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Relay to latch TT to prevent abandoned calls until buffer tank fills ?

Dave Carpentier
Dave Carpentier Member Posts: 171
Problem: My design allows for the TT terminal on the boiler to be abandoned during in-floor zone switching, and that could be mid-burn before the buffer tank is filled (ie, boiler is not up to setpoint yet).

Solution (maybe ?): Bridge on to the burner fan's 120v ac connection with a relay to "hold" the TT until the boiler (and thus the buffer tank) are up to setpoint, regardless of what the zone switches are doing. Once the fan turns off post-burn, then the relay is "reset" back to monitoring the zone switches. The zone switches will then turn on and off as per normal, switching the boiler's circ on and off to match. But, once the burner starts, I want it to run up the full 20 deg differential.

I didnt look thru many 120v ac coil relays, but one I found showed 1.2mA for coil current, I dont think the fan motor will care about this little load alongside it. The fan speed itself is controlled by a separate PWM circuit, the circuit Im bridging to is just the power supply to it.

Workable ?


30+ yrs in telecom outside plant.
Currently in building maintenance.

Comments

  • mattmia2
    mattmia2 Member Posts: 5,508
    why not a latching relay that is reset by an aquastat in the tank?
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    edited May 21
    No tank aquastat, I was planning to use ODR on the boiler.

    Adding: ... with a 20 deg swing on the setpoint.
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 16,286
    Why does the buffer need to be filled? With two pipe arrangement flow Is direct to loads. The boiler and it pump only run when the buffer is to cold, regardless of ODR or setpoint control. If you wanted to, balance the boiler circ to 8 gpm or whatever the max system load is. On design days all boiler flow goes to system, nothing to tank. You don’t need the buffer involved at design condition.
    I think you are over thinking the system maybe?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • 109A_5
    109A_5 Member Posts: 122
    edited May 21
    I'm, certainly no expert with these systems, but wouldn't that circuit that you purpose latch up permanently until some safety device shuts it all down? Isn't the call to the TT what originally starts the process that turns on the burner fan?

    To me you need an aquastat (or like device) in a well in the boiler or some other convenient place (well in the buffer tank, or the boiler return pipe from the buffer tank, aquastats (or like devices) can be strapped to pipes) to shut down the extended call.

    For simplicity sake the aquastat (or like device) could (electrically) be just another zone. If you want to keep that tank at temperature all the time.

    What about one of those multi zone control boxes? Do they have a delay that would extend the XX to keep the TT called for the zone switching dropout time? Often they have a priority zone, DHW loop maybe, if that type of functionality is what is desired.

    If the ODR on the boiler provides the desired functionality why do you need to latch the TT for an extended time? Will the boiler ODR give aquastat like functionality ? What keeps the boiler from going over 180 degrees or your desired temperature if lower? Are you trying to reduce boiler cycling and keep the buffer tank topped off also?

    Why open the end switch circuit with the relay? Another call may come in during the extended TT call.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Jamie Hall
    Jamie Hall Member Posts: 18,920
    As noted, the circuit shown, once latched, will never drop out. Also as noted, if you want to maintain buffer tank temperature, use an aquastat.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    Thanks all. It may be that Im trying to fit a square peg in a round hole (have file, will travel).
    For this boiler (but Im still looking for others), the TT signal enables the internal pump always, and the burner will cycle with a 20 deg swing around the ODR setpoint. It seems to me, during a zone call where the burner is running and the zone releases, then the burner stops. After a short period, a different zone could open and re-trigger the TT.. the burner would start again (it never had the time to hit setpoint in the previous call).
    At design temp or colder, I should be able to tweak things so that the zone calls are continuous (collectively, there's 7 of them), so that the boiler's circ is running full time and the burner is near steady state. At warmer temps, zones will cycle (although I may be able to tweak to minimize this).

    The circuit above ensures that once the burner starts, it (and the boiler's circ) will run until it hits setpoint. At setpoint the burner turns off, so the relay releases the TT back to zone end-switch control. Im not looking to lock the burner on , Im looking to lock the TT down while the burner is running. I picked the vent fan circuit because I wanted to stay away from the gas valve controller (extra safety). The vent fan does have a pre and post runtime, so the TT will be held a bit more than required.

    @109A_5 - A buffer tank aquastat with ODR with all of the setpoint adjustments that the boiler has would work, but would seem like spending the same money twice. A control box with time delay would still end up randomly shutting down the burner mid-stride (unless it could sense when the burner is running). The DPDT relay that opens the end-switch connection was a mistake. Here's the corrected one. The solid lines are what I already use on my CI boiler and will adapt that to the new boiler. The dashed lines are the proposed "latching" thing. Thanks for noticing that.



    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • Jamie Hall
    Jamie Hall Member Posts: 18,920
    The way your system should work is that the burner should fire when the water temperature in the buffer tank/boiler circuit falls below the outdoor reset temperature, and should stop when the buffer tank/boiler circuit reaches that setpoint.

    The various zone valves should power the zone circulating pump, which pulls water from the buffer tank and circulates it to the zone(s) calling when asked by a thermostat in that zone.

    Your problem is, I expect, that for some reason the zone valves are hooked up to the boiler burner, not to the zone circulating pump.

    You do have two independent pumps, don't you? I hope?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • motoguy128
    motoguy128 Member Posts: 394
    I’m confused. Why do you need the buffer tank up to temp? If there’s no call for heat, why store hot water?
  • hot_rod
    hot_rod Member Posts: 16,286
    You are missing the point right here:
    the TT signal enables the internal pump always, and the burner will cycle with a 20 deg swing around the ODR setpoint. It seems to me, during a zone call where the burner is running and the zone releases, then the burner stops.

    The TT signal to start pump and boiler comes from the buffer tank. Either via a separate setpoint control, or via a boiler sensor. The buffer will always get charged before the boiler and pump stops.

    The buffer tank, regardless of how you control it just supersizes the boiler. You are turning a 3 gallon boiler into a 33 gallon.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    @Jamie Hall - I agree with your first 2 paragraphs. The Nti doesnt seem to do that, nor other brands that Ive browsed thru the IOM of. Buffer tanks just dont seem to be a popular approach ? My zone valves (end switches) control the secondary circ but also have to send the heat request to the TT (for this boiler anyhow). The boiler will have its own primary pump (either internal or external). Just to clarify, this isn't an existing system.. Im setting up to replace my CI.

    @motoguy128 - True. On a spring day, the buffer can cool right down because new SWT will appear nearly instantly when heat call starts. My circuit was for a "once the burner starts, let it complete it's run up to setpoint" approach based on the limitations of the proposed Nti boiler.

    @hot_rod - The TT signal to start pump and boiler comes from the buffer tank. Either via a separate setpoint control, or via a boiler sensor. The buffer will always get charged before the boiler and pump stops. Yes. I think that's the square peg meets round hole currently. The Nti doesnt seem to work this way. Now that I have a pretty good list of requirements, Im going to go to the supply houses and see what the hydronic sales guys have to offer. The Nti proposed was just by phone, Im going to bring my system diag down in person. A different supply place has IBC, Lochinvar and Navien.. I didnt find anything suitable in the IBC IOMs yet, maybe the other two brands do ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 16,286
    The zone valve end switches just need to turn on the distribution pump, they don’t interact with TT. The tank is the inly component talking to TT
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 18,920
    Or to put @hot_rod 's point another way -- it the zone valve end switches are interacting with TT -- the boiler -- something is miswired. Someone read a wiring diagram wrong. Someone misinterpreted something. Who knows. But it's wrong.

    And the manufacturer of the boiler has absolutely nothing to do with it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    On the Nti, if the zone switches dont interact with the TT, then the boiler isn't aware of a heat request.
    I called Nti tech support to ask about the optional "System sensor", he said that's only in use during cascade mode. He said as long as TT is on, the boiler's circ will run and the burner will cycle as it needs to. If you remove TT, then everything is off (from the boiler's perspective, there's no longer a request for heat).

    Originally, I considered just strapping the TT. Then the boiler's circ would run full-time and the buffer would be at setpoint all of the time.

    I'll continue my quest for a boiler than can more properly integrate with a buffer tank. Hotrod had a good point in a different thread about trying to avoid Rube Goldberg type controls.
    If anyone knows of a residential-level brand/model that could do this, let me know..
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • 109A_5
    109A_5 Member Posts: 122
    edited May 22
    In regards to your original post and your second wiring diagram, if the ODR will break the latched up functionality your relay circuit creates (with no other side effects), it would probably work. However that being said, I am not sure I would want to bank on someone else's ODR algorithm, since when an embedded controller's software detect a condition outside of 'Normal' they either do strange things or error out and shut down. Also I am not sure that method is the most efficient use of fuel.

