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  1. in hot water

    in hot water New Member

    Joined:
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    SW Missouri
    I have been running my system with a delta T function on the boiler pump this season. The control has a data logger built in and I will post some graphs when it runs for a week or so. Nice warm weather has the solar handling the load lately.

    With a system piped like this I think you get near ideal operation. The delta T pump on the boiler is ever changing it's speed, and flow rate, based on what the boiler is producing at any given time. So the pump matches the boilers output. It also protect the boiler against cool return temperatures by reving down the rpms (flow rate) as the fire dies, or the load exceeds the boilers output. I notice mine tends to run at 40- 50% speed most of the time. if I let the system and buffer go cold, it will run 100% to catch up. Again based on the return to the boiler.

    The tank acts as a buffer and hydraulic separation point. So if for some reason the pump on the system size was larger, or a high head circ, the two pumps will always get along, hydrauliclly speaking.

    The distribution circ is a delta P or delta pressure pump. It has power all the time, no need for a relay. When all zones are off it "sleeps" at a 7 watt current draw to keep the electronics and display lite up. If one zone calls, the pump detects the need for additional flow, wakes up and runs about 20W or whatever the zone requires. As additional zones call, the pump speeds up to match this load. This is all calculated inside the electronics built into the pump. It learns, and memorizes you plumbing hydraulics!

    The delta P pump, in this case an Alpha 2 by Grundfos is also and ECM (electronically commutated motor). It uses a rare earth magnet design and consumes 40- 60% less energy than a standard circulator doing the same job. So it is possible for you to move a 100K or larger load with 40W of consumption per pump at design conditions. On mild days or light loads the system may be running 20W or less per pump.

    So now you have a system with low fuel costs for the energy conversion (wood) and an extremely low electrical consumption with auto adapt pump functions. And return protection without a parastitic device like a 3 way valve, additional piping, etc.

    One small downside of this EZ piping is the tank must be maintained at the temperature required to handle all the loads at any given time probably 170- 180 °F for most applications. A 3 way zone valve could be added to bypass storage and feed directly to the loads.


    hr

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  2. Gooserider

    Gooserider Mod Emeritus

    Joined:
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    Loc:
    Northeastern MA (near Lowell)
    Looks nice, though that's an awful funny looking log in the wood boiler %-P ... Will probably add this to the tidbits sticky..

    One thing I've heard suggested as a possible drawback to using a ΔT controlled pump as a return protection unit, as you have it, is that if you had an extremely low return temp, it would be possible that the pump would need to run so slowly to keep the return temp high enough, that you might get excessive boiler output temps... I don't know how true this would be, but I could see how it might be an issue if there wasn't some provision to do some level of conventional protection of returning some hot mix to the boiler input...

    Gooserider
  3. DaveBP

    DaveBP Minister of Fire

    Joined:
    May 25, 2008
    Messages:
    1,047
    Loc:
    SW Maine
    I haven't yet wrapped my mind around the use of a variable speed circulator for return protection. I'm only half way to the bottom of my first coffee, though.

    I don't see how slowing the flow rate of water from the bottom of the storage tank will raise the temperature of that water. What kind of return temps are you getting from storage with your setup?

    Or does it work by bringing in that cold water at a rate that the boiler can heat and 'stay ahead' of the condensation that would ordinarily occur if the boiler were overwhelmed by water of the same low temp? And, as Goose wondered, does it do that without raising the output temp more than you might want under all states of burn? Do you have your boiler modulated down from max burn?

    What control are you using for this boiler circ? Is it trying to maintain constant supply temperature from the boiler?

    I hope this system design works well. Except for the return protection, it's virtually identical to one I posted recently. Gives me a little more confidence in it, to say the least. About as simple as it gets, isn't it.

    Looking forward to those graphs, HR.
  4. in hot water

    in hot water New Member

    Joined:
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    My EKO came with a snap switch installed on the top of the boiler. It turns on the boiler pump at 65C off at 60C. So that simple switch controls the boiler output.
    I think that pump could also run on a variable speed function, i haven't had time to try it. I'm on the road for a week but I will post some of the data logging when i get back.

    hr
  5. Gooserider

    Gooserider Mod Emeritus

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    Northeastern MA (near Lowell)
    That makes sense, but I still don't see how that would give good return protection if the storage / load return was at a very low temperature... The extreme case would be something like an ice melt system, but even with a regular setup, I could easily see the low-side storage temp getting down towards 100°F if the system did a NoFo style super charged DHW setup, and all the loads were low temp floors (i.e. the kind of setup we think is ideal...) If you had decent stratification, and ran the top of the storage down to say 110°F, what would the bottom of the tank be? I'd guess somewhere around 80-90°F...

