Wastewater Heat Recovery

sparkchaser · 11-14-11, 10:31 PM

Hello all,
I've been looking around this site and didn't find a thread on wastewater heat recovery, so I guess I'll try and start one.

Several years ago I read about a heat exchanger for bathtubs and showers comprised of a copper 2 inch drain pipe wrapped with 3/8th inch copper soldered in place, then wrapped with insulation. As the shower is running, hot water goes down the drain, and COLD water supply is routed through the smaller tube on the way to the shower. Most of us probably don't run the shower at maximum temperature, so the COLD water which is flowing and mixing with the hot water (so it doesn't scald us) is now WARM water, thus requiring less HOT water. A variation on this theme would be a larger heat exchanger in the main drain pipe, with the smaller pipe going to hot water tank inlet.

So, does anyone have any experience with this concept? I know a few years ago there was such a product on the market but I haven't seen or heard of it since. Perhaps some of us can try this out! I have a houseful of girls so I stand to gain a lot from this! I'm thinking maybe 2 feet of 2 inch copper wrapped with as much 3/8th inch tubing, or 1/2 inch if I can get it to bend that tight, probably using a mandrel and putting the larger tube in a lathe while wrapping the smaller one on. Then solder, and wrap in reflective bubble wrap insulation, perhaps followed by fiberglass batt. I have room under my house to install it. I'm also thinking of trying a piece of 1/2 inch PEX in a U- shape taped to the bottom side of the main drain line, for about a total of 30 feet or so (remember u-shaped) then wrapped in reflective bubble wrap and fiberglass. Then tie that into hot water tank inlet. I already have the bubble wrap insulation and the fiberglass. Perhaps also insert two thermocouples for HX inlet and outlet temperatures. I really wish I had a data acquisition device.... hmm... next little project?

11-14-11, 10:31 PM	#1
sparkchaser Jack of all trades Join Date: Jun 2010 Location: Washington Posts: 27 Thanks: 3 Thanked 1 Time in 1 Post	Wastewater Heat Recovery Hello all, I've been looking around this site and didn't find a thread on wastewater heat recovery, so I guess I'll try and start one. Several years ago I read about a heat exchanger for bathtubs and showers comprised of a copper 2 inch drain pipe wrapped with 3/8th inch copper soldered in place, then wrapped with insulation. As the shower is running, hot water goes down the drain, and COLD water supply is routed through the smaller tube on the way to the shower. Most of us probably don't run the shower at maximum temperature, so the COLD water which is flowing and mixing with the hot water (so it doesn't scald us) is now WARM water, thus requiring less HOT water. A variation on this theme would be a larger heat exchanger in the main drain pipe, with the smaller pipe going to hot water tank inlet. So, does anyone have any experience with this concept? I know a few years ago there was such a product on the market but I haven't seen or heard of it since. Perhaps some of us can try this out! I have a houseful of girls so I stand to gain a lot from this! I'm thinking maybe 2 feet of 2 inch copper wrapped with as much 3/8th inch tubing, or 1/2 inch if I can get it to bend that tight, probably using a mandrel and putting the larger tube in a lathe while wrapping the smaller one on. Then solder, and wrap in reflective bubble wrap insulation, perhaps followed by fiberglass batt. I have room under my house to install it. I'm also thinking of trying a piece of 1/2 inch PEX in a U- shape taped to the bottom side of the main drain line, for about a total of 30 feet or so (remember u-shaped) then wrapped in reflective bubble wrap and fiberglass. Then tie that into hot water tank inlet. I already have the bubble wrap insulation and the fiberglass. Perhaps also insert two thermocouples for HX inlet and outlet temperatures. I really wish I had a data acquisition device.... hmm... next little project?