Today David Velan of Ecodrain paid us a visit here at South Mountain so my colleague Brice Delhougne and I could see his product firsthand. A few years ago David got interested in capturing the waste heat in shower water and other hot waste water. Others have done that (Powerpipe) but they have been limited to applications where the vertical heat exchanger, usually 4-6 feet long, can fit, and still be higher than the wastewater outlet from the building. Ecodrain's innovation is a wastewater heat exchanger that can be mounted horizontally.
In the photo below, you can see the inlet and outlet, which is 2 inch PVC, and the side taps for the inlet and outlet for the potable water. The unit is about 56 inches long. The flow is countercurrent - the wastewater on top flows one way, and the potable water below flows in the opposite direction and picks up heat across the copper interface. Depending on the relative flow rates, and the pitch of the unit, the Ecodrain recovers 30-45% of the energy in the wastewater.
David went through many evolutions before arriving at his product. It has a double wall heat exchanger configuration that should satisfy codes (the product has a UPC acceptance) and square section tubes on the potable water side to maximize heat exchange contact area. The upper portion of the unit is PVC and is smooth to minimize any buildup of solids. Here's a cross section:
One of the Ecodrain innovations is seen in each square tube - it's a plastic insert designed to keep the flow highly turbulent to increase heat transfer.
The bottom of the unit has a drain hole so that any leaks become obvious quickly.
The unit is designed to work with very slight pitch, like a typical plumbing waste line, but it can be pitched at more severe slopes, and the increased velocity of the wastewater increases heat recovery.
The unit can be plumbed so that the preheated water flows to the cold side of the shower, or to both the shower and the cold inlet of the water heater. The latter equal flow configuration will harvest the most BTUs.
Let's do some Marc's Sloppy Math. Say a family uses 30 gallons/day of shower water and 1/3 of that energy is recovered. That's about 625 kWh/year. At $0.20/kWh (MA residents are about to see a 30-35% rise in the supply portion of their electric bills due to last winter's natural gas price squeeze!) that's $125/year. The unit costs $440, and let's say it ends up at an installed cost of $1,000. There's a simple 8 year payback. With natural gas this will be worse. To get 625 kWh/year from PV would take about 500W of panel, which costs more than the Ecodrain installed.
One application David related to me is using the Ecodrain in cases where people are running out of hot water. Recovering drainwater heat effectively stretches the storage capacity of a water heater.
David kindly left us with one and we're looking for a good application, so we can monitor its performance in an actual situation. We were impressed with the iterative thoughtful engineering embodied in the product, it's rugged construction, and the testing Ecodrain has done to show energy recovered and its clog-free performance.