Low Loss Header

ALH_3

That's one of the reasons we decided to make our own. The brass adapters were always a pain and the design of the Viessmann LLH is already wide. So the stainless ones we're making are 4 inches wide total, and they incorporate an automatic air vent and 1 1/4" NPT connections.

Have you observed any temperature differences in the LLH with and without the insulation?

-Andrew

PS

Replacing my old gas boiler with Vitodens 200 and IDWH. System is hot water, single-pipe diverter tee w/ split loop (single zone) to standing CI rads (~60 kBTU/h capacity - well matched to design day loss), existing circ is on return. New system will use OA reset, DHW priority, constant circulation, pumping away.
My dilemma is the 2 proposals - one proposes using a low loss header w/ separate circs for heating and DHW, the second proposes direct piping to boiler and only utilizing integrated circ and solenoid valve (6-24 or 8-32). Which approach is best? I'm not really sure of P/S or LLH applicability for my system. Any opinions?
FYI - Both pros are highly qualified, but neither measured piping or looked at existing circ pump (heating only). My mains are 1.25" and branches are all .5", longest branch is ~35' (supply and return).

Ted_5

Both systems will work

but I lean towards the use of the LLH. If you do, the Vitodens pump will do both boiler pump and DHW pump. If the guy, not using LLH is sure of your flow rates and head pressures, then it is a good application. If they are not sure that the Vitodens pump will do the job, then use the LLH.

Ted
Viessmann rep.

PS

Thanks Ted - I guess that is ultimately my question. I partially understand the potential need for the LLH (if the integrated pump cannot provide enough head to move all that system water, install the LLH w/ distribution circ to decouple the system loop from the boiler, allowing both the system and boiler loops to circulate with proper flows?). Without measuring any flows or nameplate data from the existing circ, how could one come up with one approach or the other? It seems one (direct pipe) is just using experience and the other (LLH) is just being conservative.
With the LLH, is there a need for another circ on the IDWH (VM 53 gal)?

Mike T., Swampeast MO

To find the flow requirement for a diverter tee system believe you'd have to completely reverse engineer the system (including heat loss and radiation ability) to see if the built-in circulator has enough power. Just knowing the current pump specs won't help unless you know total head loss. Just knowing total head loss won't do much good if you're trying to determine how low you can go with flow. For that you'll have to know heat loss, radiation ability (at temps lower than the "standard" 180°), pressure drop at each rad, etc., etc.

Don't suppose you'd have the original plans for the system lying around somewhere?

Since it's also variable speed (based on weather) you'd have to determine the allowable speed variance to ensure you still get balanced flow at warmer outdoor temps.

Models 6-24 and 8-32 have a diversion solenoid in the DHW production kit that diverts flow to the DHW tank. None of their system examples show a circulator for the DHW with these two boilers.

Don't forget that the LLH isn't like regular primary/secondary. The LLH ensures that the boiler return temp is as low as possible, e.g. same as return from the emission system. Such is not true with regular primary/secondary piping.

PS

That's what I figured, Mike. Thanks for the reassurance. I guess what concerned me most was what happens if the non-LLH approach doesn't work. That's alot of rework (piping, additional circ, etc).

Steve Thomas (Foley Mechanical)

Vitodens

PS-
I Just finished a Vitodens with this exact same set-up. You do not need a seperate pump for the indirect. depending on what model you have a sol. valve and an indirect kit can be added to the system to allow the system pump to operate as the indirect pump. I would also suggest that you set this system up with constant circulation.

Mike T., Swampeast MO

I guess what concerned me most was what happens if the non-LLH approach doesn't work.

What I [think] would happen is that you'd get very uneven and/or insufficient heating. In both cases the boiler would probably start cycling around its target temp when it should be (based on current heat loss) modulating.

Cosmo_3

LLH baby

The worst thing you can do is vary the flow of water in a diverter T hydronic system. What will happen is that you will get uneven heat across the radiation system when the flow is reduced. I would personally go with the Low Loss Header, you don't necessarily have to use Viessmann's, (although it is Awesome), one can be made up out of big pipe w/ T's. Just keep the system circ always on during the heating season and you will be extremely comfy....AHHH

Cosmo Valavanis

Dependable P.H.C. Inc.

ALH_3

Or

You can make one from stainless steel. Of course it will look better powder coated Vitosilver.

Another one of Dale's ideas...

-Andrew

ALH_3

Internal Pump

If it's an 8-32 you need the LLH for sure.

With the 6-24 and less than 4gpm total system requirement or so (assuming approx 250ft 1/2" tube lengths for each loop) you might get by without the LLH.

These are just rules of thumb to start questioning whether you need the LLH or not.

-Andrew

heatboy

Don't suffer from........

the deep pocket short arm syndrome. For the ridiculously small amount of money the LLH costs, considering everything it can do (auto air elimination, sludge settlement, assured flow, etc.), it just makes sense to use it.

hb

PS

I assure you, with the price of the VM boiler and IDWH - I'm not looking to shave a few $. I'm simply trying to differentiate the technical pros and cons of each approach, as ultimately I'm looking for maximum system efficiency, however I don't want an overengineered setup for a very simple application. Your points in re sludge, air elimination are ones I hadn't considered. Thanks.

