Collaboration for AquaponicsSustainable EnergyA Low Carbon Emitting Energy Source for Urban AquaponicsSystemsTeam Members:Chris ChapmanBrandon JacksonDaniel NeumannBen SteffesNate WeberAdvisor:Dr. Chris DammSubmitted:5/18/12MILWAUKEE SCHOOL OF ENGINEERING – ME 492DESIGN REPORT
Page 2EXECUTIVE SUMMARYAquaponics is a new and emerging practice which joins agriculture and aquaculture. Although there arefunctioning systems in existence, the fact that aquaponics is so new has left the optimization of theoperation overlooked. Through this analysis, a best practices manual will be developed and help makeaquaponics an efficient and more sustainable process. The best practices manual will help to determinean efficient way to power varying sizes of aquaponics operations and provide an engineered approachtowards making the system cost effective and environmentally responsible.Aquaponics systems are cyclic in nature where fish effluent provides nourishment to plant life while theplant life, in return, filters toxic fish waste from the fish tank water. Background information is providedto show advantages of aquaponics over more traditional methods of farming as well as the primarytypes of aquaponics systems in use. Important aquaponics design parameters used in this proposal arehydraulic 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 pumpand aerate the water. All of the aquaponics systems studied utilized an elevation difference betweeneach component of the system thus requiring a pump. Water aeration is essential to achieving high fishstocking densities and also functions to keep nutrients suspended in the water. Artificial lighting powerestimates 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 toimplement and therefore is considered.An interactive Excel spreadsheet where a user can input design parameters was created. The user canutilize this tool to estimate pumping, aerating, and artificial lighting power requirements as the scalechanges. A publication by the University of the Virgin Islands (UVI) provided a representative aquaponicssystem 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 inthe design and construction of other aquaponics systems.Power calculations made with the interactive Excel spreadsheet were verified by the values quoted bythe UVI system. Pumping resulted in a power requirement of ½ Hp which was exactly what was specifiedby 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 toachieve 18 hours of grow time per day throughout the year in Milwaukee, WI. The artificial lightingenergy 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 sourcesatisfies two different power requirements. In the design presented in this paper, natural gas will satisfyboth heat and power requirements for an aquaponics system. This is known as combined heat andpower (CHP). The generator will provide electrical power for water aeration, circulation, and artificiallighting. The thermal capacity of the CHP system will be used to maintain tank temperatures atapproximately 80 F year round. The benefit of using cogeneration for this application, when properly
Page 3sized 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 loweroperating expenses.To quantify thermal demand on the CHP system from the aquaponics pond, a comprehensive thermalmodel was developed. Primary sources of heat transfer were identified, they include: conduction intothe ground, evaporation, convection, and grow bed losses. Radiative heat transfer was determined to bean insignificant source of thermal gains/losses and was thus not included in the developed thermalmodel. Convection estimates from the side of the tank were based of empirical equations developedfrom flat plate analyses. Surface evaporation was determined from an empirical model designed toestimate evaporation from indoor swimming pools, while surface convection was determined from anenergy loss ratio developed by I.S. Bowen.Due to the high uncertainty inherently present in the thermal modeling, an investigative study wasconducted to measure the accuracy of the model. This experiment was conducted in the PsychrometricChamber installed in the Johnson Controls Laboratory at the Milwaukee School of Engineering. Resultsfrom this study yielded excellent correlation between the measured and predicted heat transfer for allmechanisms of losses studied. Based on this successful verification, the thermal model developed wasused to create the load profile for the aquaponics pond, which was used to both size the CHP systemand 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 heatexchangers to recover thermal energy.2. Use commercially available CHP generator set to provide electricity for pumps and lighting andhot water for the aquaponics tank.Complications were found when considering both design options. Using a natural gas engine led toproblems with supplying power to artificial lighting, adapting to multiple tank systems, addinglubrication to two-stroke engines, efficient heat recovery, safety issues, and space demands. An issuethat 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 atpower factor of 0.98 that is single phase 240 V at 60 Hz. The maintenance cycle allows for 4000 hours ofcontinuous use (166 days) before an oil change is required. The system is only 25% efficient atgenerating electricity; however, the combined efficiency of the ecopower system is 90%. An additionalbenefit to the Marathon CHP system is that it has a built-in controller that allows for thermal loadfollowing; therefore, the system can adapt changing thermal demands by varying engine operationconditions.The ecopower system is already equipped with all necessary heat exchangers; as a result it only becamenecessary to design a heat exchanger for the aquaponics tank. Both metals and non-metallic materials
Page 4were considered for the heat exchanger design. Ultimately, 2205 Duplex stainless steel was selected asthe build material due to its low environmental impact. The design heat exchangers were sized todeliver 12.5 kW into the aquaponics pond through lengths of submerged piping. A mixture of Propyleneglycol 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 systemconfigured to meet the energy demands of an aquaponics system. Additionally, the design process wasdetailed in a report to guide CHP design and improve energy efficiency for different size aquaponicssystems. Software was developed to complement the detailed design report which can be used forparametric studies.
