control systems
The control system reduces energy in three ways: by employing energy-efficient appliances or modifying less-efficient appliances, by automating systems to make them run more efficiently, and by giving homeowners the tools they need to make efficient decisions.
The Solar Decathlon competition requires all teams to have similar-sized appliances that run for the same amount of time. This brings up the questions of 1) whether or not to get larger appliances to increase comfort, while competitors will be using smaller ones that consume less energy, and 2) when many teams are donated the same appliances, how do you get a competitive advantage?
Our answer to the first question was to compromise between efficiency and aesthetics, and to accept slightly less efficiency, knowing that our controls system would more than make up for this in other areas. In response to the second question, we used less energy by modifying an already efficient drawer freezer system to act as a refrigerator, which runs for a much shorter time than an average refrigerator (this idea came from http://mtbest.net/chest_fridge.html).
We faced challenges with wiring a home built by many people (students) and built in parts. Because the house has structural insulated panels for walls, and because we needed to access the floors up until the house was on the National Mall, we decided to use a raised-access floor system, such as is used in computer labs. This gives us access to color-coded and numbered wires simply by removing four screws and pulling up a panel, allowing us to make changes and repairs and to finish installation after the rest of the house is built.
The automation system controls parts of the lighting, HVAC, solar hot water, and appliance systems. For example, lights are controlled depending on a touch screen input, a wall switch input, light levels in the room, and whether the room is occupied. The HVAC system controllers by Distech Controls, Inc. reads indoor and outdoor temperatures, inputs from the touch screen, and other environmental conditions, just like a thermostat decides when and how to heat and cool the house. Similarly, the solar hot-water system determines whether to heat a hot-water tank or an auxiliary heating tank that helps to heat the home. And finally, the automation system allows the occupant to turn on and off certain appliances remotely, so that standby loads can be avoided while the appliance is awaiting use and so that some appliances can be scheduled for use only during off-peak energy usage times.
Besides these controls, the touch screen also provides information on environmental data from the house, as well as energy usage by circuit and by room, so that individual loads can be seen in real time and overall energy usage can be tracked over time. This allows homeowners to see how much energy they are losing to the dishwasher, for example, during a given week or month.
Homeowner Application
Although our system is much larger, and more expensive, than what the average home needs, being able to monitor and control lighting, appliances, hot water, and HVAC systems is very useful. A small relay board, a few sensors, and a computer running a controls network will allow homeowners to be much more in touch with the functioning of their homes, particularly in larger settings where keeping track of energy usage, light states, etc., in every room becomes a difficult task.
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Equipment:
- Honeywell sensors – Total Retail Cost $5,450 (donated)
- Hubbel relay board, relays, sensors – Total Retail Cost $8,950 (partially donated)
- Distech Controls, Inc. Lonworks-compatible free-programmable controllers – Total Retail Cost $2,875 (donated)
- 3M 17 inch touchscreen – Total Retail Cost $825 (donated)
- Echelon software – Total Retail Cost $350 (donated)
- MicroDaq.com solar insolation sensor – Total Retail Cost $450
- Assorted power supplies, router, controls module, contact sensors, phone jacks, glass shatter detector – Total Retail Cost $500
