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Batch solar water heater

Post in 'The Green Room' started by hemlock, Sep 28, 2011.

  1. hemlock

    hemlock Feeling the Heat

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    east coast canada
    Hello,
    Does anyone have any experience with a "Batch" style water heater? I plan on building one this winter for next spring. The "Build It Solar" website has given me some good ideas/plans. It will only be used during the spring/summer/early fall months due to freezing. If anyone has any experience with these, or has any advice, it would be appreciated. Thanks.

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  2. semipro

    semipro Minister of Fire

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    No but I'm thinking about it. I'd be interested to see what you end up doing.
  3. maple1

    maple1 Minister of Fire

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    Not sure what that is.

    Link?
  4. hemlock

    hemlock Feeling the Heat

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    I stink with computers, so I can't post a link - but if you go to the "Build Its Solar" website, and look under solar water heating, you'll see it.
  5. WES999

    WES999 Minister of Fire

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    Mass north of Boston
  6. hemlock

    hemlock Feeling the Heat

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    I would like something like you built (nice job by the way), but space for the heat exchangers would be an issue. The prime reason I'm leaning toward the "batch" style is that it can be placed outside. I would have to drain it every October, and refill every spring.
  7. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    There are a lot of plans for solar batch heaters here:
    http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Batch

    Also some reports from people who built them and how they have done for them -- usually good.

    You will need to drain the batch system and bypass it for the winter, so you lose solar heating over the freezing part of the winter.

    The hardest part for most people is finding a good tank to use. Sometimes plumbing/HVAC outfits have new hot water tanks that have some slight damage and they can be used.

    If you scroll around on the same page as the link above, there are plans for drain backs, thermsyphons, and others -- so you can get an idea what the differences are.

    Gary
  8. billjustbill

    billjustbill Member

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    Loc:
    Texas
    I built a 40 gallon solar batch heater back in the late 1970's. The tank came from a hardware store and was a galvanized "non-bladder" pressure tank. The plans came from a magazine called "New Shelter".

    Back in the 70's, double pane glass was kin to the cost of gold!, I had a local aluminum window company make the wide single pane glass window, much like an outside storm window. It had two vertical panes with an aluminum support strip as the centerline. Here in North Central Texas, the batch heater worked great in the warm and hot months, as my well water comes out of the ground at 56 degrees. But, I was limited to using it between the last freezing temp day and the first freezing temp day of the late Fall, then drained for the winter.

    My two concerns had to do with the building materials in the plans and the weight. With the main structure built from a 2x4 framework, and the double cusp reflector made from reflective Mylar held on with contact cement and thin sheets of Masonite. The hot temps in Texas gave me cause to worry about possible fire from the high heat and always dry building materials. The outside of the structure was sheeted in 1/2" plywood, then tar papered and shingled to match the roof.

    The other worry was the sheer weight of 40 gallons of water, plus the weight of structure, itself.. I have a low pitch Ranch style home and a 14'x40' patio. I built the assembly on the house side of the seam between the roof overhang and where the patio hot-tar roof attached. That way, the majority of the weight was carried on the outside wall of the house; not the rafters. The plumbing was fairly easy using the CPVC hot water plastic pipe and running it was fairly easy as it went down the outside wall and under a pier-and-beam home where it came up in the water heater closet. Having any overhead water pipes was just asking for water damage from a broken pipe.

    Never had a problem the 3 years I had it up and going. In fact, the plans called for a special black oxide tape that bonded to the tank. When the tank kept popping its own pressure/temp popoff valve, I had to go in and spray the whole tank with a shiny black to stop it from popping off. When a hailstorm hit the county, and a new roof was in order, I had it taken down and never replaced it. The tank went to my brother to heat his kid's shallow round above ground pool....

    If I were to ever do it again, I'd build the new structure with all metal and cement board. Plus, I'd build it vertical and elevated about 2' above the ground. I'd use at least double pane glazing, the build insulated doors I could close on the cold nights to keep the 40 gallon tank warm....

    If the DIY approach is your thing because of the challenge or the cost, look at all the types to get the one that works with your solar exposure and you building skills. The better answer would be to buy one of the drain-back model hot water solar systems with its own insulated transfer tank and take the 30% tax credit....

    Bill
  9. GaryGary

    GaryGary Feeling the Heat

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    Hi Bill,
    Another approach is to buy a commercial collector only and build the rest of the drain back system like this one:
    http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
    As long as the collector is SRCC certified, the whole system qualifies for the 30% federal rebate.

    Four possible scenarios for doing a drain back system:

    - Build the whole drain back system yourself as described in the link above: No federal rebate. Cost about $1000

    - Use a commercial collector and build the rest per link above: 30% federal rebate. Cost about $2400 less 30% is about $1700

    - Buy a full kit of off the shelf parts to do a drain back. Costs -- varies, but about $5000 less 30% rebate is about $3500

    - Have a professional solar outfit install a commercial drain back system. Costs about $8000 less 30% rebate is about $5600


    These are just approximate and vary with the system size and quite a bit with where you live.
    I assumed two 32 sqft collectors.
    Some places have state rebates, and some of these apply to systems that are 100% DIY -- our out of pocket costs after the MT $500 rebate was under $500.

    Gary
  10. hemlock

    hemlock Feeling the Heat

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    Thanks, guys. I'll let you know how I make out. So far, my biggest trouble is finding a cheap storage tank.
  11. Seasoned Oak

    Seasoned Oak Minister of Fire

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    30 years ago a local Hdwe store had a simple system for sale. Tap water collector was empty until it got a certain temp then a pump filled the collector but the temp sensor was in the collector so when the temp fell the collector drained back. Collector only had water in it when it went over 100F approx. 12 months of use anywhere.

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