proceedingsedge.rit.edu/content/p17420/public/final documents/p17420... · web viewbased on our...

Multidisciplinary Senior Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: P17420

COMPOST BASED GREENHOUSE HEATING SYSTEM

Brett KajganichIndustrial Engineering

Fintan McManusElectrical Engineering

Devash DedhiaMechanical Engineering

Carson PrattElectrical Engineering

Neil AsraniMechanical Engineering

Siddharth KiniMechanical Engineering

ABSTRACT Our project presented the challenge of heating a greenhouse, so that it is capable of producing crops, such as kale, during the winter months. The project was presented to RIT by a non-profit organization called Seedfolk. Our goal was to accomplish this using a compost pile as the primary heat source. Much research was done on this topic to determine the best compost ratio, and pile size, that would be needed to accomplish adequate heat. The next challenge was determining how to transfer the heat generated from the pile to the soil beds. After much discussion, research, and analysis, it was determined that the best way to do this was a closed loop, hydronic system that involved a storage tank and two circulating pumps. In addition, temperature and humidity need to be monitored and regulated, so sensors had to be installed and programmed to give usable data. This way, our customers could use the information to make any necessary adjustments to the circulating pumps or the aeration fan, so as not to “kill the pile” (have it stop producing heat) before the end of winter. In terms of the size of the storage tank and the amount of heat that needed to be generated, the worst-case scenario of the coldest possible week of the winter was taken into account and used as the basis for the heat generation requirement. In this way, we hope to mitigate being surprised by a cold snap that is likely to happen during the winter. We were able to produce a compost pile that generated temperatures of up to 140 degrees Fahrenheit. Time will tell if the system holds out throughout the winter.

NOMENCLATURETMY3 meteorological chart - _____________NEMA 4 - ________________

INTRODUCTION (BACKGROUND)Currently, Rochester, NY is ranked the 5th poorest city in the country with approximately 135,000 residents struggling with food insecurity. As a result, issues of food access and education are critically important to Seedfolk. In order to bridge the disconnect between the lack of food access in the city with those who need it most, Seedfolk believes that our communities must transform the way they relate to the food that they eat. Therefore, the desire for a four-season greenhouse was born.

Copyright © 2017 Rochester Institute of Technology

Proceedings of the Multidisciplinary Senior Design Conference

Seedfolk City Farm has a 24’x24’ greenhouse at The Gandhi Institute, located on South Plymouth Avenue. They grow a number of different vegetables, and provide educational opportunities for children in the neighborhood to learn about leadership and farming. Presently, however, the farm is not optimized for use during the winter months. The main reasons for this have been the challenges in designing a system that can heat the greenhouse throughout the harsh Rochester winters without taxing the electrical grid too severely, if at all, and a relatively low operational budget. However, the ultimate goal of Seedfolk, and our project, is to have a greenhouse that is operational year round.

Some of the other attributes that Seedfolk would like to see accomplished include: providing a heating system that utilizes bio-thermal heat, specifically compost in this instance a system that is easily regulated (temperature and humidity) and needs minimal follow-up/maintenance

once put into placeA system with these characteristics would provide children in the Seedfolk program a great opportunity to learn

about indoor growing, and what is required to grow crops year-round successfully. The engineering methods used to arrive at the final design are detailed in the sections that follow, as well as details of the features and capabilities of the final design. The funding for this project was provided by ASHRAE, and was a budget of just under $5,000. The big ticket items for this project was the compost pile, which totaled around $1,000, and the circulating pumps/tank, which also totaled in at around $1,000.

METHODOLOGY The chart below shows the elements of the planned system at a high level:

The main purpose of this project is to maintain the greenhouse space at a certain temperature so that crops such as kale could grow during the winter months. Additionally, the “greenhouse space” includes the soil-beds where the crops are being grown as well as the ambient air temperature inside the greenhouse. Through research, we found that the optimum soil temperature for kale seeds to germinate is between 45 °F and 75 °F. To accomplish the task of maintaining the soil between this temperature range, we have four subsystems in place for this project.

The first subsystem is the compost pile, which is the thermal energy source for our greenhouse heating system. The second subsystem includes a hydronic piping system that ensures efficient heat recovery from the compost pile, which generates the thermal energy. The third subsystem is the storage tank which acts as the intermediate storage mechanism for our working fluid for heat transfer, which is water. Lastly, the fourth subsystem includes a piping mechanism for the soil-beds, which is where the crops are being grown. This mechanism acts as the heat distribution system in the overall system design and is ultimately what will keep the greenhouse at an optimal growing temperature.

NOTE: Near the end of this 28 week effort, due to time constraints, it was decided to focus on heating the air inside the greenhouse, and not the soil. The capability to heat the soil beds will be added at a later date.


