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Zone Balancing, Boiler Protection, Buffer Piping/Control

D107D107 Posts: 1,581Member
edited November 17 in Gas Heating
Now entering our first heating season with our new gas-fired Peerless MI-03 installed last Spring, some observations:

2 CI rad zones, 1 baseboard. Heat Loss 38K, Boiler Net: 50K. DHW: Turbomax 45. Hydrostat 3200+. Piped in series. Longest zone 190ft (11-12ft head?) Total piping all zones, including boiler and near boiler return 1.25” piping about 400ft. which would be around 10 gallons plus the 6 CI rads. Say 20 gallons total volume? VT2218 Circ set for ∆T. Taco Sentry Zone Valves; Caleffi Circ Setters Cold start, hi limit 160º.

Concerned about low return temps.

1. Cycle Example: Daytime, outdoor temps high 30s. Call for heat from one CI rad zone. Any hot water in boiler left over from prior heating or DHW cycle is purged by circ. Boiler fires, circ pumps, boiler temps may go as high as 130+ then quickly go down to 115. Circ is then stopped by Hydrostat for 30-60 seconds on Circulator Hold until boiler temp reaches 125; circ starts, boiler temp again goes to 130s then within a minute falls to 115, etc. This can happen 6-7+ times in a 20-minute cycle. Not sure if the Hydrostat Circulator Hold is adequately protecting the boiler from the low temperatures. At the end of the 20 minute cycle boiler temp is usually mid-140s, sometimes higher.
2. In cycle the VT2218 is pumping anywhere from 3-12gpm. It usually settles on 3-6gpm. The circuit setter does not really have the power to throttle circ down completely to their settings. So if I test the flow of the setters when circ is pumping 9gpm, flow can show about 4-5gpm; if I test it when circ pumps around 3-4gpm, flow shows about 2.5-3. I understand that this throttling up and down is the nature of the ∆T circulator setting. Some Wallies had advised me that this circ would be fighting the circuit setters. Will it be helpful to slow down the flow to 2gpm so as to give the boiler more time to heat the cold return water? Perhaps I can try changing the mode to Fixed Speed? (One CI rad zone’s loss is 10K, the other 17K. We haven’t yet had the two CI zones call for heat at the same time but that would increase the cold return water issue.)
3. I thought perhaps we could switch out the VT2218 with the Turbomax DWH VR1816 ∆P circulator since that might be able to balance the flow on the fly with however many zones are calling.
Perhaps pros think the Hydrostat Circ Hold function is protection enough?

Comments

  • ZmanZman Posts: 5,262Member
    Do you have a drawing of how all this is piped? Getting the zones balanced should be the easy part. It is not clear to me how you are managing condensate protection.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • D107D107 Posts: 1,581Member
    edited November 11
    @Zman See photo--hope that helps.



    I think originally, since there isn't that much water volume, and a full heat loss was done, we didn't anticipate this much influx of return water to the point that it would interfere with proper cycling. This may be one of those cases where despite the proper sizing of the boiler on paper, we could have used a 100mbh or greater firing than our 70mbh firing.

    My thought was --naive as it may be--that if we could reduce supply flow to 2gpm, that would help keep the boiler temp above 130.
  • ZmanZman Posts: 5,262Member
    edited November 11
    Reducing the flow rate is only going to increase the delta t and return even colder water. Increasing the flow will tighten the delta t and increase the return temp.

    It is quite likely that your radiators are so large that the boiler will never be able to get itself above condensing temps. I hope this makes sense. If your total radiation has a rated output of 200,000 BTU with 180-degree water and you only have a 50,000 BTU boiler, the house will heat just fine but the water temps may only get to 120 degrees. The radiators will give up BTU's in accordance with the laws of thermal dynamics, not what you wish they would do.

    Yours would be a good application for a mod/con boiler or a primary-secondary arrangement and a smart mixing valve with outdoor reset and boiler protection.

