Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

Corn Fired / Fuel Oil Back-Up Primary Secondary Boiler System Concept - Please Check My Work?

blumeri8blumeri8 Posts: 10Member
Hello All,

I currently have an old school Triad fuel oil boiler that is plumbed / controlled old school as well. The boiler is plumbed directly to the zones (not primary secondary), has one pump that is controlled by aquastat, and the boiler is fired by one central thermostat. I have 10 zones, however its acts like one big zone as I have no zone valves. I have one large return manifold with a row of 10 gate valves to manually balance / throttle the loops. (Like I said, old school.)

What I want to do:

Since I live on a farm, I would like to plumb in a corn-fired boiler in parallel with my existing fuel oil. The fuel oil would be the back-up. I plan to use primary/secondary piping because the corn boiler does not like flue gas condensation. I also plan to have the zone circulator controlled by the thermostat and boilers controlled by aquastat the same way most modern systems are controlled.
Please take a look at the file I have attached.
I detail my piping, calculations, operation of the corn boiler, and the control system. (The fine folks at Tekmar are really helping me out.) I would like some general guidance as to whether I am missing components in my system or am on the wrong path. I have been reading the Dan Holohan books so I hope I am close.

My main questions include:
-Do I need additional bypass lines in my boiler loops to further protect against low return water temps? ESBE valve?
-Do I need a balancing line between my main zone supply and return lines if I choose to not add electric zone valves to my system? I think I can just use the existing manifold gate valves I have to throttle/balance to achieve target 40 delta T?
-If I chose to add zone valves, I would group my 10 loops into 3 sub groups with 3 "sub manifolds." I feel that one zone valve / thermostat per floor is sufficient. Would I then add a balancing line between the main supply and return? What valve would I put in this balancing line? Are gate valves suitable to balance with? I have seen expensive "circuit setters" with flow meters, but don't know much about them.
-Are my purge stations in the correct spot? Goal is to be able to purge zones separately from boiler/ primary loops.
-Do I need a ball valve to close off my zone loops when purging the primary loop? Or will the closely spaced Tees be enough to keep the purge in the primary loop?

Any help is appreciated!

Thanks!
-Adam

Comments

  • blumeri8blumeri8 Posts: 10Member
    Bump
  • hot rodhot rod Posts: 7,957Member
    I can't seem to open your attachment, try again or take a pic and post.

    Do you have a buffer tank planned for the corn fired boiler? Most solid filed boilers work best with some buffer.

    if not, a hydroSep is a good way to connect multiple boilers, it gives you 4 important functions. Air, Dirt, magnetic, and separation in one component.

    Yes the corn boiler would need return protection, unless the onboard control provides that to the tekmar?

    The cover shot shows a typical piping. The buffer tank could be exchanged for a hydrosep.

    Balance valves or globe style are preferred for accurate balancing.


    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ScottSecorScottSecor Posts: 118Member
    Blumer has a bunch of documents he attached in his power point. I am not too computer savvy, but I'm hoping the his sketch shows up. I did not attach the other pages.


  • blumeri8blumeri8 Posts: 10Member
    Thanks for the replies guys. The buffer tank is an item I had not considered or was even aware of. I skimmed thru hotrod's attachment (will read thoroughly when I have a chance) and it looks like the purpose of it is to help prevent the corn boiler from overheating which was one of my concerns. It looks like buffer tanks are quite large correct? Space might be an issue. As for the hydraulic separator: wasn't really aware of these either. At first glance, (will research further when I have the chance), they appear to be a cousin of the closely spaced Tee. My initial plan was to utilize these in my system. Basically I followed pg 109 in Dan Holohan's "Primary/Secondary Pumping Made Easy!"
    Please see the below pictures of my initial plan for system control. I was going to run pumps P2 and P3 continuously during corn burner operation. Pump P4 comes on as needed from thermostat call. I was hoping by running P2 and P3 constantly, it would help move some water and hopefully help to prevent boiler overheat. I realize these are short loops of pipe right within my boiler room and may not lower the temp much. I was planning on having a Tekmar 150 over ride the thermostat and activate P4 to remove heat from the corn boiler before it over heats and shuts down. How often that happens, I was not sure, but was hoping I could adjust the variable BTU setting on my corn boiler to minimize this and not overheat my house.

