The Design
More information about the design process and design intent can be found in our project proposal.
The test-bed is a model representing rooms in a home, attached to a forced air heating and cooling system. The rooms are monitored with sensors to relay data back to our control system. The control systems have the task of analyzing that data and controlling the forced air system with the goal of keeping a constant temperature throughout the rooms. A separate system is used to simulate environmental changes such as drafts, open doors between rooms, or cooking. With the data collected by the control system we hope to gain knowledge through statistics and graphs about the fastest and most efficient ways to control the temperature in our model.
Mechanical Design
As planned, the model is comprised of two levels, separated by a plywood floor with a Plexiglass ceiling (for external inspection): an upper level of two rooms, walls made with foam core, each with a supply duct, a return duct, and a temperature sensor, and a doorway between them; and a lower level, the "basement", where the ductwork and circuitry lie suspended below the rooms. The ductwork was simply constructed from four pieces of 3"-diameter tees, two connected in series on each side of a homemade furnace. The model has legs, one at each of the four corners, serving both the purpose of elevating the ductwork off the ground and the purpose of being able to flip the model over in order to view the basement from above.
Model from Above
Model from Below
View of One Room from Top
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This scaled down two room version of the model instead of the proposed four room design was a result of budgetary and time constraints. Moving the design from two rooms to four has a scaling effect that was not within the scope and time of our project. For example, the number of duct tees doubles, the number of actuated dampers doubles or more, the number of sensors and indicators doubles as well. Also considering the connectivity issues when attaching these systems to the PC/104 stack we felt we didn't have the time to experiment with the multiplexing required to accomplish this. We believe that this change in the design still reflects the design intent of the project and still allows us the flexibility to run interesting scenarios with it.
The two actuated systems in the model are the furnace and the damper assemblies:
- The furnace is the subsystem that both forces air through the system and heats and cools that air. Our design for this system is to use a heatsinked peltier with two fans blowing over either side in order to maintain a high voltage differential. The fan choice was kept as simple as possible by using computer case fans.
- The damper assemblies consist of a damper inside the duct connected by an axle to a gearbox and 12V DC brush motor assembly. We chose to use a gearbox actuator assembly to simplify the connection needed between the damper and the actuator, anticipating possible challenges with mount all the pieces into and onto a round duct.
Early Sketch of Damper Actuation
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The mechanical design also allowed room for mounting all the electronic and control systems in the basement and its dimensions were chosen to allow it to fit into our project locker. Part of the mechanical design was also a desire for a polished aesthetic look. We wanted our finished model to be visual appealing and inviting so we took care to spend time on the aesthetics of the model.
Electrical Design
Electrical design can be broken up into sensing, actuation, and status display. The sensing aspect of the electrical design allows for a thermistor to be placed in each room of the model, and for a potential to be read that changes with temperature and can be transformed into an actual temperature reading. Sensing also includes a utilizing a resistor to measure the amount of current consumption of currently activated motors. This allows us to stop the motor once it has reached an end state and begins consuming more current than it does when it is able to turn the damper.
Actuation is divided between control of damper motors and the furnace. Motors are controlled bi-directionally to allow opening and closing in accordance with desired state. The default state for internal intake and return dampers is open, and external dampers are closed. This state provides a closed system, where air is recycled. The other actuated system, the furnace, must operate two fans (internal and exhaust) where both are on by default to prevent heatsink overheating in a case where the peltier is on and fans cannot be controlled. Additionally, the peltier within the furnace must have bi-directional heat pump functionality, where internal temperature can be either increased or decreased with respect to external temperature
In addition to actuation and sensing, status LEDs in each room can be turned on and off to indicate whether current system status is within a target temperature range or not.
Software Design
The software provides the overall intelligence between sensing, actuation, and status indication. Based on individual room temperatures, the software will decide whether to heat the system, cool the system, or leave the heating/cooling system off to maintain temperature. It provides manual control for the target temperature, and which dampers are open or closed. When dampers are to change state, it must also monitor current usage to ensure that the motors are not making futile attempts to move the damper beyond the designed range of motion. Damper states represent the current environmental constraints within which the temperature control system must operate to optimize system temperature. In addition to these functions it provides status indication both within the model and on the computer (when in tethered operation). Green LEDs are turned on within the rooms once target temperature for that particular room has been reached, and analytical graphs are displayed on the computer indicating how temperature is changing over time.
About Project
The Home HVAC model was designed and built as an experimental test-bed for developing a smart HVAC control system. The model itself uses the design principle of independance of functional requirements to give as much flexability to the model as possibile; this allows for many interesting scenarios and experiements to be run in a controled system before implementing them in an actual home system. The purpose for the control system is to limit the temperature differential within a room and between rooms to make for a consistant and comfortable living enviroment. This is accomplished through the use of mechanical systems, electrical systems, and software. The idea for the project came from a personal dissatisfaction team members have with drafty rooms, hot and cold spots, and unresponsive thermostats in our own homes.
Team Info
- Ned Cameron
- Ned is a senior in the Mechanical Engineering department. He has concentrated in MEMS, Nanotechnology, and Mechatronics while fulfilling the requirements for his degree. After graduation, he will work as Application Service Engineer for Informance International in Northbrook, IL.
- Ted Reynolds
- Ted is a senior in the Mechanical Engineering department. He is a co-op engineer with ITW in Glenview where he plays on the volleyball team. He enjoys sleeping little and cooking lots. Considering he still has another year left, Ted has not given much thought to his future, but wherever he may be, he plans to have the best HVAC system on the block.
- James Snyder
- James is a first year graduate student in Biomedical Engineering. He has recently completed an undergraduate degree in biology at Northwestern University (concentration in Neurobiology), and currently works with the MacIver Lab studying sensorimotor integration in weakly-electric fish.