    Back to the question of balancing, you should be able to turn the circ to a fixed speed with all the zones open and balance your zones, then go back to fiddling with the settings.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • D107D107 Posts: 1,581Member
    edited November 12
    @Zman Total Loss design day is 38K; total btu gain is 35K--I think we figured that with 160 degree water. I do understand what you're saying. Rads aren't gigantic. I hear you on the primary secondary, ODR, mixing valve, etc. Original idea was to keep it simple. Obvously you don't think the hydrostat 'circulator hold' is enough protection by itself. Appreciate your input; getting a little concerned about this.
  • ZmanZman Posts: 5,262Member
    I don't think cutting in a mixer would be too ugly. You could do it this way and just run the reverse indirect circ whenever heat calls that way you maintain boiler flow and use the tank as a buffer.
    You would fix the condensation problem and get outdoor reset as a bonus.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • D107D107 Posts: 1,581Member
    edited November 11
    @Zman Thanks for putting the graphic together. The original idea was to do a buffer but idea was changed. Wouldn't there have to be additional piping changes for a buffer --like those 'short large-sized headers" to get the hydraulic separation? Right now there's 1.25" in and out of the Turbomax but I think the actual connections are 1.5"

    ...and you mean using the reverse indirect circ as sort of defacto primary secondary? Would this avoid having the two circs in series?
  • ZmanZman Posts: 5,262Member
    The turbomax is a reverse indirect. It will also make a great buffer tank. My sketch is a little unconventional but should work nicely with minimal repipe.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • gaabbeegaabbee Posts: 25Member
    @D107 Do what Zman suggested. I have a turbomax set up as a buffer and it seems to be working out great. What Zone valve controller do you have? Does it have a priority zone?

    The way mine is set up is when a zone calls for heat both the primary and secondary pumps turn on. Primary pump pushes water through the boiler and turbomax which in your case would be the vr1816. Once the purge is done at around 140* the turbomax aquastat calls for heat. Mine is set at high of 170 with 30* delta. Set the boiler high limit to 180* low is 0.

    Make the turbomax aquastat the priority zone. When you hit your low limit this will keep the vr1816 pumping and shut off the vt2218 and let the turbomax recover. Once the turbomax is satisfied the vt2218 will turn back on and heat the other zones until it all repeats. Hope this makes sense.
  • JohnNYJohnNY Posts: 2,364Member
    D107 said:

    Would this avoid having the two circs in series?

    You've got pumps in series? That's got to be corrected. I can't tell from your picture.

    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • D107D107 Posts: 1,581Member
    edited November 12
    @JohnNY No, as far as I know circs are not in series. I asked that because I was wondering if Zman's suggested solution--knowing he couldn't see the full setup with just that one photo--would put them in series. Apparently not. More photos below.
    @gaabbee Zones are controlled by t-stats through TACO ZVC 403 and Turbomax via SR501. Not sure about "a priority zone," except that we have DHW priority. It seems like Zman's idea will remove the need for a thermic valve.

    Back when heat loss was being done and modcon considered we figured that to heat the house 140 would be the design day supply temp, averaging out at 130. We keep the turbomax aquastat cutout nominally at 150, cut in at 135. Gauge probe is high in the tank whereas aquastat probe is lower, towards the middle, so temp down there could be 5-10 degrees lower.

    Originally we had thought of piping for buffer, and were told there had to be two short oversized headers entering and leaving the turbomax as per attached diagram in order to get the hydraulic separation. Not sure why this wouldn't have to be done for the suggested change.

    (I had thought, again probably naively, that getting a t-stat with more frequent cycles would keep the return water warmer.)











  • hot_rodhot_rod Posts: 11,872Member
    The heat emitters are always in charge of the boiler temperature. With some cast rads you have a bit of mass in the system. You do need a boiler return protection function in a system like yours.

