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Thread: Heat Recovery Unit for shower

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  1. #1
    DIY Junior Member C Williams's Avatar
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    Default Heat Recovery Unit for shower

    I love showers. I love long showers. Let's say I take an "hour power shower".

    With that in mind I've been thinking of installing a heat recovery drain system for an upstairs shower. I'm currently thinking of "Power Pipe" but I'm sure there are others.

    First, does anyone here have any experience with these good or bad. And second: Typically one would install this in line with the cold supply for the hot water tank but since my tank is a good distance from where the heat recovery unit would be, it would be simpler to install this in line with the showers cold supply. I'm not sure if I would need a fancy mixing valve to make this feasible. Any thoughts?

    Thanks.

  2. #2
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    I think you should try it. What size is your hot water tank?

    I am going to install a second hotwater tank in my mechanical room and strip it of any insulation. My plan is to use the warmth from the room to pre-heat the water overnight to about 24 degrees C.

    When we have demand for hot water the water will first enter the secondary hot water (holding tank) and then feed the proper hot water tank. I think this will save me hundreds of dollars if not thousands over the next ten years.

    An investment like this will take years to break even. Don't expect to see a return on your investment any time soon.

    JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Plumber jimbo's Avatar
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    You need to rely on recommendations from the manufacturer about install options. Their engineers should have the answers to those questions.

    What are you wanting to accomplish with this? Certainly some energy will be recovered. How much...check their research. Figure that the water cools considerably as soon as it starts running off your back. It gathers on the tile floor, and eventually into cold uninsulated drain pipes. So if you expect this system to give you longer showers, I don't think that is going to happen.

    I assume you have a tankless water heater?, since if would take about a 200 gallon tank-type to provide an hour shower@!!

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    Moderator & Master Plumber hj's Avatar
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    The recovery amount will be so miniscule that it is doubtful you would ever notice its effect. To get heat transfer heat source and the water have to be in contact long enough for the transfer to take place. Usually this is done with a twisted "labyrinth", a long transfer pipe, such as a flue, or multiple small tubes with a lot of surface area. Your shower unit will have none of these.
    Licensed residential and commercial plumber

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Here in North Vancouver the water temperature entering the hose is icy cold. I would think even a 10' section of cast pipe with the copper feed line twisted around would improve things somewhat.

    Is there any test data on the subject that anyone has found?

    I would love to know more about this subject.

    JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

  6. #6
    DIY Junior Member C Williams's Avatar
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    Here is a 2007 study by the Canada Mortgage and Housing Corporation.

    Drainwater Heat Recovery Performance Testing at CCHT

    The in situ effectiveness testing looked at how long the shower could be run before the water temperature dropped below 37C (98.6F). All DWHR devices resulted in significantly longer hot water availability times than the benchmark time of 28 minutes. Configuration A results ranged from 39 minutes to 62 minutes. Configuration B results ranged from 53 to over 75 minutes.
    Some Canadian provinces are offerring rebates for these.

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by hj View Post
    The recovery amount will be so miniscule that it is doubtful you would ever notice its effect. To get heat transfer heat source and the water have to be in contact long enough for the transfer to take place. Usually this is done with a twisted "labyrinth", a long transfer pipe, such as a flue, or multiple small tubes with a lot of surface area. Your shower unit will have none of these.
    Incorrect. This is the most common layman's misunderstanding of how heat transfer works: "in contact long enough." It's not the residence time but the heat transfer coefficient and area, along with the driving force (delta T). Liquid film coefficients are quite high.

    If you look at the designs of the drainwater heat recovery units they can achieve reasonably good recovery. The layout is typically one of countercurrent, falling thin film exchanger, often with a multi-parallel path coil in close contact on the other side. Combine these with the excellent heat transfer properties of water and you have a functional design.

    I evaluated a few designs a year or so ago the same way as I did when doing heat exchanger design including--thin film types--for a living (and I've not yet had any exchanger I designed/specified underperform.) I started out skeptical of some of the claims, but when I began reviewing the drawings I achieved similar results with my own calculations of heat transfer coefficients, pressure drop, effective area and such.

    Higher volume/long duration shower users will get more benefit than low volume users. For high volume, minimizing pressure drop requires more parallel coils and heat transfer efficiency declines somewhat, but that is more than made up for by the greater total Btu's recovered.

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Some great information shared thank you all.

    I have three little girls and they all have bath and shower time after dinner. This is my biggest demand time for hot water.

    What do you think of a second tank as a holding tank? I would think in a 24 hour period the holding tank would have enough hot water or at least warm water that the recovery of the main hot water tank would be quicker and shorter. And in doing so cheaper.

    I have even thought of wrapping the spare tank with my hot water heat return legs. Tapping any heat out of them and making the temperature of the holding tank even warmer???

    JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

  9. #9
    DIY Junior Member TonyG's Avatar
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    Default Showersave

    Try this system, more efficient than powerpipe in SAP for the same size, 2.1m length. installation methods outlined on web site www.showersave.net

  10. #10
    DIY Senior Member jch's Avatar
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    Cool. Hadn't heard of them before.

    I chose Power-Pipe because:
    - it had been tested by the National Research Council (Canadian Govt Agency) for efficiency (rather than just having manufacturer-reported numbers)
    - it was on the Government approved list for rebates (ecoEnergy program) http://oee.nrcan.gc.ca/residential/p...retrofit/13302
    - it had the highest efficiency rating (for the size) of all units tested
    - it was available at Sears and Big Orange (in case I had to return it).

    ShowerSave says their 2.1 metre tall unit has an efficiency of 66% (http://www.showersave.net/about/what-is-shower-save/), whereas the same size of Power-Pipe (R4-84) has an efficiency of 66.7% (essentially the same).

    So I'd choose whichever one was more convenient to get (or cheaper). It looks like the ShowerSave is around $1500, whereas the Power-Pipe only cost me $695 from Sears.ca

    Either way, it's worth doing.
    ----------
    - John

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