    Do you guys think my plan could work? Would a buffer tank be a better option? How does a hydraulic separator (seems similar to closely spaced tee) substitute a buffer tank storing heat to prevent boiler overheat as hotrod implies?

    Also, why is an additional bypass and boiler protection valve needed in the boiler loop to blend and raise return water temp? I though this already happens when the zone heat returns to the primary loop? Holohan's book also suggests this and I never understood. Is this like a belt and suspenders kind of deal? Just an additional protection? Thanks for the help!







  • blumeri8blumeri8 Posts: 10Member
    Ok guys, so I've been reading thru hot rods attachment and understand hydraulic separators a bit better. Seems like a hydraulic sep will not only combine air eliminator and strainer, but basically eliminates my primary loop and P3. A couple questions: is a circulator and boiler protection valve basically interchangeable to the thermoblock? The thermoblock looks to very expensive. It looks like figure 6-14 in hot rods attachment is the way to go. They claim that pellet furnaces may have enough control to not need a buffer tank. Since my unit has a variable BTU timer I think this will be the case. So in conclusion, it looks like figure 6-14 and my initial design do the same thing. It's just a matter of cost. Is having an expensive hyd separator cheaper overall than having another pump, another loop, and separate air/dirt separators. Also , with figure 6-14, how to size the headers and boiler loops? I was going to use 1" on my original system. Also, I assume the circulator in thermoblock still runs continuously ? Thanks guys!
  • hot rodhot rod Posts: 7,957Member
    Correct, the buffer tank serves multiple functions. Witlessness short cycling of the boiler on low load days, can be an overheat zone, and performs the same task as primary secondary. 80- 120 gallons would be a good start.

    Pumps really only need to run when there is a clan for heat, or the boilers are running.

    This attached drawing is a good example of what you are trying to design with boiler protection shown also.

    An a link to a bit more reading and drawings, etc.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • blumeri8blumeri8 Posts: 10Member
    Wow, am I getting my education today...thank you very much for all the reading material...a lot of good stuff here...I now understand how buffer tanks work. I understand they help all solid fuel systems run more effiencently however their necessity seems to depend on the type of system. It seems that solid wood systems need a buffer tank more than a pellet system because they cannot control their output like a pellet system. Also, it makes sense that a highly zoned system needs a buffer tank because there is a possibility of only 1-2 zones calling and therefore increasing the chance of overheat. However, my system seems to have a couple things that help it. First is that this particular boiler (LDJ Amaizing Heat) has a variable capacity BTU which basically adjusts the length of the high fire cycle time. The boiler can adjust from 80000 to 165000 BTU. ....Based on how many feet of baseboard I have, I calculated 116000 BTU hour system load based on 170 degree average water temp. Also, while I do have 10 loops, I really only have one big zone because my system has no zone valves. The entire system gets heat every time the thermostat calls. Therefore, I gotta ask...is there any sure fire way to tell if you absolutely need a buffer tank to avoid overheating before installing the system ? I honestly don't really want to deal with the expense and hassle of a buffer tank. Furthermore, I really don't have the extra space for it. I would rather just install a 1" hydraulic separator. On the other hand, I don't want to have to tear apart my new system, and spend even more time/money to take out the hyd sep and replace with a buffer tank if I find out that I have issues. Given the specific boiler I am installing, calculated heat load, and the fact that I have essentially one whole house zone with 10 balanced loops, what is your opinion? Do you think I'll be ok going with the hyd sep? Thanks again...
  • hot rodhot rod Posts: 7,957Member
    It's hard to give you an exact answer on the value of a buffer. If the boiler output is that controllable it may not be absolutely required. Even with modulating pellet boilers many manufacturers still suggest some buffer capacity.

    With a automatic feed and modulation I would not worry about over-heating, but more short, inefficient cycles that wear components prematurely.

    Keep in mind your design load may only be a few weeks a season, so the boiler needs to modulate to the load on the other 80% of the heating season.

    At the very least use a hydroSep, it will add a bunch of nice features and assure efficient hydraulics.

    Then again, you might find a 120 gallon insulated tank for about the same $$?

    A tank like in this drawing is a fairly common off the shelf tank, 2" connections are needed for the separation function up top.

