THERMAL ENVIRONMENT MODELING AND OPTIMIZATION OF GREENHOUSE IN COLD REGIONS

Thermal simulation models for the time-dependent heating requirement of greenhouses are very important for the evaluation of various energy-saving technologies, and energy-efficient design of greenhouses based on local climates. A quasi-steady state thermal model “GREENHEAT” was developed using the programing language MATLAB for simulation heating requirement in conventional greenhouses. The model could predict the hourly heating requirement based on the input of hourly weather data, indoor environmental parameters, and physical and thermal properties of greenhouse building materials. The model was validated with measured data from a commercial greenhouse located in Saskatoon, Canada, and the monthly average error in prediction was found to be less than 5.0%. This study also reviewed various energy-saving technologies used in greenhouses in cold climate, and the GREENHEAT model allowed selections of commonly used ones in the simulation. The GREENHEAT model was used for evaluating the impact of various geometrical parameters on the heating requirement of the single span and multiple-span conventional greenhouses located in Saskatoon. Results showed that the east-west oriented gable roof greenhouse could be more energy-efficient for the multi-span gutter connected greenhouse whereas quonset shape as a free-standing single span greenhouse. The large span width could be beneficial for the single-span greenhouses, but the impact of increased span width could be negligible on the heating demand of multi-span greenhouses. The model was also used for an economic feasibility analysis of year-round vegetable production (tomato, cucumber, and pepper) in northern Saskatchewan, and tomato was found to be the most economical vegetable as compared to the cucumber and pepper. Another heating simulation model CSGHEAT was developed to estimate of the supplemental heating requirement of mono-slope Chinese-style solar greenhouses (CSGs). This model is also a quasi-steady state thermal model using the programming language MATLAB, and it can simulates the hourly heating requirement of CSGs. The model was validated with experimental data from a CSG located in Winnipeg, Manitoba. The average error for prediction of the hourly heating requirement was found to be less than 8.7%. The model sensitivities to various geometrical and thermal parameters were studied. The results indicated that the thermal properties of cover, thermal blanket, and parameter insulation were the most important design parameters in CSGs. Finally, the heating requirement in CSGs was modeled using TRNSYS simulation tool, and the predictions were compared with that of CSGHEAT. The result indicated that TRNSYS had serious limitations for modeling of greenhouse thermal environment, thereby high uncertainties could occur, thus was not suitable for greenhouse simulation

Thermal modelling of a passive style net-zero greenhouse in Alberta: The effect of ground parameters and the solar to air fraction

Agricultural greenhouses can provide a suitable microclimate for crops to thrive under extreme weather conditions. The operations of these greenhouses are expensive due to the energy requirement of the active thermal conditioning systems required to maintain the growing environment for crop production. Engineering of these greenhouses to utilize clean renewable energy sources is critical and necessary to mitigate their carbon footprint, paving the way to a more sustainable agricultural industry. This paper presents numerical modelling of a net-zero passive solar greenhouse in Alberta, Canada with winter temperatures below freezing. The indoor microclimate of the greenhouse is modelled using the detailed radiation model of a transient simulation tool, TRNSYS. The paper investigates the effects of ground parameters and the solar-to-air fraction on the numerical results. The paper includes a cost comparison between crop production in the traditional and passive style greenhouse

