Collaboration for Aquaponics Sustainable Energy A Low Carbon Emitting Energy Source for Urban Aquaponics Systems Team Members: Chris Chapman Brandon Jackson Daniel Neumann Ben Steffes Nate Weber Advisor: Dr. Chris Damm Submitted: 5/18/12 MILWAUKEE SCHOOL OF ENGINEERING – ME 492 DESIGN REPORT P age | 1 P age | 2 EXECUTIVE SUMMARY Aquaponics is a new and emerging practice which joins agriculture and aquaculture. Although there are functioning systems in existence, the fact that aquaponics is so new has left the optimization of the operation overlooked. Through this analysis, a best practices manual will be developed and help make aquaponics an efficient and more sustainable process. The best practices manual will help to determine an efficient way to power varying sizes of aquaponics operations and provide an engineered approach towards making the system cost effective and environmentally responsible. Aquaponics systems are cyclic in nature where fish effluent provides nourishment to plant life while the plant life, in return, filters toxic fish waste from the fish tank water. Background information is provided to show advantages of aquaponics over more traditional methods of farming as well as the primary types of aquaponics systems in use. Important aquaponics design parameters used in this proposal are hydraulic loading rate, hydraulic retention time, fish tank size, grow bed area and water flow rates. Mechanical power requirements of an aquaponics system are primarily due to the needs to both pump and aerate the water. All of the aquaponics systems studied utilized an elevation difference between each component of the system thus requiring a pump. Water aeration is essential to achieving high fish stocking densities and also functions to keep nutrients suspended in the water. Artificial lighting power estimates are also given for supplemental lighting needed for an 18 hour grow period in a greenhouse. Although artificial lighting is not required for aquaponics, it is an option that farmers have chosen to implement and therefore is considered. An interactive Excel spreadsheet where a user can input design parameters was created. The user can utilize this tool to estimate pumping, aerating, and artificial lighting power requirements as the scale changes. A publication by the University of the Virgin Islands (UVI) provided a representative aquaponics system that was studied in order to obtain key proportioning constants that facilitate scaling of systems. The system proposed by the University of the Virgin Islands can be used as an effective starting point in the design and construction of other aquaponics systems. Power calculations made with the interactive Excel spreadsheet were verified by the values quoted by the UVI system. Pumping resulted in a power requirement of ½ Hp which was exactly what was specified by UVI. Aeration was 1.1 Hp which is 26% lower than the UVI system. An estimated 51.9 MWh would be required to run artificial lighting to supplement sunlight in order to achieve 18 hours of grow time per day throughout the year in Milwaukee, WI. The artificial lighting energy takes into account the changes of the daily natural sunlight available through year. The proposed energy system for aquaponics is cogeneration. Cogeneration is when one fuel source satisfies two different power requirements. In the design presented in this paper, natural gas will satisfy both heat and power requirements for an aquaponics system. This is known as combined heat and power (CHP). The generator will provide electrical power for water aeration, circulation, and artificial lighting. The thermal capacity of the CHP system will be used to maintain tank temperatures at approximately 80°F year round. The benefit of using cogeneration for this application, when properly P age | 3 sized for the thermal load, is an overall efficiency as high as 90% compared to an efficiency of 35%-40% for coal-fired power plants. This results in a reduction of greenhouse gas emissions along with lower operating expenses. To quantify thermal demand on the CHP system from the aquaponics pond, a comprehensive thermal model was developed. Primary sources of heat transfer were identified, they include: conduction into the ground, evaporation, convection, and grow bed losses. Radiative heat transfer was determined to be an insignificant source of thermal gains/losses and was thus not included in the developed thermal model. Convection estimates from the side of the tank were based of empirical equations developed from flat plate analyses. Surface evaporation was determined from an empirical model designed to estimate evaporation from indoor swimming pools, while surface convection was determined from an energy loss ratio developed by I.S. Bowen. Due to the high uncertainty inherently present in the thermal modeling, an investigative study was conducted to measure the accuracy of the model. This experiment was conducted in the Psychrometric Chamber installed in the Johnson Controls Laboratory at the Milwaukee School of Engineering. Results from this study yielded excellent correlation between the measured and predicted heat transfer for all mechanisms of losses studied. Based on this successful verification, the thermal model developed was used to create the load profile for the aquaponics pond, which was used to both size the CHP system and develop an economic model. Two main design approaches were considered for a CHP energy solution and are listed as follows. 1. Use a natural gas engine to supply mechanical demands for pumps and integrate heat exchangers to recover thermal energy. 