    As others have stated, having a modular control approach that the controls don't outreach the demarcation points of that module or section eliminates your current issue. I think the point of engineering is figuring out how to make all the components play nicely together.

    However more issues will probably crop up. If your new high tech boiler trips out or fails do you want your pumps running continuously until someone figures out there is a problem? Vacation? They could run for weeks. Are all the pumps supervised by the boiler ?

    If this were my project instead of coming up with a relay 'band-aid' for every system anomaly or engineering oversight that comes up and keeping with a modular control structure approach like others have suggested I would use a PLC. Since you can have modular isolation and overall supervision in one package. An example; If after a TT call the expected temperature rise is not detected the TT call could be terminated along with pumps being shut down so the pumps are not running for no good reason. After a period (defined by you) it could retry, after say 2 retries it just gives up and displays the error why. How many Crossbar switches are still in operation today? Technology with better function and features has replace them.

    Some side notes; I thought buffer tanks (large ones) were more for Solar type systems where heat is not on an almost instant demand like with a boiler. I can see some Pros and Cons for a buffer tank use in your case. Also I'm having a mental debate if your circulating pump for the 'In-Floor' section is in the best place. I don't know what 'Best Practice' is in this case. Turbulence and currents in the buffer tank and the "Large Pipe" manifolds could inadvertently restrict the flow of heated water to the the the 'In-Floor' section increasing boiler run time. A different pump location may minimize this but may cause other undesired effects.

    In other words if the part of the 'In-Floor' loop that gets the actual heated water becomes restricted (for any reason) you won't get heat to the 'In-Floor' zones, yet the pump will still pump water through those zones. Will the 'Mixer' valve 100% cut off the bypass path? It may be also very dependent on the relationship of the 'Mixer' valve to the pump. Does the 'Mixer' valve care where the pump is for best efficiency?
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • hot_rod
    hot_rod Member Posts: 16,286
    anything could call on the boiler and pump via TT. A light switch, setpoint control, snap disc on the tank, even a jumper wire.
    The ZV and any distribution pump just pump from the tank, really no interaction with the boiler is needed.
    The distribution system could call from a cold tank for that matter if you had a heat pump that heated or cooled the tank.

    Or another simple way is call the buffer an indirect tank, disable or "time off" the priority function. The boiler really has no idea what it is being called to heat, it just sees a closure on TT or DHW contact, fires until that signal is gone or satisfied.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 18,920

    On the Nti, if the zone switches dont interact with the TT, then the boiler isn't aware of a heat request.
    I called Nti tech support to ask about the optional "System sensor", he said that's only in use during cascade mode. He said as long as TT is on, the boiler's circ will run and the burner will cycle as it needs to. If you remove TT, then everything is off (from the boiler's perspective, there's no longer a request for heat).

    Originally, I considered just strapping the TT. Then the boiler's circ would run full-time and the buffer would be at setpoint all of the time.

    I'll continue my quest for a boiler than can more properly integrate with a buffer tank. Hotrod had a good point in a different thread about trying to avoid Rube Goldberg type controls.
    If anyone knows of a residential-level brand/model that could do this, let me know..

    Well, to a limited extent tech support is correct: if T-T isn't closed, the boiler isn't aware of a heat request. If T-T is closed, the boiler will run and the circ will run and heat up your buffer tank.

    Now what seems to be missing is the notion that T-T doesn't have to be closed by the zone valves. In fact, it shouldn't be. Why this seems to escape acknowledgement here I do not know, but it does. So let's try this one more time:

    Your T-T needs to be closed by an aquastat on the buffer tank. Preferably one which is controlled in turn by the outdoor reset. AND NOTHING ELSE. The zone valve end switches need to energize the secondary zone circulation pump -- possibly through a relay -- AND NOTHING ELSE.

    There is nothing Rube Goldberg about this. It's about as simple as it gets.

