Point Of Use Thermoelectric Powered Automated Irrigation System

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GRC Transactions, Vol. 39, 2015 Point of Use Thermoelectric Powered Automated Irrigation System for an Intesive Shallow Bottom Heat System Using Waste Geothermal Hot Water and Steam Condensate in Iceland William Foley1, Robert Dell1, C. S. Wei3, and Runar Unnthorsson2 1 Center for Innovation and Applied Technology, Mechanical Engineering, The Cooper Union, NY, USA 2 Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland, Reykjavik, Iceland 3 Mechanical Engineering, The Cooper Union, NY, USA Keywords Waste hot water, irrigation system, automation, heated ground agriculture, geothermal heated soil, cascade utilization Abstract In Iceland there is a super abundance of waste hot water from geothermal power plants at a temperature between 130-160°C. Some of this is re-purposed to heat cold water and is used for district heating and heated swimming pools. This waste energy source has also enabled the growth of out of zone plants, enhanced agricultural production by 20%, and extended the growing season by using the authors’ energy intensive shallow system of bottom heat that incorporates existing heated sidewalk technology. Complete autonomy of the field tested heated garden system is not possible without an independent, sustainably powered irrigation control system. Long term plant studies on the plant growth have been limited due to the lack of scheduled and reliable watering cycle as plants die during the growing season. The authors have also designed and constructed an automated thermoelectric powered irrigation system that was developed for the maximum plant growth of the Icelandic heated gardens. It has a subsystem that records soil moisture and ambient temperature. When the soil is too dry it is irrigated by opening a valve connected to a municipal water line. An identical irrigation system is currently in use for the author’s heated green roof experiments at The Cooper Union in New York City that uses waste heat from a Combined Heat and Power (CHP) system as the heat source. The system allows for long term maximum growth experiments while increasing the system’s sustainability. Introduction The geothermal heated garden and heated green roof systems were originally developed by Professor Robert Dell, Founding Director of the Center for Innovation and Applied Technology, at The Cooper Union, with support from the authors. The heat is passed through a network of pipes which warms the growth media and accelerates plant growth [1] [2] [3] [4] [5]. The authors developed and have been testing in Iceland since 2007 an energy intensive year round shallow system of outdoor heated ground agriculture that is analogous to heated sidewalks [1] [3]. The authors have developed three gardens using four different waste geothermal sources a. The first geothermal heated garden was installed in 2007 at the Agricultural University of Iceland at Reykir, near Hveragerdi. It uses waste geothermal condensate with a traditional shell and tube heat exchanger that uses a pump in a closed loop. The second test bed was installed and operated from 2011 to 2013 at Náttúrulækningafélag Íslands (NLFI Spa and Medical Clinic) in Hveragerdi. It used a gravity feed to recover the waste hot water from the clinic’s heated pool. NLFI also provided the third heat source using the waste hot water from a contiguous geothermal greenhouse. The third heated garden was installed in 2010 at the Keilir Institute of Technology (KIT) at Asbru in Reykjanesbaer. It uses district heating hot water in raw and discharge modes as the author’s fourth source. Each location also had an identical control garden that was not heated. 117 Foley, et al. The author’s previous experiments with these intensive bottom heated gardens indicated an increase in the evaporation rate of moisture from the soil in the heated gardens. In 2012 Iceland experienced a warm summer and less rainfall. All cucumber plants transferred to the gardens that summer died due to dry soil. Tomato and zucchini plants were temporarily damaged [3]. Plants in the heated beds will wither and die faster than in control beds if left unattended during periods of sparse rainfall. The authors have designed an automated irrigation control and data collection system to enables the heated gardens to operate independently of weather constraints [6]. Having the irrigation system powered by thermoelectric generator that uses on site geothermal heat sources adds to the sustainability of the heated garden system and diminishes its dependence on the electrical grid. This paper will present and describe the design, construction, and implementation of unique efficient irrigation geothermal powered control system and its benefits for the Icelandic heated gardens. Control System The temperature increases from the hot water pipes in heated green roofs/heated gardens enhances the evaporation rate of water in the soil when compared to unheated control beds. The author’s long term studies on the plant growth have