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Critique this diagram please.

There is actually 11 pumps on the secondary not zone valves and in effect yes, they are somewhat redundant. My units require 12.5 gpm each so the primarys ensure that they receive this because the secondaries will not, given the fact that only 2 or 3 run at any time.


  • All valves are in place although not shown. Fill is at expansion tank. Primary pumps have check valves downstream, all secondaries have IFC. Primaries pump 12 gpm each for a system total of 24 gpm. I'm finding the secondaries are causing the offline circuit to circulate slightly. I view this as desirable. My intent here was to eliminate the secondary loop pump. I'm looking at putting another of these systems in and I'm looking to either improve on what I have or change it entirely. Keep in mind I really LIKE eliminating that extra pump.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    I'm rather confused. Is there one boiler that would be off to the left side of the sketch. Perhaps two boilers?

    Presume I'm seeing three zone valves, correct? What's the "X" inside the circle at the right side?

    Doesn't appear to be like any "primary-secondary" layout I've ever seen. The essence of primary-secondary piping and pumping is that it allows the secondary circulator(s) to operate independently of the primary--e.g. the primary circulator won't move water through the secondary circuit(s) and the secondary circulator(s) won't move water through the primary circuit.

    I presume this is a rather large system as 24 gpm can move LOTS of heat...
  • ALH_4
    ALH_4 Member Posts: 1,790

    Why are you using parallel primary pumps instead of one larger pump? What temperature drop are you using to calculate 24GPM flow rate? What heat wource is this connected to? Is it a high temperature or low temperature system?
  • Jed_2
    Jed_2 Member Posts: 781
    Where's the

    Primary/Secondary? Looks like redundant circs. Do they both come on with "call"? Why parallel? "X" would indicate a S/O valve, hence, series; but definately not P/S.

    Incomplete sketch! What's with the split return?

  • JohnNY
    JohnNY Member Posts: 3,226
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.

  • We are pumping through two separate water heaters that are staged together, each requiring 12.5 gpm. I didn't want one big pump because I didn't want full flow through both units when one was off cycle. Plus, knowing it will only run both units on extreme days I figured it was cheaper electrically splitting the load between two pumps. It is a low temp system. Right now I'm running 110* but they can go up to 140* water out. The "X" off to the right is a ball valve that remains full open. The manifold is 2" copper and the connector with the ball valve is 1 1/2".
  • steven E.HEAT
    steven E.HEAT Member Posts: 47

    What is it that your trying to accomplish ???

  • I'm trying to eliminate the need for a 24 gpm secondary loop pump to avoid the extra electricity it would take to run one. I'm trying to make the system as energy efficient as possible. it's up and running and, with minor exceptions that can be easily corrected, it works just fine. Believe it or not, the diagram was submitted to and approved by the equipment manufacturer. The main circs run on call from the heaters and at least one will run almost continuously while the secondaries operate on call from the zone stats.
  • Uni R_3
    Uni R_3 Member Posts: 299

    Why not just buy a real boiler? Modulating condensing boilers are not that expensive, they are cheap to vent and they include great controls. With a Prestige your application would use less 100 watts of electricity, not including the 11 branch circs and associated zone controllers. That 100 watts includes its built in circulator, that's a 4X savings there! Better efficiencies as well on the gas consumption side. Would it use 10% less NG? I dunno... something tells me that although its likely more what's far more important is which solution is far less likely to break down or clog up within a few years? Do the people in the households truly understand and know that the reliability of their heating system is being jeopardized? They truly are an experiment. Just twinning the tankless practically doubles the risk of at least one of them failing and the service being urgent.

    You don't need to waste energy with those huge pumps and the much lower efficiency in NG... that's like two really green sins most likely due to the false notion that short term green is more important.
  • ALH_4
    ALH_4 Member Posts: 1,790

    Any way you can re-evaluate the temperature drop and cut your flow rate in half?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Scrambled Eggs

    What is this arrangement supposed to be heating at such a low temp ? Would be correct to assume each heater connects to the lines at left?