    I'm not sure ∆T circulation is ideal for that system either, here is the reasoning behind constrain ∆T operation.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • D107D107 Posts: 1,581Member
    edited November 12
    @Hotrod Well with CI rads, don't think we're low thermal mass. We can easily switch VT2218 settings to Fixed Speed. Do you also feel Zman's suggestion would work with the piping as is? Even without the 'short, large-sized headers' for hydraulic separation? I'll have to figure out something soon--don't want this thing to be condensing away too long. That hydrostat 'circulator hold' was probably only meant for temporary use to get the boiler through the initial ten minute cycle startup, not for repeated use during the cycle. But I will ask Hydrolevel.
  • JohnNYJohnNY Posts: 2,364Member
    That piping, no matter how hard I try to follow it, is not a very good configuration.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • D107D107 Posts: 1,581Member
    edited November 13
    @JohnNY Thanks; my amateur eye can't really detect a problem except the lack of condensation protection piping/valves. I'm sending another photo with a wider view that allows you to see the return and supply together top to bottom. The question is what can be creatively salvaged, re-worked, etc. to either follow Zman's idea or beyond that.



  • D107D107 Posts: 1,581Member
    edited November 12
    Having spoken to installer, I think before anything else I'm going to put the circuit setters wide open and see if that raises return temps any. As Zman had said, throttling the speed was probably increasing the ∆T. Perhaps that was delaying the warming of the return water. We can probably go up to 4gpm on each zone without a problem. At some point might also switch from ∆T to Fixed Speed mode.
  • ZmanZman Posts: 5,262Member
    To me, the beauty of the reverse indirect is the buffer component. Since you need condensate protection and will love what outdoor reset does for you, this is a win. What I am suggesting is very similar to this, just piped differently. http://www.ergomax.com/New-Tanks.htm
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Rich_49Rich_49 Posts: 2,536Member
    JohnNY said:

    D107 said:

    Would this avoid having the two circs in series?

    You've got pumps in series? That's got to be corrected. I can't tell from your picture.

    I disagree JohnNY . This system appears to be set up as a 2 pipe buffer system . The VR1816 is the boiler circ and the VT2218 is the system circ . I could be mistaken but don't think so
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • D107D107 Posts: 1,581Member
    edited November 12
    @Rich_49 Originally the intent was to set up as buffer but there were some issues so it was decided to just set up as reverse indirect. VR1816 is the Turbomax circ and VT2218 is pumping the heating zones. Zone valves are on the return. I should have more to report in a few days and of course will be looking closely at Zman's diagrams. Hard to gauge the level of protection afforded by Hydrostat's 'Circulator Hold' feature. At this point I don't think we can do any major re-piping but perhaps as has been suggested, that won't be necessary.
  • gaabbeegaabbee Posts: 25Member
    So I have been thinking a lot about your system but mainly because you have a lot of the same brand components as I do. If you are trying to avoid a re-pipe here is what I would do as long as the vr1816 and vt2218 are hydraulically separated. Not sure if I missed that part.

    Get rid of the zvc 403 and sr 501. Get a zvc 404 with priority. I would wire the 3 zone valves in slots 1,2, and 3, and then wire the turbomax aquastat on zone 4 as priority and use the jumper slots 3 and 4. The hydrosat will get connected to the "TT" end switch. Wire the vr1816 as the primary pump and the vt2218 as the secondary pump. This will allow the turbomax and boiler to never drop below the set low limit.

    In theory this should allow your boiler to perform like this. Turbomax set at a high of 160* low of 130*. Hydrostat high of 170* low at 0*. Pre-purge and circulator hold settings activated.

    If a DHW load lowers the turbomax temp to 130* the boiler will fire. Once the boiler water passes 126* the vr1816 will turn on until the turbomax reaches 160* then shut everything off.

    If a zone thermostat calls for heat the above will all happen the same except that now the vr1816 and vt2218 will both turn on. If the turbomax temps are between 130* and 160* already the pumps will purge down the water temps to 130* which then fires the boiler. Once temps hit 160* again the fire will turn off and the pumps will continue to purge down until the zone is satisfied or reaches 130* again.

    When a zone is calling for heat and a DHW call from the turbomax the priority setting will shut the vt2218 off and let the vr1816 continue to satisfy the turbomax. Then resume the zone heating.

