Series Boilers?

Discussion in 'Boiler Forum' started by Ralphxyz, Jul 28, 2012.

  1. Ralphxyz

    Ralphxyz New Member

    Messages:
    6
    Location:
    Long Island, NY
    A couple of years ago a new boiler and radiation company called Slant Fin had a series boiler package
    where if you had a 200,000 btu load you installed two 100,000 btu boilers. The idea was that one of the boilers would do the early season heating and the second would kick in as the outside temperature got colder.

    I have no idea how successful this concept was but have always liked the idea.

    I would like to implement the same idea but have been out of the heating buisness for a long time so have forgoten how the controls would have been set up.

    Any help would be appreciated.

    I'd gladly go into details on my new project if you would like, I think it is a novel idea.

    But I need to know what control components would be needed and how to set them.

    I would be doing a mixed three zone install.

    Ralph
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    With the advent of modulating boilers, this is no longer that great of an idea. A modulating boiler can adjust in the burner range of around 20-100% of its maximum output and is MUCH more likely to match the required load than a binary system that makes jumps in 100K steps!

    Under ideal conditions, a boiler runs constantly just matching the heat loss of the structure. This is impossible to do with a fixed output, even serial setup system.
  3. Ralphxyz

    Ralphxyz New Member

    Messages:
    6
    Location:
    Long Island, NY
    Thanks for the reply Jim, now that is interesting.

    I have been out of the heating field about the time that modulating boilers came along so I am not familiar with them.

    Let me layout what I am working with, I am open to all suggestions.

    I have a single residence with a 120,000 btu oil boiler non zoned with a up stairs and down stairs with baseboard radiant heat and a zoned garden room with radiant heat in the floor on the first level.

    The house is going solar and the owners want to get rid of the oil burner.

    Going to a ground source heat pump is not practical, because of expense if nothing else.

    So we are looking at replacing the oil burner with a electric boiler.

    Breaking the heat loop up into 3 zones. I suppose we could go with a staging electric boiler I was just wondering if using multiple boilers might be a good idea. Plus "most" residential electric boilers are maxed out at 65,000 btu's to get larger boilers it appears you have to go into the commercial class which is more expensive.

    So anybody have some good ideas on what could be done?

    Thanks,

    Ralph
  4. Ralphxyz

    Ralphxyz New Member

    Messages:
    6
    Location:
    Long Island, NY
    Hey thanks Jim for the reply and the insight!!

    The ideal conditions concept is very intriguing.

    I will start a new thread outlining my project.

    Thanks again.

    Ralph
  5. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    At Long Island style electricity pricing, you're not going to get much operational cost savings out of an electric boiler compared to oil, and it may be even more expensive.

    But in an L.I. climate you can do EXTREMELY well with ductless air source heat pumps- almost as good as ground source heat pump efficiency at a small fraction of the up-front cost. A typical 3-zone 2.5-ton system would usually be well under $10K even for the highest-efficiency models. With a best-in-class version you should be able to run a seasonal average coefficient of performance (COP) of ~2.8-3.0, compared to ~3.5 for a typical GSHP, or 1.0 for an electric boiler. An example of somebody heating exclusively with a mini-split in a very comparable climate can be found here. Mind you he's an energy nerd living in a tighter-than-average house and willing to let some rooms run cold, but then again it's a ~$3500 single-head unit with only a 12,000BTU/hr nominal output, but it's WORKING, and working reasonbly. With multiple heads and compressor sizing appropriate to the actual heat loads, most L.I. homes are likely within the range of ductless heat pumps, or could be with some insulation & air sealing upgrades.

    It's highly unlikely that the heat load of your house is anything like the 100KBTU/hr you get out of the 120K oil burner, and in fact it's VERY likely to be under 50KBTU/hr at +15F (the approximate 99% design temp for much of L.I.) All good heating systems start with a careful room by room heat load calculation using realistic design temperatures. Only a fairly large house with minimal insulation and single-pane windows would actually need 100KBTU/hr of boiler in your climate. (My ~2400' circa 1923 bungalow in central MA with single-pane double-hungs + storms and known insulation gaps has a measured heat load of ~30KBTU/hr @ +15F. When I moved in it was heated with a gas-fired boiler with an output of 118K- more than 3x the actual heat load at the local design temp of +5F. Oversizing of 3x or more is very common in this region.)

    Even if it would take too much money in insulation windows and air-sealing to get the design-condition heat load into mini-split territory, running the baseboards with an electric boiler as the backup to the mini-split wouldn't be a stretch, and the heating costs would be less than half what it would be running on electric boiler alone.

    "going solar" has many different meanings in different contexts- can you elaborate on what that means in your terms?
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