    As I understand it, if you had the water returning from storage at even 100°F, it would be excessively low entering the boiler, and thus potentially cause condensation no matter how slowly it was being pumped.

    You do put a qualifier in your last paragraph;
    and if you were keeping the tank that hot, I agree the only time the return temp would be an issue is if bringing the system up from a full cold start. But from what I've seen most of our members are running their tanks down a LOT lower than that, and we even encourage people to add more emitters to their system in order to be able to run lower temps, so I'm not sure that applies.

    I don't want to seem like I'm giving you a hard time about this, but you are one of our top "expert" members, so I want to understand why you seem to think this is OK (if you do) even though it seems at first glance not to match the usual advice about mixing some of the output water back into the return to get it's temp up to the 140°F minimum...

    Gooserider
  6. in hot water

    in hot water New Member

    Joined:
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    Loc:
    SW Missouri
    In this example there would be a supply and return sensor. The supply sensor sets the "target" temperature, lets say 180 °F If the boiler can produce the heat as fast as the emitters are distributing it the pump would run 100% speed. As the return drops from a large high mass load as you indicated, the supply would also drop as the boiler can only produce X amount of BTUs. So the controls sees this drop and reduces the pump speed to allow the boiler to run hot enough, above dew point.

    If the load decreases and the boiler warms the temperature control on the boiler reduces or shuts down the fan, damper, or whatever the burn control is. Anytime you have a high mass system you need a mixing and protection device, be it a cold slab, snowmelt, buffer tank, etc.

    What the buffer does is decouple that large load from the boiler. So the buffer tank, or injection system is a lot like slipping the clutch in your truck to get a heavy load going from a standstill.

    Really the boiler is "injecting" btus into the buffer or hydraulic separator at a rate consistent with what the boiler can safely produce. Think of that Delta T pump as a variable speed injection system. It does exactly what a 3 way thermostatic does, just with a pump instead of a wax cartridge.

    Better yet, IMO is a 3rd pump to circulate just through the boiler. That is how I have mine piped. The boiler pump starts when the boiler temperature reaches 65 °C.

    Then the delta T pump sips the energy away at a rate matched exactly to what the boiler can produce. Should a large cold load hit the delta T pump slows. If the boiler temperature drops to 60 °C the boiler pump stops until it can warm back to 65 °C. So sort of a dual protection, but at the cost of another pump and control.

    I like the boiler pump with a loop from return to supply as it mixes the boiler and prevents hot spots and assures proper GPM as the HX was designed to a certain flow rate. This pump assures that is always handled.

    Check out this Taco link. Look at the GHSP example, which could be solar or wood sources. This might give a better explanation. I'd like to see Taco draw up a wood boiler example also. The Taco and Grundfos MixiMiser both come with thew two sensors to control my drawing above. The solar controller can do it also by using the max and min temperature settings.

    http://www.taco-hvac.com/uploads/FileLibrary/DELTAT(TD07).pdf

    hr
  7. Gooserider

    Gooserider Mod Emeritus

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    Loc:
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    That makes sense, and its how I understand such setups would work - except that as I understand the whole argument for using return protection, it doesn't really matter how hot the boiler is overall, it is still a problem if the return water enters the boiler and cools the point on the firebox next to the inlet below condensing - it just means you get a lot of damage in that one little spot... What I'm not seeing is how your proposed system would prevent that...

    Exactly, and that's what I'm not seeing... Taco says you should see at lest 130°F coming into the boiler, we generally say 140-145°F. The pump can slow down, and thus control the ΔT coming out of the boiler, but I don't see any way it can increase the temperature of that incoming water...

    Partly, It certainly allows you to pull BTU's out of the buffer at a different rate than what the boiler is making, but assuming the tank is set up to minimize mixing, the coldest water at the bottom of the tank is what goes back to the boiler, so the tank really doesn't do anything to give return protection.

