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If we can send cameras hundreds of millions of miles into outer space to shoot photographs of Saturn, then shouldn’t we be able to invent solar PV, create airtight buildings, and find ways to re-use heat or cooling energy from the ground and water, including wastewater?
The answer is yes, and that’s what we’re doing. (We’re also still extracting coal, oil and gas from underground and burning it, but that’s another story.) One of the most sensible technologies creating waves in North America, is reusing heat and cooling energy from drain water and sewage.
Although it’s been done in Europe and elsewhere for many years, extracting energy from the water that goes down our drains was only recently approved in the U.S. Before the dawn of the current clean energy age, the ‘yuck factor’ probably prevented engineers from taking a serious look at the technology. But again, if we can bounce communication signals off orbiting satellites, shouldn’t we be able to create a heat exchanger that seals in the stinkiest effluvia?
In 2014 the District of Columbia Water and Sewer Authority (DC Water) needed more office space and decided to build a proper headquarters on top of an existing pumping station, about 170,000 square feet, on the bank of the Anacostia River. The building would serve as an example to the masses, targeting LEED Platinum, and employing efficient clean energy technology. One of the opportunities under study related to the fact that in the winter sewer water is about 20 degrees warmer than the outside temperature, and in the summer it’s about 20 degrees cooler.
It was a dream come true for a sewage connoisseur like Lynn Mueller, the “Sultan of Sludge” from SHARC Energy Systems in Vancouver. Back in 2010 Mueller recognized the basic physics and energy potential of drain water, traded in a spectacularly rewarding geothermal career (perhaps), sold his company and began visiting bad smelling wastewater facilities in various countries. “I’m not sure if it was a step up, but I’m glad I did the sewage tour,” Mueller says.
He was determined to improve on existing configurations, eliminate the odor, simplify maintenance, and boost efficiencies. Since then he has installed effective modern systems in the UK, Europe, Australia and Canada. It was almost inevitable that he would receive a call from DC Water, which is now depending on a SHARC system at the new headquarters and is achieving impressive energy and water savings every year.
“They’re saving about 35 percent on air conditioning and 85 percent on heating,” Lynn says. “They’re also saving 4 to 6 million gallons of water each year that would have been used by the cooling tower if they were not using wastewater energy instead. There’s no odor, except during the annual cleaning, and we use a high-speed fan to blast that out.”
“On extremely hot days we use the cooling tower, but most of the time our cooling and heating energy comes from sewage,” says Don Posson, corporate director of Engineering at SmithGroupJJR (Detroit), who partnered with Skanska (New Jersey) on design-build for the new headquarters. “The real innovation is the way the system separates particulates from wastewater. It results in not clean water, but 90 percent of particulates are screened out, giving you better heat exchanger performance.”
Posson notes that DC Water undertook a life cycle cost analysis comparing various systems, and concluded that the SHARC offered high energy efficiency, low yearly maintenance and low installed costs. He explains that raw wastewater passes through a separator, which removes solid waste and sends it back to the sewer. Liquid waste is then passed through a heat exchanger, which extracts thermal energy, to heat or cool a completely separate stream of clean fluid. The energy-depleted wastewater returns to the sewer. Heat pumps distribute the clean, heated or cooled fluid through the building in the same way as a conventional boiler and radiator system would.
Other sustainable features at DC Water include lighting sensors, passive solar design principles and rainwater collection. The latter employs a 30,000-gallon tank that supplies all of the building’s toilet flushing and irrigation needs. The structure’s atrium lobby offers a public education area with cutaways that reveal some of the modern systems being used.
Mueller describes SHARC wastewater energy systems as trouble-free, but not maintenance-free. They are only sold with accompanying service contracts because a trained service technician does quarterly checkups and a full internal cleaning each year. “Everything is continuously monitored online and it’s a back-flushing system, so maintenance checks are generally unremarkable,” he says. “But we care about our reputation and the annual cleaning ensures reliable efficiency and long equipment life.”
The company has begun to expand into systems for different applications such as a product called the Piranha, for multi-unit residential projects; and another configuration that’s in final testing for single-family homes. It involves solar energy and is designed for markets like California.
Around the same time and also located in the Washington DC area, the American Geophysicists Union (AGU) determined the need for a complete retrofit of its 5-story, 25-year-old building, including the installation of a wastewater energy system.
