecting the ventilation rate: the inlet velocity, the temperature difference between the inside and outside of the greenhouse, the air density difference between the inside and outside of the greenhouse, total indoor radiation, and the internal heat source of the crop, and the coefficients of their correlations with the greenhouse ventilation rate were 1.0, −0.83, −0.72, −0.72, and 0.68, respectively. A natural ventilation rate model for plateau areas was developed, with the ARE, RMSE, and R² between the sample values and fitted values determined to be 4.55%, 0.543 m³/s, and 0.9997, respectively. The model was validated by predicting the greenhouse ventilation rate in winter (3 January 2022), and the ARE, RMSE, and R² of the sample values and predicted values were 9.726%, 8.435 m³/s, and 0.9901, respectively. This study provides a theoretical basis for further research on greenhouse ventilation characteristics in high-altitude areas. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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23 pages, 9331 KiB

Open AccessArticle

Simulation of Thermal Performance in a Typical Chinese Solar Greenhouse

by Jian Ma, Xuejing Du, Sida Meng, Juanjuan Ding, Xuan Gu, Yuxue Zhang, Tianlai Li and Rui Wang

Agronomy 2022, 12(10), 2255; https://doi.org/10.3390/agronomy12102255 - 21 Sep 2022

Cited by 6 | Viewed by 2359

Abstract

A Chinese solar greenhouse (CSG) is used as a horticultural facility that provides high efficiency thermal storage performance to produce vegetables in winter. Quantifying the thermal performance of the surrounding structure including the back roof, soil, and north wall is helpful to improve [...] Read more.

A Chinese solar greenhouse (CSG) is used as a horticultural facility that provides high efficiency thermal storage performance to produce vegetables in winter. Quantifying the thermal performance of the surrounding structure including the back roof, soil, and north wall is helpful to improve the thermal performance of the CSG. The objectives of this study were to evaluate the performance of the heat transfer inside a CSG and analyze the thermal characteristics of different parts of the surrounding structures including solar gain, heat flux, and conduction heat transfer. The model was validated using experimental data from clear days and cloudy days during winter in Shenyang City, Liaoning Province, China. It indicates that the calculation method and model is valid and that EnergyPlus, which has been used in the thermal building field, can be used as a design tool to optimize solar energy storage and structure of greenhouses. The minimum temperatures of all components inside the CSG were maintained over 5 °C, even when the outside temperature reached to −22 °C, which showed good heat preservation in cold weather. Soil received the most radiation heat compared with other surfaces inside the CSG and contributed heat to the interior air to maintain air temperatures during the night. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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23 pages, 1997 KiB

Open AccessArticle

Genetic Algorithm for Cost Optimization of Different Multi-Tunnel Greenhouse Design Alternatives

by María S. Fernández-García, Desirée Rodríguez-Robles, José Ramón Villar-García and Pablo Vidal-López

Agronomy 2022, 12(9), 2145; https://doi.org/10.3390/agronomy12092145 - 9 Sep 2022

Cited by 1 | Viewed by 1979

Abstract

Greenhouses are employed worldwide to protect crops from meteorological conditions as well as to control some plant production variables. As multi-tunnel structures are amongst the most used, in this article, we focus on cost optimization of both the steel structure and the concrete [...] Read more.

Greenhouses are employed worldwide to protect crops from meteorological conditions as well as to control some plant production variables. As multi-tunnel structures are amongst the most used, in this article, we focus on cost optimization of both the steel structure and the concrete foundation of this greenhouse typology. Firstly, three structural alternatives composed of three tunnels and differentiated portal frames were dimensioned conforming to the European design of steel structures, namely, Eurocode 3; meanwhile, the foundation was calculated through a previously validated matrix method. Then, genetic algorithms were employed to optimize for cost each proposed design and to evaluate the relative weight of each element in the overall steel consumption. Moreover, the influence of the greenhouse design on the final cost was also assessed, and it was found that the most cost-effective solution corresponded to the optimized greenhouse alternative exhibiting a 3.5 m separation between portal frames and the combination of a steel profile and plastic gutter (i.e., M3OPT at 15.14 €/m²). Finally, from the study on the influence of the portal frame separation, a further cost per square meter reduction was found for a design with the so-called structural gutter (i.e., steel profile and plastic water collection system) as support for the arches and a 4.5 m separation at 14.21 €/m². Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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19 pages, 4222 KiB

