The simple workings of a drain water heat recovery device.Credit: gfxstar.ca, Inventroment Energy Solutions.

Canadian researchers from Natural Resources Canada tested the effectiveness of several DWHR devices at the Canadian Centre for Housing Technology.For an Ottawa household in which four people each take 12 minutes showers every day, a DWHR will save $150 a year in energy costs (at present, Canadian dollars are about equivalent to U.S. dollars). That’s about three times as much energy saved as the energy used to run an energy-efficient 20-cubic-foot refrigerator for a year. Over the 30-year lifetime of the DHWR, which costs about $800 including installation, the device will save the household close to $3,000.

The Canadian researchers created a Web-based Drain Water Heat Recovery-Energy Savings Calculator where building contractors, plumbers, and homeowners can go to estimate the cost effectiveness of several DWHR devices on the market. You just need to know the model of the device, the temperature of your shower water, estimated shower times, and so on. Right now it is set to work for Canadian locations. For U.S. homeowners, you have to pick a city in Canada. The calculator will be updated as newer technology is developed and tested.Here are some Web sites where you can find out more about DWHR devices that were submitted for testing at the Canadian Centre for Housing Technology:

• Power Pipe www.renewability.com
• ECO-GFX www.gfxstar.ca
• Retherm www.retherm.com

If a million households in the United States installed DWHR devices, we’d save a collective $150 million in annual energy costs, or about the equivalent of 1.25-billion kWh of electricity–or a ginormous amount of carbon dioxide in air from the natural gas not burned and electricity not generated.

Solar hot water systems should be in use everywhere in the country. They are not terribly expensive to install, and the payback period on them is much shorter than it is for solar photovoltaic. Even in cold climates, it is possible to have a system with a heat exchanger and an antifreeze filled loop, so that the system can be run, even when nighttime temperatures are below freezing.

But the appearance of rooftop mounted panels is a drawback. Lots of people find solar panels, whether they are hot water or photovoltaic, to be unattractive. While it looses some efficiency by being out of direct sunlight, Dawn Solar offers a concealed solar hot water system. "The Dawn Solar System uses heat generated by the sun shining directly onto a roof. Solar energy is absorbed and transferred into a concealed, patent-pending collection system that is hidden just below the roof tiles. There is no ugly collector that is visible from the street."

The website offers few details about the configuration of the system, but presumably it uses some kind of pipe or tubing running just under the roof to collect heat from the attic space in the water for use in the building. The case study they offer is a distillery in New Hampshire (pictured) with the tubing running under the metal roof of the building. This is tied in with their other building systems and contributes to the radiant floor heating and the domestic hot water for the building.

The same week I came across this system, I also got an e-mail that included a suggestion of a similar system that someone had installed as a DIY project in his own attic.

Homeless Dave, who invented the Pedal Powered Washing Machine, is also a blogger who conducts interviews with a range of people on a teeter totter in his back yard. Most of the interviews are of local interest to Ann Arbor, though he has also hosted a former US president. A recent interview with the central power plant manager for the University of Michigan brought up some discussion of a couple of DIY projects that he had installed in his home, including one that struck me as being very similar to the Dawn Solar system. Homeless Dave sent me an e-mail about the interview and suggested it as material for possible DIY articles. There isn't enough information in their discussion to make a useful DIY article on its own, but if you are really inclined towards doing a DIY installation of this type, I think you may find some inspiration from this.

A few things occurred to me as a result of this that would make a DIY installation easier. For one, Wickboldt's system uses PVC pipe. While this can be installed fairly easily, there are joints that have to glued and pipe that has to be cut to do this. However, PEX tubing, which is also used in underfloor and in-slab radiant heating, is a continuous length of tubing, which could be pulled into the attic much like electrical wire and then threaded back and forth through the rafter spaces, much like the system described. Small diameter PEX would also have more surface area to diameter, so that it would potentially heat the water faster than the PVC version. There are also clips for installing underfloor radiant heating systems that would be equally appropriate for this application. And, again like an underfloor radiant system, efficiency of the system might be further improved by adding radiant foil insulation (as well as helping keep the attic cooler).

Let me know if you undertake a system like this. I'm interested in other examples of this and seeing how viable a possibility this would be for direct heating or even just pre-heating water for household use. This seems like a very viable possibility, and I'm interested in gathering more information to help make this a more useful system that more people can install and use in their own homes.