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Critique my zoning idea

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by OH_Varmntr, Nov 2, 2013.

  1. OH_Varmntr

    OH_Varmntr New Member

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    My current setup is as follows. I've got a 2-story home with a full basement totaling 3,600sq ft. I have a 100k BTU air handler in the basement that supplies forced air heat to the basement and first floor. I have another 100k BTU air handler in the attic of the house that will supply the second floor of the house with forced air heat. It is currently not hooked up.

    I've had a Central Boiler 6048 installed for a year now. It holds 400 gallons of water. I currently have a Taco 009 pump supplying a series circuit containing a domestic hot water HX followed by the basement air handler. I bypass the basement air handler in the summer months to heat my hot water but that's not important. I'm looking at installing the attic air handler but do not want to plumb it in series with everything else.

    I have a 5* temperature drop between the OWB and the 155* thermostat housing. That figure is taken from the digital readout on my OWB minus a readout from a digital thermometer I have installed at the inlet of the thermostat housing. I have 75' of ThermoPex buried 18" down to supply the house. Those are the only temperatures I have measured at this time.

    At this time I have hot water flowing through my house 24/7 and I feel that I am wasting wood. I realize that any heat lost in the house is actually heating the house but I want to heat my house with forced air heat, not radiant heat. That's a different discussion entirely though.

    I want to limit water flow to the house by installing an electronic 3-way valve at the OWB outlet that will direct water back into the OWB when I am not calling for heat. This will bypass the 75' run of ThermoPex and I believe will reduce the amount of wood I will burn. I will be installing a temp controller on my hot water tank that will signal when it needs heated up again and each of the air handlers will have separate thermostats. Each signal will be interlocked so that only one zone can call for water at a time. I'll be using electronic ball valves for the zone valves.

    The Taco 009 pump is a high head pump and coupled with the interlocks and check valves I'm wanting to use I believe I will only need that one pump for this system. I have attached a few crude layouts of my current system and the system I'm looking at doing.

    I'd appreciate any criticism of my idea as to why it will or will not work, thank you!

    Attached Files:

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  2. stee6043

    stee6043 Minister of Fire

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    Any reason you wouldn't simply want to turn your existing pump on and off with the thermostats as opposed to the three way valve/recirc idea? It would surely be less expensive and would save you the electricity you're currently wasting running your circ 24/7. Net effect is the same and the setup would be much more simple.

    That being said, I don't think modulating and/or recirculating your supply water will have any measurable impact on your wood consumption. That 6048 is a monster compared to your load and I'm afraid that's a big reason you're blowing through wood, not because the circ is running when you don't necessarily want it to. The outdoor units are built more for loading convenience (huge firebox, load once a day) and not necessarily efficiency. You're not going to overcome this with controls I fear.

    For reference I'm heating 3200 square feet in Michigan and my peak/design heat load is something in the 50k btu/hr range. Your boiler is putting out 250k btu/hr I do believe.
  3. OH_Varmntr

    OH_Varmntr New Member

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    The inside hot water line runs through the attic where my future air handler will be. I have high head pressures and if the pump is shut off without a way to seal off the line to the attic the water will drain and create air pockets. I have a fitting in the attic the bleed the air off but it is manually operated. If flow stops because of an air pocket while I'm at work I could lose heat and it is my only source of heat.

    I overbought the 6048 for future outbuilding plans.

    I have zero doubts I will save some wood since the HXs won't be transferring heat 24/7.

    The circ pump draws hardly any current.
  4. maple1

    maple1 Minister of Fire

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    Unless my quick figuring missed somehting, at my rates (0.16/kwh), it would cost about $20/month to run a 009 24/7.

    Whether that is 'a lot' or not is a matter of opinion, but my electric hot water heater keeps our family of 5 in hot water for $30/month.

    Guess that doesn't add much to the specific topic though, sorry.
  5. OH_Varmntr

    OH_Varmntr New Member

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    Taco 009 uses approx 140 watts per hour. 140 x 24 x 30 = 100,800 watts. 100.8kW at .16 per kW = $16.13 a month. My rates are cheaper but can't remember exact number I'm away from home. I have an 85gal hot water tank FWIW.

    If I stopped the pump I'd need to install a normally closed electric valve to keep return water from draining from house to OWB when not calling for heat. The pump has a check built in.
  6. OH_Varmntr

    OH_Varmntr New Member

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    Ok now that I'm home...

    In September I used 1091 kWH and that equated to $108.01, so I'm paying 10.1 cents per kWH.

    So, 140 watts per hour x 24 hours a day x 30 days a month/1000 = 100.8kW at .101 per kW = $10.18 a month to run my Taco 009 nonstop.