    When it is all set up correctly it really is a thing of beautiful harmony. Just make sure those pumps are hydraulically separated.
  • D107D107 Posts: 1,581Member
    edited November 13
    @gaabbee Thanks so much for all your thinking on this. I was just thinking today that I hoped that some control wizardry could substitute for moving pipes around. I have some responses below:
    gaabbee said:

    So I have been thinking a lot about your system but mainly because you have a lot of the same brand components as I do. If you are trying to avoid a re-pipe here is what I would do as long as the vr1816 and vt2218 are hydraulically separated. Not sure if I missed that part.

    Would the two Bell & Gossett Hydrotrol Flow Control Valves A07177C on the turbomax and boiler returns respectively maintain that separation? While I think(?) ideally the two circs should be pumping in totally opposite directions from each other off of a supply tee, in this case they are at a 90º angle to each other (pumping away) which I'm hoping is OK. But this is not set up primary secondary, no closely spaced tees. The photos show this.

    Get rid of the zvc 403 and sr 501. Get a zvc 404 with priority. I would wire the 3 zone valves in slots 1,2, and 3, and then wire the turbomax aquastat on zone 4 as priority and use the jumper slots 3 and 4. The hydrostat will get connected to the "TT" end switch. Wire the vr1816 as the primary pump and the vt2218 as the secondary pump. This will allow the turbomax and boiler to never drop below the set low limit.

    I recall the installer conferring with the Hydrostat people and they were insistent that the Turbomax have its own control, that it couldn't be added onto anything with the zone valves or t-stats. However they probably weren't thinking of your scheme.

    In theory this should allow your boiler to perform like this: Turbomax set at a high of 160* low of 130*. Hydrostat high of 170* low at 0*. Pre-purge and circulator hold settings activated.

    I'm not sure if I'd want to set the Turbomax as low as 130--due to Legionnaire's issues. Maybe 140. Right now the swing is 150-135. And I guess in summer adjustments could be made to your setup.

    If a DHW load lowers the turbomax temp to 130* the boiler will fire. Once the boiler water passes 126* the vr1816 will turn on until the turbomax reaches 160* then shut everything off.

    If a zone thermostat calls for heat the above will all happen the same except that now the vr1816 and vt2218 will both turn on. If the turbomax temps are between 130* and 160* already the pumps will purge down the water temps to 130* which then fires the boiler. Once temps hit 160* again the fire will turn off and the pumps will continue to purge down until the zone is satisfied or reaches 130* again.

    When a zone is calling for heat and a DHW call from the turbomax the priority setting will shut the vt2218 off and let the vr1816 continue to satisfy the turbomax. Then resume the zone heating.

    When it is all set up correctly it really is a thing of beautiful harmony. Just make sure those pumps are hydraulically separated.

    I agree, hydraulics is a fascinating, endless subject. In addition to this I'll be getting a Honeywell T6 t-stat that has many cycle length variations. My current main floor T-stat overshoots by a degree or two and then even on a cold day like today, takes hours and hours to call for heat again, meaning very cold return water, a feeling of a 'cold 70,' and then a long recovery from the defacto setback as it makes up almost two whole degrees. I also completely opened up the circuit setters which sped up the process a bit and cut down on noise. And when I insulate boiler room heating and DHW piping that should also help. But in the end I agree it seems some kind of protection will have to be added based on what I'm hearing here from pros.

  • D107D107 Posts: 1,581Member
    @Zman Thanks again for pointing me towards possible solutions. I understand that for heating purposes, the slower the flow the wider the ∆T, the less heat, etc. and you say even colder water would return. It's that colder water part that's confusing to me. A circ hold is the ultimate flow reduction, yet that is meant to protect the boiler, even though of course it prolongs the cycle.

    On a typical cycle I have 62º return water hitting a 5 gallon boiler with up to 8gpm sometimes, such that the circ hold is going on off bouncing between 125 and 115 for 15-20, then boiler reaches higher temps towards end of 20-25 min cycle.