Proceedings of the Multi-Disciplinary Senior Design Conference

Prototype System:Since the team of students doing this project did not come into it as “compost heating experts”, it was decided that a prototype system would be built. This provided the benefits of gaining hands-on experience with compost, its properties, and how it handled air flow to move heat around. It also provided an opportunity to check some of the assumptions used to model and analyze the full-scale pile that would be built at the Seedfolk site.

A test pile was constructed in Dr. Stevens’ lab; it was placed in a small storage container and was connected to scaled down versions of the other subsystems. The test pile produced heat satisfactorily and after several days reached a peak temperature of 45 degrees Celsius. It was decided to increase air flow to test the effects of that change in a key system parameter; within a few hours, the pile “crashed”. This gave the team a valuable insight into the aeration of the final compost pile, as it was discovered that the main reason that the test pile crashed so suddenly was due to over aeration. This information helped prepare us for the actual compost pile, so as not to make the same

mistake again.

The picture to the left depicts the Mechanical team in front of the test pile. It was constructed in Dr. Stevens’ lab using the same compost mixture as the final pile. It was constructed in a smooth, plastic container, and was insulated using fiberglass.

Subsystem Design:

Thermal Energy Source for Heating System: The thermal energy source in our system is a 44 cu. yards rectangular compost pile which is a combination of Horse manure, brewers grain, wood chips and sawdust. This design ensures an optimum 30:1 carbon to nitrogen ratio that is required for favorable decomposition of the compost pile mixture. Moreover, the composition and ratio of the mixture of the compost pile is of paramount importance in order to satisfy the thermal load requirements of the greenhouse space. Based on our heat transfer calculations and

data collected for temperatures and solar radiation in the Rochester area from the TMY3 meteorological chart, the greenhouse space requires an average thermal load of 3.7 kW. This calculated value takes into account thermal losses from the greenhouse space that would be caused by infiltration of air and overall construction of the greenhouse structure itself. Hence, based on this thermal load, we conservatively designed the size and composition of our compost pile mixture. Also, to ensure minimal thermal energy loss from our compost pile, we covered the top of our pile with hay bales, as well as the sides. The 12” thick layer of hay bales provide an adequate insulation barrier for the compost pile subsystem. The figure to the left shows the compost pile, and hay bale structure as it is being built. The compost pile is adjacent to the west wall of the greenhouse.



Heat Recovery to Storage Mechanism: The method with which we heat our working fluid, which is water, as it passes through the pile, is through the use of heating pods. There are a total of five heating pods placed strategically within the pile. The structure of the heating pods can be seen in the picture on the left and on the next page. Each pod consists of flexible steel wire wrapped around wire mesh into a 3’ diameter with a 4’ overall height. The pods have PEX tubing wrapped, or coiled, around with a 3” spacing between each loop in order to ensure efficient heat transfer to the water from the compost pile. The cold water passes around the pod and then heats up. The heated water is then transferred to a manifold inside the greenhouse, which is linked to all five heating pods. This transfer of water from the compost pile to the manifold is accomplished through the use of a circulatory pump shown in Figure 1, which can be found in the appendix. This electrically powered pump can handle the appropriate pressure losses through the piping system and efficiently pump the water through the pipes. This assertion is based on our calculated flow rates for efficient heat recovery from the compost pile.

This picture on the left shows one of the pods after it was assembled and prior to it being placed into the compost pile. The tubing length wrapped around each of the wire mesh “frames” was 140’, based on calculations and analysis as the heat transfer was modeled.

Storage Mechanism: The storage mechanism in our system is a 500 gallon water tank (picture at left) which connects to both the compost pile and the soil piping mechanism. This storage tank acts as an intermediate link between the other systems. The storage tank collects the heated water from the compost pile, where it then collects at the top of the tank. Then, through a process called stratification, the hot water starts settling at the bottom of the tank because it is denser. There is a pump attached to the bottom of the tank which pumps the hot water from the tank to the piping layout for the soil. The way we transfer the water to and from the tank is through two PVC manifolds which are attached to the side of the greenhouse.


Figure 2: Pod Layout

Figure 4: Storage Tank


Heat Distribution: The goal of this subsystem is to heat the root zone of the soil beds, and keep the soil at 45-50 °F during the winter months. The soil heating will be done by dividing the total area of the soil to be heated inside the greenhouse into five areas. Thus, the hot water from the storage tank will be pumped using a circulating pump (shown in Figure 1 in the appendix) into a ¾ inch PVC conduit which will be connected to ¾” LLDPE tubing. This tubing will provide the heat to these areas. Furthermore, water passing out of each area through the LLDPE tubing will be connected to a return line conduit, which will be connected to the tank. The tubing will be looped in each of the heating zones. These heating zones will be separated by 8”. Of the five heating zones, four of them will be heated on the surface, whereas the zone coinciding with the walking path at the center of the greenhouse will be 1” below the soil surface, to minimize risks from tripping.

