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boiler suggestions, buffer tanks

2

Comments

  • jrkeat
    jrkeat Member Posts: 71
    Hot rod:
    > If you use that AO Smith tank, remove side nipples, get a 3/4- 1-1/4 or 3/4- 1-1/2 copper to male adapter to increase the port sizes. Or a specific hydronic buffer with large side ports.

    Aren't those side nipples dielectric? Aren't I going to get galvanic corrosion if I directly install brass into those ports?
  • SuperTech
    SuperTech Member Posts: 2,137
    > @jrkeat said:
    > Hot rod:
    > > If you use that AO Smith tank, remove side nipples, get a 3/4- 1-1/4 or 3/4- 1-1/2 copper to male adapter to increase the port sizes. Or a specific hydronic buffer with large side ports.
    >
    > Aren't those side nipples dielectric? Aren't I going to get galvanic corrosion if I directly install brass into those ports?

    No need to worry about use of dielectric fittings in a closed system.
  • hot_rod
    hot_rod Member Posts: 22,018
    A lot of those smaller electric HW tanks have multiple 3/4 side ports, this is a 20 gallon, box store brand tank.

    If you use the 3/4 ports I would use a 3/4 male X 1-1/4 copper adapter. Probably 1-1/4 is as large as I would go, you have about 5 fps velocity in that 3/4 reduction at 8 gpm flow.

    If you use the 1" element holes, these swage nipples are a nice smooth transition, McMaster Carr has a wide selection in steel, SS, or brass.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • jrkeat
    jrkeat Member Posts: 71
    I redid the layout, mostly so that I could compile a parts list. Between the smaller boiler, smaller clearances, and running the DHW horizontally off to the right, there was a lot more space, and it's much less of a mess.

    Prompted by your suggestions, I changed the loop structure, though I partly did my own thing. (The Laars doesn't have an extra temperature sensor, and I wanted to stick with them.) The two groups of radiant floors are now on a loop that has the tank on one end. The pump connecting this subsystem pumps at full speed when the there is a radiant call and boiler is firing. (This will load the boiler, and result in a stratified tank.) When there is a radiant zone call is still but the boiler isn't firing, the pump transfers 0.3 GPM. This is enough that the primary will know when the temp drops too much in the radiant loop, but it will take an hour for the primary loop to mix up the tank. So the radiant zone will be able to suck hot off the top and put cold on the bottom.


  • hot_rod
    hot_rod Member Posts: 22,018
    The control board does show a connection 13/6 for system sensor maybe just for cascade feature?

    It does have a 0-12V input that could not only remotely fire the boiler, but modulate it also. You would need a separate control to send the signal, with a sensor in the buffer.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    Interesting! That "system sensor" can definitely be used when cascading. I'm not sure if it interacts with the outdoor reset--I see what Laars has to say. Does you Lochinvar interact with the ODR correctly?

    Do you see anything wrong with the system as designed?
  • jrkeat
    jrkeat Member Posts: 71
    Laars says the system temp will use the ODR.
  • hot_rod
    hot_rod Member Posts: 22,018
    Be interesting if you could find a 0-1 or 4-20Ma control to run the tank, but it looks like you lose the ODR function when you use those connections? A system sensor would perhaps be the easiest.

    I'm not sure you need that 3 gpm bypass circ and valve, seems like maybe you are over-thinking the buffer interface and control?

    I have done quite a few buffer tanks from 6- 500 gallon with just a sensor in the tank either from the boiler directly, or an after market control.

    I have a large Caleffi/ Resol control on my 500 gallon buffer that runs a wood boiler input, solar drainback, DHW via a plate HX, and radiant supply function. A motorized 3 port valve on ODR via a tekmar control. I think your boiler control has all the logic you need if an optional sensor is added?

    Looks like it also has a ramp delay, and/ or space heat output limiting function, so you should be able to dial that boiler in very nicely to both DHW and heating loads.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    Seems like the Laars gives me what I'd need to do the sensor in the tank.