  • It's heating about 12,000 sq ft of house as long as you're counting the basement and garage in there.

  • I've been trying to avoid retyping this all again but these are not tankless, they are these new fangled air source to water amonnia based heat pumps. I posted extensively on them under the "Can we talk brand names here." thread. They require 12.5 gpm per mfgs specs. Yes, they are quite aware of the experimental nature of the system. So am I. Our contingency plan is if it don't work we'll fix it. It's been running since October with only minor tweaking needed so far. I'm just bouncing this off you guys to see what you all have to say and see if there's a better way to do it. The primary pumps must deliver 12.5 gpm to the units.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Figure out what it is

    I am a true believer in a clear piping diagram to figure things out. Take a look at this. Did I reproduce what you are doing ??
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    Great response
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Piping - This look ok ??

    I believe this gerneralized arrangement of components should solve your concerns.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Piping w Primary Secondary

    Without knowing much about what your system is doing, this might be a better choice
  • Uni R_3
    Uni R_3 Member Posts: 299
    My bad

  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Alternate Piping w same supply temps

    This may serve your needs better. Perhaps if you tell us more about the loads, we can give you better advice.

    PS I'm waiting for the wife to come home for dinner so I have a few more minutes of time on my hands.
  • Hey Glenn,

    those are great drawings,,is that some kind of software program?

  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    Thanks for the comment Dave. I have almost 15 years with Microsoft Publisher so I've become proficient at it. Cheaper and easier to use than most CAD programs or Visio.

    More interested if you thought I drew what he was doing and my proposed drawings made sense.
  • Ohhhhh,

    so you were just "showing-off", killing time huh?(Sure wish I could draw like that!)LOL.


  • That's a better depiction, thanks! Just to reiterate, they are not conventional heaters.
  • Brad White_9
    Brad White_9 Member Posts: 2,440

    With that arrangement on the secondary side, you're going to get ghost flow due to the closely spaced tees not being "closely spaced". In other words, the circulation in the main loop will cause enough pressure drop between the supply and return of the secondary loops to give you flow you don't want.

    The secondary tees have to be no more than 4 pipe diameters apart. (That's main loop diameters) At 25 GPM you're pushing the limits of 1 1/2" copper.

  • All very nice and I truly appreciate your efforts but you've added the pump I'm trying to eliminate. I am familiar with true primary secondary but in this case I'm tryig to use the primary pumps or more correctly the heat pump pumps to push the water around the loop as well as through the equipment. I'm half considering using zone valves and a modulating pressure or flow control valve in the connector on the next one but I'm afraid I'll come to a situation where more valves will open than one pump can handle and then I'll be starving zones. The second pump will only come on with a drop in loop temp to a predetermined setpoint.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    ghost flow

    I assume your referring to drawing #4. Ok - so is there a way to provide the same supply temps without causing the ghost flow? Check valves wouldn't help prevent this?

  • I'm experiencing no ghost flow through the secondaries, unless, of course, I close down the ball valve in the 1 1/2" connector. I DO however get ghost flow in the offline heat pump circuit that is caused by the secondaries. I don't mind this however because it keeps the offline unit and circuit at operating temp and avoids a big shot of (in this case) cold water that the system must absorb each time the second stage unit kicks in. I purposely put 1 1/2" for the connector to create a little restriction there and make the water (glycol) a little more interested in flowing through my secondaries. The only real problem I'm having now is excessive pressure at the 30# relief valve is causing it to weep. The answer to that is replacing it with a 45# valve, per Robur.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    In situation like that

    Where you may wind up with widely differing flow requirements between the equipment and the zones, the safest bet is primary secondary. I wouldn't get all that upset with the second primary circ because you don't need a very large one to get the job done. Depending on the length and the diameter of your primary loop, a 15-58 will likely do the job. The head presented by your equipment will also enter into that calculation so check that out.

    What size is your main loop?

