Energy water and systems

Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

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Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

Steven W. Van Ginkel, Thomas Igou, Yongsheng Chen*School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, GA 30332, United States.

Citation

Van Ginkel, S.W., T. Igou, and Y. Chen. 2017. Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA. Resources, Conservation and Recycling 122:319-325. Https://doi.org/10.1016/j.resconrec.2017.03.003 (Links to an external site.)

 Background

This paper compares the efficiency of California Based traditional vegetable agriculture to hydroponics and aquaponics systems. Efficiency is defined by water usage, energy and nutrient input as it relates to crop yield. California is the leader in fruit and vegetable agriculture; therefore the rest of the United States is reliant on their system. However, California is also susceptible to severe drought, which can lead to reduce yields. Additionally, California has very large watershed, which can cause runoff of fertilizers in ponds, lakes and other bodies of water. Therefore to mitigate the environmental footprint of agriculture production, the author’s suggests that future generations focus on urban agriculture. Aquaponics is a system that allows the production of vegetables and fish, while reducing the input of fertilizers, and using waste byproducts as the source of nutrients. The authors show that this system reduces the nutrient input, water usage and is more productive that traditional based vegetable production. Therefore the purpose of this paper is to compare and contrast the productivity of each system.

 Experimental Design

California vegetable data was derived from www.casestudies.ucdavis.edu. Data was taken for several crops including tomato, spinach, strawberries, peppers, and broccoli. The data displays yield, nutrient input, energy input for each crop. The data was normalized by dividing each component by yield per acre. For hydroponics, there was one grower who grew lettuce and leafy greens in shipping containers. The data was normalized for energy (lighting and cooling) and water usages over a year divided by yield per container. For aquaponics, there were three growers, one from Hawaii and two from University of Virgin Islands and Atlanta, GA. All growers used deep-water culture and grew leafy greens. The data was normalized for energy and water utilized over a year divided by the yearly productivity. Data from all three systems was then compared using statistical analysis.

 Results

Areal Productivity

When comparing hydroponics and aquaponics there was no significant difference in the areal productivity. However, there was a significant difference between the ponic-systems and the California-based system. Ponic-systems were found to be 10 to 29 times more productive than the California-based system. In addition, areal productivity in hydroponics could be substantially improved increasing vertical production in closed environments.

Energy Usage

Hydroponics uses 30 times more energy (lighting, cooling) than the California-based system. There was no significant difference in energy usage between aquaponics and California-based system. However there were differences in energy usage between aquaponic growers, therefore it is would be wise to compare each aquaponic grower to the California-based system in the future.

 Water Usage

California-system uses 66 and 8 times more water than hydroponics and aquaponics. There were differences in water usage between hydroponics and aquaponics, however the authors suggests that results maybe skewed due to the lack of data points.

Conclusion

Based on the authors study, it seems that ponic-systems are overall more efficient than California-based system. They believe that these systems should be integrated into urban cities. By integrating such systems, cities become less reliant on vegetable and fruit production from California. At the same time it reduces the negative environmental footprint. Nevertheless, the biggest challenge will be to address the socio-economic challenges in integrating the system into urban environments.

Design for an Improved Temperature Integration Concept in Greenhouse Cultivation

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Original paper: O. Ko¨rner *, H. Challa Design for an improved temperature integration concept in greenhouse cultivation Farm Technology Group, Department of Agrotechnology and Food Sciences, Wageningen University, Mansholtlaan 10, 6708 PA Wageningen, The Netherlands Received 22 July 2002; received in revised form 15 November 2002; accepted 28 December 2002. https://doi.org/10.1016/S0168-1699(03)00006-1

     Heating energy represents more than two-thirds of a typical greenhouse total energy consumption. Is currently well known that the average day and night temperatures are what controls how fast plants develop. As the temperature increases, crops develop much faster, but there is a significant cost associated, which typically leads to an increase in energy consumption. To mitigate the cost and become more efficient in the control environment production, an approach to improve temperature integration concept could play an essential role in energy savings. Temperature Integration Concept is based on the ability of crops to tolerate temperature deviation from their biological set points. The integration concept manipulates temperature, aiming to be compensated within a pre-set period without having adverse effects on plant growth.

     Theoretically, a crop with more dynamic and flexible temperature boundaries could potentially play an important role, so this study aimed to improve the temperature integration concept by introducing dynamic temperature constraints. A modified temperature integration procedure was designed combining the usual long-term temperature average over several days and fixed boundaries for daily average temperature with short-term temperature averages over 24 hours with a very flexible temperature limit. The overall idea is based on a concept called the Freedom for temperature fluctuations. This concept allows the temperature to freely fluctuate due to the environment without being controlled by heating or ventilation. Temperature fluctuation increases with longer averaging period and increasing temperature bandwidth, which allows longer periods of several days, which enables compensation of warm or cold periods resulting in higher energy savings.

     The proposed regimen for temperature integration was performed by modeling and simulation techniques (MATLAB version 6.0) using tomato as a model crop. Variables such as air temperature, outside radiation, relative humidity, and CO2 measurements were input in the model with a fixed time of 5 min over one year. Measurements such as setpoints for heating, ventilation and CO2 concentrations were calculated with a climate control model (CCM) which provide enough information for calculating relative humidity, air temperature, energy consumption, and natural gas consumption. For accuracy, energy loses where also consider into the model. Two reference temperature regimens were used for comparison:  BP= commercial standards, setpoint increase linearly, and a Bpfix= night and daytime heating and ventilation temperature setpoints were fixed (uncommon practice). The heating setpoints were 18, and 19 °C and ventilation set points were 19 and 20 °C for night and day, respectively. The weather prediction was also used for providing data into the model simulation. Validations of the CCM model was performed in four semi-commercial Venlo-type greenhouse compartments.

     Two temperature integration regimens were model by the Autor: RTI (regular temperature integration) and MTI (modified temperature integration) both with a bandwidth of +/- 2, +/- 4 and +/- 6. The modified regime model (MTI) resulted in more energy saved when compared with regular temperature integration model (RTI) and the BP controls. Energy-saving increased with temperature bandwidth in all cases evaluated. Fluctuation during a cold time (winter) was observed. Overall, yearly greenhouse energy saving increased by up to 23% compared with the BP regime (temperature with a bandwidth of +/- 6 C). Compared with regular temperature integration energy-saving increased relatively with 14%. Interestingly, the setpoint for relative humidity profoundly influenced energy-saving suggesting further focus in future evaluations. When evaluating the different temperature dose-response data, they observe than an increase in the duration of maximum and minimum temperature increase energy saving and gross photosynthesis of tomato plants, which can be traduced to more photosynthetic efficiency. In conclusion, the conceptual design for advance temperature integration control seems to be promising for energy reduction. The distinction between short- and long-term processes in temperature integration lead to an increase in energy savings. A more advanced flexible humidity control concept could probably help to decrease energy consumption further since the highest energy saving was achieved when no humidity control was used.