Open AccessArticle

Performance Evaluation of a Water-Circulating Tomato Root-Zone Substrate-Cooling System Using a Chiller and Its Effect on Tomato Vegetative Growth in Chinese Solar Greenhouse

by Xin Liu, Shiye Yang, Xinyi Chen, Shengyan Liu, Ruimin Zhou, Liangjie Guo, Yachen Sun and Yanfei Cao

Agronomy 2022, 12(8), 1922; https://doi.org/10.3390/agronomy12081922 - 15 Aug 2022

Cited by 5 | Viewed by 2117

Abstract

A high-temperature environment is one of the most important factors limiting the growth of crops in Chinese solar greenhouses during summer. To reduce the substrate temperature of summer plant cultivation in a Chinese solar greenhouse, we proposed a water-circulating tomato-root zone-substrate-cooling system (WCTRZSCS). [...] Read more.

A high-temperature environment is one of the most important factors limiting the growth of crops in Chinese solar greenhouses during summer. To reduce the substrate temperature of summer plant cultivation in a Chinese solar greenhouse, we proposed a water-circulating tomato-root zone-substrate-cooling system (WCTRZSCS). The system used water as the circulating medium, a chiller as the cooling source, and polyethylene raised temperature resistance (PE-RT) pipes laid in the substrate as the cooling component. The greenhouse was divided into test area TS₁ (one PE-RT pipe), TS₂ (two PE-RT pipes), and a control area CK (no PE-RT pipe) for the root-zone substrate-cooling test. The results demonstrated that (1) in the summer, WCTRZSCS can effectively reduce the substrate temperature, and (2) WCTRZSCS improves the temperature conditions for tomato vegetative growth. There were significant differences in plant height, stem diameter, dry weight, fresh weight, leaf area, net photosynthetic rate, total root length, and total root projection area between tomatoes in the test and control areas (p < 0.05). The TS₁ and TS₂ growth rates were 60.2% and 81.2% higher than CK, respectively, and the light-utilization efficiency was 56.3% and 81.3% higher than CK. (3) The system’s cooling energy consumption per unit ground area was 35.2~67.5 W·m⁻², and the coefficient of performance (COP) was 5.3~8.7. Hence, WCTRZSCS can effectively reduce the substrate temperature in the root zone, but the profit by tomato cannot offset the cost of using WCTRZSCS. Through the optimization of and improvement in the system, its economy may be further improved, and it is expected to be applied in practical production. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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14 pages, 2553 KiB

Open AccessArticle

Effects of Elevated CO₂ Levels on the Growth and Yield of Summer-Grown Cucumbers Cultivated under Different Day and Night Temperatures

by Hiromi Namizaki, Yasunaga Iwasaki and Rui Wang

Agronomy 2022, 12(8), 1872; https://doi.org/10.3390/agronomy12081872 - 9 Aug 2022

Cited by 2 | Viewed by 2161

Abstract

The effects of elevated CO₂ (eCO₂) levels on field-grown cucumbers have been extensively studied. However, the variations in photosynthate accumulation in summer-grown cucumbers simultaneously exposed to eCO₂ and varying day-night temperatures (DNF) still remain unexplored. This study aimed to [...] Read more.