    The house is heating fine, but I am concerned about thermal shock. What kinds of temp swings could cause that?
  • gaabbeegaabbee Posts: 25Member
    At a slower pump speed the water has more time to release its energy in the radiators. You only have 5 gallons of hot water in the boiler and maybe 15 gallons of a lot cooler water at a cycle start, so by the time its getting back to the boiler it has given off all its energy. At a faster pump speed it will retain more of that energy rather then emitting it.

    Now if you do what zman and I said by using the turbomax as a buffer you now have the 45 gallons plus the 5 gallons of hot boiler water to push through the system. You will have more then enough hot water in storage to keep the return temps up.

  • D107D107 Posts: 1,581Member
    @gaabbee Thanks again. Attached are two drawings from Caleffi, one the correct way and the other incorrect. This seems to be what you were talking about. But note there would have to be two closely spaced 'fat headers' for hydraulic separation for this one. I didn't know if you thought there was already separation from my last post with the flow valves, etc.

    It will probably take a few weeks to put all this together if it's decided to go this way. Do you perceive any thermal shock risk in the meantime?

    In the interim I'm intending to raise the room temp from 65 to 68 and try to increase the cycle rate so that a new cycle starts before the rads cool down back to 62º.





  • gaabbeegaabbee Posts: 25Member
    edited November 14
    @D107 Yes I'm sorry I was thinking there was separation. Not sure about the thermal shock part. I know it's just not ideal right now. A higher load could help. I looked at my turbomax manual again and it seems you are pipe exactly like it shows for zone valves but I feel like your controls are not correct. I think they wanted both pumps to be on when ever a zone calls.

    Just to make sure I see this right. Your vt2218 only turns on when a zone calls. Your vr1816 only turns on when the turbomax calls? Anyway to easily make both pumps turn on when a zone calls?
  • D107D107 Posts: 1,581Member
    Correct on the circs. How to wire what you suggest is beyond my amateur pay scale. But it must be possible. I’m going to pm you.
  • SuperJSuperJ Posts: 514Member
    edited November 15
    D107 said:

    @gaabbee Thanks again. Attached are two drawings from Caleffi, one the correct way and the other incorrect. This seems to be what you were talking about. But note there would have to be two closely spaced 'fat headers' for hydraulic separation for this one. I didn't know if you thought there was already separation from my last post with the flow valves, etc.

    It will probably take a few weeks to put all this together if it's decided to go this way. Do you perceive any thermal shock risk in the meantime?

    In the interim I'm intending to raise the room temp from 65 to 68 and try to increase the cycle rate so that a new cycle starts before the rads cool down back to 62º.





    You're on the right track. Here's what I would do, it would require a bit of minor repiping...
    -Swap your pumps, use the delta P pump against the valves, it will play nice with the circuit setters.
    -Then set your flow controls aggressively to avoid diluting the tank too fast.
    -Use the delta T pump, but in constant speed mode as the primary pump (set the flow at a fixed speed to maintain an approx 20degF delta). The delta T pump has a boiler protect mode but I'm not sure if it would actually be useful in your application without adding a third pump. You could do something like the diagram you posted, and then get another pump. Perhaps get a another simple 3 speed to use as your primary pump, use the VT as your low temp protection (like the diagram), and use the VR as your secondary pump on the other side of the tank. The tank would give a call for heat which would start both the primary pump and the tank charge pump. The secondary pump would run off you zone control panel whenever any of your zones called, and would run in a pressure control mode.
    -Set up the boiler piping to maintain the turbomax as the buffer tank. (only the turbomax control would start the boiler and primary pump). The boiler will be oblivious to the zones.
    -Use the boiler control to stop the secondary pump if the boiler return gets too cold but keep the primary pump running. (or better yet cut a thermostatic mixing valve into the primary loop to keep RWTs up).
    -If using the turbomax as a buffer you need to make sure there is a control to stop your secondary heating pump if the tank gets too cold it would be preferably to allow simultaneous house and tank heating unless the tank get too cold (like less than 125F). This will ensure longer boiler run cycles.
    -A Cadillac option would be to use a 3 way mixing valve with outdoor reset and boiler protection on your house heating supply. Lower water temperatures will ensure longer run cycles, more even temperatures throughout the house, and will keep the tank hot longer between boiler run cycles, and reduce heat lost to piping in undesirable places. And ensure that the tank stays hot for DHW (if you place the sensor properly).
  • D107D107 Posts: 1,581Member
    edited November 16
    I think the pros here have pointed out just about the only way(s) this will work out. It's a bit of a rude awakening, given the detailed heat loss, etc. and a boiler net that was 25% above that. We should have less than 20 gallons of water in the boiler and piping, so hard to imagine the return water being such an issue. The 10 CI rads are not gigantic, 400 EDR total.