THERMAL ENVIRONMENT MODELLING OF THE MONO-SLOPE SOLAR GREENHOUSE FOR COLD REGIONS

The extremely cold outdoor temperatures in winter continue to be a barrier for the greenhouse growers. In Saskatoon, for example, it is less than -31.5℃ for 1% of the year (ASHRAE, 2013). This limits the growth of the greenhouse industry in Saskatchewan which has around 250 billion square meters of farmland, and accounts for 38.5% Canada’s farm area (Statistics Canada, 2016). Due to this fact, most traditional Canadian greenhouses in the Canadian Prairies shut down during the coldest months (from November to February) because of heavy heating bills. However, the local demand for food in the winter has been increasing in Saskatchewan due to a rise in population and consciousness of healthy food. If compare traditional local greenhouses with other greenhouse production techniques, Chinese mono-slope solar greenhouses do not primarily rely on supplemental heating. They rely on solar energy to maintain the indoor temperature. Fortunately, Saskatchewan has the most hours of sunshine annually in Canada which theoretically provides a favorable environment for the establishment and development of mono-slope solar greenhouses (Environment Canada, 2017). This also greatly reduces heating costs. The objective of this study was to evaluate the thermal environment and predict the energy consumption of solar greenhouse production in Saskatchewan. This was done using an existing simulation model RGWSRHJ that was developed by Chengwei Ma in China (Ma, 2015). Several modifications were made to make the model SOGREEN that is suitable for the cold climate in Saskatchewan. These modifications included meteorological year data invoking, advanced front roof covering, summer solar screen, and so on. Later, the modified simulation model SOGREEN was validated using field data that were collected in a solar greenhouse in Elie, Manitoba. Solar greenhouse production was simulated under the weather conditions in Saskatoon, Saskatchewan. Finally, the energy consumption was analyzed using the simulated data to select the most suitable and economical energy resource for solar greenhouse production in cold regions. From the validation results, there were 9.6% and 13.7% discrepancies in the model’s predictions of indoor temperature and relative humidity, respectively. This has demonstrated that the modified model could simulate the thermal environment of a solar greenhouse with a relatively high accuracy. While the simulation results confirmed that a large amount of energy was used for supplying heat from November to March, there was almost no supplemental heat needed between April and August. This illustrated that solar greenhouses can fully utilize the solar energy, dramatically reducing the annual energy consumption. From an energy cost analysis, $26378.56,$2498.51 and $2610.00 was spent for supplemental heat with electricity, natural gas, and coal. Therefore, among these three energy resources, natural gas was the most affordable and most environmentally friendly option for greenhouse production. Compared with the natural gas expenses of Grandora Gardens, vegetable production in a solar greenhouse can save as much as 83.6% in energy costs. This demonstrates that solar greenhouse production in Saskatchewan is in fact economical for the Canadian Prairies

Energy performance and climate control in mechanically ventilated greenhouses: A dynamic modelling-based assessment and investigation

Controlled environment agriculture in greenhouse is a promising solution for meeting the increasing food demand of world population. The accurate control of the indoor environmental conditions proper of greenhouses enhances high crop productivity but, contemporarily, it entails considerable energy consumption due to the adoption of mechanical systems. This work presents a new modelling approach for estimating the energy consumption for climate control of mechanically ventilated greenhouses. The novelty of the proposed energy model lies in its integrated approach in simulating the greenhouse dynamics, considering the dynamic thermal and hygric behaviour of the building and the dynamic response of the cultivated crops to the variation of the solar radiation. The presented model simulates the operation of the systems and the energy performance, considering also the variable angular speed fans that are a new promising energy-efficient technology for this productive sector. The main outputs of the model are the hourly thermal and electrical energy use for climate control and the main indoor environmental conditions. The presented modelling approach was validated against a dataset acquired in a case study of a new fully mechanically controlled greenhouse during a long-term monitoring campaign. The present work contributes to increase the knowledge about the dynamics and the energy consumption of greenhouses, and it can be a valuable decision support tool for industry, farmers, and researchers to properly address an energy efficiency optimisation in mechanically ventilated greenhouses to reach the overall objective of decreasing the rising energy consumption of the agricultural sector