This drawing below provides an illustration of how the heating pods are placed within the compost pile. It also shows how the pods are connected to the circulating pump, and how the pump is connected to the storage tank.

System Controller:An Arduino Mega microcontroller board was selected to implement the desired control scheme. This device interfaces with a variety of sensors for input and several solid state relays to adjust outputs. The state of the system is determined using measurements taken by the sensors, and water flow rates are adjusted to maintain the desired temperatures. Power for the Arduino is provided over USB from the User interface controller. Serial communication between the system controller and the user interface controller enabled the adjustment of target temperatures or humidities in the system, as well as the collection of a datalog for all of the control operating parameters.

Sensors:Selection of sensors was based on enabled the observation of parameters critical to maintaining the greenhouse and compost pile states. The greenhouse sensors were chosen to measure ambient temperature of the soil beds and the water temperature for our heat transfer lines. The compost pile requires both temperature and humidity to be kept within a desired range, so soil-safe sensors capable of measuring both temperature and humidity were specified. Cables were constructed to connect the sensors to the junction box containing the controller, and logic level shifters were included for sensors that operate on a different voltage than the I/O voltage of the Arduino.

Electrical Outputs:Four DIN Rail mounted solid state relays enable the Arduino based system controller to switch AC motors on or off. Two of the solid state relays are used to measure the two pumps used to circulate water between the storage tank and the compost pile or soil bed heat transfer lines. The remaining two solid state relays operate a small fan and water pump used to aerate the compost pile and add lost water (respectively).

Control Enclosure Design:The control enclosure is a NEMA 4 enclosure constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water and that will be undamaged by the external formation of ice on the enclosure. The dimensions of the junction box are 16”x16”x8” with spare space for additional terminal blocks or components. The main power feed for the enclosure is a 12 AWG, 3 conductor cable with a standard straight plug end. The enclosure can be plugged into either a standard wall socket or a photovoltaic system’s inverter. The control enclosure has main 15 amp thermal magnetic circuit breaker to ensure electrical safety of the its devices. There are



three 2 amp thermal magnetic circuit breakers used to electrically protect the aeration fan and the two circulation pumps. A 120VAC outlet is used to provide power to the Raspberry Pi 3 and its associated components. Low voltage DC components are separated from 120VAC components to reduce noise on those devices. All of the internal devices are DIN rail mounted.On the exterior of the enclosure a LCD touch screen is mounted to give the end user a graphical user interface. The greenhouse temperature sensors will connect to the enclosure using M12 4 pin connectors and compost pile temperature sensors will connect using M12 5 pin connectors. Flex conduit and connectors are used to route power to the 120VAC pump and fans. The images below show the enclosure and controls inside.

User Interface Controller:A Raspberry Pi 3 microcomputer board was selected to implement the desire graphical user interface and data logging system control scheme. The Raspberry Pi 3 is a power microcomputer with low cost that can be used to carry out various complex tasks. This device interfaces with a LCD touchscreen for user input and data logging feedback. The GUI will also display running status of the aeration fan and the circulation pumps. Temperature and



humidity parameters can be adjusted to ensure proper heating of the greenhouse. The Raspberry Pi 3 monitors the status of and collects data from the Arduino microcontroller over serial USB.

Power Consumption:It was intended that the entire system would run off a properly sized photovoltaic system, to support one of the customer requirements of minimizing consumption of energy from non-renewable sources. The following table lists the major component power consumption. The hourly and daily power consumption rates are calculated with various duty cycles depending on the needs of the system. The power consumption of the entire system can be found in the table below.

Transition from Design to Build:As with any project, there were some obstacles and logistical challenges that arose as the team transitioned from the design phase to actually building on the Seedfolk site. These obstacles put us with a narrow window to get the build accomplished. We were able to successfully put in place the necessary systems in time for winter. One of the major challenges was the ordering and delivery of materials. There was much back and forth about the design, as it received more and more input from our customers and professors. This caused many items to be shipped with overnight shipping, as we wanted to make sure that we were ordering the proper materials. This put a significant dent in our budget, as the shipping costs began to add up. Another challenge was the logistics of getting everyone on the site working at the same time. Everyone involved in the project had other commitments than this project, so getting everyone together sometimes proved to be difficult. To mitigate this, constant communication took place, so that the mechanical team could work on the site at separate times than the electrical team and the customers, and so on. This was able to work by constant updates about what was accomplished each time someone worked at the site, and what more needed to be done, when, and by who.

