DWHR – Drain Water Heat Recovery – Follow-Up

We have discussed this so-simple-why-has-it-not-been-invented-before water heating conservation device known as the DHWR in prior posts:

ecoENERGY Report – Part 7 – Recommendations

ecoENERGY Report – Follow-up – Drain Water Heat Recovery (DWHR) Device

As a result of these posts, I received several follow-up questions as if I was some type of expert. I am not. So, I contacted Andre Cayer of Watercycles Energy Recovery, Inc. who provided answers to the following questions / comments [which have been edited by myself for brevity]. We are appreciative of Andre for taking the time out of his very busy day to add clarity:

Question / Comment #1:

Is there a maximum distance between the fresh water pipe. the vertical drain pipe and the hot water heater for the DWHR device to work effectively and efficiently? For example, in our basement the fresh water pipe coming up from the basement floor is right next to the hot water tank, however the vertical drain pipe is at least 8 feet away.

Answer:

The only real issue is one of pressure loss. Because the incoming fresh water is being heated by the DWHR device to just above room temperature, there is very little energy loss. I do not consider 8 feet away very far. I do consider 6 feet to be very close. 

Question #2:

Will the DHWR warm all of the fresh coming into the house? I would think that residents of the home would still want cold water coming out of their cold water taps.

Answer:

The DHWR device will not impact the temperature of the cold water in the house in any manner as the only cold water that will enter the DWHR device will be the water that was routed to the hot water heater.

Question #3:
What is the risk that the grey water will eventually start to mix with the fresh water after say 20 years or so or due to product manufacturing defect? What tests have been done on the design and / or quality control steps during the actual manufacturing to guard against this? 

Answer:

There is almost no chance for the grey (i.e. used) water to mix (contaminate) the fresh water. The fresh water is under pressure (50-80 psi depending on your area) entering the home and if there was a leak for whatever reason, the fresh water would leak out to the grey.

That said, due to the low volumes and lack of pressure in a drain stack in a residential setting there is very little chance of the copper wearing out and the only way for it to leak would be from a puncture. There are no seams or connections under the coil. Type M copper water line is acceptable in many provinces but we use Type L which is sufficient for most commercial applications and thicker than Type M.

Question #4:

Would there be any advantage to wrapping insulation around the outside of the DWHR pipe after installation and use, i.e. use wrapping that is available for hot water tanks?

Answer:

We get this question a lot; some people really want to do it but insulation is to prevent change in temperature. When temperatures are very close there is not much change. I do not recommend it though I do believe there is a nominal value in doing so.

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Comments

  1. mike says:

    re: question #2:
    I’m not an expert, but I believe your answer isn’t complete. I believe most mftr.s and installers (strongly) recommmend the fresh water from the dwhr br routed to the house’s hot water tank AND the cold line. In this case then, while (and only while) someone is showering (or anything w hot water is draining – ie. dishwasher, washing machine) the cold water will not be as cold.
    the thinking behind this is that if you’ve warmed the fresh cold water, then you won’t need as much hot water to acheive a comfortable showering temperature. This contributes significantly to the energy/money savings.
    Obviously, if this were a show stopper for someone, the dwhr could be hooked up solely to the hot water tank.
    But remember, the vast amount of the day there is no hot water draining so you would get your ‘normal’ cold water.

    • Phil says:

      The writings I’ve found at Minnesota Power DO detail that the water is routed to the water heater AND cold water. HOWEVER… preventing a change in temperature in water you do not want influenced is quite simple. You just route the cold water PRIOR to the DWHR unit to your sink so you can access cold water but proceed to route the water AFTER the DWHR unit to your shower (where you don’t really need cold water), washing machine, etc.

  2. Dan says:

    Hi Mike,

    That was the response I received from my contact with one of the companies manufacturering a DWHR.

    As I have written, we did not install it in our home as the pipe leading the grey water from our home is behind drywall, a mirror, a sink and a cabinet in our basement bathroom … and I wasn’t prepared to go through all that work.

    If there someone who has installed a DWHR or a manufacturer of a DWHR unit who can advise on the installation setup they used or should be used, please let us know.

    Thanks,
    Dan

  3. rwilson says:

    I like the idea of drain water heat recovery units because it surely helps to save on energy. When you consider not wasting the hot water in sewerage but instead use the heat from the away flowing water. Simply a fantastic idea. Of course the materials are not free but an idea to develop further.

  4. Rick says:

    What do you do in the case that all of your drain pipes run horizontal?

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