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Closely spaced tees

JC2001 Member Posts: 3
I know that this question has been asked before, and it might even have the exact same thread title, but I am still a little confused.

 I am putting together a heating system for my home and have spent the better part of a year researching hydronic heating systems. I am now assembling the control panel (circulators, valving, air eliminator, etc.) and I am wondering about closely space tees on my primary loop. I understand that my secondary loops should run off closely spaced tees, but with a 1-1/4" primary loop, it seems like the closely spaced tees would be unnecessary.

I have attached the schematic. Any advice would be really appreciated.

FYI, some details on the installation:

House size=1800sqft

Design temperature=15F (Vancouver Canada)

Boiler=Triangle Tube Prestige Solo 110

Indirect DHW: Smart 50



  • Gordan
    Gordan Member Posts: 891
    Not like that

    Closely spaced tees are there to hydraulically separate circuits from each other. So, the way you've got it, your boiler loop is separated from your primary loop, which is separated from your secondary loops. You've got circulators on your boiler loop and on your secondaries, but not on your primary - so by what means will water make it around that loop?

    Hydraulic separation is needed when your flow in one circuit has to be independent from the flow in another circuit. There are situations when boiler loops that are separate from primary loops are necessary or a good idea, but I don't think yours is one of them. Your boiler should probably be piped into the primary loop - in other words, no closely spaced tees. Another way to do it is the way it's suggested in the manual, with closely spaced tees on the boiler but not on the zones, but if I'm understanding what you're trying to do correctly, you're hoping to feed some of the return from the high temp zones to the radiant, and that you wouldn't be able to do with the manual's suggested piping arrangement.

    One thing confuses me: what's the purpose of the three-way diverter valve on the high-temp zone return?
  • CMadatMe
    CMadatMe Member Posts: 3,086

    Gordy is on op of it. Need a primary pump. How are the towel warmer zones controlled? Thermostatics on them?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • JC2001
    JC2001 Member Posts: 3
    ...good point


    Thanks a ton for the response.

    OK, I think I get it. The TT Solo110 manual had me question myself, so I added the closely spaced tees on the boiler loop, but didn't notice that they didn't have the closly space tees (hydraulic isolation) on the secondary loops. So I will do away with the closely spaced tees and pipe the boiler directly into the primary loops as you suggested.

    And you are correct that I want to pipe the high-temp return to the radiant, so the closely spaced tees on the secondary loops are required.

    As for the diverter valve on the high temp return, the problem is that I will be doing upstairs radiant heating in two stages.

    stage 1- run the affordable slant fin baseboards in the upstairs rooms.

    stage 2 (in a couple of years from now) - rip up the upstairs flooring and lay down in-floor radiant heating.

    So while I am running the baseboards upstairs, I would rather have the option of having the high temp water to both sets of baseboards (upstair and downstairs) by diverting the high temp return downstream of the radiant loop.

    I hope that this makes sense. Your explanation on my previous problem is much appreciated.

  • EricAune
    EricAune Member Posts: 432
    Check the DHW piping

    The PS110 has an pipe connection on the bottom of the cabinet for the DHW supply.  Your return should be piped back to the boiler loop.  The MBCA will allow for DHW priority.

    I don't agree with eliminating the tee's however, I would use a "moose antler" piping configuration for isolation with closely spaced tees at the boiler.  Proper placement of the expansion tank and zone pumps will allow for the TT to run smoothly.

    Keep it simple.
    "If you don't like change, your going to like irrelevance even less"
  • Gordan
    Gordan Member Posts: 891
    edited November 2010
    Yep, missed that.

    The way you have things laid out now, if you pipe the boiler into the primary loop you'll be pumping toward the expansion tank, which is a no-no. Good catch, Eric. The tank would have to be moved to the return side of the boiler. (Not necessarily the air separator, though.) Regarding the explanation for that three-way valve, it's still getting stuck in my throat: if you divert the return to after the radiant tees, you're no longer in closely spaced tee land; you've got circuit takeoffs from the primary that are nested within each other or interleaved. Does that mean that you won't have effective hydraulic isolation and/or that it won't work? Not necessarily, but it probably means that you should know exactly what you're trying to achieve and how you're going to do it before you venture into that territory. "Moose antler" (i.e. what's in the manual) and closely spaced tees are clear and easy.
  • Gordan
    Gordan Member Posts: 891
    Taking a step back

    Although it may seem like a good idea now, buying and installing baseboard only to replace it with in-floor radiant later may be more trouble and expense than it's worth. Often it's more the idea of radiant floors than the reality that draws people in - I know I was fixated on that myself, but eventually decided on radiant ceilings everywhere. They're an easy retrofit for most situations, cost you only about 1 1/4" of headroom, and you don't have to worry about what rugs you put down or where you locate furniture. You may appreciate being done and able to settle in for good.

