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Piping Reverse Indirect

ScottSecor
ScottSecor Member Posts: 395

I am finally upgrading my heating system. New boiler is 110,000 BTU input gas fired mod con, new reverse indirect is 34 gallon with very large domestic coil. There are four small high temperature zones (total 43,000 BTU) that I plan on using a variable speed circulator and four zone valves. There is one radiant zone (16,000 BTU) that will have a dedicated RMB to control the temperature of the radiant water. I plan on using the reverse indirect primarily for dhw needs, this includes two full baths and the dreaded whirlpool bath tub.

I am very much aware that I could easily heat the house with a much smaller boiler. I also realize that if I had the room for something like a 120 gallon indirect I would likely never run out of dhw with the small boiler (recovery time might be a little excessive...). Unfortunately, there is no basement (Levittown style cape, expanded a few times) and the system will be installed on the second floor, with a large drain pan under all of the equipment..

I've been following page 33 of the Caleffi Idonrics #17 guide, Figure 7-3 very closely (except my house will have a single boiler). The heating side of the reverse indirect tank comes with 1.25" steel nipples. My plan in to put a 1.25" black union on the threads (inlet and outlet) and immediately up-size the piping to 2" steel with two cast iron tees. The bull of the tees will feed the radiant and the high temperature zones. The run of the tees (1.25") will connect to the boiler and primary circulator. I'm hoping the reverse indirect will meet all of our dhw needs and act as a buffer tank, especially with only one or two zones operating. In my mind the two sets of closely spaced 2" tees will act as a hydraulic separator.

My first question is there are no check valves shown in this drawing, do I need any? On page 34 of Idronics #17 check valves are shown near the bottom of the reverse indirect, Figure 7-4. My second question is can I get away with just two circulator pumps (in addition to the Taco RMB)? One pump is for the primary loop and the second is for the secondary loop (high temp).

Please see attached sketch, note the software I use does not have reverse indirect tanks so I improvised with a odd looking buffer tank. My tank actually has the boiler inlet on the top of the tank and the return on the side of the tank a few inches above the bottom.

Thank you in advance,
Scott
Robert O'Brien

Comments

  • hot_rod
    hot_rod Member Posts: 15,064
    Get the tank connections to 2" as close as possible to the tank. 2X1-1/4 bell reducers, reducing ell or the reducing tee.

    Check at boiler pump, the internal one is fine.

    Webstone valves at the return connections for quick and easy purge.

    Air vent on top of the tank somehow. I'd still have a micro bubble device somewhere, in the boiler piping would work.

    A DiscalDirtmag would be great to handle all 3 functions.

    Should not need any additional checks, the Alpha with zone valves would not need a check either. No harm with the check at the boiler.

    The tank will need to be hot all the time to supply quick dhw
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HVACNUT
    HVACNUT Member Posts: 4,209
    edited April 2017
    You need to refer to the Purefire installation manual. Near boiler piping is extremely important and using a Turbo Max or standard indirect, piping off the boiler is the same. The DHW heating circuit tee's off before the closely spaced tee's and the space heating circuit(s).
    I don't see a need to increase the indirect piping to 2". The aquastat on the Turbo Max should be set at 180 or whatever you program your maximum limit for DHW on the Purefire, and install a thermostatic mixing valve on the domestic, set to 120.
    I don't know what you mean by using the indirect as a buffer tank and the piping diagram doesn't seem correct.
  • hot_rod
    hot_rod Member Posts: 15,064
    The two pipe buffer tank that Scott is considering is a unique way to pipe the tank and offers some nice benefits.

    The short large headers at the tank become the primary/ secondary, or more accurately a hydraulic separator.

    The installation manual only shows "old school" primary secondary piping, the two pipe buffer/reverse indirect is a great way to assure multiple functions, and assure the boiler gets adequate flow.

    Here is a good read on the various ways to pipe buffer tanks, pros and cons.

    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

    HTP use to build the Peerless Pinnacle I believe, looks like the same Gianomni heat exchanger is still used in this version.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ScottSecor
    ScottSecor Member Posts: 395
    Bob, thank you for the insight. Fortunately, I've been pondering this system for quite some time, as such it allowed me to look at every drawing (examples) I could find. This included this website, Idronics, Siggy's site and columns to name a few. I appreciate all of your help and especially your easy to understand sketches. I've installed a Caleffi dirt separator in the return near the boiler and a Caleffi air separator on the supply (both with twelve times the diameter to the inlet). Yes, the heat exchanger is very similar to the HTP boilers we've installed years ago.

    HVACNUT, I am familiar with the Pure-fire manual as we've been installing them almost exclusively for the last five years on commercial and residential jobs (except for steamers). We almost always install the residential Pure-fire boilers with a Peerless PP indirect tank as we've had a few problems with the PT model. As Bob pointed out this is not the typical indirect, but a reverse indirect (large coil for dhw, tank is filled with boiler water). My goal is to prevent short cycles when say the 8,000 BTU zone calls by itself. At the same time, I'm hoping the extra 30,000 BTU input will help when dhw is at peak demand.

