Any experiences with the Bosch AE 125 (Electric) Tankless?

Discussion in 'Tankless Water Heater Forum' started by STyler, Oct 2, 2009.

  1. STyler

    STyler New Member

    Messages:
    43
    Location:
    Rock Hill, SC
    Wish I knew. I'm just planning on providing overkill so I don't have to worry about it. I'd guess wash temp would be closer to 95-100 F.
    Last edited: Oct 24, 2009
  2. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    OK, so 5 GPM with half the water supplied by a heater set at 160 F would give you a ~30 minute shower.
    Two 80 gal tanks would give you one hour.

    Or, if you can get heater elements that put ~35 kw into your 80 gal tank you have in effect made yourself a 5 GPM 100 F "tankless" heater.
    The problem now is to find a 35 kw, 146 A, 1.6 ohm heating element that is mechanically compatible with your existing heater. You probably won't find one; it would get so hot the water would boil locally and impede heat xfer.

    Another way, using any 300 gal. tank holding 2500# of water.
    It takes 1.3 therms, 37 kwh, to heat this 300 gal by 50 F.
    At 4500w from your regular WH it takes 8 hrs @ 0.6 GPM to fill the tank with hot enough water.

    To avoid math errors and do tradeoffs put this on a spreadsheet.
    Last edited: Oct 24, 2009
  3. STyler

    STyler New Member

    Messages:
    43
    Location:
    Rock Hill, SC
    Is having the water heater wired for simultaneous operation an option to reduce recovery time?

    Side note: Why do the WH mfg'ers show the annual operating costs of 40, 50, 65 and 80 gallon units all roughly the same (just a few dollars difference)?
  4. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Two of us use 35 therms/month to heat the water. The WH gallon size may not correlate that well to family size. Normal use is 70 gal/person/day of water. Maybe half of that is hot water.
    I guess there could be some Economy of Scale with larger heaters.

    Or, they're just lying. :eek:
  5. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    Typically residential units, regardless of tank size, use (2) 4.5KW elements.
  6. STyler

    STyler New Member

    Messages:
    43
    Location:
    Rock Hill, SC
    Thanks for the help.

    Going to try and make a tank work. Then just wait and see if I need to add to the system.
  7. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Because the Energy Guides are written for an average U.S. home's estimated hot water use, regardless of water heater size. (I think 2.6 residents is one of the assumptions.) Actual use will vary widely by region because of annual average incoming water temperature, not to mention individual habits, etc. With a family of four in a midwestern climate I use only about 60% of the Energy Guide total and a quarter of that is standby losses.
  8. Terry

    Terry Administrator Staff Member

    Messages:
    15,412
    Location:
    Bothell, Washington
    One of my customers uses an Electric Tankless for washing wine barrels.

    Like you, he needs an endless supply of heated water.
    Once the job starts, he's washing until every last barrel is clean.
    He has a winery, and I've seen how many barrels he has to clean.
    The other wineries in Woodinville use tankless too.
    If you use electric, the electrician brings in the proper breakers and wire for it.
    They use much more power then a two element tank heater.
    A two element tank heater only heats with one element at a time.
    So unless you have plenty of stored heated water beforehand, you will run out.
    Or you can also use gas.

    Last edited: Oct 30, 2009
  9. Dana

    Dana In the trades

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    3,020
    Location:
    01609
    As an aside, high volume continuous flow washing apps like this are where drainwater heat recovery systems can often pay big dividends, boosting the apparent-power of the HW heaters by 6-10kw while cutting the power use in half. (Probably easier to consider retrofitting into a winery than in a stable though, eh? ;-) )
  10. STyler

    STyler New Member

    Messages:
    43
    Location:
    Rock Hill, SC
    It's very difficult to get water usage requirements from my daughter, but after grilling her, it appears that the usage during that 1 hour per horse wash cycle is not as constant as I initially thought.

    Since I have a near-future need for a 50 gallon tank heater, I think I'm going to try that unit in the barn and wire it for simultaneous element operation and see if that is a workable (and much cheaper) option for the barn. If it can meet the demand, I'll leave it in, if not, I'll switch over to tankless and use the 50 gallon unit in another application.

    Currently looking at the Rheem Model# 83MXR52-2 (if I can find a supplier or Home Depot sells a GE equivalent). Anybody know of any issues with this model in simultaneous operation?
  11. kraemerr

    kraemerr New Member

    Messages:
    1
    Location:
    Texas
    Electric Tankless less than 1/2 the cost of propane

    Electric tankless compare to propane at about $1.00 to $1.25 per gallon depending on your region of the country. Current propane costs run about $2.30 a gallon delivered.

    Check out the 32KW SEISCO, its made in Houston Texas and has the most advanced digital power management of any of the electric tankless. Better temperature control and no flickering lights. It also detects flow by temperature, not flow so you can use with preheated water like solar, geothermal or a good old electric tank on a timer to take advantage of time of day rates. It should give you 5 GPM at a 40 degree rise. It also works in HARD WATER without a softener, try that with a gas tankless!

    They have an optional "load shed" relay that allows you to control any thermostat controlled load so it doesn't run at the same time as the water heater. This allows the SEISCO to fit on existing electric panels where other electric tankless may not. Its got a 20sec delay and 3 minute cycle time so you can use with cheap A/C units with confidence.

    Their service is in Houston, not India or Germany so you can get an English or Spanish speaking rep and parts ship in a day
  12. Dana

    Dana In the trades

    Messages:
    3,020
    Location:
    01609
    Got math? Tengo matemáticas?

    1kwh =3412 BTUs assuming 100% efficiency on the electric tankless

    1 gallon of propane= 91600 BTUs burned in a 0.60EF HW tank, call it 55000BTUs delivered to the water, which mean's you're getting 55000/3412= ~16kwh-worth out of a gallon of propane.

    Burned in a 0.80EF tankless call it 73000BTUs delivered to the water, or 73000/3412=~21kwh-worth per gallon of propane.

    In my neighborhood electricty costs a bit north of 15cents/kwh, so running the electric tankless is equivalent to $2.40-3.15/gallon propane, depending on what type of propane HW heater you're burning it in.

    The average rates in your home state of TX are 12cent/kwh, so there you're talkin' $1.90-$2.50/gallon equivalency, about 2x the numbers you're presenting.

    See: http://www.eia.doe.gov/cneaf/electricity/epm/table5_6_a.html

    Methinks you've got the math rong.
  13. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Yep, without the relative rates the comparison is meaningless. And Dana was actually using pretty low values for incremental EF for propane. More likely is something in the mid 70's. Storage losses get tacked on as a fixed quantity.

    Texas electric rates have been high because they did a bunch of conversion to nat. gas assuming it would be cheap long term. Electric hit 15 cents/kwh back in about 2005 while I was there, but I suppose it has dropped since then. It's one of millions of examples of the standard investment cycle stupidity by big business and utilities. It's funny how everyone acknowledges the cycles exist then do their economics and investment planning with no respect for those same cycles.
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