Let’s Get HVAC Out of the Sewer
Wastewater thermal extraction technology has come of age
Lynn Mueller, founder and CEO of International Wastewater Systems Inc. (IWS), has been involved in wastewater thermal extraction for some time now. Maybe no one else would tackle the effort, but it’s a technology that has come of age. Mueller’s company went public last year, and it continues to expand and garner attention. So much so that IWS’s newly released PIRANHA heat recovery system won the AHR 2016 Green Building Product of the Year Award.
Thanks to a joint venture between International Wastewater Systems Inc. and Renew Energy Partners LLC, California will receive 1,000 PIRANHA thermal heat recovery systems. The PIRANHA is designed to provide the domestic hot water (DHW) needs in 50-100 multifamily housing units.
Exhaust recovery ventilators (ERVs) are designed to save energy in businesses and homes. With an ERV, air exhausted from the building exchanges energy with the makeup air coming back into the building, which helps precool or preheat the makeup air depending on the seasonal conditions. Essentially, the PIRANHA does the same thing with exhaust water, or wastewater, recovering unused energy for other purposes such as DHW, heating, or cooling.
The potential for energy recovery with wastewater is staggering. According to the U.S. Department of Energy (DOE), 350 billion kWh of usable energy goes down the drain each year. This is enough energy to heat 5 billion average-sized homes in the dead of winter for an entire day (24 hours) or heat 69 billion DHW tanks from room temperature to 130°F. This is a remarkably large quantity of energy that is not being recovered.
Even if the temperature is subzero outside, the average temperature of the waste water leaving homes and buildings is around 70°. Our sewer discharge is a combination of drainage from our showers, washing machines, dishwashers, sinks, and toilets.
Many of these sources are warm as they are discharged into the sanitary sewer. Even those not heated, such as the toilet tank, assume room temperature after a few hours inside the conditioned space, carrying valuable Btu down the drain. In Vancouver, British Columbia, Canada, the city built a wastewater energy plant to displace natural gas (NG) heating, and city leaders are convinced that through the use of geothermal heat pumps (GHPs) and some smart strategies, they can meet their goals. A July 26 article on Vox.com examined this large wastewater heat recovery system, and a video interview with Brian Crowe, director of water, sewers, and district energy for the city of Vancouver, also examines the plant (http://goo.gl/xruUOA). Incidentally, Vancouver is Mueller’s hometown.
The PIRANHA thermal heat recovery systems that are going into California represent the entry-level portion of this technology as the units will be primarily used for recovering energy for DHW needs. Another IWS product introduced some years ago is the SHARC, which is compatible with more applications, such as residential, commercial, and district cooling and heating applications. This is the junction at which wastewater heat recovery and air conditioning, heating, and refrigeration professionals become fully engaged. There will soon be buildings and designs crossing our collective desks with these waste energy recovery systems in the design, and they’ll be part of the central HVAC systems.
Primarily, waste energy recovery systems are viewed as, or treated as a source of, energy, like a boiler, and, alternatively, will operate as a heat sink, like a cooling tower. Geothermal heat pumps (GHPs) are the central component of the thermal extraction/rejection portion of energy recovery. GHPs use available energy in liquids between 25° and 110° and are able to absorb and reject heat to and from them. GHPs are thermal energy pumps that concentrate heat energy through the Carnot Cycle and deliver final temperatures from well-below freezing to 140° above for uses such as space conditioning, refrigeration, or domestic hot water.
Of course, these applications are well-suited to be a hybrid of waste energy — as the primary source/sink — and earth-coupled systems. The earth-coupled portion of projects is reduced in both scope and cost by taking advantage of the wastewater thermal energy heat source and sink.
Hydronic systems are amazing because they effectively channel Btu within a pipeline, unlike air-source systems. GHPs make the magic happen by simply managing Btu entrained in liquids to whatever temperature is needed at the time. GHPs are the center of the energy universe for renewable and sustainable energy systems.
In an interview, Mueller shared that this California venture is an example of how his company is able to fast-track market penetration with emissions-reducing technologies and make the installation free to owners. In Mueller’s eyes, this allows owners to sit back and save energy and money.
A recent Green Tech Media headline read, “Vancouver Leapfrogs Energy Efficiency, Adopts Zero-Emissions Building Plan.” Technologies that reduce greenhouse gas (GHG) emissions are in high demand; and wastewater energy recovery has greater potential to reduce on-site GHG emissions and save energy than perhaps any other building technology. Just as ERVs have entered into building codes, wastewater energy recovery is right behind. This is a technology that’s ready to emerge.
Publication date: 11/14/2016