    How would you physically put the sensor in the tank? Is it water proof? Do I drill a little hole in a fitting and feed the wires through and seal it with silicone?

    One downside--and maybe you have a way to address this--is that the buffer tank will be kept warm a lot of the time, unless I explicitly shut it off in the spring. Say there are days when it's 70 during the day and 40 during the night. The thermostats will never trigger the heat, but the ODR will kick up the tank temp over night.

    Seems like it would be better to have two sensors. Use the one at the top of the tank when the boiler is off and the one at the bottom when it's on. You can do this easily with a DPDT relay. Otherwise, you have to set the thermostat delta T really wide so that the boiler won't immediately start firing right after it switches off.
  • jrkeat
    jrkeat Member Posts: 71
    Actually, now that I think of it, if I put the buffer in the main loop as you suggest, it will be active whenever there's DHW call. So it will be hot all year.
  • hot_rod
    hot_rod Member Posts: 22,018
    Best sensor method is in a dry well in the tank, if a tapping is available. Sensors read accurately enough if pushed tight against the metal tank and insulated behind. The metal tank and fluid inside will be about the same temperature.

    Hose clamp them onto a pipe is another common method.

    If the boiler is run on ODR, the tank should not heat, nor a heat load call when temperature outside is above 68F, typically.

    If you use the onboard control it should have a wide adjustment range, a 10- 15° differential should work. You need to get it up and running and make adjustments to all the settings that best suit your application.

    If you read Idronics 17, control logic and suggested settings are included with the various piping examples. There may be one that serves as a starting point for your needs.

    The beauty of hydronics is the infinite adjustability, knowledgeable owners and DIYers can tweak and monitor better than installing contractors making multiple 1 hour callbacks to make minor adjustments.
    Once you have and understand the control logic fiddle with it. You may need to get some design day conditions to set max. temperatures requirements.

    Many recent projects indicate load calculation predicted water temperatures are higher, maybe 10° or more than the system actually requires. Start with the design number and back down to the lowest possible SWT would be my suggestion.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    How do I not use the buffer while the DHW is running if I use your system where the buffer is on the primary loop? (Otherwise I'm keeping the buffer warm all year.) Could I use an extra circulator and run it off the CH pump line? I still wind up using the same extra pump that's in my diagram, so I save only a couple of parts.
  • hot_rod
    hot_rod Member Posts: 22,018
    The manual is vague on pump capacity available to run additional distribution or an indirect.

    It shows two heating piping drawings and one indirect only, odd not a combination heat & indirect?

    This was one of my favorites, it can work even on water tube type HX if you know the head loss and circulator capacity. The 120V zone valve wires directly to the DHW output terminals. Tank control to DHW enable.

    It provides the shortest path and hottest SWT to the indirect. On priority all heat calls stop, nothing changes in buffer temperature. No heat added to buffer or P/S piping in WWSD. You have a boiler and indirect in the loop, period in the no heat season.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    I've updated my diagram to work with what you're suggesting. I'll put the system sensor in the tank. Now all the heating circuits are on one loop which runs when the CH pump line on the boiler goes high.


  • hot_rod
    hot_rod Member Posts: 22,018
    I’d still simplify it a bit more. Boiler with integral circ direct to tank. All loads pull from a large header pipe at the tank
    DHW call both the boiler circ and indirect circ run. If both circs are sized to say 8 gpm there is no tank interaction on DHW priority, 180 directly to indirect

    Boiler controlled by ODR, run to highest temperature required on design day. System sensor on the tank turns the boiler into a high volume boiler, just happens to be two pieces. Probably mid point on the tank for the system sensor
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    I think I'll stick with the dual primary circulators. Exactly matching flows from two different pumps on two different circuits sounds difficult.

    I think I'll do a two-sensor setup, just for fun. While the boiler is on and the tank is filling, it will use the bottom one. It will switch off exactly when the entire tank has filled with hot water. When the boiler is off and the tank is discharging, it will use the top one. It will switch off when the entire tank has filled with return water. I can then use a fairly narrow delta T, and it will get the switches exactly right. The sensors will be connected via a DPDT relay actuated by the CH circulator line.