    I'll have to dig up the heat exchanger efficiency tables I have for my heat exchangers and do some figuring...
  7. iceguy4

    iceguy4 Minister of Fire

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    I had a similar set up. My attic furnace leaked so much hot air ...snow would turn to ice quickly. Since I helped install it... (new construction...my house) GREAT care was taken to seal it. I put most of the ducts under a 3+feet thick blanket of fiberglass batts. I even built a room around the air handler(attic was huge with "piggy back" trusses) and exhaust through a "tell tale vent" Now in the summer it worked great.... air conditioning the whole house (4500+ feet) with a 3 ton unit!!!...In the winter I never used the heat and it still leaked! I think the pressure of hot air rising pushed through the tiny holes that are inevitable in any plenum system I have worked with. The last years I lived there, I covered the vents and returns with great success!
  8. OH_Varmntr

    OH_Varmntr New Member

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    My plan with the attic air handler and ductwork includes spray foaming the runs except for a few areas to be able to clean the ductwork and to be able remove the HX for cleaning.

    I just installed ductwork in the basement a few weeks ago, and used 3 rolls of foil tape to seal every joint and seam in the run.
  9. Clarkbug

    Clarkbug Minister of Fire

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    OH, any reason that the lines were only buried 18"? That seems a little high for staying below the frost line. Any worries about freezing the lines in the ground or in the attic if there isnt water flow through them?

    To Maple's point, if you bypass the flow with a three way valve, wont that still cause the water to run back from the attic zone? You wouldnt be pumping to the house any more, just circulating through the boiler. Sorry if I'm missing something here...

    What about installing a plate and frame HX inside your basement? That way you can have the open system outside and run that as necessary, then have a closed system in your house that you can cycle as you need to. You can run a single ECM circ with zone valves or multiple circs, one for each load. But you wouldnt have drainback from the attic with a closed system, and you could run a smaller pump 24/7 at the OWB. You would still have ground losses, but none to your house.
  10. OH_Varmntr

    OH_Varmntr New Member

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    Attached is an updated version of my crude drawing to include the above changes.
    desired setup revised.jpg
  11. stee6043

    stee6043 Minister of Fire

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    This may also be a silly question but can the vent on a central boiler be extended (up)? You could solve the drain back issue by getting the atmospheric vent opening above the highest point in your system.

    If this were rig to work on I guess I'd do the flat plate HX the guys above are mentioning. Simple, solves several problems (drain back, 24/7 circ, controls) and would be easy to install. With as much extra output your boiler has I wouldn't even remotely worry about heat loss across the HX. Size it properly and never look back.
  12. Bob Rohr

    Bob Rohr Minister of Fire

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    The amount of wood consumed is directly related to the loss of that heat energy. With an outdoor burner, much of the loss is from the boiler to the outside ambient conditions. Insulation limits that but never stops it. same with that vent hole in the top of the OWF. Next you have the loss in the trench piping. Whatever % if left is available to heat the structure.

    There is only so much you can do with control logic to limit the amount of wood burned to cover these losses. Of course the lower the operating temperature, the less the losses.

    I think the best method is to separate the OWF piping from the building piping. The OWF pump really only needs to run when there is a heat load in the building, or the underground pipes are in danger of freezing.

    You need to pay attention to the laws of thermodynamics and fluids when you start adding piping and heat emitters above the level of the water in the OWF. Depending on the operating temperatures you could see some boiling in the uppermost part of the piping.

    Freeze protection for the piping in the attic could be provided with antifreeze if you separate the piping with a HX. It's the loss of power, freeze protection that you want to keep in mind, either with a circ that could run off a battery, or antifreeze.

    There is a section in this journal that explains the math behind open system piping.

    http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_10_us.pdf

    Attached Files:

    Cornell3786 likes this.
  13. OH_Varmntr

    OH_Varmntr New Member

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    The vent could be extended up, but then I'd have to increase the water level to above the highest point in the system as well. That would leave me with very little room for expansion without losing any out the vent.

    Bob Rohr, thank you for that information. I'm currently running my water at 190*, and considering my attic HX is going to be roughly 15' higher than the water level in my OWB, I'd need to lower that if I chose to run a single system.

    I'll have to look into running separate systems.
  14. Clarkbug

    Clarkbug Minister of Fire

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    OH, to address your previous question, you would need to add an expansion tank in your house to a closed system, but you wouldn't have to install any other storage.
  15. OH_Varmntr

    OH_Varmntr New Member

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    Ok thanks. That makes it nice so it will heat up a smaller quantity of water quicker.

