Vitodens Expansion Tank Location

Brad White_9

Hey Gang,

The Vitodens is coming along, vent is in, distribution being pressure tested and cleaned. Getting ready for final connections.

The Vitodens literature shows the expansion tank on the supply outlet of the boiler, not "pumping away" by my definition. Anyone know why this might be? Why not, for example, on the return line coming back from the LLH?

My original inclination was to put the expansion tank off of the Sprirovent just after the LLH on the supply side, just before the manifold and circulators. Any reason why not? Pros/Cons/Experiences either way?

Thanks!

Brad

S Ebels

Question FROM Brad?

Har! Couldn't resist.......sorry

I've puzzled my own noggin about Viessmann's suggested/recommended exp tank location myself. To me, it's wrong because it defeats the purpose of the tank somewhat. Locating it on the higher pressure side of the system, albeit after the pressure drop from the HX of the boiler, doesn't allow the tank to "see" the true system pressure. It goes against everything I know about the PONPC theory which our host here has described so succinctly on many occasions and in many of his books.

I pipe the tank off a tee which we install in the boiler drain location at the bottom of the LLH. We also use another tee off that as the feed water connection point for the pressure reducing valve. The LLH becomes the PONPC for the whole system allowing the boiler pump and the system pump(s) to "pump away" from it.

Works great, less fillling!

I have to go back and detail a job with a 6-24/LLH combo on Monday. I'll take some pics and post them up here.

Unknown

pumping to

i've wondered that myself, but i tend to trust those german engineerers. they must have a good reason, probably something to do with the head loss of the HX? if you stick with manufacturers instructions you can't go wrong it does fairly specifically state in the piping layout section of the manual: "note location of expansion tank..."

I looked inside the baxi 330HT and the built in expansion tank connects just aft of the pump and HX as well, so it isn't just some crazy viessmann practice.

Brad White_135

LOL Steve- You got me!

I do ask now and again... there is a LOT I do not know and learn from everyone, you included.

I like the LLH idea for it then becomes the PONPC for both boiler and radiation side circuits as you said. How simple, brilliant, wish I thought of it.

I always have a drain valve at low points so with one on the "Viessmann Recommended" point as well as my original Spirovent bottom connection. If I am wrong, a quick switch can be had and I can see the differences...

Thanks Steve!

Brad

Brad White_135

Zac

It was that very note in the manual that prompted me; so specific yet so counter to what we know.

Steve's LLH suggestion seems to suit both aspects very well and is worth a try.

There may be a reason for the Viessmann recommendation, but heck, I cannot figure it out...

ALH_4

LLH

With the Low Loss Header, the outlet from the boiler essentially is the same as the suction side of the boiler pump. As long as the expansion tank isn't connected between the boiler pump and the boiler or on the discharge side of the system pump, it's good.

-Andrew

Brad White_135

Thanks, Andrew...So, then

stick with the Viessmann recommendation?

The discharge of the boiler is the discharge of the boiler circulator, is it not? Yes, it does go through the heat exchanger first, but it would seem to be on the discharge side, whether in heating or DHW mode. Does Steve Ebel's LLH connection point make sense too?

S Ebels

I mutter a lot but

Rarely do I make sense according to the everlovin' woman that's put up with me for the last 31 years...... Be that as it may......

On the first few Vito's we installed, per their instructions, I observed a fair "bump" in the pressure gauge as the boiler pump cycled on when it started and when the solenoid would shift for DHW production. I kind of filed this away in the clutter I call my mind and just let it perk for a while. On a subsequent install that had to be packaged very tightly, I was hard pressed for a place to hang the tank in the recommended location. So I improvised. The tank was hung above the ceiling in the closet and I piped it to the location I described on the LLH.

When we fired that job up, I noticed that the pressure gauge hardly wiggled when the boiler pump cycled. Had to be a good thing as far as I was concerned and we've done them all like that since. We have 7 or 8 running like that IIRC and have no problems occuring with them whatsoever.
The pressure seems to be more stable and the LLH definitely seems to catch ALL the air going through the system. I have to try putting an automatic air vent on top in place of the manual one Viessmann ships with the LLH. I'm betting that it will work like a charm.

I should run this past someone at Viessmann some day and see what they think.

ALH_4

yes

I've always pumped into the boiler return on a 44/60 Vitodens, and the small ones are that way with the internal pump. On a small Vitodens, anywhere in the boiler loop is essentially the same, unless there is significant head loss in the boiler loop. I've never piped a small Vitodens with less than 1" pipe for the boiler loop, so the head loss was always negligible.

I agree that the bottom of the low loss header is the ideal place for the expansion tank. I made a low loss header for Gary Wallace that had two ports on the bottom for a boiler drain and a port for the expansion tank. In the top we were always putting two ports in for the thermowell and an auto air vent. With an auto air vent in the top of the low loss header, there are no air problems at all. For being a Viessmann part, I am surprised their low loss header does not yet incorporate these features.

-Andrew

S Ebels

As promised

Here's a couple pictures showing an 80% complete Vitodens install with the exp tank piped off the bottom of the LLH.

