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primary/secondary loop

Weezbo
Weezbo Member Posts: 6,232
the picture you have looks normal to me except the bypass with no control stradgey other than to remove the handle...thats sorta elusive even to me. are you into making it stronger like structurally?

by puting a Uie on both ends of the pipe(with the air scoop) and reconnecting them with another length of pipe you would have a secondary(boiler ) loop and primary loop then that pipe could have secondaries,taken off of it for radiant manifolds...if you have an indirect you might find that it would work a shade better by snatching the supply and return off the boiler supply and return...

as i understand you the water is shooting out of the boiler at present straight into the slab..so now i wonder is this a special new kind of condensing boiler..? if so, then, there may be some reason the delta t is that tight... especially if the room temps and supply and return temps are close..

there are lots of controls these days some pumps have means of determining very subtle changes thru sensors if the pumps have a vv on them then you need someone to physically be there on site before making any changes.while simple they have a slightly advanced stradgey interconnecting them.

Comments

  • Dave_61
    Dave_61 Member Posts: 308
    primary/secondary loop

    I have a copper tube low mass boiler which nees to be repiped. I posted to the wall and had someone draw me a schematic, which I have attached. I have since had several heating contractors come to the house and they would either give me an astronomical price or never call back.
    I have finally found someone willing to take this on for a reasonable price. He agrees with the schematic with a few small changes, and I was wondering if they would be OK.
    He put 2 temp probes on the main inlet and outlet pipes on the boiler and found that the delta T with my current piping with the furthest zone running is about 1 degree.
    He proposes putting a proportioning valve between the 2" close set tees on the boiler loop to adjust the flow as needed to keep the delta t at about 20-25.
    He also wants to connect the ends of the supply and return manifolds into a loop so that where in the picture it says "To Zones" and "From Zones"....those would be connected in a loop together. Currently, the supply manifold (where all the 007 pumps come off) and return manifold (where all the zones return) are each dead-ended with air vents on the ends.
    The plumber feels that by connecting the supply and return manifolds together, you will be pushing the water through the main boiler loop and around through the manifolds instead of just going round and round the boiler loop. He says that if the delta t is too high, then you can open the proportioning valve between the 2 closely spaced tees to bring it down.
    What do you think about that setup?
    Thanks.
    Dave
  • Supply House Rick
    Supply House Rick Member Posts: 1,404
    Dan's Book

    Pumping Away is a fixture on my desk. This will explain Primary/Secondary. This is a great read for everybody...
    Rick
  • Dave_61
    Dave_61 Member Posts: 308
    Hey Weezbo

    Actually, the bypass in the picture was one that had been incorrectly installed. It will be completely removed and a proportioning valve put between the 2 tees at the top of the loop (to the right of the air scoop).
    The delta T should be about 20-25 degrees per the manufacturer. We have 5 loops coming off the manifolds. (3 hydroair units, the indirect, and a small radiant loop).
    We still have alot of noise (sounds like a low-flying plane when the burner is on). Hopefully the repiping will solve all this. It seems like the noise started after No-Burst was added to the system. It was quieter with the Herchem antifreeze in it. Have you heard of this?
  • Dave_61
    Dave_61 Member Posts: 308
    Weezbo,

    Here's the revised schematic. Sorry it's sideways. Does it appear OK?
    Thanks.
    Dave
  • hr
    hr Member Posts: 6,106
    The bigger issue

    with low mass boilers is the multiple, and changing loads. What happens when just the small radiant load calls? that boiler may bounce on and off in 15 second cycles. I have seen this many times with multiple, micro zones low mass boilers. It can lead to condensing in the HX and flue piping. Be sure to check both.

    If it were me I would add a buffer or replace that boiler with a condensing modulating boiler that better adjusts to the various loads and will not have condensing issues that you have not addressed in those drawings.

    Also any "device" between those closely spaced tees will change the dynamics of P/S piping. Any slight restriction will induce flow where you might not want it :) As will the various load circs changing the flow in that loop and across the "device" you describe.

    Sounds like you are swapping one problem for another instead of solving the bigger issues?

