Vitodens on Gravity Conversion w/TRVs

Mike T., Swampeast MO

albiet much smaller than needed with a digital burner?

My off the cuff comment is if the built-in circulator can deal with the heat-up phase with extremely low head loss and I provide "sediment traps", why is the low-loss header required? Yes, I realize that the boiler's efficiency will drop during UNUSUAL periods of high flow, low delta-t, but I still wonder if burner modulation is going to suffer in the common conditions.

As long as the brain can understand that the system side of the low-loss header is already producing the exact conditions that the boiler wants (low temp, high delta-t, low flow) everything should work with the utmost thermal efficiency. But if it's making <I>any</I> assumption to the contrary everthing goes kerflewey!

OH I WISH I COULD WRITE TECHNICAL GERMAN!!!!!

Vitodens certainly has a very good control system and it must have been designed with TRVs as the optimal emission control, but TRVs are NEVER mentioned in the U.S. Technical Design Manual!!!!! It's all about lots of @*#&ing pumps!

p.s. There is a <I>really</I> strange sentence on the final page of the U.S. Technical Design Manual under the MOST IMPORTANT THING--"Design Considerations". Not in front of me now, but it states, "systems of high volume must be connected through a 3-way mixing valve." People keep telling me that it's an error...

ANY GERMAN GUYS OUT THERE????????????

Mike T., Swampeast MO

I've been writing privately about this, but don't seem to be getting answers. HELP!

The "requirement" of the low-loss header on a TRVd system (even a big, high volume gravity conversion) still really bothers me and the more I study the more I wonder.

In my personal case I MUST keep a specific reset curve. It is not however high, reaching only 140° or so at outside design temp. I have radiant floors running "wild" off of the constantly circulating mains and the radiation is not particuarly well-balanced. Every "law" of heat transfer I see utterly GUARANTEES that I will have a high system delta-t (in the 30° - 40° range) at this supply temperature. Flow will be LOW. During temperature maintenance flow will NEVER exceed the 6.2 gpm max. Typical flow should be in the 2-3 gpm range.

This appears to be a highly probable scenario:

Heat required: 44,000 btu/hr. System supply temp 120°. Delta-t 40°. System return temp 80°. System flow 2.2 gpm.

Is the built-in boiler circulator (with the low-loss header installed) going to modulate down below 2.2 gpm in fulfilment of the VPrimary < VSecondary requirement? If not, the only other thing I can see happening is that the burner will start cycling instead of the smooth modulation that is desired.

S Ebels

You could set your max pump speed to 35%. That should limit the flow to about what you want. I think it's coding level 2 code 045.....I think?

If'n it were mine, I might be inclined to add a 10-20 gallon tank instead of the LLH and let the boiler circulate to and from that. Connect your gravity side to the tank and let it floooooooooow. Just a thought, off the cuff.

marc

a couple of tips

on the vitodens, if you ask viessmann they will give you a drawing of p/s piping without low loss header, the pump conmes set at 65 % for heating which we usually leave right there, dont make the mistake of thinking the little pressure bypass valve will do all you need, i would install a pdbp on the system side also. just a few tips, hope this helps. marc

S Ebels

Mike

Are you planning on maintaining the gravity side of the system sans circulators or are you going to pump that side also?

Mike T., Swampeast MO

Only the provided circulator

into a gravity conversion with TRVs.

3/4"------------1 1/4"---------------3"

boiler (6')---transition--(4')----main (5')