been limited due to the lack of scheduled and reliable watering cycle as plants die during the growing season. The autonomous irrigation and soil moisture monitoring system presented in this paper was created to ensure a sufficient level of water in the soil for plant health. The system was designed to monitor soil moisture in the heated and unheated control beds. The control system writes the soil moisture and temperature values to an SD card. When the moisture falls below a preset low moisture threshold, the controller turns on a pump that draws water from a reservoir. The pump continues to run until the soil exceeds the preset upper moisture threshold. There is only an approximate 5 second delay between the sensor detecting the threshold and the pump turning on or off. An Arduino Uno microcontroller is used to record data and control the pump for its simplicity and use as a prototyping tool. A new and independent data collection and automated irrigation system was designed and built by the authors. The Arduino Uno was chosen for its low cost, simple coding language, and the ability of the Arduino platform to incorporate shields that expand its capabilities. The length of watering time is controlled using PWM signals. A scaled version of the full automated watering system was designed to test the irrigation system and the assembly of its components in the lab before the roof instillation. The components tested included: a small container filled with water, a 1m strip of drip hose system, the data acquisition system, a 1/8 HP Phobya DC12-220 12V water cooling pump, and an indoor heated garden Figure 1. Moisture Sensor [7]. test bed. The same procedure used to calibrate and test the irrigation system on the Cooper Union roof and in Iceland Button was first simulated during these tests. The Arduino Uno controller is Thermocouple coupled with an SD card shield attachButton ment. The Arduino collects soil moisture data using a DFRobot Soil Moisture Sensor (Arduino compatible) Immersion Gold, shown in Figure 1. The sensor Arduino measures the voltage across the – the Moisture more water in the soil the higher the Sensor Platform voltage reading. The Arduino with SD card shield wired to the breadboard is shown in Figure 2. Irrigation Controller Hardware. Figure 2. 118 Foley, et al. The moisture sensor output is an analog signal that ranges from 0 to 5V. The microcontroller converts the analog signal into a digital signal with a 0 to 1023 range. A value of 0 represents a completely dry environment and 1023 represents completely wet. When the sensor is immersed in completely dry soil the system reports a value of 0. When the sensor is immersed in non-distilled water the sensor reports a value of 1023. The field capacity is the moisture content of a field after water stops draining through the ground and stays suspended in the soil. A field reaches its capacity when water potential ranges from -0.1 to -0.33 bar, which is the energy difference between free water (zero energy) and water in a sample such as soil [8] [9] [10]. The capacity of a soil to hold water depends on the quantities of clay, sand, silt, and organic material. The overall system cost was $612. The sensor was calibrated to the specific soil type it is monitoring. The calibration used for the soil at the Agricultural University of Iceland garden couldn’t be used for the New York City test beds due to the different soil types at each location. Different soils compositions have different maximum water holding capacities. Calibration Procedure Two soil samples were prepared for sensor calibration. A soil sample in a solid container was allowed to air dry for several weeks. A second container with a hole at the bottom for drainage was filled with soil and water and was manually mixed until water began to drain from the container’s bottom. The soil sample was considered to reach its maximum moisture capacity when free drainage of water from the container ceased. The sensor was placed in the dry sample. A button on the breadboard was pressed. The button sent a signal to the Arduino to take a reading from the sensor. This reading was the dry soil calibration point. The sensor was then put into the wet sample and the same button pressed again. This second moisture reading was recorded as the saturated soil calibration point. At this point the Arduino was fully calibrated and assigned a value of 0 to the dry sample and a value of 100 to the wet sample to report the soil moisture level on a 0-100 scale. The digital value of the dry sample is reported as 0 while the saturated condition typically results in a digital value of 700-900, depending on soil type. If the soil is oversaturated, i.e. if the amount of water in the soil exceeds the field capacity of the soil, the sensor will report a moisture value over 100. Local air temperature data was simultaneously collected using a K-type thermocouple. The signal that the thermocouple generated was too low for the Arduino to measure. For this reason a breakout amplifier (MAX31855) was used to boost the signal to a 0-5V range [11]. The collected temperature data was saved to the system’s SD card. Agricultural University of Iceland — Irrigation and Data Collection System An irrigation system was installed for the heated gardens at Reykir. Holes were drilled at25 cm intervals through the treated wood bed separators that ran parallel to the greenhouse. All of the holes were drilled at soil surface level to enable an unimpeded water flow. A 100-meter coiled Porous Pipe was pulled straight and weaved through the holes. The porous pipe had a 13 mm inner diameter and an 18mm outer diameter. It had an operating pressure of 0.25 to 3 Bar and releases water at a rate between 2 and 4 liters/hour. The pipe is operable 10 to 15 cm underneath the soil. The pipe used ½” or 16 mm sized hose fittings. Figure 3. Plan of Agriculture University of Iceland (Peter Ascoli). 119 Foley, et al. Figure 3 is a plan view of the Agricultural University gardens. The black line represents the irrigation hose locations. The colored dots represent the plants and where they were located in the garden. The eight beds in the top half of the image are the heated beds and the bottom eight are the control unheated beds. Figure 5 shows a photo of the complete installation of the irrigation lines. The figure shows the hose laid in straight runs throughthe holes drilled in the wooden frames and bent wire anchors fixed the lines in place. Municipal water flows through the irrigation system of the garden. A PRA/PB.1390 Ribiland Digital Water Timer [12] was installed inthe water supply line inside the adjoining greenhouse. The outlet of the timer connected to the garden irrigation system through a garden hose which extended from the greenhouse through a pipe buried beneath the soil which enters the garden. This pipe also encases the source and return for the garden hot water. Figure 5 shows the entire garden with plants placed in each bed with the irrigation pipe fully installed. The plants are located between irrigation lines. A dry and a wet soil samples were prepared for moisture sensor calibration. The control system was kept in the greenhouse in a sealed container to keep moisture from damaging the electronics. The moisture sensor was calibrated in the garden. The wires for the sensor were passed through the underground pipe. The sensor was Figure 4. Porous Irrigation Pipe Layout. Pipe Position Fixed by Wooden Frames. attached to the wires running between the greenhouse and the garden and monitors the moisture in bed 7, shown in Figure 6. A solar panel was also brought to Iceland to charge the system’s Figure 5. View of Agricultural University Garden with Complete Irrigation Installation and Plant Placement. Figure 6. Moisture Sensor in Bed 7. batteries. The near constant cloud cover during the summer of 2014, reduced the solar panel’s usefulness and reliability. Icelandic Automated Irrigation System Results Figure 7. Control System Container. The author’s automated irrigation system at the Agricultural University of Iceland collected moisture data beginning in the summer of 2014. The water control system was placed inside the greenhouse while the moisture sensor was placed in bed 7. The Arduino microcontroller and breadboard were kept in a sealed plastic container shown in Figure 7. 120 Foley, et al. The container is used to protect the device from environmental damage. Figure 8 shows the moisture data collected from June 27th through July 12th. A one minute sampling rate was set for this trial. At the beginning of the test the moisture level of the bed is at about 85. The peaks in level indicate rainfall. The dips show periods where itdid not rain and moisture from the soil evaporated. During the summer of 2014, south of Iceland experienced frequent rainfall. The moisture data collected reflects the recurrent rain since the moisture level in the soil ranged between 85-100% over the time data was collected. The code used for the Icelandic data collection did not implement a moving average for the moisture data. A moving average for the th moisture data was implemented in Figure 8. Moisture Sensor Test with Moving Average, June 27th – July 12 . the code after the authors had left Iceland. As a result there is signal noise associated with the raw data. A 20-point moving average was superimposed over the raw data in Microsoft Excel. The moving average cuts the noise to show a more accurate representation of the moisture level in the soil. The control system was powered using a standard 5V wall plug-in power adaptor. According to the Arduino Uno specifications, the board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. This low supply voltage may have also contributed to the noise in the data recorded by the moisture sensor. [13]. A thermoelectric generator [14] [15] [14] [16], developed and patented by Professor Dell, C.S. Wei and George Sidebotham, is a reliable source of power for the controller because it powered by the constant and stable supply of waste heat from a geothermal steam pipe to generate electricity. The generator has been field tested at the Agricultural University of Iceland greenhouse situated adjacent to the heated garden. It was installed inside the greenhouse on an exposed steam pipe carrying 100°C steam. The generator was wired to an LED array to demonstrate the electricity generated by the device. Figure 9 shows the Icelandic installation. The thermoelectric generator has been successfully used to recharge batteries [15], power web cams [14], power wireless communication systems, and power a Tekkotsu Calliope2SP robot at CIAT [15]. The thermoelectric generator at CIAT was used to test charge the irrigation system battery and to simulate the use of waste geothermal heat from an exposed Figure 9. Thermoelectric Generator Installation at the Agricultural University of Iceland [16]. 