    Can I mount thermowells in the location of the drain valve and the hot water tap on top? Maybe for the lower one I could put in a tee and include the valve on the side.
  • hot_rod
    hot_rod Member Posts: 22,018
    No harm in experimenting on your own system. The thermocline in the tank is ever-changing as you flow thru it with different gpm requirements.

    I tried reversing the flow in a large horizontal buffer I had on my wood boiler, load in one direction, unload the opposite.

    I saw a Euro design multi energy tank at a trade show once. It had a track or channel running down the side, you could slide sensors to any level and pinch it against the metal. It also had a lot of side ports allowing you to pull the various temperature loads from the thermocline and avoid busting up that layering in the tank.

    I've found sensors tight against a metal surface, and insulated are plenty accurate, maybe a tad slower response is all.

    Also assure the flow into and out of the tank is diffused to help stratify the tank. I built a slotted dip tube on my side port tank..

    Really no problem balancing flow rates, a Quicksetter could be used, many of the new circulators have gpm readouts on them.

    Trying to save you a redundant circulator, assembly parts and lifetime power consumption. That is a tricky circulator to size and buy, 8 gpm flow at very low, maybe a foot or two of head.

    I've never found a good primary loop circulator for that lopsided requirement, high flow rate- low head.

    Avoid piping in any air traps where you loop up and back down as shown. An air bubble caught up there puts you out of business.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTechBillyO
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    > Avoid piping in any air traps where you loop up and back down as shown. An air bubble caught up there puts you out of business.

    Thanks!

    Can I just put an air vent at the top of that loop that goes into the pump? Actually, it would be pretty easy to run that pump straight into the end of that header.

    Similarly, do I need to do anything about the high points int the radiant tubes? The current system has air vents on the two returns--I'm not sure if that's necessary.

    For that matter, should I have one on the top of the hot water heater?

    A separate issue: For my indirect indirect lines, I'm worried about the flow rate. My 007 (all the 007s except the 007e will be pulled from the current systems) looks like it will pump 14 gpm (5.6 ft head), or 5.4 fps. Should I care that I'm over the 4 fps limit? They actually want you to pump 14 gpm for full capacity, and suggest 1" pipe.
  • hot_rod
    hot_rod Member Posts: 22,018
    Yes, straighten out the piping, the shortest distance without up and downs. Not a bad idea to have an auto air vent, at least a manual on the high points in the system.

    5 FPS is acceptable in hydronics in my opinion. Assure your fluid is good and clean, mineral free to avoid problems.

    So the pump curve is a fingerprint of what the circulator is capable of. The best information is gained from plotting the system curve, lay it over the top of the pump curve.

    Where the curves cross establishes the OP, operating point where the circulator is going to actually operate. Use that point to determine the actual flow velocity.

    Step by step how to determine that and plot a system curve here.

    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_18_na.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    BillyO
  • jrkeat
    jrkeat Member Posts: 71
    I just found the equivalent feet of 1" pipe (34 outside the tank, 12 inside) and used a table to find (https://www.engineeringtoolbox.com/pressure-loss-copper-pipes-d_930.html)

    GPM Head (ft)
    10 3.0
    12 4.2
    14 5.6

    The 007 curve reaches 5.6 at about 14 GPM.

    An updated layout. It's not any straighter, but it doesn't have a high point:

  • hot_rod
    hot_rod Member Posts: 22,018
    plot those points on the 007 pump curve, looks like right about 12 gpm is what you will actually flow.

    Notice the 008 also crosses at that point. One is a flat curve, the 008 a higher head, steep curve circulator.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    I'm not seeing the same thing. Curve 5 is the 007. At 14 GPM, I see roughly a 5.6 ft head. I've taken the Taco brochure and circled what I think is the intersection point.


  • hot_rod
    hot_rod Member Posts: 22,018
    You are correct, I was looking at the wrong green line on my version.
    Plot the 3 points you noted to develop the system curve. Where it crosses any circ curve is the OP.
    If your numbers are correct a 005 would get you 12 gpm which is more in line with what I would expect for a 120K boiler, maybe even 8- 9 gpm with the actual boiler output number. The boiler HX spec would be helpful.

