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Boiler Setup for 5 Zone Baseboard

cvh8601cvh8601 Posts: 4Member
I'm looking to replace my 40 yr. old Peerless oil fired boiler. My main interest is improving efficiency of the system.

Current boiler is 130,000 BTU/hr rated, and cycles frequently based on heat calls from each of the 5 zones. Slant-Fin calc says my heat loss is ~60,000 BTU @ 10F (Maryland) so i'm probably 2X oversized on the boiler and also based on that calc i have 2-3X the required baseboard length in every room except 1 that is a little short (vaulted ceiling, 2 sets of older french doors to exterior and adjacent to un-conditioned garage). I currently have no outdoor reset or any fancy controllers.

I did replace the two original 1/4HP circulators with Taco 007e's which are amazing but thats somewhat beside the point.

DHW is handled separately although my existing system has a tankless coil. I don't need DHW from the boiler with the new system.

After browsing the forum here for a bit it seems like the setup I have is very inefficient, especially in terms of the zones. Ideally (I think) I'd like to see a system where the boiler keeps a hot water buffer tank at a temperature controlled by an outdoor reset and the zones draw from the tank rather than the boiler. Then the boiler only focuses on keeping the tank at the set point. That seems like a reasonable way to increase the system mass sufficiently to reduce the short cycling from randomly timed zone calls.

It seems like that is an atypical setup. Does the forum have any thoughts or guidance on how to get a better boiler setup in my case?

Comments

  • IronmanIronman Posts: 5,129Member
    Are you looking to stay with oil?
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • cvh8601cvh8601 Posts: 4Member
    Maybe.

    I'm too far from a natural gas line for that to be an option, I've looked into geothermal but having sufficient ducting run to the basement would be too invasive and the payback period is too long. Propane would be more expensive on a BTU/gallon X efficiency X price in my area basis.

    The only other real option beside oil I think I have is to run my a/c / heat pump on 1st and 2nd floor and get mini splits for basement. I'd be slightly sad to leave so much baseboard around the house unused as well.
  • Robert_25Robert_25 Posts: 184Member
    edited September 1
    You would save a considerable amount of oil just by upgrading to a new cast iron boiler of the appropriate size with an indirect water heater.

    If you are looking for something that can handle the small-zone calls efficiently, check out System 2000 boilers. They have a unique control setup that purges residual heat in the boiler into the DHW tank.
  • STEVEusaPASTEVEusaPA Posts: 3,083Member
    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf
    Page 32 or 45, with or without dhw.
    Overall a good read as the smallest oil boiler will short cycle with all the zones.
    How many gallons of oil did you use last season & what’s your city/state?
    steve
  • cvh8601cvh8601 Posts: 4Member
    I've looked at the system 2000, but I'm not looking to heat DHW with oil so that may or may not be worth the additional investment.

    I'm north of DC in Maryland. We've used roughly 1,000 gallons of oil each of the past two winters. Obviously I'd like to take as big of cut off of that as possible.

    That PDF is great, the systems you've pointed out less the DHW are exactly what I was thinking - thanks for posting the link!

    Now only to find a contractor that can successfully design such a system - any tips for the Montgomery county MD area? I think I have enough info to start cooking up a system design myself as well.

    Also, any thoughts on efficiency improvement with/without the buffer, regardless of reducing short cycling? And any thoughts on whether a high or low mass boiler would be the best companion to a buffer tank?
  • John RuhnkeJohn Ruhnke Posts: 797Member
    edited September 3
    Lower the water temps. Again I will say this because it deserves to be said twice. Lower the water temps.

    First off I want to say AFUE is a total disaster as a energy efficiency calculation. So don't pay any attention to that. With the baseboard oversized, you wont need as much btu's per foot and this makes for a opportunity to lower the water temps.

    The system 2000 is a excellent high temperature boiler. If you have hydro air and need steady high water temps or have undersized heat emitters than that is the boiler to choose. The system 2000 does such a great job in the energy efficiency area because it has a low water content, pulls energy out of the flu gas and the control does an excellent job pulling the energy out of the boiler after it shuts down. But it has one flaw. It requires high water temps. Energy Efficiency gets bad through out the house after it leaves the boiler with higher water temps.

    According to the BNL study these two boilers were within 2% in the lab test. This did nothing to test energy efficiency losses after the water leaves the boiler and travels around the house.

    I would choose the Buderus cast iron g115 with a Tekmar 400 and some 527 thermostats. This will give you outdoor reset with indoor feedback. The system will learn your cycle lengths and run the lowest water temps possible. You can set the min return to 110 degrees. It also does post purge to the dhw. This will save you more money than the system 2000. This slow gentle steady heat is way more comfortable too. That is why people choose radiant heating.

    So in a higher water temp system where you are forced to run the buderus at higher temps, than the system 2000 is the choice because it already runs high water temps and is very well designed. The system 2000 heats up and cools down quicker and is more energy efficient at the boiler. But not after the boiler.

    But in an ideal situation, designing from scratch, lower water temps will always win out in both energy efficiency and comfort.
    John Ruhnke
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • John RuhnkeJohn Ruhnke Posts: 797Member
    About a buffer tank. I like the idea of the buffer tank. It is really helpful in energy efficiency. It pulls the heat out of the boiler and stores it in a tank. This is great for stand by loss and reducing short cycles. It is a great idea. If you could find a good control package that utilizes this than it might be a good idea.

    You can accomplish the same goals with post purge either to the system or dhw. On a higher mass boiler like the buderus it will take long enough to heat up from cold to keep a cycle long enough. The Tekmar 400 also can synchronize the zones so that no zone will run too short a cycle. If you use the Buderus boiler with the Tekmar 400 I don't see a need for a buffer tank. The 400 is not designed to be used with a buffer tank.
    John Ruhnke
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • IronmanIronman Posts: 5,129Member
    Call Dan Foley of Foley Mechanical in Lorton, VA. You won't find any better.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • John RuhnkeJohn Ruhnke Posts: 797Member
    I edited my first comment in this thread after thinking. I said the system 2000 had a fatal flaw of high water temps. I changed that to flaw. Personally I don't like high temp systems. The System 2000 does everything else so well, such a good job that the word fatal was a bad choice on my part. It has overcome its flaw and is a good choice for most situations.
    John Ruhnke
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • cvh8601cvh8601 Posts: 4Member
    I appreciate the input - you have been most helpful. I'm going to try and get in touch with Mr. Foley and go from there.
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