    I got a great deal in the boiler (primary) circulator and decided to go with the Grundfos Magna1 32-60 instead of the recommended 26-99 needed to achieve the twenty degree delta T. As such there is no built in check valve, I think I'll add a spring check to the buffer tank piping.
  • HVACNUT
    HVACNUT Member Posts: 4,209
    Sorry @ScottSecor. Thought you were a HO. Guess I am old school. Do you know who designed that piping arrangement or where to find literature? I would like to see the finished install when you're done if you could post some pics.
  • ScottSecor
    ScottSecor Member Posts: 395
    HVACNUT, I did the design with TACO HSS software, been using it for many years. I would not say the software is easy to use, but like most things it gets easier as you get familiar with it. I've already made some minor changes to the drawing I posted, but the design will basically stay the same. I'll certainly share some photos in the future.
  • Steamhead
    Steamhead Member Posts: 14,863
    HVACNUT said:

    Sorry @ScottSecor. Thought you were a HO. Guess I am old school. Do you know who designed that piping arrangement or where to find literature? I would like to see the finished install when you're done if you could post some pics.

    Scott is actually the second Secor generation on the Wall. We remember his dad, Ken, who was quite active here before he retired.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    Robert O'Brien
  • hot_rod
    hot_rod Member Posts: 15,064
    HVACNUT said:

    Sorry @ScottSecor. Thought you were a HO. Guess I am old school. Do you know who designed that piping arrangement or where to find literature? I would like to see the finished install when you're done if you could post some pics.

    Here is a link to a journal showing thermal storage piping options.

    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

    The idea came to us after seeing how the Austrians buffer their wood and pellet boilers, while attending a trade show in Europe.

    The main difference with two pipe is flow from the boiler can go directly to the loads without going across the tank as in a 4 pipe buffer. With multiple loads, at various flow rates, that is a nice benefit
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Paul48
    Paul48 Member Posts: 4,470
    "The main difference with two pipe is flow from the boiler can go directly to the loads without going across the tank as in a 4 pipe buffer. With multiple loads, at various flow rates, that is a nice benefit"

    I don't understand it then.....How is acting as a buffer then, if it is not buffering the load?
  • ScottSecor
    ScottSecor Member Posts: 395
    In my first example the tanks acts like a buffer when boiler is producing 30,000 BTU and small 10,000 zone is calling for heat. In the perfect world, 1 gpm goes into buffer and 2 gpm goes to heating zone. Boiler runs a little longer and dhw is now ready for someone to turn on faucet.

    In an extreme case, boiler is producing 60,000 BTU as every zone just happened to open at the same time, practically no water is flowing to the tank. As the heating thermostats begin to become satisfied, the energy begins to flow to the tank and the buffer tank is again "fully energized."

    In my case the boiler is grossly oversized for the heating load. However, according to my math, the boiler is almost perfect for the dhw demand (worst case). Despite the fact that the boiler has a five to one turn-down ratio the input is still too high for just one or even two small zones. The buffer should help this rather common scenario in my house.
  • hot_rod
    hot_rod Member Posts: 15,064
    When the load gpm is less than the boiler flow, the flow then goes into the buffer. Really that is the one main goal of a buffer to absorb excessive boiler output on low load conditions.

    It also stores energy to lessen cycling, and in Scotts case, provides the DHW production. He chose a good model, it's tall and has a lot of HX square footage.

    Here is a graphic that is close to Scotts installation, and maybe flow rates? Assume he has a 10 gpm flow from his fixed speed boiler pump on that 110,000 boiler.

    If there is a load requirement of 8 gpm, for example, 2 gpm flows through the tank, 8 gpm from the boiler directly to the load. The 8 gpm flow never interacts with the tank, as it does in 4 pipe tanks.

    it doesn't sound like he will ever have a 10 gpm load requirement, so some flow is always going into the tank. In his case, with a reverse indirect, he needs horsepower to provide DHW when none is stored in the tank, per say. the DHW is in the multiple copper coils.

    It's primary secondary piping concept essentially. And the reason that those header pipes need to be large enough to allow the flows to get along, as they change as ZVs open and close, a hydraulic separator really.

    When all loads satisfy, full boiler flow, say 10 gpm will recover the tank to setpoint. the boiler will fire again when the buffer temperature drops, so some energy is always stored and the low water content boiler does not need to fire on every call.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Paul48
    Paul48 Member Posts: 4,470
    I understand, but what is the advantage of only buffering excess flow from the primary and therefore unused heat, as opposed to running your secondary sides off closely spaced tees, prior to the indirect and buffering all heat produced?
  • hot_rod
    hot_rod Member Posts: 15,064
    The secondary side IS taken off before the tank? But it can also access the tank when the boiler is off, not need to run a primary pump, as you would with closely spaced tees.