The effects of elevated CO₂ (eCO₂) levels on field-grown cucumbers have been extensively studied. However, the variations in photosynthate accumulation in summer-grown cucumbers simultaneously exposed to eCO₂ and varying day-night temperatures (DNF) still remain unexplored. This study aimed to investigate the effects of DNF different CO₂ conditions [ambient CO₂ (aCO₂; 400–600 μmol mol⁻¹) and eCO₂ (800–1000 μmol mol⁻¹)] on dry matter production and dry matter distribution in summer-grown cucumbers under two DNF treatments (35/10 °C and 25/20 °C, day/night). We observed that long-term eCO₂ exposure increased C assimilation and photosynthate accumulation in leaves, resulting in feedback inhibition of the leaf area. Under both DNF treatments, the total dry matter distribution to fruits under eCO₂ conditions was approximately 15% higher than that under aCO₂ conditions. Furthermore, soluble sugar content and C:N ratio increased with long-term eCO₂ exposure, indicating increased C allocation, photosynthate accumulation, and distribution. However, low night temperatures (LT) inhibited respiration and increased dry matter accumulation by 30% under eCO₂ conditions. Additionally, eCO₂ increased fruit fresh weight by 8% and 12% under both DNF treatments compared to aCO₂. This suggests that long-term eCO₂ exposure and varying DNF exhibited different effects through different metabolic mechanisms on cucumber growth at high temperatures. eCO₂ conditions probably increased dry matter distribution to improve fruit quality, and LT treatment altered the respiration rate to restore photosynthesis, thereby increasing photosynthate distribution to fruits. Therefore, a combination of CO₂ enrichment and DNF can be used to improve fruit quality and yield at high temperatures. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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32 pages, 17379 KiB

Open AccessArticle

Real-Time Temperature Distribution Monitoring in Chinese Solar Greenhouse Using Virtual LAN

by Shiye Yang, Xin Liu, Shengyan Liu, Xinyi Chen and Yanfei Cao

Agronomy 2022, 12(7), 1565; https://doi.org/10.3390/agronomy12071565 - 29 Jun 2022

Cited by 2 | Viewed by 1941

Abstract

The internal air temperature of Chinese solar greenhouse (CSG) has the problem of uneven spatial and temporal distribution. To determine temperature distribution at different locations, we designed a greenhouse temperature real-time monitoring system based on virtual local area network (VLAN) and estimate, including [...] Read more.

The internal air temperature of Chinese solar greenhouse (CSG) has the problem of uneven spatial and temporal distribution. To determine temperature distribution at different locations, we designed a greenhouse temperature real-time monitoring system based on virtual local area network (VLAN) and estimate, including interpolation estimation module, data acquisition, and transmission module. The temperature data were obtained from 24 sensors, and the Ordinary Kriging algorithm estimated the temperature distribution of the whole plane according to the data. The results showed that the real-time temperature distribution monitoring method established was fast and robust. In addition, data validity rate for VLAN technology deployed for data transmission was 2.64% higher than that of cellular network technology. The following results are obtained by interpolation estimation of temperature data using gaussian model. The average relative error (ARE) of estimate, mean absolute error (MAE), root mean square error (RMSE), and determination coefficient (R²) were −0.12 °C, 0.42 °C, 0.56 °C, and 0.9964, respectively. After simple optimization of the number of sensors, the following conclusions are drawn. When the number of sensors were decreased to 12~16, MAE, RMSE, and R² were 0.40~0.60 °C, 0.60~0.80 °C, and >0.99, respectively. Furthermore, temperature distribution in the greenhouse varied in the east–west and north–south directions and had strong regularity. The calculation speed of estimate interpolation algorithm was 50~150 ms, and greenhouse Temperature Distribution Real-time Monitoring System (TDRMS) realized simultaneous acquisition, processing, and fast estimate. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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22 pages, 8533 KiB

Open AccessArticle

Modeling-Based Energy Performance Assessment and Validation of Air-To-Water Heat Pump System Integrated with Multi-Span Greenhouse on Cooling Mode

by Adnan Rasheed, Hyeon Tae Kim and Hyun Woo Lee

Agronomy 2022, 12(6), 1374; https://doi.org/10.3390/agronomy12061374 - 7 Jun 2022

Cited by 8 | Viewed by 2387

Abstract

The purpose of this study was to conduct a modeling-based energy performance assessment and validation of an air-to-water heat pump (AWHP) system, in the cooling mode, integrated with a multi-span greenhouse using TRNSYS software. We used the building energy simulation (BES) model to [...] Read more.

