Home Inspections Inc.

Green Home Solutions – Drain Water Heat Recovery

By November 13, 2012Blog

Drain Water Heat Recovery

The key to a sustainable home is through the reduction and recycling of the energy it consumes. One of the simplest ways of achieving the latter is with a drain water heat recovery system (DWHR). A DWHR reduces the total energy consumption of the water heater  20 to 30% by using the warm waste water to heat the incoming supply water.

How it works

A DWHR pipe is most effective when hot water is being used and discharged simultaneously such as showers and sinks. As the warm water is consumed in the shower, it travels down the waste plumbing stack where it clings to the walls of the pipe. The system captures the heat by moving the cold incoming supply water around the waste plumbing stack. To the right you can see a good illustration of how it works.

 

Drain Water Heat Recovery System

Efficiency

The efficiency of a DWHR ranges from 20 to 60%.  One of the largest contributing factors to its performance is the length and diameter of the pipe. The other factor is the shape of the supply water pipe wrapped around it. A rectangular supply pipe is more efficient than a round pipe due to the increased surface area contact with the waste stack. Another important consideration is the number of supply pipes that are used. Early designs only utilized one pipe which considerably reduced the water pressure. Current designs deploy three to four supply pipes which have minimized this effect.

Benefits

  • It’s passive and requires no maintenance.
  • It has a long lifespan (50+ years).
  • The payback period is 2-6 years due to its low cost and ease of installation. A typical solar water heater costs 80-90% more and is not very effective in the winter.
  • It reduces the rate in which the water heater temperature drops allowing longer showers.
  • Increases the lifespan of your water heater by reducing its load.
  • It’s compatible with all water heating systems.
  • It’s environmentally friendly and reduces greenhouse gas emissions.

Will it work for you?

DWHR systems work for almost all homes but are ideal if they have more showers than baths. The main shower must be positioned above the location where you would like to install the drain water heat recovery system.

A local Kitchener inventor, Gerald Van Decker, has perfected this technology with a product called the Power-Pipe. It can be purchased at  Home Depot or Sears online for $500 to $1000. A plumber should install the unit, but it’s a project a skilled homeowner could accomplish.