    What do your zone loops consist of? ( # of ft and diameter of pipe/tube)

    What flow rate is required in each of the zones?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Last Attempt - Sad Face

    This piping should insure equal flow through both heat pumps if they're on. If you think you are going to starve the zones for heat, that seems to indicate there should be some means to detect this and turn on the second unit. What type of control arrangement are you using ?? How do the zones signal the heat pumps to come on . What decides which unit fires. You said these units are staged together. Are you using a sequencing control of some kind ? I.E. Tekmar 262 ?
  • Joe_75
    Joe_75 Member Posts: 57

    Yes have bull side of the closely spaced tees same size as primary piping. Supply goes right teeing off to radiation. Return goes left and returns tees into it.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    What about inserting a check between the drop to the boilers as shown here? I re-read your earlier post and you stated you didn't want one big pump because you didn't want full flow through both units when one was off cycle. Wouldn't this accomplish that?

    Enough --- had dinner getting in trouble with the wife. Will check back in morning to see what everyone thinks.
  • Weezbo
    Weezbo Member Posts: 6,232
    i think a low loss header would work..

    and you would be happier with the performance.

    either make a Chubby header with secondary supply and return tied into the chubby header with closely spaced T's
    and pump away from the low loss header or Buy a manufactured low loss header like a Caleffi...

    take a look at Hot Rods Non - Ferrous Low loss headder *~/:)

    that would be the ticket. :)

    The question that just came to mind is ....do these heat sources have any issues with too large of return temps vs. supply side? or is it strickly a flow thing?

    What are the current return temps to the equipment? outside air temp, supply side? the unit you have has 12.2 flow rate min up to 48?

  • Tell the wife I'm sorry. If it's any consolation I think I got in trouble with mine too. ;)

  • Return and supply temps are not an issue with these. You can't exceed 158* return. Current return temp is ~ 100*F. Setpoint is 110* with a 10 * differential. First unit fires @ 105*ouput, I BELIEVE the second will fire when the common control senses stage 1 is not keeping up. I'd have to double check on that.

  • Main loops to the units are 1" HePEX x 140' round trip, plus 15 for the unit plus about 10 ft of 1" copper each. We used 1" instead of 1 1/4 because we had some tight corners to get around. We, meaning myself and my Wirsbo distributor/designer, looked at the velocity charts and it was all within acceptable velocities so we went with it. Yes we ARE pushing it. I did learn a valuable lesson in bigger pipes means smaller pumps however.

    There are too many zones to list accurately. Again, my Wisrbo distributor and I sized everything according to the book. Yes, if all zones are running they will want more than 25 GPM. This never happens. Its actually sized for 50% chilled glycol for A/C. Getting heat around is not a problem. There are 5 zones of floors and 6 zones of hydro heat/cool. I'm ran the floors and 4 out of 6 zones of hydro heat on low fan speed all winter here (CT)and the house has been very comfortable.
  • FRANK_24
    FRANK_24 Member Posts: 80
    Your drawing

    Glen, PLEASE tell me what program you used to create that drawing. And PLEASE don't say it is a CAD drawing.
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    Still not sure about your plan............

    Here's a basic drawing showing two heat sources piped in parallel, a single primary circ and all secondary zones receiving the same supply temp.

    I asked above regarding flow through your primary loop and you said 25GPM. Is the primary loop 1" pex and 140 ft long? If so you're going to need a multi stage type pump to achieve that kind of flow. A typical circ (15-58, 26-99 or something like that) is not going to deliver that much flow.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    I mentioned in earlier post a bit higher up the chain - I use Microsoft publisher. It's not hard to use. If you decide to try it, I can foward you a collection of symbols that I have collected and/or made over the years.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    Thank you. There is a good article in PM Engineer this month that addresses this point - also with several interesting variations.

    I noticed you printed your entire screen. Where did you get your CAD program ?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    Noticed your post of the job pics. Quite impressive. Nice work.
This discussion has been closed.