    The piping is a 3 pipe direct to load method. When load and input match all the boiler output goes to load. If loads modulate off a portion of flow goes thru tank. Boiler(s) run until tank reaches setpoint temperature.

    A flat plate HX could also provide DHW from the tank.

    A return protection valve on the corn boiler, the oil boiler may have a protection mode or the tekmar could provide that.

    Control options are shown in the reading I attached. Corn boiler is stage 1, oil would only fire if the corn was unable to keep up, or it failed to light off. A fairly simple control logic.

    The loads could also be fed via an outdoor reset function to maximize storage and keep efficiencies up.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • blumeri8blumeri8 Posts: 10Member
    Hot rod,

    A couple questions ,

    Can you please share an example of this off the shelf 120 gal tank that is of similar cost to the hyd separator ? It's seems the hyd separator I would use would be like a calleffi 548006A 1" separator. Just over $400 on Supply House.com. The calleffi Thermocon tanks are $1500- $2000. Unless this 3 pipe method you are referring to requires a different type of tank? This is my next question...can you detail the 3 pipe method? The files you sent only cover the 2 pipe and 4 pipe method...this 3 pipe method u show has pipes going into the top of the tank. I thought the flow had to remain horizontal so the hot and cold water stays separated in the tank?
    Also, is there a dirt separator inside these tanks like a hyd sep? Or do you need a separate one? Are these pressured tanks nothing more than an insulated tank with fittings in the correct locations? Just wondering if a person could make one by welding fittings into say an old propane tank mounted vertically and then cover the tank with insulation . thanks!
  • hot rodhot rod Posts: 7,957Member
    You are correct in the pricing difference. i was think more like a Sep 4 price around $500.00.

    A plain steel tank at SH in 82 gallon is around $500 also, but you would need to insulate it.

    Idronoic 17 explains 2 versus 4 tank piping, and thermal storage in general.
    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

    3 pipe adds one more feature in that return, lowest temperature is directly to the boilers for best efficiency. With 3 pipe there is less blending of the tank.

    The 2 pipe originated in Austria, it is how pellet boilers are piped to storage. John Manning devised the 3 pipe to drive heat pump efficiencies with lowest return temperatures, same for boilers.

    The benefit I see for a buffer in your system is the low load days. the boiler charges the tank ti180F. The zone pulls from the tank via a mixing control based on outdoor temperatures. On less than design days the temperature to the baseboard would modulate down. This provides less boiler cycling.

    If the baseboard is sized correctly and meets the load on design day with 180F, for example, anything less than design could use a lower supply temperature.
    If adjusted properly you may get constant circulation on the baseboard.

    Where are you located?


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • blumeri8blumeri8 Posts: 10Member
    500 bucks for a tank is more like it. What do you recommend for insulation? ...also I think I understand the 3 pipe a bit better after I stared at your schmatic a bit more. Basically the flow is still horizontal because you have a Tee at the top of the tank, not an elbow ...correct? Also, you say the TEE at the top needs to be 2"? Does the rest of the main piping need to be that large or just the tank outlet? I was going to have 1" mains. Also I have some questions about the tank you specified...the size tank we are looking at has 1" fitting at the top...do we need to find another tank? Also, the specs say the tank is rated for up to 140F...is that an issue? Lastly, where would I place the upper and lower sensors in a set up like this?. I live in southeast Michigan an hour north of Detroit, so it's cold, but not insanely cold. -Adam
  • skalorskalor Posts: 11Member
    blumeri8 said:

    Hot rod,



    A couple questions ,



    Can you please share an example of this off the shelf 120 gal tank that is of similar cost to the hyd separator ? It's seems the hyd separator I would use would be like a calleffi 548006A 1" separator. Just over $400 on Supply House.com. The calleffi Thermocon tanks are $1500- $2000. Unless this 3 pipe method you are referring to requires a different type of tank? This is my next question...can you detail the 3 pipe method? The files you sent only cover the 2 pipe and 4 pipe method...this 3 pipe method u show has pipes going into the top of the tank. I thought the flow had to remain horizontal so the hot and cold water stays separated in the tank?

    Also, is there a dirt separator inside these tanks like a hyd sep? Or do you need a separate one? Are these pressured tanks nothing more than an insulated tank with fittings in the correct locations? Just wondering if a person could make one by welding fittings into say an old propane tank mounted vertically and then cover the tank with insulation . thanks!