    Wondering if somehow this boiler is undersized. the average CI cycle supply temp rarely gets above 135. The largest Peerless I could go to would be the MI-04, which, at 75mbh net, has a 50% higher net than the MI-03 but still allows a 5 inch vent to line up with my chimney liner. But even that might need a buffer. I'm hoping that our Mi-03 won't be too small even with the buffer and won't need to deplete too much heated water from the Turbomax on every heating cycle.

    Originally the Turbomax was supposed to be set up as a buffer, and the larger 45 size was chosen since figures showed the ideal buffer size for us was 50 gallons. Against a 50mbh net boiler perhaps not the greatest choice. Wondering if in the meantime I should turn water auto feed off to prevent flood in case of thermal shock boiler cracks.
  • SuperJSuperJ Posts: 514Member
    D107 said:


    But somehow this boiler is undersized and the average CI cycle supply temp rarely gets above 135. The largest Peerless I could go to would be the MI-04, which, at 75mbh net, has a 50% higher net than the MI-03 but still allows a 5 inch vent to line up with my chimney liner. But even that might need a buffer. I'm hoping that our Mi-03 won't be too small even with the buffer and won't need to deplete too much heated water from the Turbomax on every heating cycle.

    Your boiler isn't too small if it's keeping you house small. You are just experienced thermal equilibrium where your emitters are able to output the full capacity of the boiler at 135F.

    Oversizing a boiler is not a valid boiler protection strategy

    There are about a half dozen ways to protect your boiler and some them will only cost you a couple hundred dollars max DIY.

    Look at some of @hot_rod s posts with some Caleffi diagrams, and pick one. Using the Turbomax as a buffer and installing a thermostatic valve on the boiler return to mix the hot supply into the return until it reaches a safe temperature is probably the most straight forward.

    Your boiler is only undersized if it's running constantly and your house is cold. Low return temperatures are not an indication of an undersized boiler, in fact they are a good thing that shows you have oversized emitters which gives you more future flexibility on heat sources.

  • D107D107 Posts: 1,581Member
    @SuperJ Thanks for the explanation. Not something I can DIY myself but sounds like with a good drawing--I guess hotrod's are detailed enough--the installer can take care of this.
  • D107D107 Posts: 1,581Member
    edited November 18
    @SuperJ Things are in motion and we should have a plan soon. Like your suggestion that the Turbomax can be used as a buffer for two different purposes: for low return protection AND to be 'sipped' by the boiler to lessen the frequency of heating cycles.

    You mentioned 'placing the DHW sensor properly.' As far as I know the Turbomax has a single dedicated well--in the middle of the tank--for the aquastat. So not sure how that can be adjusted.

    Here are additional details I received on how the controls could work.

    If you look at the wiring diagram (pdf attached) for the zvc404 the 4th zone would be the turbo max and have it’s aqua stat wired as the 4th zone thermostat and then jumper slots 3 and 4 for the circulator instead of a zone valve. There is a note about doing that.