The purpose of this study was to conduct a modeling-based energy performance assessment and validation of an air-to-water heat pump (AWHP) system, in the cooling mode, integrated with a multi-span greenhouse using TRNSYS software. We used the building energy simulation (BES) model to investigate the performance characteristics of the AWHP system for greenhouse cooling. We modelled the components of the AWHP system, including the fan coil unit (FCU), water storage tank, and water circulation pump integrated with the greenhouse model. The proposed model included all the components of the experimental system. We validated the proposed model by comparing the simulation results with those obtained from field experiments. We investigated the cooling energy supply to the multi-span greenhouse, greenhouse internal air temperature, heat pump (HP) output temperature, and coefficient of performance (COP). We evaluated the performance of our model by calculating the Nash–Sutcliffe efficiency (NSE) coefficient of all the validated components. Furthermore, we performed linear regression analyses (R²) to determine the relationship between the different parameters. NSE values of 0.87, 0.81, and 0.93, for the greenhouse internal air temperature, the energy supply to the greenhouse, and the HP output water temperature, respectively, validated the prediction accuracy of the model. Moreover, R² values of 0.83 and 0.39 indicated that cooling loads are more dependent on ambient solar radiation than ambient air temperature. Furthermore, an R² value of 0.91 showed a linear relationship between the HP’s energy consumption and ambient air temperature. The average daily COP of the HP system was 2.9. Overall, the simulation results showed acceptable correlation with the experimental results. The high NSE values validated the high predictive power of the model. The proposed validation model can be used to improve the performance of systems by optimizing the control strategies and capacities of the equipment (e.g., the HP, the FCU, and the area of the greenhouse). We have provided detailed information to enable engineers, researchers, and consultants to implement the model for their specific needs. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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14 pages, 2013 KiB

Open AccessArticle

Greenhouse Thermal Effectiveness to Produce Tomatoes Assessed by a Temperature-Based Index

by Jorge Flores-Velázquez, Fernando Rojano, Cruz Ernesto Aguilar-Rodríguez, Edwin Villagran and Federico Villarreal-Guerrero

Agronomy 2022, 12(5), 1158; https://doi.org/10.3390/agronomy12051158 - 11 May 2022

Cited by 4 | Viewed by 2537

Abstract

This study proposed an indicator to calculate the regional thermal potential from the local temperature. A probabilistic function curve generalized as a complementary error function (erfc) was used to assume the temperature curve follows the normal distribution and considered only the [...] Read more.

This study proposed an indicator to calculate the regional thermal potential from the local temperature. A probabilistic function curve generalized as a complementary error function (erfc) was used to assume the temperature curve follows the normal distribution and considered only the portion of the curve where the appropriate temperatures for the crop are located (wi). The Greenhouse Thermal Effectiveness (GTE) index was calculated using (a) the data of measured temperature (outside) and simulated values from inside of the greenhouse, and (b) the normal temperature data from five meteorological stations. Estimations of GTE using average daily temperature (°C) throughout the year indicate that, with an annual mean temperature of around 14 °C, the GTE is 2798 degree units and inside the greenhouse its value goes up to 5800. May is when the highest temperatures occur and when the highest amount of GTE units can be accumulated. The range of temperatures in the analyzed stations were from 13 to 21 °C and the GTE calculated per year was from 2000 to 7000. The perspective will be to calculate if this energy will be enough to grow tomatoes (or other crops) without extra energy for heating or cooling. If more energy may be needed, estimating how much would be the next step. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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14 pages, 4037 KiB

Open AccessArticle

A Study on Optimum Insulation Thickness in Walls of Chinese Solar Greenhouse for Energy Saving

by Hui Xu, Juanjuan Ding, Tianlai Li, Chunyan Mu, Xuan Gu and Rui Wang

Agronomy 2022, 12(5), 1104; https://doi.org/10.3390/agronomy12051104 - 30 Apr 2022

Cited by 5 | Viewed by 2415

Abstract

Chinese solar greenhouses (CSGs) are characterized by unique walls to reduce the transmission of heat and promote the energy conservation in winter production, which promotes cultivation in the northeast region of China in winter. Effective selection of insulation material is important for the [...] Read more.