    If you haven't already I would check out the boiler section on hearth.com. A lot of knowledgeable guys over there as well and most are DIYers. It's quite popular to utilize old propane tanks as buffer tanks and they are readily available and cheap.

    I have a propane and pellet boiler in parallel with a 120 gallon buffer running a 4 pipe arrangement. I don't have any return temp protection on the pellet boiler but the propane boiler kicks on if the buffer drops below 140F. Only happens in single digit temps because my pellet boiler is undersized but I wanted it that way. Looks like you have a well thought out system so far.

  • blumeri8blumeri8 Posts: 10Member
    Skalor,
    Thanks for the advice . I was at first thinking an old propane would be a good cheap solution ....then a guy at work made a big point I hadn't thought of...when you put water on the inside of a propane tank, how do you handle the rust that will likely occur? Probably shouldn't run rusty water thru the circulators...does a dirt strainer help this? A treatment that can be added to the water? How to clean the tank prior to install?

    This had me thinking that propane tanks were a bad idea, but if you say a lot of people do it, it must work. I would sure like to as it is a cheaper alternative unless I go a DHW approach

    what are your thoughts on Ergomax ? Seems like a reasonable alternative because they are similar cost to a manufactured buffer tank...so why not save the space and combine with water heater . I was just hoping to maybe find a reverse unit like Ergomax that also has a electric /gas burner supplement . I don't want to run boiler in summer time. Right now I have electric hot water heat and my current boiler is fuel oil. Eventually I will replace with propane, so maybe I should get a propane / indirect hot water heat now. Trying to plan for future but $$$$$$, lol.
  • hot rodhot rod Posts: 7,957Member
    edited May 1
    I have a 500 gallon LP trank as my buffer, mounted vertically. I imagine the boiler is just plain steel. If it is a closed system, once the O2 is consumer there will be no rust or corrosion. The open system OWF use corrosion inhibitors for protection as they see constant O2 ingress.

    I priced this 82 gallon galvanized tank yesterday, around $382 in my area, 1" connections. HW tank wraps at the box stores run about 40 bucks.

    I have a whole selection of scratch and dent insulated tanks if ever you are in the SW Missouri area :) 35- 120 gallon, 200 bucks.

    I don't see all the spec on the boiler, looks like it holds 18 gallons ? 1" connections?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Posts: 206Member
    Save your money install a steel compression tank sized for your system and airtrol valve for you combined system. Dan talks about them in his book "Pumping Away" from page 52 to page 56. He also mentions them in his book "Classic Hydronics" as well. He has the same steel compression tank that was there when he and Mrs. Holohan moved in to the house.

    If you contact AHONA in New York they offer insulated re purposed used propane tanks that are guaranteed, pressure tested, plumbed and insulated with sprayed foam insulation and ready to work. they also offer stacked foam insulated propane tanks for hot water storage.
  • blumeri8blumeri8 Posts: 10Member
    Ok guys,

    So as you know, I'm torn between two routes:

    1. Thermal Storage tank to combat boiler overheat in idle mode.
    2. No tank and Hydraulic separator in its place. Control system and auxiliary aquastat to override thermostat to turn on zone pump when needed to dump boiler heat into the house during extended periods of idle mode to prevent boiler overheat

    I'm convinced that there are affordable alternatives for buffer tanks, therefore cost of the tank seems to not be an issue anymore.

    Space is in fact still an issue but I could probably make it work.

    I have talked to the fine folks and Big M manufacturing (the company that currently makes these boilers) and was told the following:

    They use method 2. He claims they know a guy that has a large thermal storage tank and he uses more corn overall to heat up that large quantity of water. I understand his point, however, on the flipside, once the stored water is at temp, the boiler won't have to run as much to heat the house. So I honestly don't know which theory to believe.

    I do know this: The guy at Big M told me that Idle mode, the boiler makes roughly 15-18K BTU. This isn't much, but given the boiler holds only 18 gallons, it will overheat. Granted, the loop going from the boiler to the Hyd separator would run 24/7 and would remove a little heat. However, with method 2: It seems that when the controller tells the pump to dump boiler heat, the house should remain fairly comfortable. The fact that we only have 18 gallons of near hi-limit water to get rid of and only 18K BTU sent to 116K BTU of baseboard all at once ( no zone valves) that I should have little worry of my house getting to warm during "heat dump" cycle. It seems like I have plenty of baseboard to absorb the 18K BTU.