Given that the organization studies the earth, reports on climate change and makes recommendations on clean energy, its leadership felt that the envelope and old equipment in its home should be replaced with contemporary sustainable systems, to signal its commitment to a new and different world. The original goal was a net-zero energy building, but Building Services Manager Matthew Boyd believes the final metrics will reveal the project to be energy positive.
For wastewater energy AGU selected an older, well-proven design by Huber of Germany, which includes an open wet well connected to the sewer. To avoid odor problems the well is housed in a separate building. It takes advantage of gravity for some of its flow and settling of solids. Compared to the SHARC it may be slightly less efficient and more expensive in some applications but is doing the job for AGU.
“Our water-to-water system has an EER of 21.5, which equates to a COP of 6.30.” says TR Gregg, business development manager for Huber USA. “It will provide 500 kW of cooling capacity and 220 kW heat output. Wastewater is a great, reliable source of thermal energy. There are a lot of enquiries in North America right now because there is increasing regulatory pressure to reduce the temperature of sewage. And our system can help with that.”
AGU combined wastewater energy with several other sustainable technologies, allowing them to hit the positive energy benchmark, according to Matthew Boyd, AGU building services manager. They installed a formidable rainwater collection system and also Zehnder radiant cooling sheetrock ceiling panels. They are slim, quiet, healthy, comfortable, attractive, and compatible with low temperature systems. One university modeled a life cycle analysis of Zehnder panels and found a 26 percent cost benefit.
They also installed a Living Wall. You may have seen walls full of plants in various atriums. However, the Nedlaw system selected by AGU holds the patent that allows ventilation air to blow through the plants, absorbing C02. This means more ‘fresh air’ with less outside air, which saves energy in modern, tight buildings.
And AGU has an excellent envelope. “There are 8 inches of spray foam, creating walls and ceilings at R-52,” Boyd says. “Also, we used SageGlass electrochromic glazing, which gives us control over tinting.” Windows are triple pane, with a five-layer ceramic coating, so a touch of low voltage electricity (DC 5 V) can darken the glass to absorb and reflect heat and glare. At other times they can be returned to a clear state, maximizing daylight and solar energy.
The building also generates solar energy actively through a 250 kW, 719 panel array that covers a little more than the entire roof. An interesting twist on this system is that some of the DC power generated by the panels is made available, unconverted, directly to LED lights and workstations through USB ports. Phones and laptops would continue to operate in the event of a catastrophic grid failure. Resilience!
All of these systems are balanced, monitored and operated using sophisticated integrated building controls from Siemens. Sometimes we don’t give enough credit to the role controls play in optimizing these divergent systems and helping them all work together to create clean energy savings. In this case they generate more clean energy than the system is using.
Any discussion of preventing energy from literally ‘going down the drain’ would be incomplete, without mentioning PowerPipe and similar products. These passive pre-warming devices are used mostly in houses, but sometimes as well in multi-unit residences and small food processing facilities.
At James Madison University, in Harrisonburg, Virginia, a three-story dormitory building call Wayland Hall was recently renovated to LEED Platinum. Enhancements included geothermal heating, rainwater collection and drain water heat recovery. There were a couple of bathroom groups on each floor, with one PowerPipe unit used for each group. The initiative was modeled to save approximately 80 percent on the ASHRAE 90.1 baseline for domestic hot water energy.
It’s simple technology that can be installed quickly wherever a shower drainpipe can be accessed. There are no moving parts. It’s just a basic copper heat exchanger. It transfers heat energy from shower water going down the drain, pre-warming incoming cold water, and reducing the hot water heating load.
According to PowerPipe President Gerald Van Doecker, in a few countries, states, and provinces, drain water heat recovery is either in the building code or moving towards it. He says it is in some of the 2015 IECC guidelines, and that there is a credit available for it in the U.S. There are a few suppliers of PowerPipe and similar products around North America. Most plumbing distributors know where to find them. Van Doecker says that different sizes in his product line help homeowners save from 42 percent to 72 percent on water heating energy.
I’m resisting the urge to close with a joke about the lack of energy and abundance of sewage in the Washington DC area, but apparently that would be inaccurate. I guess there is more than enough of both.
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