Chinese solar greenhouses (CSGs) are characterized by unique walls to reduce the transmission of heat and promote the energy conservation in winter production, which promotes cultivation in the northeast region of China in winter. Effective selection of insulation material is important for the CSG based on the energy consumption and economic analysis. However, choosing the thickness of the insulation material in walls often discussed with the structure of CSG. There is a lack of research combing the optimal insulation thickness for improving the energy conservation. The aim of this study was to find the optimum insulation thickness during the energy conservation based on the structure of walls, the energy consumption in local climatic conditions, the cost of insulation material, and economic payback period over a lifetime. By the economic analysis of insulation thickness, thermal resistance, lifetime energy saving, and payback period, three kinds of typical walls (clay brick (CB), hollow concrete block (HCB) and fly ash block (FAB)) combed with four insulation materials including the expanded polystyrene, the foamed PVC, the perlite, and the rock wool were calculated. The optimum insulation thickness can be found when energy savings reached the maximum. In the northeast region, the association of FAB with rock wool as the insulation layer was the most economic composite wall structure. The optimum insulation thickness was 0.05 m, with the cost only 5 USD/m². The thermal resistance of composite wall had a significant effect on the payback period. When thermal resistance increased from 0.2 to 1.2 m²K/W, the payback period varied from 0.4 to 4.3 years. What is more, the energy consumption in local climatic conditions had a more significant effect on payback period. It can be assumed that insulation materials are more favored in cold climatic regions where heating degree-days over 1600 °C days for payback periods is less than 2 years. These results have strong practical and economical significance in saving energy and improving the environment of CSG. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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Review

Jump to: Research

27 pages, 2298 KiB

Open AccessReview

Greenhouse Natural Ventilation Models: How Do We Develop with Chinese Greenhouses?

by Jingfu Zhang, Shumei Zhao, Anguo Dai, Pingzhi Wang, Zhiwei Liu, Bohua Liang and Tao Ding

Agronomy 2022, 12(9), 1995; https://doi.org/10.3390/agronomy12091995 - 24 Aug 2022

Cited by 6 | Viewed by 3179

Abstract

Greenhouse technology has advanced over the past few decades in terms of environmental control (e.g., indoor temperature, relative humidity, and CO₂ concentration). Ventilation is an effective way to adjust the indoor climate. Natural ventilation has gained significant research attention recently because of [...] Read more.

Greenhouse technology has advanced over the past few decades in terms of environmental control (e.g., indoor temperature, relative humidity, and CO₂ concentration). Ventilation is an effective way to adjust the indoor climate. Natural ventilation has gained significant research attention recently because of its low energy requirement. To evaluate the ventilation effectiveness, the ventilation rate is often used. This review summarizes the published review papers related to greenhouse ventilation. Ventilation models are reported under different conditions, including wind-induced, buoyancy-induced, and combined effects-induced ventilation in greenhouses. The influencing factors are described, such as the wind and buoyancy strength and distribution, greenhouse geometry, and vent arrangement. Various methods assessing natural ventilation in greenhouses are introduced, consisting of tracer gas techniques, the pressure difference method, the energy balance method, the emptying fluid-filling box method, and numerical simulation. The values of the key coefficients deduced and used in the literature are listed. This paper reports what has been done in the world and where we can start to develop dynamic ventilation models for solar and tunnel-type greenhouses in China. Further valuable investigations are discussed. The pressure distribution function in greenhouses with horizontal openings, a model for cross-ventilation induced by combined wind and buoyancy force, and an analytical plant-considered ventilation model with higher applicability are described. To ensure the accuracy of the ventilation models, other environmental variables, especially geography-dependent ones, can be added. More criteria are suggested to evaluate the ventilation performance rather than the ventilation rate to provide a comprehensive assessment. Full article

(This article belongs to the Special Issue Frontier Studies in Agricultural Greenhouse Equipment and Systems)

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