Results:The design has been fully implemented. The one change that was made to the initial design was switching from

heating the soil directly to simply heating the air. Data has been logged over a three day period to test the effectiveness of the design in an effort to determine the probability of the success of the project. Data was collected beginning Sunday afternoon until Tuesday morning, for the purposes of this paper. Data is continuously being collected once every five minutes. The pile’s temperature was recorded at 55 degrees Celsius (131 degrees Fahrenheit) on Sunday evening. This temperature comes from the average of the sensors that are placed within the pile. By Monday morning, the pile was down to 44 degrees Celsius. On Tuesday morning, the temperature of the pile was 43 degrees Celsius. This caused us to shorten the cycles of the fan. The feeling was that we were drawing too much air out and over aerating the pile. After adjusting the fan and pump cycles, the temperature of the pile jumped up to about 48 degrees Celsius by Tuesday afternoon. As for the greenhouse, on Sunday afternoon the temperature of the air inside the greenhouse was a little over 3 degrees Celsius (38 degrees Fahrenheit). By Sunday night the temperature had increased to almost 7 degrees Celsius (44 degrees Fahrenheit). The max temperature of the greenhouse came on Monday afternoon and was a pleasant 11 degrees Celsius (52 degrees Fahrenheit). The greenhouse was sitting at a little over 8 degrees Celsius (47 degrees Fahrenheit). Assuming the soil temperature reflects the air temperature, these conditions are suitable for growing, although a constant air temperature in the range of 10-15 degrees Celsius would be ideal.

Conclusion:In conclusion, this particular project started in the fall of 2017 and concluded in December of 2017. The project

followed the senior design process. Customer and Engineering requirements were generated, in addition to a morphological table and use scenarios. The goal of this particular project was to heat a greenhouse throughout the


Table 1: Power Consumption


winter months using a pile of compost as the main heating source. Several designs were created and discussed among the team and customers. Originally, the team settled on a hydronic based system that involved heating the soil using piping that lay just below the surface of the dirt. Due to time and budget constraints, it was switched to simply heating the air of the greenhouse. After a couple days of testing, the temperature of pile has reached a max temperature of 55 degrees Celsius to this point. The air of the greenhouse has reached a max temperature of 11 degrees Celsius. Over a two day span, the pile quickly dropped in temperature before leveling out. We believe that this due to the fan cycle when the system first got up and running. For the future, it is recommended that the customer employs shorter and more infrequent fan and pump cycles. This will help extend the pile life in an effort to keep it producing heat during the harshest of the winter months. In terms of customer handoff, we have made it as simple as we could to provide a functional user interface that will allow the customer to monitor key parameters. These parameters include humidity, pile temperature, and greenhouse temperature. With this information, the customer can adjust the fan and pump cycles as needed to balance the aeration and heat production. In addition, as you can see in Figure 2, located in the Appendix, nearly all of the Engineering Requirements have been met or exceeded. Although, running over budget by approximately ~$500, this project was a success based on the high temperatures generated by the pile and how the greenhouse has increased in temperature since the since the system has been functional. As students and as a team we got invaluable benefits to doing this project. The mechanical team got valuable hands on experience in design and bringing a design to fruition. This includes hands on experience in getting the design built. This goes for the electrical team as well. They got experience in determining electrical output of a design and choosing the proper sensors that will get the job done. The industrial engineer got valuable experience in managing a project from start to finish in addition to communication between the project team and the customer. He also got experience getting the two other team of students to work together, as their systems are separate in nature, but need to work together in order to have a proper system. If we were to do things differently, we would ask for more clarity on design questions from the customer. We would also reach to quicker and firmer decisions. However, even though we went back and forth on some different designs, we are more than satisfied with the final result, and will take the experience we gained from this project into the workforce with us.

Appendix:


Figure 1: Circulating pump used for the system


Acknowledgements:On behalf of the Senior Design team responsible for this project, we would like to sincerely thank everyone

who had a hand in making this a successful project and learning experience. First off, our customers, Seedfolk and the Gandhi Institute. We would like to thank you for your support and allowing us to do something beneficial for you and the community. We would also like to thank our guide for the project, Professor Kaemmerlen. His guidance, knowledge, and support have been invaluable during this process. Our next thanks goes to Dr. Rob Stevens, who was a major technical resource and greatly helped the team throughout every step of the design process. Finally, we would like to thank RIT for providing the opportunity to use the skills and knowledge that we have acquired throughout our time here towards a practical use.


Figure 3: Summary of Expenses

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