    Does that Mascot have the Korean Kiturami heat exchanger, or their own style?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    Yes, it's a Kiturami heat exchanger and motor, apparently a Grundfos 15-58 knockoff.

    Why is the oversized 007 a problem? The tank is designed for that flow speed. Given the primary/secondary separation, why would the boiler care?
  • hot_rod
    hot_rod Member Posts: 22,018
    That’s why you see all those circulator options 😉. You should be able to find one close to the actual output of the boiler. Call it 100K, at a 20 delta you need to move 10 gpm. 1” copper suggested flow rate of 10- 11 gpm. Really no good reason to over pump or over flow the tubing.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    The 006 and 006e3 are good matches (just under 10 gpm), but it doesn't seem worth buying a new pump.
  • hot_rod
    hot_rod Member Posts: 22,018
    jrkeat said:

    The 006 and 006e3 are good matches (just under 10 gpm), but it doesn't seem worth buying a new pump.

    If you want a truly balanced system, adding a balancing valve serves that purpose, dial the flow to EXACTLY what you want, or need. But really no reason these days to over-size and choke down with a wide selection and variable speed circs available.

    If you want to use what you have, then you will get what the circ provides? It's not grossly oversized according to your numbers. Installers like adding Quicksetters to actually see what is flowing and make small adjustments.

    If you ever do decide to upgrade any/ all circs by all means look into ECM versions.

    A typical PSC wet rotor circ runs maybe 19- 22% efficiencies, you can double that with ECM circulators, plenty brands and models to choose from.

    Really it always comes down to how much $$ you want to spend for what level of control, efficiency, serviceability, etc. The sky is the limit :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    I've been thinking thorough the most recent version of the system, and seems like it has a problem.

    Consider the main radiator loop. It presents a load that is above the modulation limit of the boiler, but below it's potential output. We want the boiler to run continuously at a modulated output.

    Let's assume that the buffer starts with all hot water.

    A call comes for the radiator loop. The radiator loop starts sucking water from the top of the buffer and putting cold in the bottom and running the main radiator loop. The boiler will see the ware from the buffer as a load, and will run at full output.

    This will continue until the tank is at full temperature and then....the boiler will switch off!

    So the boiler will actually duty cycle rather than modulate.

    In the case of the smaller loads, we are fine with the duty cycling--it sill run a full power for a couple of minutes and then run the small load for tens of minutes.

    Duty cycling with a 60k BTU load and a tank that stores 5k BTU will amount to short cycling, though. And we won't get the efficiency benefit of modulating down.

    What are your thoughts?
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    Both of the other designs I proposed still work. The first one runs the buffer pump whenever one of the small zones has a call. There were two disadvantages: stratification is destroyed after the boiler stops firing (which doesn't destroy the value of stratification during charging of the buffer), and the boiler pump and the buffer pump run all the time while the call is still on. If the loads are ever greater than the minimum firing rate, then after the buffer is charged it will modulate down to match the load. The original diagram looks a lot more complicated, but it's not at all: everything just got squeezed into the left side of the wall.

    The second one puts the radiant loops on a pump-run subsystem. When the boiler stop firing, it continues to inject a little water back into the primary loop so that the boiler can monitor its temperature. This does all the stratification correctly, except for the mixing that happens through the 0.3 gpm route.
    There are a couple of extra parts. As with the other one, the boiler pump and the buffer pump run continuously whenever there is a call from a radiant zone.

    The major thing that using the tank temperature to control the boiler gets me is that the boiler pump and the other pump don't run much. With either of these other proposals, I should get another ECM pump. I don't see how to get around the failure to modulate, though.
  • hot_rod
    hot_rod Member Posts: 22,018
    jrkeat said:

    I've been thinking thorough the most recent version of the system, and seems like it has a problem.

    Consider the main radiator loop. It presents a load that is above the modulation limit of the boiler, but below it's potential output. We want the boiler to run continuously at a modulated output.

