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    Lochinvar Cascade Operation With Smaller Leader (8 Posts)

  • BigRob BigRob @ 4:14 PM
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    Lochinvar Cascade Operation With Smaller Leader

    I’d like to use a WHN55 as the leader and WHN199 as a
    follower.  The 199 would also heat an
    indirect tank.  Can any of you provide
    some practical comments on this type of setup? 
    The service manual doesn’t say you can and doesn’t say you can’t have a
    smaller leader.  It does mention that
    when the leader and follower are different sizes an “efficiency mode” is
    automatically selected.  Some questions:


    -Could I select lead/lag in this configuration or is it
    locked out?  The lead/lag description in
    the service manual seems better than the efficiency mode


    -I’m concerned the transition from the WHN55 to the WHN199
    might not be smooth.  The description of
    lead/lag addresses this, but the efficiency mode does not.  I’m assuming that Lochinvar has taken into
    account since “efficiency mode” is set when different boiler sizes are
    connected.  Whats get me is the sentence that
    “both boilers modulate together” in the service manual.  Can anyone clear this up for me?


    -I’m assuming when both units are firing and there is a DHW
    call, the non-DHW boiler will ramp up to 100% if needed.  Is this a good assumption?


    Any tips, tricks, experiences are appreciated.


    Thanks!
  • Mark Eatherton Mark Eatherton @ 8:28 PM
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    Contact the factory...

    Specifically Paul Rohrs.

    I did this once, but didn't use the 2 wire bus to make it work. I used an outdoor reset/ 3 stage controller.

    The physical plant was sized as 1/3 (for smaller boiler, stage 1) and 2/3 (for larger boiler, stage 2) and at a certain point if required, both boilers were fired 3/3's (stage 3).

    Interestingly, even when I showed up at design condition, I NEVER saw the 3/3's capacity running. If memory serves me correctly, I also had done something with the programming of the different controls, but it's been a LONG time ago that I pulled this one off.

    The last pair I installed were set up lead/lag rotational (when one boiler gets 50% more run time than the other boiler then it becomes a lag boiler) and when the lead boiler hit 50% of capacity, it would bring the second boiler on, and lower both to 25%capacity,and then bring them both up and down together until one boiler was again able to maintain.

    But that's been a few years ago, and I do know that Lochinvar has made some changes to their controls since then.

    Call Paul, he will know, and in the off chance that he doesn't, I guarantee he knows who does know.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • BigRob BigRob @ 8:45 PM
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    Thanks

    I'll do that. You would think this is a use case they would know about. I'm not too worried about balancing the load since the 199 would be firing DHW. I wish they made a floor standing fire tube. Have you seen and good stands for wall mount units. The boiler room has limited wall space due to piping.

    Thanks again, Mark.
  • Mark Eatherton Mark Eatherton @ 9:14 PM
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    Rack 'em...

    Could make a free standing floor rack out of Unistrut.

    There are also some OEM makers of racks, but not sure they make them for wall mount units. HSS? Or, hang them off the ceiling joists.

    And you're welcome.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • BigRob BigRob @ 3:25 PM
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    Leader..

    I got a hold of Paul. Super helpful. He said Lochinvar recommends using a smaller boiler as the leader. I'm happy to get the confirmation. Now I need to decide if DHW should be a zone or piped directly to the 199. I was hoping to just go low temp for heating and not mess with a mixing valve for the 12 thin slab zones. There will be 5 Myson convectors sized for low temp, too.

    The pro of the zone is a little redundancy, although the 55 will take longer to get the outlet temp to 190 for the indirect tank, so not sure it's worth the added complexity of the mixing valve. Admittedly, it's not that much more complex. I just love to keep things simple. There is a decent amount of DHW use as it's a condo building. Plus, most of the year is pretty mild, and with the diversity of the heating loads, I don't think heating would be interrupted except on the coldest of days. In that case the 55 should keep the loop temp from plummeting.
    This post was edited by an admin on February 28, 2014 3:29 PM.
  • Mark Eatherton Mark Eatherton @ 3:45 PM
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    Use both for DHW...

    Pipe them into a reverse indirect, stage their DHW settings so the 55 fires first, last and most often, and the big boiler to handle peak loading. Set the boilers production temperature on both for 150 degrees, and let the boilers cycle in and out as necessary. I've actually done this before and it works fantastic. The little boiler fires constantly covering the system standby losses if they are huge, and it stays in the condensing mode ALL the time.

    Glad to hear Paul was helpful. He always is.

    I am going to get by there during Comfortech 2014 in Nashville this fall and get caught up on what's new. One of the most innovative companies I've ever seen. and they listen to their customers…

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • BigRob BigRob @ 4:08 PM
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    DHW

    I need to use an existing normal indirect, unfortunately. I like the reverse indirects a lot. Have you tried the Mark Method with a normal indirect?

    To be clear, did you pipe the DHW as a zone or direct? I am assuming direct.
  • Mark Eatherton Mark Eatherton @ 8:45 PM
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    Direct...

    and beware of coil limitations in BTUH transfer capacity. Driving a tack with a sledge hammer doesn't work in this case.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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