Off Grid DHW heater Control

I would like to use a highly efficient condensing hot water heater like the AO Vertex, but the OEM is telling me that the controls would not work well with the daily cycling of power that would occur when our inverter went into sleep mode. Essentially we would need to reset the temps and clear excessive cycling faults each day upon power up. Does this really make sense. How do others off grid get around this with the newer more sophisticated modulating controllers for DHW??

Comments

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Off Grid DHW heater Control

    What is the sleep threshold for the inverter? Why can't you (at the expense of SOME wasted power) leave some load burning 24/7? A ten watt load for ~ 10 hours is only 100 wh.

    Tony

    PS. This is why I still like the standing pilot water heaters. I fire the pilot on mine usually after lunch to do lunch dishes, and leave it lit through evening showers, so the waste from the pilot is minimal. I also have a thermo damper so it isn't loosing room heat all day an night.
  • audredgeraudredger Solar Expert Posts: 272 ✭✭
    Re: Off Grid DHW heater Control

    What inverter do you have?
    Is there no an on mode vs seek?
  • System2System2 Posts: 6,290 admin
    Re: Off Grid DHW heater Control

    Magnum Magnasine MS4448-AE pure sine wave inverter is being used. I would rather NOT keep the inverter on all the time just to run a controller. I had thought about isolating the controller portion of heater on a separate leg with a marine battery/inverter that is kept recharged. The powervent would off course be enough load to activate the inverter whenever needed.

    I had intended on using a Bosch hydoignite tankless, but found out I would need a powervent anyway for horizontal venting and I decided to also use the DHW for radient...this led me to the AO Vertex (or similar). Or even the Navien. But the controller load on more sophisticated heaters is where I am concerned...releative to the 24/7 load (albeit small).
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Off Grid DHW heater Control

    What about a smaller inverter dedicated for only the water heater. Might run more efficiently 24/7 that an additional load on the magnum at idle.

    What is the draw on the water heater both at idle and at full fire? Suresine 300 is reliable and very efficient, and reasonably priced.

    Tony
  • peterakopeterako Solar Expert Posts: 144 ✭✭
    Re: Off Grid DHW heater Control

    I am using a ( siemens ) !LOGO plc and made the program myself it runs direct from DC and if requird to start the pump the inverter starts up whitout aproblem.
    I specialy used a DC version to avoid problems.

    Greetings from Greece8)
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,352 ✭✭✭✭✭
    Re: Off Grid DHW heater Control

    This is a common problem and you do need a 500 watt source to run electric fired ignition on this water heater or for a gas dryer or most of the horrible gas ovens that are out there.

    If you want to really be efficient and not have all this headache. Consider using a normal gas heater with the hydronic loop fittings, and drain back solar hot water collectors. You can go out the wall without a powered vent also. Not sure about if the sunlight hours in your location will math out for deep winter. They do out here...It will cost more upfront but will pay back quickly if the math is right.

    It is hard to give up search mode but as the others have said it might be the way to go if your math still points to the vortex because of the winter sun hours in your location.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Off Grid DHW heater Control

    David,

    Are you saying that the AO Smith water heater uses a ~500 watt hot surface ignition device? Boo hiss!

    The Rinnais, the Takagis and I believe the newest generation of Palomas only require ~75 watts. Most of that is for the combustion blower, and a bit for the control board and ignitor.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,352 ✭✭✭✭✭
    Re: Off Grid DHW heater Control
    icarus wrote: »
    David,

    Are you saying that the AO Smith water heater uses a ~500 watt hot surface ignition device? Boo hiss!

    The Rinnais, the Takagis and I believe the newest generation of Palomas only require ~75 watts. Most of that is for the combustion blower, and a bit for the control board and ignitor.

    Yes to ignite and then it goes off. Kind of like a gas dryer but not as bad as a gas oven igniter that is on the whole time the flame is on. In baking that can be 50% of the time the oven is on.

    The beauty of the Vortex and other condensing water heaters is they are more efficient than a tankless, use a 1/2" only gas line, and can keep up with a tankless. So for hydronic they are the cats meow, except the pesky stand-by current and the lousy ignition circuit power.

    It will get better... for instance the green button on the LCD remotes allow you to controll the display power and the new stand-bye losses allow the tv to be controlled by remote with an offgrid inverter in search mode.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Off Grid DHW heater Control

    Too bad that there is not a DC powered unit out there, yet.

    I mentioned in another post about the variety of DC currents ( 5 ) used in one of the control boards and it seemed so strange that, for us off grid types, that we need an inverter to take DC to AC and then the unit converts it to DC again...???

    As an alternative to having a a large inverter running, it would be possible to have a separate small 12 v battery, with a single panel or 2 for charging, and dedicated minimal inverter to power the water heater... just trying to think outside the box a bit.

    The solar heat collector I like...

    HTH
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • System2System2 Posts: 6,290 admin
    Re: Off Grid DHW heater Control

    Just got response from AO today...this seems so high for standby consumption????

    "The FLA of the Vertex100 with mini igniter is 1.1A during purge/ignition/operation, and 0.25A during the standby at 120V power input, which means the power consumption is 132WH during operation and 30Watt-hour during standby."
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