Pex-Al-Pex expansion noises

Gordan

I'm sure that this is due to some fundamental error in my installation, but there it is: I'm getting subtle ticking from my radiant ceilings. I'm already on outdoor reset and constant circulation - in fact, I don't even have a thermostat on the system at this time (although I'll add it.) The rub is that my heat loss is low enough to cause the boiler, a TT PS-60, to cycle across a roughly 15 degree range every nine minutes or so. I've been thinking about adding a buffer if this turns out to be a major irritant for me, but I'm not convinced that this would really moderate the temperature swings, as opposed to merely making them less frequent. Any tricks up the collective sleeve that would help even out the temperatures going to the tubing? Adding secondary reset mixing should, I suppose, fix it, but it seems a little... excessive. This is MCBA 5, and I think that the differential is not adjustable... if it were, narrowing it in conjunction with a buffer would be a possibility...

Gordan

For instance...

Would piping the buffer in series, on the supply side, have the effect of "tempering" the supply from the boiler - that is, averaging out the highs and lows - resulting in a steadier supply to the system? The system is direct-pumped right now, and I'd ideally like to keep it that way rather than mix supply and return. But "tempering" such as I describe above would not impact the return temps, just stop the supply from bouncing up and down.

Zman

Argg!

Gordon,

I am curious about your install. I would like to avoid a similar problem. What type of plates are you using?  Do they touch or overlap?

I think a buffer tank and reducing the differential is a good approach. I would ask triangle tube about this. There are many settings that are not in the manual. Maybe they can help you with the differential.

Another option would be to control the boiler with a 3rd party 0-10 vdc.

Carl

Gordy

Tick tack

Gordan



Is this all the time, or shoulder season? Usually pex-al-pex is the meow with plates to avoid this scenario. Ah speaking of plates were they the extruded omega style?

Gordan

Construction

Plates are thin omega-groove from RHT, single-channel. They're sandwiched between pre-existing plaster ceiling and 1/2" sheetrock. The sheetrock is attached to 1x2 furring strips, and between them are runs of foil-faced polyiso with grooves routed into the straights and the plates contact-cemented to it on one side (to hold up the works until the sheetrock goes up.) Contact seems good. Each 2' plate has 3/4" to 1" between them. In my zeal to maximize coverage, I didn't leave a lot of room on the ends of runs, but calculating the expansion based on provided linear coefficients made me believe that expansion in the tubing would be minimal - certainly over a ten to fifteen degree differential, and on runs that are twelve feet or less between bends.



As to the symptoms, as I mentioned, the ticking is subtle, and it happens across the entire surface of the ceiling.



As for other settings, yes, I've seen the Euro manual for the MCBA and the CH hysteresis enable/disable ones are missing from the parameters you get when you enter the code. Is there a super-secret code that unlocks more of them, that I don't know about? :-)

Gordan

We've only had shoulder season. :-)

Not sure how this will behave once heat loss climbs high enough that cycling is eliminated but I don't see what could possibly lead to it continuing if the temperatures along the loop are constant. This is radiant ceiling, so plates are the usual thin type, 12" o.c. See above for construction details. :-)

Gordan

Duplicate

Gordan

Triplicate

knotgrumpy

What ever happend

With this, Gordan?

Gordan

Nothing yet

Basically, when the boiler is not cycling (and creating wide temperature swings) everything is graveyard-quiet. But when it's switching between DHW and space heating there's a big temperature swing; this can cause a slug of water that's 50 degrees hotter than what's in the tubing to start with, and this'll cause a bit of a racket. The issue is with the lightweight heat transfer plates as much as (if not more than) it is with the PEX-AL-PEX. I intend to add an in-series buffer on the supply to temper these swings, as well as reduce the cycling when outdoor temperatures are above the thirties.



For you, this shouldn't be a concern. You'll have dozens and not hundreds of feet of tubing and it won't be all coiled and sandwiched between rigid surfaces as it is in radiant ceilings. Just make sure that you give the tubing some room to move through any penetrations without binding, and you'll be fine.

SWEI

primary-secondary piping

May be worthy of your consideration here.

Ironman

Differential

Gordon,

I know the differential is adjustable on that control with other boiler manufacturers. Check the parameter settings in the manual.

pipeking

can u say automatic transmission

well u didn't say u were making dhw too! i would very much urge u to use a buffer or low loss header, or at the least p/s pipe config. this will act as your auto trans. and shift between differant temps smoothly. i would also think that your short cycling like crazy?

Gordan

Alas...

There's a wealth of settings that are available on the MCBA but Triangle Tube turns them off on the Prestiges. You do get some extra settings with the "secret" installer code over the four (!) that are available to the home owner, but these are a paltry subset of what the control supports.



I should say, TT turns them off for this market, because the Euro versions of the same boilers have most of those settings available. But I guess we simpleton Americans just can't handle all that control, durrrrrrrrr!



Even some of the settings they DO have, don't appear to work correctly. DHW post-pump, for instance. After trying to set this I was point-blank told by the tech support that it gets overridden if there's a continuous call for heat during the DHW call. So, instead of the DHW circ continuing to be energized during the post-pump period, the CH circ gets energized instead. This could arguably be called a feature if you don't care about the supply water temperature going to your space heating, but it's useless to me for the purpose of getting rid of that slug of hot water from the DHW call.

Gordan

Indeed

What I'm planning to do after this heating season is to put my remote manifold (which is what supplies all the radiant ceilings) on a hydraulically separate circuit like so:



Manifold return ----- (System return tee - System supply tee) ---- Buffer inlet (top)

                                                                                                  V

Manifold supply --------------- Alpha ----------------------------------Buffer outlet (bottom)



I figure that this will give me the best shot at stabilizing supply temps to the manifold while still ensuring low return temps.



The rest of my system (heavy plates between the joists and my "superconvectors" (TM) :-) ) aren't sensitive to temperature swings so I will leave them direct-pumped.

Gordan

Not really short-cycling...

Cycling, yes, at anything over about 38 F outdoor temp, but that's a feature of my low heat loss (33,000 BTU/hr at 15 F OT) compared to the boiler output.