    Let's assume that the buffer starts with all hot water.

    A call comes for the radiator loop. The radiator loop starts sucking water from the top of the buffer and putting cold in the bottom and running the main radiator loop. The boiler will see the ware from the buffer as a load, and will run at full output.

    This will continue until the tank is at full temperature and then....the boiler will switch off!

    So the boiler will actually duty cycle rather than modulate.

    In the case of the smaller loads, we are fine with the duty cycling--it sill run a full power for a couple of minutes and then run the small load for tens of minutes.

    Duty cycling with a 60k BTU load and a tank that stores 5k BTU will amount to short cycling, though. And we won't get the efficiency benefit of modulating down.

    What are your thoughts?

    The tank will supply directly to the load if it is charged, no flow between the boiler and tank.

    When the tank drops in temperature to the set point of your control sensor the boiler will fire and adjust to its output to the load it sees. Some flow will go directly to a low gpm load, some to start charging the tank.

    If you could pull all the loads via an ODR control you could get more drawdown, pull off only the amount of energy required at a given time. If you run the boiler and tank as one, then the ODR regulates tank temperatures.

    Pros and cons, running a tank above 140 or so will limit condensing mode and lose some of the boilers efficiency.

    Running the tank at lower "condensing" temperatures, limits the drawdown. Lower tank temperature= lower heat loss, so that is part of the balance act also.

    So you need to decide which logic suits your interest best, longer drawdown, less boiler cycling, would be a hotter tank.

    Buffers used on solid fuel pellet or cordwood boilers we run to the highest possible temperature, long boiler runs, but also long drawdown cycles.

    To optimize boiler efficiency, run the lowest possible SWT, or return temperature actually.

    Sensors are located in the supply and return of the boiler itself watching the delta and modulating accordingly. If the load is low, say 5 gpm to one load, the boiler will modulate it's firing rate to that. Once running you can watch that interaction on most control screens temperature across the HX and fan speed or firing rate %.

    Without this mod con control logic, you would have a boiler always at 100%, it would` be a "con" without the mod :)

    Basically a mod con modulates by the fans speed. The faster the fan is called to run, the higher the firing rate. A negative pressure gas valve responds to the fan speed. So to change output, limit it, ramp it, you basically tell the fan to operate at different rpms.

    If you know the exact flow rates of all the loops, loads and boiler, you could predict the amount (gpm) going past or thru the tank at any given time.

    Basically you are building a 20 gallon boiler out of your 3 gallon boiler, but also gaining more flow control with the tank also being a hydraulic separator.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • jrkeat
    jrkeat Member Posts: 71
    Thanks for the detailed response.

    Do you agree that if I put the system sensor in the tank, the boiler will switch on and off, even if the load is big enough that the boiler could modulate down? (My analysis indicates that it will continue to charge the buffer tank until is up to temperature and switch the boiler off, even if we have, say, a 50% load from the radiators.)
  • hot_rod
    hot_rod Member Posts: 22,018
    Does that boiler have a pump that modulates? Some brands do. Some give you a 0-10V output to modulate a circ designed to take that input. I think some of the new Taco circs accept a 0-10V signal.
    Ideally you would modulate the flow thru the boiler with the firing rate, so if you had a 50% load, the burner modulates down and so would the flow rate, That control logic would eliminate to some degree the tanks requirement, but as of yet no boiler I know modulates below about 7,700 BTU/hr. So if you have loads below that, and you will at below design days even if you had a smallest load of 7,700 btu/hr.

    Right now, lets say the boiler circ is fixed speed, always moving 10 gpm. If you have only a 5 gpm zone calling, 5 gpm goes to the load, 5 gpm starts recovering the tank that has been pulled down.

    If you put a number to what temperature the tank has pulled down to, and you know the flow rate and temperature recovering it, you could calculate the time to satisfy the tank, with or without loads.

