|College or School:||CoE
|Article Type:||Issue Feature
|Feature Intro:||A retrofitted 1920s-era home gives practical lessons for net-zero use of outside energy and water.|
When the bungalow at 545 Hayes St. was built just outside the Purdue campus in 1928, coal was the leading source of central heating for those U.S. homes that had central heating, and the first big wave of electrical appliances was just arriving. Today, Purdue’s ReNEWW (Retrofitted Net-Zero Energy, Water and Waste) house is a test bed for sustainable technologies that take major steps toward net-zero use of outside electricity, fossil fuels and water — while keeping a high degree of comfort and convenience for residents.
Sponsored by Whirlpool Corp., ReNEWW aims to do far more than demonstrate state-of-the-art technologies and appliances. “We are looking at getting more efficiency by integrating what have been stand-alone devices,” says Eckhard Groll, the Reilly Professor of Mechanical Engineering and principal investigator for ReNEWW. “We eventually would like to deliver not just individual appliances but an entire home, all integrated and working together, making it the most energy-efficient environment that consumes the least amount of water.”
As the three-bedroom ReNEWW house adds resource-saving features, its flows of energy and water are meticulously measured, notes Stephen Caskey, a PhD student in mechanical engineering who studies ways to cut down on thermal energy loss and acts as a project manager for ReNEWW. For example, with more than 20 flow meters installed, “we can tell how much water is used when someone fills up a cup or a pot of water in the sink,” he says.
Success in the home is assessed not just by the flows of energy and water but by the quality of life for three Whirlpool project engineers living in the house. “We live as we would normally live, aiming to accomplish the big goal of net-zero use but still keeping a significant level of comfort,” says Andrew Batek, one of the three engineers, who are pursuing graduate degrees at Purdue under the Whirlpool Engineering Rotational Leadership Development (WERLD) program.
Steps to sustainability
ReNEWW kicked off in 2013 by gathering extensive baseline information on energy and water use in the house as a conventional home using natural gas to provide heat and hot water.
2014 brought a comprehensive energy retrofit including window and door replacement, blown-in insulation, energy-efficient household appliances, and a geothermal vertical-loop heat pump that delivers heat and air conditioning. A new metal roof was topped by a solar photovoltaic array, whose surplus power can be stored in batteries in the basement or sold to the local electrical grid. An accompanying solar thermal hot water system can improve the array’s efficiency or aid in warming water in the home.
Removing the need for natural gas, these enhancements slashed the house’s consumption of outside energy from about 170 percent of what a newly built home would require to near zero. (It doesn’t quite reach net-zero because of demand from the project lab in the basement.) The first round of retrofitting also brought practical lessons, like the need to heat the roof photovoltaic array from the bottom up during the winter, so that snow melted from the top of the array doesn’t clog the lower array.
Next came water use. In the summer of 2015, the ReNEWW team began gathering runoff from the 1,600-square-foot roof, which is filtered and stored in two 1,500-gallon underground tanks. The water then is filtered again and disinfected by two ultraviolet treatments to make it potable.
Roof water is expected to provide about half of the 60,000 gallons of water consumed yearly in the house. Using treated “gray water” from the shower to flush the toilets is expected to cut about 30 percent of home water usage. Additionally, the team is experimenting with a heat exchanger to recover heat from the shower-drain water. The researchers also will explore whether this treated water can aid clothes washing or the first round of dishwasher cleaning — two other major hot-water hogs.
Kohler Co. is partnering to provide the extensive water-flow instrumentation that tracks water usage throughout the house. “It’s quite powerful for a company to have a real test bed like this,” Groll says.
Further down the road toward net-zero, ReNEWW engineers are examining opportunities to cut down on thermal energy losses by integrating kitchen or laundry appliances. One example is to capture and reuse the heat in the heated air normally released from the back of a refrigerator. A refrigerator heat exchanger that works with water rather than air could be smaller and more efficient, and could help to warm water for the dishwasher, for instance. Kitchen appliances typically sit close together, and if engineers can create a suitable mechanism to store heat for release on demand, that could offer an even more efficient appliance suite, Caskey says.
This year, ReNEWW’s fourth phase will take on the house’s waste stream, adding composting toilets and trying to cut landfill waste as close as possible to zero. Researchers are now painstakingly collecting and poring over the current household waste products, and starting to brainstorm about puzzles such as plastics that don’t recycle. “We’re paying attention to what we’re doing and ways to minimize that for all of the waste going out of the house: recyclable, landfill, compost and combustible,” says Todd Graham, one of the Whirlpool engineers living there.
Practical energetic approaches
Unsurprisingly, bringing new thinking and technologies to the quest for net-zero operation is complex and costly. “You wouldn’t get payback for what we’ve done to the house; it would be cheaper to tear it down and rebuild it,” Groll says. And payback for net-zero electrical use may be a greater challenge in Indiana than in other states where electrical rates are far higher.
Beyond measuring energy, water and waste flows, ReNEWW will help to suggest how consumers react to resource-saving home environments. “People living in the house definitely add a different kind of feedback,” Caskey says. In their daily lives, the residents instantly spot some adjustments that save energy, but not all of them, he points out. This ad hoc human factors data will aid in studying issues like, do the radically revised plumbing arrangements still produce a comfortable shower?
Before moving into the house, “I didn’t think about particular behaviors I have, like how long I let the shower water heat up,” says Elizabeth Bourgeois, Whirlpool engineer and ReNEWW resident. “Living here, you learn that you can quantify and understand your impact; you just have to take the time to create the awareness of your behaviors.”
These behaviors add up, she points out. “And if 6 million people in Indiana think like this, the behaviors will add up really quickly.”