    What do you all think?
  • hot rodhot rod Posts: 7,957Member
    The manufacturer should have the best feedback for actual operation. If the unit can modulate that low, or go off completely I would not worry about over heating or a buffer tank.

    I've only installed one corn burner boiler in my years. The Kansas corn he used turned into a sticky mess, maybe not cured properly?
    Auger, feeder and burner cup issues almost daily. He switched to burning pellets from that first experience on. Corn is a tricky fuel to burn efficiently, too many variables. Pellets are dried, blended and compressed for a high energy fuel source.

    Over-heating prevention is super simple to add with a NO zone valve and some fin tube, shown below. Use a large diameter with a slight pitch to facilitate no power thermo siphon.

    If you follow the wood burner chat rooms, over-heating is a rare occurrence unless a door is left open or door gaskets fail. More an operator error problem. With an auger feed and fan inducer that boiler should stop quickly like a fossil fueled type.

    The buffer, in my mind is more for storage and lessen cycling on mild, low load days, not over heat protection. Tanks make it nice to use outdoor reset and just supply the required temperature at all conditions.

    True the buffer tank jacket loses some energy to the space. Is the installation inside the building envelop? If so it is not really loss.

    Keep in mind the very best place to store your energy is in the un-burned corn :) Once you start combusting, and energy transfer a portion continues to slips away.

    I would still use a separator, eliminate one pump from a P/S piping and add the other required functions all in one component.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • blumeri8blumeri8 Posts: 10Member
    Excellent , looks like I'm going with the hyd separator ...a few more questions:
    What is the rule of thumb for the near boiler piping? Can I get away with black pipe up to the hyd separator? Then copper begins out into the zones OR should all my near boiler piping be copper?

    Fill valves/ combo backflow preventers : I've heard Watts 9D is good...what's the diff between expensive ones like that and the cheaper ones like Watts series 911?

    Check valves : per the reading material provided by hot rod, the corn boiler gets a swing check and the fuel oil gets a spring check. Can someone explain to me the difference between like an expensive Taco 219-4 Flo check and a cheap Bluefin Slct 075 spring loaded check....is the only difference the fact that you can manually override the Taco? What situation would each type of valve be used for?

    Pressure relief valves: I was going to replace the used relief valves on the corn and fuel oil burner for safety sake...the corn burner has the small kind like what you'd find on a water heater ( like a watts 335-M2)....and the fuel oil has a much larger one (like a watts series 740 boiler pressure relief ) what is the difference in these types of valves and which should I use?

    Thanks for the help!
  • hot rodhot rod Posts: 7,957Member
    165,000 BTU at 80% efficiency, so you want to flow 12- 13 gpm through the boiler. 1-1/4" would be best, 1" copper or steel is probably sufficient . If you use a Caleffi 548 or Sep4 no additional air purger is needed in the piping.

    Most all circulators have check valves included, any of the small 3 speed circs would work, a Grundfos 15-58 or equivalent in any brand. Grundfos Alpha or the equivalent brands if you want to got to high efficiency circulators. Use isolation purge valves like the webstones to simplify purging and circ pump service.

    Of course I'd recommend the Caleffi 573002A fill valve combo for example:)

    Swing checks on solid fueled boilers so they can circulate under no power conditions. A swing check will open and allow thermosiphon. I really don't think you need over-heat protection with the controls on the corn boiler. No harm in adding a 3 way thermostatic return protection valve for added insurance.

    Safety relief valves are sized by the BTU/ hr rating on the label. A common 3/4" 30 psi valve for example. I'd go a step up from the small price point valves.

    With a hydrosep and all low mass heat emitters I don't know that you need a boiler protection valve. The tekmar control you choose may include a return protection function. Or the boiler(s) may have that function, which basically turns off the circ if the boiler temperature drops too low.

    And an expansion tank,use the free online calculator at Amtrol, probably a #60 size?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
Sign In or Register to comment.

Welcome

It looks like you're new here. If you want to get involved, click one of these buttons!