    I use a simulation program in the HDS software that allows you to identify all the loads, tank size, delta T and toggle loads on and off to show draw down and recharge time www.hydronicpros.com for a trial version

    I have two buffer tank sizing formulas one for fixed output boiler, one for modulating. But you already have the tank, seems you are beyond tank sizing step?

    The buffer is not a silver bullet, it just minimized undesirable conditions on micro zoned systems, give you some longer run cycles, etc.

    You can take to concept as far as you have $$. The tanks I've seen in Europe have ports every 12" down the side, stratification tanks.. Pull and return high temperature up top, medium temperatures mid tank, lowest at the bottom. It takes multiple sensors and a control that can be programed to maximize the tank use. Expensive and perhaps overkill for most.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    Hot rod, Laars support told me they use a fixed speed pump, apparently set to the primary delta T is about 25 degrees. (They have been known to get things wrong sometimes.)

    So here is hopefully the final layout:




    When there is a call from the radiant zones and the boiler is firing, the big pump that connects the radiant zones and buffer (marked by a "?") will be on. This will ideally pump at the same speed as the primary, possibly 8 gpm. (I will probably just throw one of my 007s in there with some kind of balancing valve.) This will dump the cold water from the bottom of buffer into the boiler, and be charged to the target temperature in about 2.5 minutes with the boiler at about 60% max firing rate. The boiler will then go over temperature and shut off, but the primary will continue to circulate.

    This will signal the bigger secondary pump ("?") to switch off and the little LHB08100104 to turn on. This pump will slowly suck some water off the top of the buffer and inject it into the primary loop, so that the boiler can monitor its temperature. (I've written 0.3 gpm, but the actual rate is to be decided. I don't actually know the internal volume of the boiler.) For the typical load (the kitchen only), the buffer will drain over 20-25 minutes. When cold water starts coming out the top of the buffer, the boiler will start firing in a few minutes later. The typical full cycle time will be about 25 minutes, though in the worst case it could be 10 minutes if someone managed to get a load of exactly 23,000 BTUs.

    If it works perfectly, the boiler will see the exact temperature drop that appears across the radiant loop, and the radiant loop will always see the same temperature at its inlet. Suppose the boiler has a target temp of 135, and the loop has a delta T of 15 degrees. When the boiler runs, the water it pulls off the secondary loop will be either from the radiant loop at 120 or from the buffer, which is water stored from outlet of the radiant loop at 120. If the flows match, it can send water to the loop at 135 and see 120 at the inlet. When the radiant loop pulls water form the buffer, it will see 135 until it quickly drops to 120 (probably only in theory) for a moment until the boiler kicks on.

    I also added a line so that the indirect can be run off the water heater. This involves only one pipe and an extra 3-way valve. In addition to providing a backup, it means I don't have to rush the the rest of the installation because we'll have basic hot water. I need to remove the water heater before I can think about installing the Innoflue venting, think about cumbustion analysis, etc.

    This is of course has an overly complicated solution to the no-so-important problem of perfectly buffering the radiant loops, but that's the whole point, isn't it?

  • jrkeat
    jrkeat Member Posts: 71
    Here's a wiring diagram for the pumps:


    This could be executed by connecting a bunch of RIBU1C relays to a junction box and wiring them together with wire nuts.

    Does this seem sensible, or would other people do it another way?

    Also, if have a "flame" line coming out of the Laars Mascot, but I'm not sure how to actually figure out when the boiler is firing--it seems like I could use the gas valve line. Or there's a "DC14" line going to the fan, but I'm not sure if that switches on and off. Is there a standard line that comes out of these boilers?
  • hot_rod
    hot_rod Member Posts: 22,018
    I think the best mode of operation for mod con efficiency is to always return the lowest possible temperature to the boiler.

    This 3 pipe piping does that does that. It is being used with heat pumps as that return is critical to keeping the COP as high as possible.

    As far as delta T, radiant floors want a tight ∆, 10 -15° typically. Your boiler can run as wide a 30∆ on most models. so I don't know you want to match boiler output and system requirement?

    When multiple flows merge you do get temperature blending, here is the formula for that.