121 Foley, et al. steam pipe as the power source. Another generator has been successfully operating at the Keilir Institute of Technology at Reykjanesbær, Iceland for three years. The thermoelectric generator is a reliable means of providing power to the automated irrigation system and achieves a fully sustainable and self-regulating system. A generator mounted on a steam pipe at the Agricultural University can charge batteries and power the system at all times. Use of the generator also eliminated to challenges presented by the solar panel. Discussions and Conclusions The automated irrigation system was constructed and designed by the authors to monitor and control moisture levels in the heated gardens. The system has recorded moisture data and us capable of opening or closing a water solenoid valve when the soil reaches a preset lower moisture level. The irrigation system was installed and tested at the Agricultural University of Iceland. The automated irrigation system contributes to the overall autonomy and economy of the geothermal heated garden systems and the heated green roofs. The system regulates the moisture level of the growth media or soil which provides water for plants and aids in cooling the waste hot water. The automated irrigation system functions without human involvement, which brings the heated garden system closer to autonomous operation. The heated gardens can be monitored and watered all year round and is not dependent on people to open the water line. The thermoelectric generator allows it to be independent of the electrical grid and provides a sustainable means to continuously power the system. The irrigation system is completely independent of human control, the electrical power grid, and weather conditions that would render alternatives such as wind and solar unusable. Heated ground dries up faster than unheated ground. This can result in lower growth rates, lower yields and plant in the heated ground. Summers with light rainfall in Iceland will cause a drought condition in the heated portion of the garden. The automated irrigation system monitors and records soil moisture levels -year round and can irrigate the entire garden thereby increasing its viability and sustainability. Acknowledgements The authors acknowledge the support extended by the following organizations: The Cooper Union for the Advancement of Science and Art, Center for Innovation and Applied Technology, The C.V. Starr Research Foundation, Agricultural University of Iceland, University of Iceland, Keilir Institute of Technology, Hveragerdi, Garðheimar Gróðurvörur ehf, Hveragerdi, Town of Reykjanesbaer, C.V. Starr Research Foundation, SET ehf, Reykjanesbaer and Metropolitan Building Consulting Group. Special thanks to Teresa Dahlberg, George Delagrammatikas, Yash Risbud, Mark Epstien, Bill King, Robert Hawks, Gudridur Helgadottir, Sverrir Gudmundsson, Elias Oskarsson, Borkur Blondal, Orn Einarsson, Stefan Sigurdsson, Gísli Páll Pálsson, Tryggvi Thordarson, Odinn Bolli Bjorgvinsson, Haukur Ingi Jonasson, Ólafur Sigurðsson, Haraldur Erlendsson, Halldor Bl. Hrafnkelsson, Courtland Hui, and Gloria and James Foley. The authors appreciate the contributions of Center for Innovation and Applied Technology and Laboratory for Energy Reclamation and Innovation Research Assistants: Gisel Orizondo, Rose Carla Guerrier, Nicolas Mitchell, Peter Ascoli, Judy Wu, Mimosa Miller, Malcolm Dell, Russel Sternlicht, Jay Dalal. References [1] R. Dell, R. Unnthorsson, C. Wei and W. Foley, “Enhanced Agricultural Production from an Intensive Bottom Heat System Using Waste Geothermal Hot Water and Steam Condensate in Iceland,” in Geothermal Resources Council, 2014. [2] R. Dell, R. Unnthorsson, C. Wei and W. Foley, “Repurposing Waste Steam and Hot Water to Accelerate Plant Growth in Heated Green Roofs,” in ASME International Mechanical Engineering Congress & Exposition, San Diego, California, 2013. [3] R. Dell, R. Unnthorsson, C. Wei and W. Foley, “Waste Geothermal Hot Water for Enhanced Outdoor Agricultural Production,” in ASME Power , Boston, Mass., 2013. [4] R. Dell, C. Wei, R. Parikh, R. Unnthorsson and W. 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Unnthorsson, “A Thermoelectric-Based Point of Use Power Generator for Steam Pipes,” in Geothermal Resource Council, San Diego, California, 2011. 123 124