Ghost flow where we don't want it

Jumbo

When a space heat zone calls, all zones get some heat. DHW will over heat; other zones will creep. Been this way since new 7 years ago. Heat mostly with wood, so hasn't been a big issue, but with oil at $4/gal and no snow to otherwise occupy myself, I've resolved to fix it. Haven't easily found someone local that is as conversant in similar systems as I'd like, hence this post.

 

Buderus G115 and LT28 laydown DHW. Piped P/S. P loop is 21' of 1 1/4" cu (with 11 90's) servinf 4 zones: DHW, 2nd floor Buderus radiant panels (180*); 1st floor, outdoor moderated, injection, staple-up radiant (90-135*); basement radiant in 5" slab (80*). Schematic attached. Generally conforms to real layout with simplification for clarity

.

If I understand all I've been reading, these are the problems I see: 1) DHW supply immediately downstream of P pump; return almost at boiler; 2) 2nd floor heat supply next; some 8' (+4 tees, 2 90's, 2 ballvalves and a swing check) beteen tees. 3) 12" between S/R on 1st floor injection with a ball valve between tees (???); 4) 16" bewteen tees on low-temp basement radiant, with return into the run of the tee into the P loop.

 

My ideas to fix this are: 1) move DHW pump close to boiler and change control to shut off P pump during DHW call. 2) Move P pump onto return side of loop to make room for close tees. 3) replumb supply side of P loop with close tees. 4) install check in all supply/return line. And while I'm at it, 4) relocate makeup water supply to stem of expansion tank. See image 2.

 

And also, since we mostly heat with a woodstove, when we do start up the central, the short term return water is quite cool (stat is set at 50*). Don't know what the boiler return temp might be (will install gauge), but  wondering if a boiler by-pass loop is appropriate to help protect the B.



Just want to make sure I'm not out to lunch with these changes. Not in the trade, but am a civil designer, so I'm pretty familiar with the concepts. Just need to be able to speak intelligently so I can find someone that can do the work...and have the confidence that he knows what he's doing. Any comments/suggestions would be much appreciated. Thanks.

chapchap70

Flo-cheks?

I didn't see where or if you have flo-cheks in the system.



Maybe I'm not understanding something but it seems like this could be resolved by a couple of properly placed flo-cheks so the water doesn't flow into the unwanted zones?

Steve Whitbeck

pump

You really don't have a primary/secondary piped system.

Remove the Primary pump and install it after the mixing valve for the in floor slab loop.

Tie all the returns togeather with NO connection to the supply main.

This way each loop will pull from the boiler seperatly. each loop MUST have a check valve coming off the supply main.

The indirect in the second picture is correct. It needs it's own pump and check valve.

Jumbo

No checks

Well two; one in the very bottom of the primary loop right where we go from supply to return (increasing the head differential between the secondary tees?), and a second in the injection radiant return. Haven't done the math, but checks will create enough resitance to stop flow when tees are this far apart? I've read about 1/4 psi per check? 

Jumbo

Guess I don't understand

Not a P/S loop? How's that? With the exception of the location of the return tees, the piping conforms with the schematic provided by several ( four that I have looked at) boiler manufacturers.

I have proposed to move the primary pump as you describe. But as far as joining the secondary returns and bringing to them to the return side of the primary. How does this correct the pressure differential that is creating the unwanted flow.

DHW is simple.

Steve Whitbeck

pump

The pump I want you to relocate is causing your goast flow.

You need a pump after the mixing vavle on the in floor slab loop Or you wont get enough flow if any. There isn't any pressure drop between the supply and return connections for the mixing valve. AND if you install restriction between the supply and return connections it will just increase your ghost flow.

Your first diagram is NOT  P/S it is a pumped boiler loop with the zone loops piped off of it. You need a pump and check valve on each of your zones including the indirect.

Zman

Parallel

What Steve is proposing is parallel loops that all pull through the boiler. Since cast iron boilers don't need very high flows it should work just fine. I would suggest some sort od low temp protection on the radiant slab. Unless the slab is quite small I think it will return cold water which will cause the boiler to condense.

Carl

Jumbo

Ahh, I get it. Not P/S because...

...the boiler isn't connected to the loop with its own closely spaced

tees. Hence a "boiler loop".  Understood. As far as the infloor slab, I

failed to include the pump on the slab radiant...it is there. Sorry for

the confusion. Having said that the inclusion of checks on each of the

zone loops is enough to stop the unwanted flow? Don't I still want the

supply and return tees close even with a boiler loop? Or are you suggesting the elimination of the existing boiler loop pump and tying all zone loop returns together as the boiler return, so that the only connection between the boiler supply and returns is through the zones?

Jumbo

I'm starting to get it...

...as what you guy are talking about looks more and more like the Buderus schematic. But, everything I've read says if there is any radiant in the system, some method is advisable to keep return temps up so the boiler doesn't condense. Doesn't the pump in the boiler loop provide that protection?  And if we need a pump in the boiler loop, don't we still need the supply and returns to the zone loops close together? If I eliminate the boiler loop pump (I'm all for not running an extra pump) and tie the zone returns together as the boiler return, how would we go about modulating the return temp?

SWEI

boiler return temp protection

requires either a motorized mixing valve with appropriate controls or a specialized thermostatic valve like an ESBE or a Caleffi 280/281.



A bypass will provide some protection, but is not as good on the cold size or the hot side.

Steve Whitbeck

pump

If there is a pump on the in floor slab loop then The boiler loop is OK - put the pump on the boiler loop on slow speed if it has a speed switch.

Then remove the valve between the supply and return tees that your diagram shows, this is causing pressure on the boiler loop thus causing flow in the loops even when those pumps are not running.

The indirect should be tee'd in as close to the boiler as possible.

I don't use mixing valves - I use Tekmar injection control. Much better temperature control and has boiler return sensor for low temp safty.