    Unless your floors upstairs are in terrible shape, you may find that tearing them out and dealing with all the attendant complications (trim, losing height in doorways etc.) is just not worth it.
  • EricAune
    EricAune Member Posts: 432
    edited November 2010
    Great drawing!

    You've created a very nice drawing, but don't let that limit your thinking in how to properly pipe this system.  Sometimes the drawing gets us thinking it is the only way (I know I do this often without even realizing it)

    I agree with Gordan about the ceiling vs. floors, however, I have no idea what other factors are at play here.  Maybe your floors do need attention and adding heat may not be a huge job when attending to those needs.

    Have you considered panel radiators instead of baseboard? If there is any possibility the floors will not get heated, the radiators are a little nicer to live with over the long run.  Quieter, more durable and easier to clean (just my opinion).  Either one would serve you best if you were to first consider the desirable water temperatures in keeping that TT in condensing mode as much as possible, this will add additional footage/sq. footage, nonetheless, the initial investment will be paid back many times over if you can run low temps through the entire system.   
    "If you don't like change, your going to like irrelevance even less"
  • JC2001
    JC2001 Member Posts: 3
    ...and agian, thanks for the great help.

    Eric and Gordan;

    1) I know that ripping up floors to lay down in-floor heating is going to be a lot of work. But I am in an 80yr old house, and a complete reno of the upstairs is in the 5yr plan, so temporary upstairs SlantFin Baseboards is in the plans for the upstairs, while we are going to go with some nicer panel radiators for the basement. Biasi makes some nice looping panels that aren't overly expensive.

    2) Thanks a lot for the advice on the DHW connection direcly off the PS110. I had heard about this, but I found the manual to be a little unclear. And I had looked for images of the bottom interface connections. This helps a lot. But will I still need a circulator for the DHW loop? I would think that would still be required. Otherwise it seems like a large load on the circulator inside the boiler.

    3) As per Gordan's concern over hydraulic isolation due to my 3-way valve on the hi-temp return, I am going to get rid of that valve. This seems way simpler.

    4) Now two more questions:

     - I figured that my original layout (non-moose antler) would be more efficient because I would be able to run some of the hi temp return in to the low temp upstairs radiant. But you both seem to favor the moose antler approach. I am seeing that a lot of it has to do with running the TT in condensing mode. I have planned to run the boiler at 140F. Will this achieve good condensing?

    - And possibly the most important, the placement of the expansion tank? The PS110 manual draws the expansion tank at the boiler outlet, the same way that I have it drawn. I had heard that the system should always pump away from the expansion tank...meaning that the expansion tank is at the lowest pressure point within the system. I think that because the PS110 has the circulator inside the boiler enclosure, I got a little confused. But if I review this, am I correct to assume that I should move this as close to the PS110 inlet as possible? But should I move the air eliminator as well? Is it OK if the air eliminator is at a lower point in the system?

    Again, thank you both so much for your professional advice. I am feeling more and more encouraged about this project.

  • Gordan
    Gordan Member Posts: 891
    edited December 2010
    A few more answers

    Think of DHW as another zone, with priority. Priority means that when this "special" zone calls for heat, all other zones must wait until this call for heat is satisfied. That way, the full output of your boiler is available to meet the DHW demand, which tends to be "peaky" (relatively short duration but high intensity, to overcome the large temperature differential that's required for DHW but not for space heating.)

    Now. Just like with all zoning, there are several ways to accomplish this. One is "zoning with circulators" and the other is "zoning with zone valves." And, like with other zoning, if your different zones have vastly different flow and head loss, then zoning with circulators allows you to give each zone what it needs. Given the wide range of different types of indirect tanks, this is typically what is done - you give the indirect tank the right circulator to achieve the flow it needs through the pressure drop it presents (small with a tank-in-tank type, but typically much larger with a coil-in-tank type) and you give the system and/or boiler loop what it needs, too.