Advanced Energy Modelling and Life Cycle Assessment of Indoor Agriculture

This thesis investigates the agricultural greenhouse sector in a cold climate, which requires a large amount of natural gas for supplying the substantial heating demands. The heating demand of these structures is calculated, and potential sustainable design methods are implemented to reduce the reliance on carbon-based fuels. Assessment of the environmental impacts of a bell pepper greenhouse in Southwestern Ontario, Canada heated by natural gas was studied. A life cycle assessment (LCA) method is employed to scrutinize the bell pepper greenhouse, pinpointing areas that need improvement. It was concluded that Global Warming (GW) is the significant environmental hazard among other environmental categories (3.87e-2 kg ??2-Eq). It should be noted, the main contributor to global warming is the natural gas being used as the heating resource (3.2e-2 kg ??2-Eq). The analysis is extended to explore the deployment of solar energy as an alternative source for heating. Solar energy is found to be a superior alternative in terms of emissions. Furthermore, in order to integrate solar energy into the energy supplying systems of the greenhouses, a hybrid Solar Thermal/Photovoltaic-Battery Energy Storage (ST/PV-BES) system is modeled. Evaluation of the best configuration of photovoltaic (PV) and solar thermal (ST) modules, and battery energy storage (BES) size to have the minimum Levelized Cost of Energy (LCOE) was conducted. It is proved that the system is economically optimized. Moreover, to improve operational efficiency and reduce the energy demand of commercial greenhouses, parametric optimization of major growing environment variables including cladding material and window to wall ratio as well as the characteristics of the solar thermal model elements such as hot water tank capacity and heat exchanger effectiveness was carried out. It is demonstrated that the best greenhouse configuration which is a system with 80% window area and 20% brick wall area in both lower nodes and upper nodes results in heating and cooling demand energy reduction without significantly compromising the solar energy absorption. This scenario leads to increasing system performance from 36% to 39%. It is also concluded that doubling the tank capacity improves system performance from 36% to 43% and changing the heat exchanger effectiveness has minor impacts on the system performance

Energy Systems and Applications in Agriculture

Agriculture, as a production-oriented sector, entails energy as a substantial input by which global food security is ensured. Agricultural systems require energy for farm machinery and equipment; lighting; heating, ventilation, and air-conditioning (HVAC); food processing and preservation; fertilizer and chemical production; and water/wastewater treatment/application. Increasing agriculture mechanization mitigates conventional energy reserves that escalate greenhouse gas emissions and climate change.This book aims to offer energy-efficient and/or environment-friendly ways for the agriculture sector to achieve the 2030 UN Sustainable Development Goals. The book provides cutting-edge research on next-generation agricultural technologies and applications to develop a sustainable solution for modern greenhouses, temperature/humidity control in agriculture, farm storage and drying, crop water requirements, agricultural built environment, and wastewater treatment

Aquaponics in the Built Environment

Aquaponics’ potential to transform urban food production has been documented in a rapid increase of academic research and public interest in the field. To translate this publicity into real-world impact, the creation of commercial farms and their relationship to the urban environment have to be further examined. This research has to bridge the gap between existing literature on growing system performance and urban metabolic flows by considering the built form of aquaponic farms. To assess the potential for urban integration of aquaponics, existing case studies are classified by the typology of their building enclosure, with the two main categories being greenhouses and indoor environments. This classification allows for some assumptions about the farms’ performance in their context, but a more in-depth life cycle assessment (LCA) is necessary to evaluate different configurations. The LCA approach is presented as a way to inventory design criteria and respective strategies which can influence the environmental impact of aquaponic systems in the context of urban built environments

An economic and environmental analysis of greenhouse tomato production in Norway using a model-based technique