2. Use commercially available CHP generator set to provide electricity for pumps and lighting and hot water for the aquaponics tank. Complications were found when considering both design options. Using a natural gas engine led to problems with supplying power to artificial lighting, adapting to multiple tank systems, adding lubrication to two-stroke engines, efficient heat recovery, safety issues, and space demands. An issue that was common between the two design options was short maintenance cycles due to continuous use. A solution found which resolves the aforementioned complications is the Marathon Engine System’s ‘ecopower’. The ecopower system is a CHP system that provides 2.0 – 4.7 kW of electrical power at power factor of 0.98 that is single phase 240 V at 60 Hz. The maintenance cycle allows for 4000 hours of continuous use (166 days) before an oil change is required. The system is only 25% efficient at generating electricity; however, the combined efficiency of the ecopower system is 90%. An additional benefit to the Marathon CHP system is that it has a built-in controller that allows for thermal load following; therefore, the system can adapt changing thermal demands by varying engine operation conditions. The ecopower system is already equipped with all necessary heat exchangers; as a result it only became necessary to design a heat exchanger for the aquaponics tank. Both metals and non-metallic materials P age | 4 were considered for the heat exchanger design. Ultimately, 2205 Duplex stainless steel was selected as the build material due to its low environmental impact. The design heat exchangers were sized to deliver 12.5 kW into the aquaponics pond through lengths of submerged piping. A mixture of Propylene glycol and water was selected as the heat exchanger transfer fluid due its nontoxic nature. The outcomes of this senior design project were to develop a combined heat and power system configured to meet the energy demands of an aquaponics system. Additionally, the design process was detailed in a report to guide CHP design and improve energy efficiency for different size aquaponics systems. Software was developed to complement the detailed design report which can be used for parametric studies. P age | 5 TABLE OF CONTENTS Executive Summary ....................................................................................................................................... 2 Table of Figures ............................................................................................................................................. 7 List of Tables ................................................................................................................................................. 8 1 Project Statement ................................................................................................................................. 9 2 Design Specifications ............................................................................................................................ 9 3 Background ......................................................................................................................................... 10 3.1 Background Research .................................................................................................................. 10 3.1.1 Urban Aquaponics ............................................................................................................... 10 3.1.2 Combined Heat and Power Cogeneration .......................................................................... 12 3.2 Conceptual Designs ..................................................................................................................... 13 3.2.1 Alternative Design Option ................................................................................................... 15 3.3 Initial Feasibility .......................................................................................................................... 16 3.3.1 Initial Economic Feasibility .................................................................................................. 16 3.3.2 Initial Technical Feasibility .................................................................................................. 18 4 Detailed Design ................................................................................................................................... 18 4.1 CHP Generator Set ...................................................................................................................... 20 4.2 Heat Exchanger ........................................................................................................................... 21 5 Thermal Load Modeling and Validation .............................................................................................. 26 5.1 Aquaponics Thermal Modeling ................................................................................................... 27 5.1.1 Wall Convection .................................................................................................................. 27 5.1.2 Surface Evaporation ............................................................................................................ 30 5.1.3 Surface Convection ............................................................................................................. 32 5.1.4 Base Conduction ................................................................................................................. 33 5.1.5 Hydroponic Tank Losses ...................................................................................................... 33 5.1.6 Effects of Pumping and Aeration on Thermal Energy ......................................................... 34 5.1.7 Radiation ............................................................................................................................. 34 5.1.8 MATLAB Modeling .............................................................................................................. 35 5.2 Thermal Model Validation .......................................................................................................... 35 5.2.1 Methodology ....................................................................................................................... 35 5.2.2 Results ................................................................................................................................. 37 P age | 6 5.2.3 Validation Results Summary ............................................................................................... 41 5.3 Monthly Load Profile Prediction ................................................................................................. 41 5.4 Greenhouse Modeling ................................................................................................................ 43 6 Non-Thermal Loading.......................................................................................................................... 44 6.1 Commercial Scale Raft Aquaponics System ................................................................................ 45 6.2 Pumping Power Calculations ...................................................................................................... 