Aug 122011

DWHR patent in the mailbox

Before the summer we found the time right to send in our patent application to the Patent Office. It will be some time before we can anticipate the approved Patent. For now our product is “Patent Pending”

Jun 082011

DWHR vacuum forming mold

Most of the production tools for the DWHR unit are now ready. Vidar Fagereng at Ny Plast  is demonstrating the principles of the two molds. In his hands he is holding the top piston mold that is needed to help push the heated plastic sheet into the bottom mold prior to applying vacuum suction to it. With the additional top piston mold it will be possible to manufacture the deep meandering canal structure where the grey water from the shower cabinet will be flowing.

May 152011

Production ready 3D model of DWHR

The 3D model is now refined as far as we can before actually making the product.  It consists of two main parts: a plastic enclosure and a copper pipe unit.

The Norwegian company Ny Plast will be making the mold and do the actual vacuum forming for the meandering canal structure where the drain water will flow.  It turns out that the design literally is stretching the limits of this low cost production method. The usual maximum stretch of the plastic sheet of 3x is pushed to 4x. Prior to start up they are now making a small test to see if this is possible. Two parts are needed to do this. The normal vacuum mold and in addition a “piston” mold that will push the plastic down into the canals and help the vacuum to form the part. Do hope this will work out.

The pipes will be manufactured in China. We are very pleased that we have found a company that has been given us useful advice during the design process. The pipes are now designed to be bent in their mainstream HVAC production line. This will contribute to predictable cost, consistent quality and flexible volume ramp up.

May 052011

Arthur has completed an overview of products, test results and contact information in this easy to read report. He has also taken the time to explain the basics of drain water heat recovery, including different mounting options.

You will get immediate access to the Shower Heat Recovery report by signing up to our Meander DWHR newsletter. Our vision is that every home should have some sort of heat exchanger connected to the grey water of the shower. We hope the report will help you find the best unit for your home.

Here is a list of the heat exchanger companies that are reviewed in the current revision of the Shower Heat Recovery report:


We welcome information about other companies that are not yet included.

Apr 272011


Svein Medhus, one of the owners of Meander Heat Recovery, received April 6th the Pangea enviromental  prize for having improved the energy efficiency of his family home. The prize of NOK 25.000,-  (about USD 5.000) was presented to Svein by Fredric Hauge at Bellona in Oslo:
“Individuals that stand out and take the initiative to show others how to save energy are the heroes of our time. Svein shares his energy saving home improvements on his blog Urge 4 less energy use, he has also been innovative and made a new drain water heat recovery unit for the family shower cabinet”  

The prize money will be invested in further test and development of drain water heat recovery units at Meander Heat Recovery. (Photo: Andreas Kokkvoll Tveit / Bellona)

Mar 312011

First shower heat exchager 3D model

We have been doing many temperature measurements and flow tests on our DWHR prototypes. This information has now been combined and together with our design team we have completed our first 3D drawing of the shower heat exchanger. Coldwater connects to the ½” fittings, and the graywater connects to the two 40mm drain pipes. We started out with 32mm drain pipes, but our market research indicated that there is a change going on in favor of the larger diameter.

The unit is designed to be placed on your bathroom floor underneath your shower cabinet. The drain water flows through the heat exchanger and pre heats the cold water.

Feb 192011

Prototype 3 long term testing

Testing of prototype #3 is now in its 45th week. We have been tracking cold water temperatures at the in- and output of the unit, as well as temperature difference of the drain water. From these temperatures, the performance of the heat exchanger can be calculated.

We have noticed a decrease of performance over time. This did not come as a big surprise, because we always knew that DWHR units are susceptible to fouling: the deposit of material within the unit (soap, skin flakes, hair, shampoo etc.) reducing heat exchanger effectiveness.
Our design uses copper tubing and a relatively high flow speed of the drain water to reduce fouling. Biological fouling can largely be eliminated by using copper pipes. Never the less, we found that some form of maintenance would be necessary to minimize the reduction in performance. We do not want the user to have to open the unit, nor would we like to use toxic, aggressive substances (e.g. caustic soda) to clean, so we tested with some alternative methods.

It was found that pouring 1-2 liters (½ gallon) of very hot water (e.g. waste water from boiling potatoes or pasta) through the unit restored to a great extend the performance. The reason for this became somewhat clearer when we opened the unit for inspection: the fouling on both the copper tubing and within the channels is a very loose substance that can easily be removed. So pouring in very hot water with a relatively high flow and force loosens and carries away a great amount of the fouling.