Page 5TABLE OF CONTENTSExecutive Summary. 2Table of Figures . 7List of Tables . 81Project Statement . 92Design Specifications . 93Background . 103.1Background Research. 103.1.1Urban Aquaponics . 103.1.2Combined Heat and Power Cogeneration . 123.2Conceptual Designs . 22.214.171.1245Alternative Design Option . 15Initial Feasibility . 163.3.1Initial Economic Feasibility . 163.3.2Initial Technical Feasibility . 18Detailed Design . 184.1CHP Generator Set . 204.2Heat Exchanger . 21Thermal Load Modeling and Validation . 265.1Aquaponics Thermal Modeling . 275.1.1Wall Convection . 275.1.2Surface Evaporation . 305.1.3Surface Convection . 325.1.4Base Conduction . 335.1.5Hydroponic Tank Losses . 335.1.6Effects of Pumping and Aeration on Thermal Energy . 345.1.7Radiation . 345.1.8MATLAB Modeling . 355.2Thermal Model Validation . 355.2.1Methodology . 355.2.2Results . 37
Page 65.2.3Validation Results Summary . 415.3Monthly Load Profile Prediction . 415.4Greenhouse Modeling . 436Non-Thermal Loading. 446.1Commercial Scale Raft Aquaponics System . 456.2Pumping Power Calculations . 476.3Tilapia Intensive Stocking Aeration Power Requirements . 496.4Artificial Lighting Power Estimation . 526.5Key Results . 547Combined Models and Tank Design . 548Environmental Impact. 558.1Greenhouse Gas Emissions . 558.2Hazardous Chemicals . 578.3Safety Guidelines . 589Detailed Economic Considerations . 589.1Federal and State Incentives for CHP Systems . 599.2Energy Improvement and Extensions Act . 609.3Budget . 6010Software Development . 6110.1Operation Instructions . 6110.2Sample. 6911Conclusion . 75References . 75Appendix A: Cited Email Correspondences. 80Appendix B: RETScreen . 85Appendix C: Material Safety Data Sheets . 89
Page 7TABLE OF FIGURESFigure 1: Schematic of Potential System . 14Figure 2: Solar Pool Heating System (Adapted from ) . 15Figure 3: Percentage of Total Thermal Energy Recovered . 19Figure 4: General schematic For Generator System with Net MeTering and Transfer Switch . 21Figure 5: Schematic of CHP System Incorporated Into Proposed Aquaponics Operation. 24Figure 6: Exhaust Gas Heat Exchanger Performance Table from Bowman  . 25Figure 7: Second Heat Exchanger Setup . 26Figure 8: Tank Heat Transfer Diagram . 27Figure 9: Cross Section of Tank Wall . 29Figure 10: Effects of Evaporation on Mean Molecular Kinetic Energy . 30Figure 11: Fish Tank Setup for Psychrometric Testing . 36Figure 12: Comparison of Predicted Evaporative Losses for Tank based on R.V. Dunkle and W.H. CarrierModels. . 38Figure 13: System Temperature (Top), Relative Humidity (Middle) and Heater Input Power (Bottom) forPsychrometric Testing Experiment (Trial 2). . 39Figure 14: Comparison of Predicted and Actual Thermal Losses for Tank Model (Utilizing W.H. CarrierEvaporation Model) . 40Figure 15: Prediction of Tank Wall Temperature based on Thermal Wall Convection Model. . 40Figure 16: Graphical User Interface for Aquaponics Monthly Load Profile Program . 42Figure 17: Thermal Losses by Source Obtained from Monthly Load Profile Program . 42Figure 18: Annual Profile for Greenhouse Heating from Modified Plan M-6701 . 44Figure 19 UVI System Schematic Layout  . 45Figure 20: Aquaponics Plumbing Schematic . 47Figure 21: Energy Requirement per Month to Implement 18 Hours of Daylight for a 1 kW Lighting System. 53Figure 22: Grow Light Recommended Coverage Area and Mounting Height  . 53Figure 23: Distribution of Thermal Losses for Aquaponics System . 55Figure 24: Software Title Screen . 69Figure 25: Software Inputs . 70Figure 26: Software Environment Inputs . 71Figure 27: Monthly Humidity and Temperature Profile . 72Figure 28: Sample of Software Outputs (Page 1) . 73Figure 29: Sample of Software Outputs (Page 2) .