    Your vr1816 would be wired directly to the zvc as the system pump. The vt2218 would be the secondary pump--or vice versa. There would not be any dhw pump. (Diagram in lower left corner) There’s a note again saying system pump turns on when any zone calls for heat. (Pumps hot water through the turbo max) The secondary pump turns on when any zone except priority calls. (Pulls hot water from the primary loop) This allows both pumps to run when a zone calls but turns off the vt2218 if the turbomax needs to catch up.

    The turbomax piping diagram from what I see doesn’t say anything about separation of the pumps."





  • D107D107 Posts: 1,581Member
    edited November 20
    In addition to what @hot_rod posted, I found two great articles and some drawings by John Siegenthaler re: buffer tanks.

    https://www.pmmag.com/articles/100544-the-finer-points-of-applying-a-2-pipe-buffer-tank

    Siegenthaler's comments below on flow rate into the buffer tank are interesting, though in our configuration, the Turbomax manual states we require 5gpm flow from boiler.
    The advantage of 2-pipe tanks

    A 2-pipe buffer tank places the piping leading to and from the heating load between the heat source and the buffer tank. If the load is operating at the same time as the heat source, which is common, the flow rate passing into the buffer tank is the difference between the heat source flow rate, and the load flow rate. For example, if the flow rate from the heat source is 10 gpm and the load flow rate is 7 gpm, the flow rate entering the upper sidewall connection of the tank is 10 – 7 = 3 gpm. The reduced entering flow velocity, in comparison with what the entering flow rate would be in a 4-pipe tank (e.g., 10 gpm), reduces mixing within the tank. Less mixing means better temperature stratification.

    The 2-pipe configuration also allows heated water from the heat source to flow directly to the load without having to interact with the thermal mass of the tank. This can speed heat delivery to the load during critical times such as recovering from a temperature setback, or following a “cold start” of the system.


    https://www.pmmag.com/articles/96765-alternate-methods-to-pipe-a-buffer-tank

    All that said, I think I like @SuperJ 's idea for simplicity:
    "Using the Turbomax as a buffer and installing a thermostatic valve on the boiler return to mix the hot supply into the return until it reaches a safe temperature is probably the most straight forward. " I assume we would still need the two short fat headers/tees, a sensor on the return to signal return water temperature. Or @Zman 's I-Series mixing valve.

    I realized that Hot Rod's drawing --with the "thermal clutch"--is shown as a four-way buffer; my Turbomax would have be pumped as two-way, but I'm sure the piping pros could configure that. Below is a schematic from the article and others from older posts on the Wall.

    This one below looks like my configuration--turbomax temp sensor is in center of tank. Also this shows turbomax circulator BEFORE the tee that leads to heating circulator; our heating circ is AFTER that tee.














  • SuperJSuperJ Posts: 514Member
    This first hand-sketch with the mixing valve on the return is what I would suggest. You've correctly moved the primary circulator instead the protection recirc loop.

    You want the connection points for your radiator supply and return to be close to the tank.

    The trick will be to control it in such a way that you can get DHW priority if the turbomax gets too cold, but still run space heating concurrently with the boiler when your temperatures are high enough.

    I would suggest running the turbomax aquastat to the hydrostat indirect heater terminals, and the ZVC to the space heating terminals. And running your secondary circulator off the hydrostat with DHW priority enabled.
    Setup the primary to run whenever the boiler is commanded on, you might be able to use the SR to do this.


    What @gaabbee suggested is what you're going for
  • hot_rodhot_rod Posts: 11,872Member
    For a two pipe to work properly all the connections need to be close to the tank on a pipe sized to handle all the combined flow rates. So lets say the boiler needs 10 gpm, and the distribution needs 8, the pipe into the tank needs to be sized to flow 18 gpm. I always suggest a 2" minimum. that short section becomes the hydraulic separation function, not unlike the closely spaced tees.

    TurboMax has a special software that can show you DWH performance at various tank temperatures and flow rates, You may be able to maintain the tank at 140 or lower and still get adequate DHW. Most to their reps have access to that software that Pierre developed specific to their tanks.

    Obviously the tanks with more coil area can better leverage low operating temperatures.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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