    I disagree, and this is where I see the problem - the three way thermostatic mixes hot water in with the return, so that it offers protection in addition to the BTU output limitation...

    This idea makes sense, although as you say, its another pump... That is why I sort of like the three way thermostatic, since it consumes less power...

    Actually what I would think the best boiler pump might be one that had a reverse speed / temperature relationship... As the return temp drops, increase the speed of the boiler pump so as to increase the %age of hot water getting mixed in with the return. As the return temp goes up, slow the pump until it shuts off when the return temp gets over something around 150°F

    Neat link - though you have to cut and paste it, as it isn't selecting properly by itself... I'm trying to fix it in the quoted part...
    Edit... Not sure why, but it looks like something funky about the way the parentheses in the link are handled... If I click on the link, it enters "http://www.taco-hvac.com/uploads/FileLibrary/DELTATTD07.pdf" (note, no parentheses) in the destination bar, which gets a 404 error. If I cut and paste the address with the parentheses into the destination bar, it works fine... Not sure where the issue is, but I suspect that the problem may be that the parentheses aren't considered proper characters for use in a URL...

    Gooserider
  8. kabbott

    kabbott Member

    Joined:
    Nov 19, 2007
    Messages:
    384
    Loc:
    Hampstead,Maryland
    Another interesting thread on v.s., boiler protection etc....

    I have come to the conclusion that the only sane way to do v.s. in my system is on the loads not the boiler. For instance I have 13,000 + pounds of water to
    bring up from say 70 degrees( granted this is only once per year but it still must be done), The only way to do this without some sort of bypass on the boiler
    is to run the boiler loop at higher flow than the storage loop( or cycle it bang/bang which is what i do now but it sucks when the storage is cold...) With v.s. on the
    boiler loop and no bypass no matter how slow it runs the inlet is way below condensing when the storage is cold. At this point I should clarify that I have open
    storage with coil-in-tank and a hydraulic separator. With closed storage using the tank AS the separator I see NO WAY to keep return temp up without some sort
    of bypass be it a pump or mechanical valve. IF you never let the storage drop below 130-140 the you would only need the bypass when bringing it up to temp
    for the season.

    I THINK my plan as it stands now is to run the boiler loop whenever the boiler is hot, It COULD still be v.s. based on desired outlet temp to or desired delta
    inlet/outlet @ boiler. Then use v.s. on the loads to meet minimum return temps OR desired delta inlet/outlet of my emitters to keep storage return temp
    low. So when heating via the boiler the load flow will vary to keep return temp reasonable and when heating off storage the flow will vary to keep the return to
    storage as low as possible while still keeping the wife warm (most importantly).

    This is all subject to change of course as I may have a better idea next week ( or learn something new more likely).

    No matter how you roll it variable speed seems like the "next" step for efficiency, I just wish those ECM pumps were not so darn pricey.
  9. in hot water

    in hot water New Member

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    All boilers run in the condensing mode at start up. If the boiler is sitting inside you building at ambient temperature, or in an outdoor shed at outdoor temperature conditions. It takes a period of time, even with no demand or flow through the boiler to warm up above dewpoint. Same with the flue pipe.

    What you attempt to do with controls, valves or other devices is limit the amount of time in condensing mode to limit the boilers stress.

    It doesn't matter, and the boiler really doesn't know what device is providing the temperature control. A 3 way thermostatic works, costs some pump power or head, so it's not exactly a "no energy consumption device" The laddomat tries to blend 3 way thermostatic with a dedicated circulator. VS pumping does it with pump speed. In any of the methods the boiler has to warm up before any blending can occur.

    With VS control as soon as the top portion of the boiler warms the pump starts. It may be as low as 10%, but it starts blending the warmer water at the top.

    Any of these methods will work, and all at the same rate. It takes X amount of BTU to raise the temperature of a tank, boiler or distribution, the control logic can't change that.

    What I like about the VS approch is the control can do a dozen additional tasks while modulating the pump speed for return protection. So for lets say @ 250 bucks you get return protection function, digital display, optional relay function, data logging, and with a new control we have a. iPhone app to read your system from anywhere you can get a phone signal.

    Just presenting the options, there will be Ford, Chevy, and Chrysler buyers. They all get you from A to B.

    hr
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