The growing global population levels and the resulting increasing demands for food has put a lot of pressure on the food production systems and made the agricultural sector highly energy-intensive. The intensification in global food production has led to the need to adapt production systems according to the local climatic conditions, making food production possible in areas where it was di cult before and also making the production process environmentally sustainable. One way to adapt food production systems is through protected cultivation techniques, such as greenhouses, that enable controlled indoor climate, crop protection from extreme climate conditions, pests and diseases and the possibility to extend production seasons for certain crops. Yet these techniques a ect the investments, economic performance, used resources and have certain environmental consequences. Norway, for instance, is one such region in which one of the biggest challenges associated with protected cultivation systems is the issue of low availability of natural light and heat, especially during the cold winter months. Production in such regions requires high levels of energy, yet some of these regions also have significant availability of renewable energy resources. The challenge of low light and heat can be overcome by bringing about changes in the production techniques, including greenhouse design elements, production seasons and energy sources. However, this also in turn raises the issue of environmental impact of greenhouse vegetable production in high latitude regions and especially from the use of renewable energy that is present in significant amounts in many regions with considerable greenhouse vegetable production. While there exist several studies on the di erent aspects of greenhouse vegetable production in various regions, and their resulting environmental effects, works related to the use of renewable energy sources, especially in high latitude regions such as Norway are limited. Moreover, studies regarding the environmental impact of greenhouse production of vegetables often show that there is a trade-off between the economic performance and the environmental impact. Local climate and light variability call for regionally adapted greenhouse production techniques. Moreover, the impact of a certain greenhouse design on the economic performance may not always be correlated to the environmental impact. Thus, there is a need to evaluate the impact of various production strategies on the economic potential, resource use and the environment in instances where the traditional fossil fuel is supplemented and/or replaced by energy from renewable resources. In the present work, an attempt has been made to provide a broad picture of greenhouse tomato production at high latitude regions as a result of adapting production strategies in line with the local climates in Norway, with a particular emphasis on renewable energy sources in order to evaluate the environmental impact of locally produced tomatoes that are also economically profitable. The study has been divided into three stages. In the first part, an economic evaluation of seasonal (mid-March to mid-October) greenhouse tomato production in southestern, southwestern, central and northern Norway was performed. In the second part, an economic evaluation and energy use of extended season (from 20th January to 20th November) and year-round production of greenhouse tomatoes in the selected locations in Norway was performed. Sets of plausible design elements, greenhouse climate management, different artificial lighting strategies were assessed to evaluate the impact of the greenhouse design on the Net Financial Return (NFR), energy use and CO2 emissions of the production process. In the third part, a life cycle impact assessment was conducted for a selected number of designs from the first two stages that yielded high NFR or was associated with low energy use in order to assess whether the designs that performed well economically are also environmentally sustainable. The study found clear region-dependent differences in the NFR, its underlying elements, energy use and the resulting environmental impact of different greenhouse designs with differing energy-saving and internal climate control equipment. Our results show that economic profitability can be combined with a low environmental impact under certain regions and production techniques. It was found that Kise (southeastern) was the most favorable location for seasonal greenhouse tomato production in Norway, while Orre (southwestern) was the most favorable location in terms of the economic performance and environmental impact during the extended and year-round production seasons. Moreover, our results show that night energy screens, electric heat pumps and light sources had the most impacts of the elements that were investigated on the NFR and the resulting environmental impact across the three production seasons and need to be considered while constructing greenhouses for tomato production in regions having similar climate as that of Norway. The results of this study provide interesting insights on works related to the greenhouse vegetable production and energy resources in high latitude regions with considerable supplies of renewable energy. The findings can enable local producers across Norway to design greenhouses keeping in mind the local climate, the economic profitability and the environmental sustainability and can help policymakers in devising policies that encourage local growers to adapt production strategies aimed at increasing local production that is both economically profitable and environmentally sustainable

Greenhouse production systems for people

Environmentally sound greenhouse production requires that: demand for market products is understood; greenhouse design addresses the climate circum-stances; input resources are available and consumed efficiently, and; there must be a reasonable balance of production products to the environmental impacts from system. Engineering greenhouse production systems to meet these requirements must include: a cost-effective and structurally sound facility; various sub-systems controlled to interact harmoniously together; and educated and experienced system operators. The major components of the environmentally sound greenhouse are: Super-structure and glazing (for a specific location and climate conditions); Climate control sub-systems (ventilation, heating, cooling, CO2 control, pest protection, energy conservation, shading/lighting); Monitoring and control (for system operations data; decision-support systems; and, operations control procedures); Automation systems (for quality control, and effective resource utilization); and Crop nutrient delivery system (for control of plant root zone environment). Effective greenhouse engineering design, operations and management, must incorporate input from academic, private and public sectors of society. Therefore this team of researchers, educators, industry/ business, and experienced crop production operators has cooperated to include a current real-world applications perspective to the presentation. Greenhouse produc¬tion systems are described that not only include the fundamentals for success, but also the combination of sub-systems, at appropriate technological levels to meet the design requirements and restrictions for success. The collaborators on this presentation have capabilities and experiences of successful greenhouse production systems from around the world that range from simple, low-input systems to highly complex production systems. Our goal is to emphasize the current basics of greenhouse design, and to support the symposium about greenhouse production systems for people