    Is it basically a well water expansion tank or is it especially for thermal expansion systems?
  16. Clarkbug

    Clarkbug Minister of Fire

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    It is a thermal expansion tank, specifically for hydronic heating. They are rated to handle the higher temps.

    NOTE: You CAN use a well expansion tank if you make sure that you have enough piping between the hot parts of your system and the tank so that it wont ever see high temps. I think EW uses a well expansion tank. You could hook it up with fin tube to make sure that any heat radiates out before it gets to the bladder.
  17. OH_Varmntr

    OH_Varmntr New Member

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    Thank you! I really appreciate the advice. After doing some looking around I'm going to go with a closed loop circuit inside the house. It just makes more sense, so thank you again you guys!
  18. Clarkbug

    Clarkbug Minister of Fire

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    Another plus is that it should be much easier on the control side of things, instead of trying to handle all of the various automatic valves, three ways, etc.

    Let us know how the new system works out!
  19. OH_Varmntr

    OH_Varmntr New Member

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    Thank you! I work with logic everyday at work (electrician). Just another something to play around with I was actually looking forward to building my own panel for the controls! :p
  20. Clarkbug

    Clarkbug Minister of Fire

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    Well then you can still come up with something crazy and custom to control/monitor/tweak your system. Check out some of the threads from user NoFossil. Good stuff!
  21. OH_Varmntr

    OH_Varmntr New Member

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    Ok so I've been doing some figuring and reading and some reading and some figuring.

    Here's what I've come up with and have a question. I've done some searching and have come up with some answers, but they don't seem to answer my question specifically. Maybe I am not using the correct technical terms so if the questions I'm asking have been brought up a million times before like I'm sure they have been, please point me in the correct direction on which terms I should research.

    How much pressure should I expect to see in my supply manifold from the circulator? I want to stick with 24v for the controls and 120v for actuators. The 120v Honeywell zone valves I'm looking at are rated for 10 cv flow but have a max close off pressure of only 6.5psi. If I only have one zone running then I'm not worried about that as the closed loop circulator will shut off as the zone valve is closing. However, if I have a zone waiting to run after another zone shuts off, during the transition between one zone valve closing and another opening would I see more pressure in the closing zone that could keep the valve from closing? Or would the zone that is opening keep manifold pressure low enough to allow it to close? Or am I way over-thinking this? I guess my thought process is rather clouded from trying to keep the closed loop system pressure separate from actual pump pressure.

    Two of the zones will be at the same level of the closed loop circulator. The third zone will be at roughly 25 feet above the level of the circulator.

    Another question I have is with my closed loop system. Since I am only running a single circulator and will be controlling zones with valves with zero storage, I won't be able to run more than one zone at a time, correct? If I add some storage would I then be able to run multiple zones at once? I have my control logic laid out and running only one zone at a time is not a problem at all. I was just curious.

    Thanks again you guys!

    Plumbing.png
  22. Bob Rohr

    Bob Rohr Minister of Fire

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    Seems low for a HW zone valve at 6.5 psi, usually high Cv valves have at least a 20 psi shut off. Motorized type 3 way ball valves generally have around a 150 psi shut off as they are not a spring return valve. I'm not sure that 3 way valve at the OWF serves much purpose? Why do you want to circulate around the OWF when there is no heat call?

    I wonder that a 007 is enough pump for the OWF circuit. 75 feet of what size tube? If your load is 200,000 BTU/hr. I don't think that 007 will get you there?.

    The inside circ needs to be sized for the flow rate GPM, and the pressure drop in the most restrictive circuit. You mentioned two 100K loads? That would require 20 GPM at a 20 delta T. Sure you can run multiple zones at once as long as the circ is sized for the pressure drop thru the circuit, including the HX, of course.

    I prefer zone valves on the return side, lower operating temperature and a bit less pressure to shut off against, as the piping circuit "scrubs away" some of the pump head.

    The pressure (static fill pressure) in the closed loop system needs to be high enough to "lift" the water to the highest point in the building, generally 10- 15 psi is enough for a two story building. It's the pressure that you fill the system to, that lifts the water, not the circ pump.

    A small wet rotor circ adds about 5-8 psi at the discharge if you "pump away" from the expansion tank, as you should. So the pressure at the discharge will increase to about 18psi, then that "head" pressure the circ adds will get "used up" as the fluid circulates, due to resistence in the piping, fittings, and heat emitters, plus the HX in your system. . The pressure at the expansion tank will not drop below the fill pressure if the tank is pre-charged and the circ is pumping away from the tank connection.

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  23. OH_Varmntr

    OH_Varmntr New Member

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