    I think there is a cleaner way to wire that, let me see what I can suggest.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,018
    one more shot at trying to get you to simplify to one of these. I think you are wasting a lot of design energy with that small shuttle cir, it's not adding enough value for the cost and complexity :)

    if you have not purchased the buffer, get a 4 port tank Caleffi, Boiler Buddy or other.

    The 3 port gives you what I think you want for efficiency.

    Although if you in fact you need 180F to the cast rads, boiler efficiency is a mute point :)

    With this piping off the shelf relay boxes easily run the entire system.

    When you add an indirect like this, on priority all heating circs shut down and only the DHW runs with the boiler.

    The buffer does not get involved with a DHW call, winter or summer, all flow is direct from boiler to indirect, because only one circulator runs. The relays or the boiler board can provide the priority function. Personally for simplification I would run all the pumps from the relay boxes. The only connection to or from the boiler is the TT.

    Caleffi relays boxes have a lot of customization if you do get more complicated with piping, the zone valve ZVR and zone switching ZSR (for the pumps) connect and communicate with one another via a 2 wire connection between them.


    https://www.caleffi.com/sites/default/files/caleffi/uploads/files/wiringguide-zsr-zsr101-zvr.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    > The buffer does not get involved with a DHW call, winter or summer, all flow is direct from boiler to indirect, because only one circulator runs.

    In your new designs, how do I get the buffer loop to not run when the DHW loop is on? Isn't the primary pump always on when the boiler is firing? If I switch it off externally, will the DHW pump push the water through the circulator that's in the boiler?
  • hot_rod
    hot_rod Member Posts: 22,018
    jrkeat said:

    > The buffer does not get involved with a DHW call, winter or summer, all flow is direct from boiler to indirect, because only one circulator runs.

    In your new designs, how do I get the buffer loop to not run when the DHW loop is on? Isn't the primary pump always on when the boiler is firing? If I switch it off externally, will the DHW pump push the water through the circulator that's in the boiler?

    Nope, when DHW calls IF you wire it thru the relay box all other circulators have their power interrupted.

    Boiler fires, the DHW circulator runs, nothing else. The check in the other circulators prevent any un-wanted flow along with the hydraulic separator function on the piping.


    The indirect tank temperature control wires to zone 1 on the relay box. This is a priority zone. When it calls for DHW every other pump is powered off, only that DHW pump runs.

    On the upper left in the box is a terminal DHW, that is a dry contact connected to zone one only.

    Wire it to the DHW terminal in the boiler, so the boiler should go to high fire rate to recover the DHW load quickly, and the boiler pump should power off. I think? If not the boiler pump could wire thru the relay also.

    Additionally you can enable post purge on the dip switch, it will run the pump after the boiler burner goes off to purge all heat from the boiler, stuff it into the tank.

    Exercise function will run the pumps for a minute if they go 72 hours without a call, just to keep them from locking up over the summer, no boiler fire, just pump function.

    Pumps are fused in the box, transformer has a circuit breaker, self resetting should you mis-wire any 24V side.

    One the other relay box that powers the zone valves. Wire an aqua stat on the buffer tank to one of the zones, when the tank temperature drops, and only when it drops, the boiler and its pump will run to recover the tank temperature. No flow goes to the indirect as the check in the pump prevents that. I'd add a check on the indirect return pipe to assure 100% flow stop when in heating mode.

    Others may offer some thoughts there are numerous ways to wire this.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jrkeat
    jrkeat Member Posts: 71
    edited March 2020
    So the DHW pump is on and the internal circulator is off. Can you just push the water through the stopped internal circulator like that? I don't know much about these pumps, but I would have thought a stopped pump in the flow path would be a pretty big impediment to flow.
  • hot_rod
    hot_rod Member Posts: 22,018
    Yes one circulator can flow thru an off circulator. Even if it has a small check valve it would not be much flow restriction.

    If you know the coil spec and the boiler heat exchanger pressure drop you could again plot a system curve over the pump curve and determine actual flow rate in DHW mode

    All this is knowable if you search out the head or flow resistance of that circuit
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream