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Bad news for condensing purists...(ME)



  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    'nuther way to slice it.............

    Think of your reduced firing rate in this manner.

    Let's say instead of dropping the firing rate to 30% of max we could leave the firing rate the same and variably increase the size (sq ft) of the heat exchanger by 300%.

    Pulling numbers out of the air here but let's assume a fixed input of 100K firing into a 40 sq ft HX. Now when we want to "modulate" for the sake of efficiency we increase the HX to 120 sq ft.

    The net effect, hypothetically speaking, is the same as reducing the firing rate. The gas volume per sq ft of exposed HX surface is reduced yielding longer periods of time for the heated and unheated molecules to become intimate with each other.

    Moral of the story:

    Overcrowding your molecules is detrimental to your intimacy/efficiency ratio.

  • Kal Row
    Kal Row Member Posts: 1,520
    The gov report doesn’t go far enough...

    i used Lochinvar knights on commercial bath house type jobs with 180 degree loads only, and the owners save a mint, and have the gas bills to prove it, residential type bills in a commercial application!!!

    a year ago right here on the wall, someone posted the hard math of condensing, and if you take a therm of gas and fully condense all the h2o out of the flue products, you will get a total of 9000btu in the latent heat of condensation and 1.21 gals of water, so clearly it’s not condensing that’s really saving the money but rather the “exactly matching the fire to the load without dumping any of it up the chimney” – you can run a cast iron boiler with boiler protection and modulation, and you can do the same with copper, but you still have to keep the iron or copper hot enough so it doesn’t corrode, and that excess heat, goes right up the chimney unless you have a stainless scavenger attached to the flue to extract it – but then, you still need to have cool enough water to get it all out, whereas not putting the heat in to begin with is still a much better water to go, I cant wait for modcon manufacturers to install variable speed boiler pumps – that will be perfect, with absolute control of the delta-t across the boiler, imagine a mod-con with ten cast iron rads attached with pex home runs, and only one of them is calling, – so we only need 180f water at 1gpm off the low-loss-header, and the boiler only needs to put that much btu into it, most of these mod-cons can only turn the fire down to 20% as the fire gets unstable below that, but with a variable speed pump, you can effectively modulate lower!!!

    I tell my customers that everyone pays for mod-con boilers, blown-in insulation, and radiant heat, whether they actually have it, or just keep paying for it again and again and again, every 7-10 years is entirely up to them!!

    Ps: hard experience has proven to me that fully visible cast iron radiators are a good enough “radiant heat” on the efficiency scale – for example: in a basement den where an old lady spent most of her time, I replaced 14ft of fin tube baseboard with three 6-section recessed sunrads with reflective bubble wrap behind it and the zone went from running 40min out of the hour with the lady still being cold, to running 15min out of the hour and the lady being very happy – it was like day and night!!! They don’t call them “RAY-DEE-8-TORS” for nothing – the initial saving of fin tube and the low slung design look, is far outweighed by the comfort and energy savings of radiators - and the mass in the cast iron acts like a buffer tank and smoothes out the cycles – sure full radiant is better, and the most efficient, but those CI-RADs are the most bang for the buck, of course, “far outweighed” would depend on who’s doing the “weighing” , some simply cant stand the look and builders for resale need the absolute cheapest price – so there will still be bad stuff installed for some time – though the attached pic from one of moses’s jobs looks pretty good IMHO
  • Bernie Riddle_2
    Bernie Riddle_2 Member Posts: 178

    Kal, I really admire your zeal for perfection and rarely miss reading your posts, But this one in perticular strikes a chord. I am in the prossess of doing just what you recommend, removing my 3 zones of BB in a 3 story brick house and installing 10 such CI rads on one zone.

    The boiler is mere Munchkin M80 with ODR with trv's on the bedroom rads and free flowing in the living area with thermostat. Now here is the difference I plan on pipeing them for low head loss and no primary/secondary with pressure diff bypass across supply/return to ensure adequite flow through HX no warranty worries takeing full responsibility.

    Your thoughts or recommendations as to what size pump will over come the HX head loss and deliver to all rads if need be(i believe this is the same HX as the Knight)

    It has been well established that P/S piping is not good for maximum condensing (by the way i sized the rads for 140* water)

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