    The Prestige Excellence, which has a little built-in 14 gal tank-in-tank right in the boiler enclosure, uses the same circulator for the boiler loop as it does for DHW. It has a built-in three-way valve that it uses to switch between the two circuits. But the pressure drop is low in both cases, so neither circuit is likely to be over/under-pumped.

    That's the long answer. The short: yes, you need a separate DHW circ, and using the "other" supply port on the boiler allows you to bypass the boiler circ, which you'll want to do. The control stops the boiler circ during a DHW call. It doesn't really have to do with a "large load", per se, as explained above.

    I think you're right that your original layout would achieve a higher system delta-T and lower return temps - if and while both zones are simultaneously calling for heat. I wouldn't say that I personally favor TT's suggested "moose antler" layout - it's simply better for other things; for a typical residential system the supply temperature drop between circuits would be considered a bad thing, because it's somewhat unpredictable (or at least dynamic) and therefore difficult to design for. In your case that temperature drop is desirable - or will be, once you pipe in the radiant, but not before that.

    Note that the manual doesn't actually have a suggested layout for a multi-temperature circuit, so you're on your own. The manual does have a few different layouts, however, and I think you're mixing and matching elements from them to ill effect. The layouts that have the air eliminator and expansion tank "on the supply" all use the closely-spaced tees for the boiler, isolating the boiler flow from the system flow. That means that the boiler circulator is, for all intents and purposes, not pumping toward the expansion tank, because it is on a hydronically isolated circuit and it doesn't induce flow through the system. (Its "point of no pressure change" is not the expansion tank/feed, but the closely spaced tees, and the pressure drop through the boiler circuit is negligible on either side of the circulator so it doesn't make any difference to it which side of the boiler it is on - both sides are just about equally close from those tees. On a typical mod-con boiler the pressure drop through the boiler will be much higher, and you'll see that they all have boiler circulators on the return side, pumping away from the closely spaced tees.) But look at the system pump (or zone pumps) - they're are all pumping AWAY from the expansion tank.

    Once you start pumping the system flow THROUGH the boiler, you need to move the expansion tank to the return side. There are a few diagrams that show this arrangement, too - look at the one titled "CH System Piping - Single Zone System with Single System/Boiler Circulator." Don't get confused by "single zone" - just replace that single zone in your mind with your multiple closely spaced tee arrangement. The air eliminator doesn't need to move - just the tank and the makeup supply.

    Whew! Now, on to condensing. Your boiler comes with an outdoor reset control, which is a great way to get the higher efficiency that results from condensing mode operation, but it's another thing that you have to set properly. This way, even if 140 F is your "design supply temp", you'd only be hitting it on the coldest day, and for much of the season you'd be deeper in the condensing range. It's possible to condense with 140 F supply, but it's borderline. Outdoor reset will net you much greater savings than any clever piping scheme.
  • Gordan
    Gordan Member Posts: 891
    Lost in the weeds

    Really, it comes down to this one thing: it's difficult to create a layout that would be optimal for you both now AND later, since baseboard and a radiant panel have radically different output characteristics - and panel rads are somewhere in between. So, a good compromise might be to simply go with the moose antler, size your various emitters to provide the required output at a relatively similar temperature, and use outdoor reset to keep your system temperatures low for most of the season. This means that you design your upstairs radiant now. It also means that you can likely get rid of that mixing valve and the multi-temp design. It also means that you may be able to go with a single delta-P circulator that varies the flow according to how many zone valves are open, and consumes much less electricity.
  • EricAune
    EricAune Member Posts: 432
    edited December 2010
    My idea of ideal for this situation (with a budget too!)

    I'd pipe the boiler on its own circuit (as shown in the manual, supply & return tied into the system piping through close tees).

    Indirect with its own single speed properly sized circ.

    Zone valves, and one circulator. I am partial to a certain green colored brand of both, I really like the new Sentry zone valves a lot. 

    I am a huge proponent of the Delta "T" strategy, your system could likely be designed to operate on one temperature (most can when output parameters of the emitters are considered at this phase).  With one temp and a delta t circ you would ensure the entire system to operate exactly how you want it to all the time, without the need to "adapt" to the ever changing demand due to the load.  This circ technology achieves exactly what everyone has been trying to design since the dawning or hydronica (IMHO).

    Gordan has got a lot of really really good info there and I don't think I could have said it better myself.
    "If you don't like change, your going to like irrelevance even less"
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