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Green Home Solutions

Updated on November 28, 2012

Drain Water Heat Recovery

The key to a sustainable home is through the reduction/recycling of the energy it consumes. One of the simplest ways of achieving this is with a drain water heat recovery system (DWHR). By using the warm water traveling down the waste plumbing, to heat the incoming supply water, you reduce the total energy consumption of the water heater by 20 to 30%.

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. Here is a good illustration of it in action.

The advantage of this type of arrangement is that it’s passive and requires no maintenance. It’s pay-back period is 2-5 years due to its low cost and ease of installation. A typical solar water heater costs 80-90% more and is not as effective in the winter.

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 building’s water pressure. Current designs deploy three supply pipes which have minimized this effect.

Will it work for you

DWHR systems are ideal for households that have more showers than baths. Your main shower must also be positioned above the location where you would like to install the drain water heat recovery system.

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