    The tank temperature needs to always be maintained at temperature to produce DHW, so how is that unused heat? Once it reaches setpoint the boiler inputs shuts down.

    The tank is full of energy to supply DHW and or heat loads, always.

    Also the boiler pump is fixed speed it always moves 10 gpm, that type of boiler cannot run, very well, on a variable speed boiler pump.

    Even if the boiler and pump could modulate to the lowest zone gpm, you still need or want to recover and maintain the tank for dhw.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Paul48
    Paul48 Member Posts: 4,470
    Sorry.....I guess the proper terminology is, excessive boiler output, as you put it. So as not to confuse that with "unused heat". :wink:
  • HVACNUT
    HVACNUT Member Posts: 4,209
    In a typical Turbo Max or reverse indirect application, the tank temp is set to approximately 180, bypassing ODR to provide max BTU's for recovery, and temperef to 120 via mixing for DHW. If space heating zones are stealing those BTU'S through the tank and the aquastat differential on the tank is say 10 degrees, your cycling the boiler again at max output? Or is the aquastat wired into the space heating terminals on the boiler, enabling ODR and therefore modulating output? If that's the case, your not going to achieve 180 on the indirect during the shoulder months, or in the summer due to ODR and WWSD. Do you not use ODR in this set up or is the control wiring atypical? Seems like your gaining efficiency in one aspect, but losing it in another.
    What is the sequence of operation for DHW and SH from a wiring and controls standpoint?
  • ScottSecor
    ScottSecor Member Posts: 395
    I'm hoping I can set the aquastat in the Turbomax lower than 180, and yes I have to use a mixing valve for DHW. I'm still unsure how I'm going to wire the aquastat on the tank, especially with ODR. The Taco RMB incorporates it's own outdoor sensor and since the radiant zone only needs about 100 degrees, this zone should work fine regardless of settings. The high temperature heating zones are currently running on ODR with the old boiler and it works well (old boiler to be removed as part of this project).

    My gut hunch is that the dhw will be fine throughout the heating season, even with ODR. However, during the shoulder seasons (now) and during the summer months I'm not sure what approach to take. In most residential systems we've installed with standard indirect tanks, they are piped as suggested above with two primary pumps, one for heat and one for the indirect. In my case there is only one pump so I have to turn on the pump and the boiler whenever there the tank temperature drops below set-point or there is a call for heat. I am using a Taco zone valve relay with priority and may try to incorporate that somehow for dhw.

    Ideally, the Turbomax aquastat would fire the boiler (and primary pump), modulate to high fire based on rate of rise (delta T across the boiler) and drop to low fire as the temperature reached setpoint (160?) while not paying attention to outside temperature. In reality, the boiler may not even have to fire at all for my quick showers (notice, I did not mention the rest of the families shower or bath duration times). I'm going to talk to the PB people about the control logic and see what they suggest. With three pump outputs (DHW, CH and General) the boiler, I suspect we can come up with something.

  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    edited April 2017
    I hate to be the nay-sayer, but I don't believe your proposed setup will work properly for one reason. The turbo-max has a pressure drop across it on the boiler side. This is due to the built-in injecters that are designed to swirl the boiler supply water across the surfaces of the DHW hx. In order for the 2-pipe buffer to work properly, you want a minimal pressure drop between the supply and return piping connections.
  • ScottSecor
    ScottSecor Member Posts: 395
    Harvey you bring up a good point, I'm hoping the friction loss / pressure drop is insignificant and this is not an issue. Waiting a response from the manufacturer.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,390
    > @HVACNUT said:
    > Sorry @ScottSecor. Thought you were a HO. Guess I am old school. Do you know who designed that piping arrangement or where to find literature? I would like to see the finished install when you're done if you could post some pics.

    I had the pleasure of meeting Scott last week at the Peerless factory, other than the fact he owns a home, he is far from a HO!
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • ScottSecor
    ScottSecor Member Posts: 395
    Bob, it was nice to be able to finally meet you, enjoyed your company and you sharing your "trade secrets."

    With regard to the operation of the system, I spoke with Peerless this afternoon. They suggested connecting the xx terminals on the zone valve relay to TT on the boiler. They said to connect the aquastat on the Turbomax to the dhw stat terminals. Finally the circulator pump (primary) gets tied into the general circulator terminals.

    Attempted to email Turbomax to no avail, I'll reach out to the rep tomorrow.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    http://www.thermo2000.com/pdf/en-US/manu/manual_turbomax.pdf

    You can find the pressure drop in table 4. It is fairly low. With proper pumping and the right check valves, your current diagram may work.

    .
  • HVACNUT
    HVACNUT Member Posts: 4,209
    > @Robert O'Brien said:

    > I had the pleasure of meeting Scott last week at the Peerless factory, other than the fact he owns a home, he is far from a HO!

    >>hence the apology.