    Your problem isn't finding a boiler that can more properly integrate with the buffer tank. Your problem is finding someone who will wire up the controls properly. Plain and simple.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 109A_5
    109A_5 Member Posts: 122
    @Jamie Hall, I understand a sectionalized or modular control approach. Each controls its own part and it all works in concert. Where I get lost and fascinated, is if the boiler trips out or fails, what keeps the (non-boiler) circulation pumps from not running forever except human intervention? Since in this scenario the calling thermostat will never be satisfied until a repair is made. Yes a bit different from the OP.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Jamie Hall
    Jamie Hall Member Posts: 18,920
    109A_5 said:

    @Jamie Hall, I understand a sectionalized or modular control approach. Each controls its own part and it all works in concert. Where I get lost and fascinated, is if the boiler trips out or fails, what keeps the (non-boiler) circulation pumps from not running forever except human intervention? Since in this scenario the calling thermostat will never be satisfied until a repair is made. Yes a bit different from the OP.

    Quite right -- in the instance you mention, the poor old pump will just keep on going... and going... and going.

    Usually not really a concern -- the newer pumps don't draw much power, after all, and it won't hurt anything (in fact, in an ideal world with perfect outdoor reset, that pump would run all the time anyway. Right...).

    If it were a concern, it would not be hard to put an aquastat into the system to keep the pump off if the circulating water temperature were less than some desired value. This is very commonly done with air handlers or even some hot air furnaces, to keep the fan off if there isn't heat available. It just doesn't seem to be worth it for most hot water heating systems.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    @hot_rod - defining the buffer as an Indirect would indeed let the boiler use it's remote sensor to keep the tank hot. But no ODR, just a set fixed temperature. I think Im trying to get a buffer at ODR setpoint (without buying an ODR aquastat, since these boilers already have deluxe ones).

    @Jamie Hall - I think I do understand what you're saying. Possibly a solution is an ODR aquastat calling the TT of an ODR boiler. The boiler would have to be set a smidge hotter to ensure the aquastat satisfies.
    The extras like autoboost on the boiler side could help trim any long buffer tank calls.

    @109A_5 - Many potential points of failure. Ive run out of oil more than a handful of times in the last 20 years. Come home and the air handler is running, the floor circ is running, the primary pump is running. The boiler is just sittin there blinking at me. Other parts could be a thermostat stuck, or an end switch stuck (had a few of those on the old Wirsbo MVAs) and the circ pump keeps dutifully running and running. I've always been a bit nervous about something happening to make the boiler run out of water. A LWCO guards for that.



    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 16,286
    Pretty much all mod cons have ODR, so by default so does you buffer, since a TT call runs the "system" via ODR. Or as we mentioned run the tank at a fixed setpoint and pull the heat loops off via ODR control.


    All mod cons have multiple, dependable safeties, temperature, flow, high limit, low pressure cutout, blocked flue, and a connection to make adding a LWC very easy if you think you need that. The more aftermarket controls you add the less dependable :) the system becomes, more modes of failure.

    What if you have a power outage? No amount of excessive controls will handle that condition. At some point a failure puts you out of heat, add an alarm and phone dialer if that is a big concern. My Ecobee t-stat tells me what is going on in my shop and home, temperature-wise. It sends an email notice even if the system is falling behind.

    @Jamie Hall may have the solution, hire a control person to make this work for you, if you are unclear or uncomfortable with the technology.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dave Carpentier
    Dave Carpentier Member Posts: 171
    I may have found a more suitable boiler. The Lochinvar (Epic,Knight and Noble) boilers appear to do what Im looking for.
    A heat call (from zone switches) to the TT turns on System (my in-floor) circ power, but the (external) Boiler circ power only comes on when the System Sensor (in the buffer) temperature is below setpoint ( it only comes on with the burner cycle).
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 5,508

    @hot_rod - defining the buffer as an Indirect would indeed let the boiler use it's remote sensor to keep the tank hot. But no ODR, just a set fixed temperature. I think Im trying to get a buffer at ODR setpoint (without buying an ODR aquastat, since these boilers already have deluxe ones).

    I disagree that the boiler has sophisticated controls. It has controls that sort of work for a lot of applications. If you really want to control everything exactly you need a BMS or a couple different special purpose controls.

    What you could do is keep the tank at a setpoint on the DHW call where it will be above the cut in point of the highest point of the ORD curve, that way on a heat call it won't heat on the DH curve until the tank temp drops some but then it will go up to the ODR curve cut out point. Use the differential in the DH setpoint to make a constant tank them acceptable. I think this would be easier to draw than explain in words.

    Many to most systems larger than small residential are designed for constant circulation, the circulator is designed to run 24/7/365. Running for a while during a system failure won't hurt anything as long as some valves are open(if there are any) so it isn't deadheaded. In fact circualting the water makes it less likely to freeze somewhere if there is no heat.