List of things to do yet include, wiring the LWCO, install permanent pipng to exp tank and condensate drain, insulate piping (so they can't see the ProPress fittings leaking.....NOT) detail the wiring, install feed water "pig" off the open end of the the FB-38 and a few other technicalities.

This was the first near boiler piping that Drew did all by himself with only a drawing to show him what to put where.

Ken, if you're looking at this, note the "hair" hanging out of the NPTxBSP adapter at the bottom of the LLH. It works, my friend.:)

Michael_6

the Vitodens burner and heat exchanger heat water instantly and that rapidly heated and expanding water is in the end section of the HX and the immediate supply coming out of the boiler. The water in many cases in the boiler return and system return are very low and "mixed in the LLH and supply out to the system.

Paul Pollets

Exp. Tank

In states adhering to the Pressure Vessel code, there can be no valve between the boiler and the expansion tank. If the homeowner, for example, shuts the valve, the relief valve will blow. As for the location of the tank, if Viessmann wanted the tank at the LLH, they would have provided a port.

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ALH_4

Valves

What about the factory supplied valves on the bottom of the Vitodens?

-Andrew

Paul Pollets

technically...

..an inspector could make you remove them, if the exp tank is connected and can be isolated by one of them. I've never been called on it yet, on a Vitodens install.

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S Ebels

You are of course correct

We have installed valves in that location on every job that I can recall and have never had an inspector take issue with it. The handle is removed when the job is complete and maybe that has something to do with it.

You said ......"If the homeowner, for example, shuts the valve, the relief valve will blow."

I look at that as a good thing. The relief valve gets tested for operation and the Homeowner learns to keep his hands off what he doesn't understand.

Paul Pollets

Good Point

> We have installed valves in that location on

> every job that I can recall and have never had an

> inspector take issue with it. The handle is

> removed when the job is complete and maybe that

> has something to do with it.

>

> You said

> ......"If the homeowner, for example, shuts the

> valve, the relief valve will blow."

>

> I look at

> that as a good thing. The relief valve gets

> tested for operation and the Homeowner learns to

> keep his hands off what he doesn't understand.





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Paul Pollets

Good Point!!

Until they call you with "The boiler is leaking from the relief valve...could you come over and check it, please??"

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Michael_6

vitodens no flow=no fire- no problem

Ed Nordstrom

Viessmann Vitodens Expansion Tank Location

The expansion tank location for the Viessmann Vitodens boilers is especially critical for the small series boilers (WB2-6-24, 8-32 models). Those models have a pump on the common return line and a built in 3-way diverting valve.

When that valve activates, it isolates either the DHW loop or the space heating loop by closing off the appropriate return line. Thus, the expansion tank must be located on the outlet side of the boiler [as shown in our manuals] to avoid having the expansion tank hydraulically isolated. In other words, if located on the space heating return, we could possibly see the PRV releasing when DHW is produced and during space heating if located on the DHW return.

On the larger Vitodens boiler models (11-44, 15-60) theere is no diverting valve. Our manuals show several alternate locations which will suit all kinds of installation variations while insuring positive pressure where needed.

That being said, we understand that this is confusing for people who have "pumping away" ingrained in them. Rest assured. Viessmann is not violating any laws of physics nor denying the value of pumping away. The small models just have a design feature which requires a seemingly different location, but which is perfectly fine in practice.

Kind regards,

Viessmann Manufacturing Company (U.S.) Inc.

Edwin Nordstrom

Brad White_9

Thanks, Ed

I noticed that now that piping is almost complete on my Vito.. Pressure testing revealed no air going to the DHWH so it was apparent and now abundantly clear. I have installed a tap for a tank on that side for that reason.

I am thinking of installing a small tank (#15)on the DHW production side for that eventuality but keeping the main tank (where heating will be more often in operation than DHW) off of the LLH. Any issues with that?

As always, your opinion is appreciated.

Brad

ALH_4

?

Have I misunderstood the operation of the diverting valve in the small Vitodens? As I thought I understood, the valve doesn't isolate the DHW from the space heating completely. It just switched whether the internal pump pulled from the DHW return or the LLH return. The LLH still sees the system pressure through the boiler supply supply pipe no matter what mode the boiler is in. The only way there could be a problem would be if the expansion tank was plumbed in-between the diverting valve and the pump inside the boiler.

Am I understanding this wrong? I dont currently have a Vitodens in front of me to check.

-Andrew

S Ebels

Ditto

That was my understanding also.

But I was wrong once or twice before too IIRC

Edit:
Check out the schematic on page 40 of this link,

http://www.viessmann.ca/web/canada/ca_publish.nsf/AttachmentsByTitle/dbl-5811164-vitodens-200.pdf/$file/5167-472-Vitodens-200-TDM.pdf

The drawing shows the piping that is internal on the 24 & 32 Vitodens. The DHW solenoid switches the return only while the supply side (system & DHW) of the boiler circ remains "connected" via the internal Tee in the boiler. To me, it appears that the boiler fluid can under no circumstance be hydraulically isolated from the Expansion tank if mounted as shown (das Viessmann way) or connected to the LLH (das Ebels way)

What do you think?