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Layout/Design Review

zavnetzavnet Posts: 15Member
Considering replacing my Polaris unit with a Mod/Con – put this plan together. Please provide feedback. For additional background on the current setup – see this post...

Two main questions:
1. Are mixing valves in front of each manifold an overkill -- given the biggest delta between zones is 25 degrees?
2. Is the proposed piping layout for a future wood burning boiler correct? Can it be simplified? At this point just looking to stub out… Ultimately looking to be able to run using either heating source for space and DHW.


  • hot_rodhot_rod Posts: 12,586Member
    do you know what type of wood boiler you might add? Some of them require a bit of a buffer tank to smooth them out. If you go with a gasification type wood boiler I'd add a buffer tank now and use it as a separator, buffer, and possibly to generate DHW. it could serve 3 purposes.

    So eliminate the hydro separator, the DHW tank, and have buffering online for now and later wood add on.

    Try this link for some state of the art concepts for the use of tanks in hydronics.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • zavnetzavnet Posts: 15Member
    I was thinking of flex fuel woodmaster, or something similar.
  • hot_rodhot_rod Posts: 12,586Member
    Yep, that is a fairly low water content boiler and would be best served with some storage or buffer. the sales sheet shows that also.

    Here is another link for you. The cover graphic shows about what you are considering. It also includes an instant DHW module. plenty good ideas between the covers.

    What are the 3 temperature requirements. What type of install slab or dry system? What about floor coverings. I try to keep the number of mix stations to a minimum.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • zavnetzavnet Posts: 15Member
    edited August 2015
    Hot Rod thank you for the suggestions.

    Looked at a number of postings -- the buffer tank does look like a better fit instead of the SEP. Will certainly incorporate that into the design especially given some of smaller zones which turn to be 10X less than min boiler firing rate (40K). Too bad 10:1 turndown ratio boilers are like endangered species in US (when it comes to parts and service availability).

    For the DHW I'll stick with a separate indirect - just seems a more straight forward approach (floor space is not an issue...)

    2nd floor -- 140 degrees - hardwood finish just stapled up tubes with reflective foil. Getting very poor transfer, and given last winter in the north east that's my most problematic zone.
    1st floor -- 125 degrees - hardwood floor with joist trak, reflective foil + R13.
    Basement/Garage -- 115 degrees - 4" slab on the top of reflective foil + R10 (2" owens corning).

    Future snowmelt tubes (will have a separate manifold) - under 2" of gypsum (over existing 4-in slab) + exterior tile.
  • njtommynjtommy Posts: 1,105Member
    edited August 2015
    Off topic, but
    It just seems funny to me that a lot of manufactures/ dealers say nothing about installing a mixing valve at the boiler to protect the boiler from low water return temps.
    I disagree on how they get installed in most systems. Using two flate plate heat exchangers first one is for DHW and the second for heating. They recommend you to pipe them in series of each other. It just seems to me your setting the boiler up for failure.

    I tried convincing my dad of the possible problems, but apparently I'm not an engineer and they know best. lol.
  • njtommynjtommy Posts: 1,105Member
    My dad went with a wood master 5500 wood burning boiler. I just checked it didn't say anything at all about using a mixing valve or bypass for low return water temps.
  • hot_rodhot_rod Posts: 12,586Member
    If the boiler is going to be used as a stop/start. In other words allowed to cool down during the season, I would highly recommend some sort of protection.

    Some owners that are around their homes all day manage to "keep the fires burning". In that case they maintain a safe return temperature and usually a buffer that can return some warmed water to a start up boiler.

    It can be done safely with a thermostatic valve, variable speed circulator, or bang bang control.

    I'm not a huge fan of a piped/ valved bypass, or even bypass pump. But those methods are better than nothing.

    It kind of comes down to how the boiler will be operated and controlled. Also the weather conditions. If the weather in your area warm during the heating season, of course the boiler will shut down as the load lessens or disappears.

    There are more challenges to piping a solid fueled boiler, and keeping it operating at high efficiencies.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • zavnetzavnet Posts: 15Member
    edited August 2015
    Looked through Idronics 17 and watched Utilizing Thermal Buffering In Hydronic Systems webinar (great webcast!)

    Attached are revised layouts:
    Option-1 is a 4-pipe configuration of the buffer tank/hydronic separator
    Option-2 is a 2-pipe configuration.

    Please provide feedback...

    @ Hot Rod here is quote from page 9, Idronics 17 "The higher the flow rate entering the tank, the higher
    the flow velocity, and thus the greater the mixing action
    within the tank. Mixing tends to degrade temperature
    stratification and should be avoided."

    The appeal of a two-pipe configuration is to avoid the above. I have two questions:
    1. What's the tipping point (flow rate) that's would clearly indicate to use 2-pipe vs. 4 (e.g. anything above 10gpm?)
    2. Has anyone done the math on efficiencies costs/associated with running a 2-pipe config vs. 4-pipe?

    Next question, I did the buffer tank calculation and based on the min boiler run-time I'm either in a 50 or an 80 gallon size.

    As I mentioned at the top of the post - short cycling is one of the issues I'm solving with the new layout. Considering a future wood burning boiler as an additional/alternative source wouldn't an 80-gal unit make more sense?
  • hot_rodhot_rod Posts: 12,586Member
    Excellent questions. I believe Caleffi Idronics 17 is the first time anyone in the US has really drilled down into the 2 vs 4 pipe methods. In all fairness this concept comes from our colleagues in Europe and observation visiting the European trade shows.

    The Swiss, Austrians and Germans are really the leaders in this buffering concept in my mind. The more Russia screws with their oil supplies, the more they engineer their RE systems and look for places to squeeze additional efficiency %'s. Energy storage and district systems are a big part of their think right now.

    The numbers could be crunched comparing the two methods and efficiencies. We have not taken it that far yet, at Caleffi.

    I'd bet the Europeans have. You might hit some of the UK or English version of their sites. This is one that impresses me, and there are hundreds of RE boiler and tank manufacturers over there. They have entire universities dedicated to thermal engineering, solar and heat transfer, in Europe. boilers/P4_sales_brochure_09_02_11.pdf

    I'm planning on reworking my own system this fall to a 2 pipe tank method. I have an ideal load profile and multiple energy inputs to put it to the test.

    What I do know from following the various wood burning chat rooms is more is better for thermal storage with cord wood burners. Pellet boilers and some of the more responsive cordwood boilers can live happily with a few hundred gallons, the extreme cold weather guys like 800- 1000 gallon buffer tanks for cordwood burners.

    There are no real set in stone methods, every wood burner has different wants and needs. With wood it comes down mainly to the "coast" cycle. How long can you run without tending the fire. And that is usually a lifestyle choice. Some owners camp out in their boiler rooms, others would like to drop by once a day to load the firebox.

    Wood boilers and mod cons are exact opposites. Plenty of intelligence in a mod con, they can think and adjust, stop and start easily. With cordwood it is more of an interactive sport, they like long, hot, nonstop burns, you become the intelligence.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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