47 6.3 Tilapia Intensive Stocking Aeration Power Requirements .......................................................... 49 6.4 Artificial Lighting Power Estimation ............................................................................................ 52 6.5 Key Results .................................................................................................................................. 54 7 Combined Models and Tank Design ................................................................................................... 54 8 Environmental Impact ......................................................................................................................... 55 8.1 Greenhouse Gas Emissions ......................................................................................................... 55 8.2 Hazardous Chemicals .................................................................................................................. 57 8.3 Safety Guidelines ........................................................................................................................ 58 9 Detailed Economic Considerations ..................................................................................................... 58 9.1 Federal and State Incentives for CHP Systems ........................................................................... 59 9.2 Energy Improvement and Extensions Act ................................................................................... 60 9.3 Budget ......................................................................................................................................... 60 10 Software Development ................................................................................................................... 61 10.1 Operation Instructions ................................................................................................................ 61 10.2 Sample ......................................................................................................................................... 69 11 Conclusion ....................................................................................................................................... 75 References .................................................................................................................................................. 75 Appendix A: Cited Email Correspondences ................................................................................................. 80 Appendix B: RETScreen ............................................................................................................................... 85 Appendix C: Material Safety Data Sheets ................................................................................................... 89 P age | 7 TABLE OF FIGURES Figure 1: Schematic of Potential System .................................................................................................... 14 Figure 2: Solar Pool Heating System (Adapted from [11]) .......................................................................... 15 Figure 3: Percentage of Total Thermal Energy Recovered ......................................................................... 19 Figure 4: General schematic For Generator System with Net MeTering and Transfer Switch ................... 21 Figure 5: Schematic of CHP System Incorporated Into Proposed Aquaponics Operation.......................... 24 Figure 6: Exhaust Gas Heat Exchanger Performance Table from Bowman [23] ......................................... 25 Figure 7: Second Heat Exchanger Setup ..................................................................................................... 26 Figure 8: Tank Heat Transfer Diagram ........................................................................................................ 27 Figure 9: Cross Section of Tank Wall ........................................................................................................... 29 Figure 10: Effects of Evaporation on Mean Molecular Kinetic Energy ....................................................... 30 Figure 11: Fish Tank Setup for Psychrometric Testing ................................................................................ 36 Figure 12: Comparison of Predicted Evaporative Losses for Tank based on R.V. Dunkle and W.H. Carrier Models. ....................................................................................................................................................... 38 Figure 13: System Temperature (Top), Relative Humidity (Middle) and Heater Input Power (Bottom) for Psychrometric Testing Experiment (Trial 2). ............................................................................................... 39 Figure 14: Comparison of Predicted and Actual Thermal Losses for Tank Model (Utilizing W.H. Carrier Evaporation Model) .................................................................................................................................... 40 Figure 15: Prediction of Tank Wall Temperature based on Thermal Wall Convection Model. .................. 40 Figure 16: Graphical User Interface for Aquaponics Monthly Load Profile Program ................................. 42 Figure 17: Thermal Losses by Source Obtained from Monthly Load Profile Program ............................... 42 Figure 18: Annual Profile for Greenhouse Heating from Modified Plan M-6701 ....................................... 44 Figure 19 UVI System Schematic Layout [35] ............................................................................................. 45 Figure 20: Aquaponics Plumbing Schematic ............................................................................................... 47 Figure 21: Energy Requirement per Month to Implement 18 Hours of Daylight for a 1 kW Lighting System .................................................................................................................................................................... 53 Figure 22: Grow Light Recommended Coverage Area and Mounting Height [42] ..................................... 53 Figure 23: Distribution of Thermal Losses for Aquaponics System ............................................................ 55 Figure 24: Software Title Screen ................................................................................................................. 69 Figure 25: Software Inputs .......................................................................................................................... 70 Figure 26: Software Environment Inputs .................................................................................................... 71 Figure 27: Monthly Humidity and Temperature Profile ............................................................................. 72 Figure 28: Sample of Software Outputs (Page 1) ........................................................................................ 73 Figure 29: Sample of Software Outputs (Page 2) ........................................................................................ 74 Figure 30: Sample Outputs when THermal Load Matches Capacity ........................................................... 75 P age | 8 LIST OF TABLES Table I: Comparison of Various Forms of Food Production (Adapted from [3]) ......................................... 11 Table II: Input Variables for Economic Model [13][14][15] ........................................................................ 17 Table III: Calculated Values for Preliminary Economic Analysis ................................................................. 17 Table IV: Heat Recovered from MSOE CHP System .................................................................................... 19 Table V: Marathon Ecopower MicroCHP System ....................................................................................... 22 Table VI: Glycol Comparison Adapted from [20] ........................................................................................ 25 Table VII: Definitions of Symbols Present in Side Convection Thermal Model [27] ................................... 29 Table VIII: Evaporative Constants for R.V. Dunkle Model Defined [29] ...................................................... 31 Table IX: Evaporative Constants for W.H. Carrier Model Defined .............................................................. 32 Table X: Testing Environment for Psychrometric Experiment .................................................................... 37 Table XI: Definition of Symbols Presented in Greenhouse Heating Equation ............................................ 43 Table XII: Physical Dimensions of the UVI Raft Aquaponics System [35] ................................................... 46 Table XIII: Calculating the Effective Loss Coefficient Using the Equivalent Pipe Length [39] ..................... 49 Table XIV: Summary of Power Requirements of the UVI Commercial Raft Type Aquaponics System ....... 54 Table XV: System Properties Utilized in Energy System Sizing ................................................................... 54 Table XVI: Thermal Losses for Aquaponics System ..................................................................................... 55 Table XVII: Electricity Generation Sources .................................................................................................. 56 Table XVIII: CO Emissions Based on Fuel and Source [45] ......................................................................... 56 2 Table XIX: CO Emissions for Electricity Production ( [43] and [44])........................................................... 57 2 Table XX: Natural Gas Water Heater Emissions and Efficiency [46] ........................................................... 57 Table XXI: Monthly Thermal Load Requirements as a Percentage of the Maximum ................................. 59 Table XXII: Projected Labor Costs ............................................................................................................... 60 Table XXIII: Projected Overhead Costs ........................................................................................................ 60 Table XXIV: Budget Totals ........................................................................................................................... 61 P age | 9 1 PROJECT STATEMENT Aquaponics is a new and emerging practice which joins agriculture and aquaculture. Although there are functioning systems in existence, the fact that aquaponics is so new has left the optimization of the operation largely overlooked. Additionally, the recent interest in green energy makes an engineered energy solution all the more vital. Through this analysis, a best practices manual will be developed to help make aquaponics an efficient and more sustainable process. The best practices manual will help to determine an efficient way to power varying sizes of aquaponics operations and provide an engineered approach towards making the system cost-effective and environmentally responsible. Although the best practices manual will be the main outcome of the project, the general goal is to power an aquaponics system through the conversion of rejected biomass into heat, electricity and compressed air. The designed system will reduce the carbon footprint of green urban farming and lower operating expenses. 2 DESIGN SPECIFICATIONS The overall project goals are:  To develop a thermal model of an aquaponics system and greenhouse  To determine the electrical and/or mechanical needs of an aquaponics system  To develop an economic model for a combined heat and power (CHP) system  To quantify the environmental benefit of incorporating a CHP system  To develop a best practices manual based on thermal, electrical, and mechanical needs  To create software which allows users to calculate a best practice approach In order to develop a best practices guide for an aquaponics energy system, goals and constraints must be set in order to focus the effort. The goals and constraints for both the aquaponics system and the energy system are outlined as follows. Aquaponics:  Maintain fish tank temperature between 75-85°F  Greenhouse environment between 45-60% relative humidity and 55-85°F  Consider both natural and artificial lighting for best practices simulation  Fish tank size constrained between 1,000-20,000 gallons  Aquaponics system located in a greenhouse or indoor factory space Power Production:  Less CO emissions than those required for independent generation using Milwaukee area 2 emission factors  Meet environmental standards for noise and ventilation  Provide power to aerate, heat, and pump tank water  Provide power to artificial lighting  Least environmental impact with consideration of costs  Minimize initial expense