So the consensus seems to be to go with the LLH, an additional circ on the heating zone, and use the integrated pump and valve for DHW priority. Now my question becomes - the system circ runs continuously and the boiler cycles as needed and integrated pump runs continuously also? What actually controls the two pumps? It seems my continuous circulation operation just became more complicated?

Mike T., Swampeast MO

Without the LLH, the built-in circulator functions in "system circuit mode". It runs any time the computed target temperature is above the current outdoor temperature. If the computed target is below the outdoor temp, the circulator (and all firing) stops. (Please excuse the mix-up between "above" and "below" in the original!)

While running in this mode, the circulator varies its speed based on your settings for minimum and maximum and the weather. I find no other explanations in the documentation. Since you don't "tell" the boiler how low of a temp to expect in your area, I would suspect that circulator speed is part of the "learning" function.

Nothing at all wrong with diverter-T systems, but as mentioned you'll have problems if you omit the LLH:

1) Determining if the built-in circulator is sufficient to begin with;

2) With the variable speed nature of the circulator--it will likely have to be set for a very narrow range or even constant speed. Keeping speed constant might take some toll on boiler efficiency as the temp drop is likely to decrease in moderate weather--with lower flow in such conditions, temp drop can be kept higher.

------------------------------------------------

With the temp sensor for the LLH header plugged in, the built-in circulator switches to "boiler circuit mode". In that condition the circulator would [seem] to vary speed to keep the desired conditions in the LLH. It may run any time the target is above the outdoor temp; it may shut down when it detects extremely little heat loss through the LLH. Sorry, I'm not sure.

The Vitodens really isn't designed to be connected to a wall thermostat. It's possible, but it's not really the way it's intended to be used. In your system your thermostat (presuming there is only one) would likely control the secondary (radiation)-side circulator. With an appropriate reset curve, you'll get nearly constant circulation.

One thing I found rather odd about the Vitodens control system is getting the thing to shut down in moderate weather. With the "sun dial" set at your desired room temp, it won't stop until the outdoor temp is above that setting unless you put a negative shift into the reset curve. Since cast iron rads often work with a quite shallow reset slope, it can be difficult to get the boiler to shut down at a cool enough outdoor temp while still having a high enough supply temp in cold weather.

An alternative is to set the sun (and/or moon) dial(s) to the OUTDOOR temp where you want the boiler to shut down. You then add a corresponding amount of positive shift to the curve.

PS

Thanks again Mike - I know you are speaking from your own experience. I will be sure to post some before/after pics and will undoubtedly have some "control" questions once the heating season starts.

BTW - Boiler lockouts (in my experience)are usually based solely on the outside air temp, not its relation to inside temperature. I hope the factory manuals are more comprehensive than what VW has on-line!

Mike T., Swampeast MO

By "lockout" I presume you mean intended shutdown, e.g. warm-weather shutdown?

Not really related to inside temperature--it's related to the target (supply) temp computed by the boiler which is related to the setting of the "sun" and "moon" dials. Since the Vitodens doesn't actually sense indoor temp, those settings aren't necessarily even close to the actual indoor temp. Sorry if that sounds confusing--it's a different way to look at things and it took me quite a while to figure out what was going on.

Same manuals come with the boiler.

ALH_3

Auto Air Elimination?

Have they changed the LLH recently? I haven't seen one with an automatic air vent.

-Andrew

heatboy

Make it one..........

Andrew,

We remove the manual air vent and use an adapter to convert the threads and use a high capacity standard auto vent. In this picture you can see the Taco high capacity vent on the LLH. We do this so we don't have to use any additional air elimination, aside from out initial purge.

hb

heatboy

Not much more..........

than the exposed piping connected to it, I guess. I do like the looks of the one you have pictured up there. For a couple of inches, is it worth the time and increased cost? Looks cool, though! I have looked at the Caleffi headers. They are almost double the cost of the LLH for the same function.

The larger Viessmann LLH have NPT connections. I also wonder why they don't do the smaller ones that way.

hb

ALH_3

And the Caleffi has the automatic air vent, but no well for the #5 sensor. I'm sure they're very high quality, like most of Caleffi's stuff.

We thought it would be useful to have NPT fittings, the boiler drain, the well, and the air vent.

Lots of ways to skin a cat I guess.

-Andrew

Unknown

LLH in stainless w/options

The better Header.

Makes sense to me. The LLH offered by Radiant Engineering is of welded stainless steel. No need for those HUGE brass adaptors from the Euro- threads- BSPT size to NPT. They've taken that work away. No insulation option for this unit yet but, is that really necessary? Two 1/2" taps on the top with a proven air eliminator device as well as a braised well for the Htg circuit sensor. What else could you ask for?

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S Ebels

Hey Heatboy

Draw a picture of your perfect low loss header and fax it to Lee Brooks at Earth Lee Headers. She'll weld it up just like you want. Round pipe, square stock, rectangle whatever.

heatboy

Sure, it's a better idea...........

but considering I can't even get 3/8" CFin when I need it..........