    How old is that boiler. The noise could indicate scale or build up on the exchanger walls. Sometimes a flush, will solve that. It hasn't taken on a lot of make up water by chance. This will quickly coat those copper tubes and not only cause noise issues, but greatly reduce the flame to water efficiency.

    Trade up to ciondensing equipment, solve the load issues and watch the fuel savings soar :)

    hot rod

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  • Dave Stroman
    Dave Stroman Member Posts: 763


    I made the drawing for you months ago. It is the most basic p/s you can get. It seems that everyone you talk to just can not get it. It is the best you can do with the boiler you have. Delta T has little to do with it. With small zones running the Delta T is almost nothing. There in lies the problem with copper boilers. There is no mass to heat up and cool off. So the boiler, like Hot Rod said, short cycles like made. I stopped using them for that reason.

    Dave in Denver
    Dave Stroman
  • Weezbo
    Weezbo Member Posts: 6,232
    i see the picture ....

    one of the minor technicalities is that even with a bridge if that boiler isnt some new fangled condensing boiler with a stainless steel exchanger roling off the back side of the burner then you will be having some small difficulties pumping heat straight at the slab and straight back to the boiler. the loop system is goin to spin water around and around thats oki dokie problem is that the radiant loop is likely less than a few gallons of water and it wants to collect some btus for the next go around and about the only way it can do that is draw heat from a source. if that source is limited to mere quarts or just a few gallons of water it has no storage capacity, this in turn means that some cooler water Must go back at the boiler in order to effect an exchange. that cooler water will then Make the boiler, that in turn adjusts the boiler Up and then sends it back into the field. What hot rod is saying to you is this,were it a condensing boiler it could dial the btu exchange out into the field on a fairly consistent rate of balanced eqilibrium...with it not being a condensing boiler ,and of low mass, it will want to "change up" very rapidly. a simple water heater with some 1 1/4"to 1"ips male adaptors spun in two the tappings of the elements with two seperate staged zones comming off the boiler with a by pass on that loop would allow the boiler to range a fair amount of time with little to no call at the boiler. a reset control would work on the buffer tank with a bit more precision, than that step function(which you may ajudicate off the water heating thermostats on the top and lower 1/4 of the boiler) it really is a satisfactory means to dial the boiler to the demand without it comming off and on every couple mins....

    with the loop you have drawn you have basically made a bridge to step down the water to the system and stepped up the return temps buh there are other things to take into account. one of these things is that when a zone calls for heat all kinds of variables change, should another call then there is another whole set of flow and pressure changes...it might even be possible to get the loop with the radiant to block out flow in a loop were it cold enough...and conversely you could get flow thru zones when you didnt want the heat to be flowing as it could bring heat to one side of a pipe ,the cooler water fall down the hotter water rise and all of a sudden you have fans going when its way warm Already :) in other words depending on the take offs for each "zone"you could get one pipe Gravity system for Free! only problem being you might not want that happening. water is not too smart buh once it finds its way somewhere ,...it Likes to keep flowing there:) the closely spaced t's on supply side and return side are basically not quite what you'd want, honest injun.i can say this as my favorite dead man just happened to be :) may his spirit always rise with the Eagle.

  • Dave_61
    Dave_61 Member Posts: 308
    But Dave,

    in order to get my system to work, would it be OK to do like he's saying and attach the dead-ended manifolds together to make a loop? In the drawing you drew, it would involve tying together where you havre the labels "to zones" and "from zones" He says that will make it work much better. I'm just at a loss.
    Dave in CT
  • Dave_61
    Dave_61 Member Posts: 308
    Hot Rod

    I am having the plumber prepipe in the boiler loop for a buffer tank. He is going to put 2 tees with shutoffs on each of them as well as a shutoff between them. Do you have a diagram as to how that can be piped/wired?
    Should we put a proprtioning valve between the 2 closely spaced tees in the boiler circuit?
    How about the other issue of bridging the supply and return manifolds together instead of leaving them deadended?
    Dave
  • Dave_61
    Dave_61 Member Posts: 308
    Weezbo,

    What if we added a buffer tank in series on the output side of the boiler. Would we still want to bridge the supply and return manifolds or leave them as dead ends (from the picture in my first post)?
    Dave
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