The scuplture made a sale.............

Steven Gronski

This message is in regards to the thread i posted in a kind of funny,joking way "Ahhhhh......the versatility of the Vitoden".
I just got home from my mail mans house and sold him on a new Vitoden for his home. The whole thing came about when he was delivering my mail and I was outside starightening out my van. He asked me about the icicle hanging of my dryer vent, and I explained to him what it actually was and that it was not a dryer vent. I took him into my basement and showed him the Vitoden and explained the principals of it and how it worked, and how that my house is set up on constant circulation and why the icicle existed.He asked me to come by his house and see if I could do something like that for him. He has the perfect set up, cast iron hot water radiators.Those would be perfect on constant circulation with outdoor reset. I looked over the job, gave him a price, and he is going to do it. I have raised the curiosity of a few neighbors that are inquiring as well from this "sculpture". What a selling tool.........to bad it couldn't be around during the summer when more people are out and about the neighbor hood.

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Mike T., Swampeast MO

Ever since seeing the first "ice sculpture" from my Vito, I've paid attention (and even nosed around) vents of "high efficiency" heating equipment. Probably all forced air though...

Only time I've seen anything similar is when the outlet is nearly on top of a shrub and then it's covered in ice. Otherwise, there might just be an intsy bitsy icicle.

The protective screen of the Vitodens horizontal termination is likely acting as the "seed" for ice to start to form. Other terminations don't have anything like it.

That said, I've been known to feel the exhaust. Have yet to feel any nearly as cool as the exhaust from my Vito.

Lurkin' Murkin'

Caged up feeling...

I don't understand what the screen is supposed to be "protecting"? The pipe and gasses aren't hot enough to burn anyone, unless contact was extensive. If it's to keep obstructions away, isn't it an obstruction in itself? Do punks in Germany throw themselves headfirst into vent terminations, for kicks???

Brad White_9

Part of a system

The centered target plate stops/diverts directed wind which would affect the internal vent system pressure controls. The cage itself is designed to hold off that plate the right distance to allow dispersion and to keep enough space for any ice formation in climates it is intended for.

I think for kicks the German police have a nice recreational relationship with the few punks they have left....

Lurkin' Murkin'

Vell, then...

This is a Natural Gas fired boiler that modulates and has the gas valve coupled to the combustion blower, right? Boilers of this design do not usually do not rely on a pressure switch for safety - but if does, it would have to have a very sensitive setting to allow modulation of the air flow down to very low airflow pressures. Is the combustion air taken at this same location (concentric around the vent) - wouldn't it be balanced, as far as wind effects? If it is, then no problem of flue gas recirculation, when the cage is blocked with ice buildup?

Brad White_9

You stated the right reasons, wrong conclusion..

The pressure balance between supply and exhaust has to be fairly precise. One paradox of low pressure drops is that a little difference seems huge by comparison.

A good strong wind against the outlet would be read as a partial blockage or at least resistance to outflow. Yes, the Vitodens will modulate to compensate for this and downfire accordingly, but the rational in us all asks, "why should it?".

Because the combustion air enters the main casing chamber surrounding the combustion chamber, there is a buffer there, a place for the air to be compressed which would lessen the effects of a "push" of air into that pathway.

If the cage is blocked with ice, that tells me it is a need for their low temperature outlet configuration.

Thus far, ours has been pretty clear with a good beard of ice below. It has only gone to about -1 thus far this year where we are.

Lurkin' Murkin'

Veddy interestink!

I just read one of the other threads here where the air/fuel ratio control is discussed. Now I see why pressure is monitored for this design. It's rather complex - are there any clear advantages to doing this way, over the more common venturi or mixer? Thanks for the discussion!

jackchips_2

Sounds like

a picture on a postcard sent in the spring is the perfect advertisement, Steve.

It will be fun to follow your progress with your many neighbor(s).

:-)

Jack

Brad White_9

Venturi or mixer

in the classic sense of larger industrial burners requires higher fan horsepowers, incompatible with house-scaled systems, is my short answer.

That is the limitation on modulation- pressures are so low in residential-level equipment, coupled with the rule of the square (pressure change to flow change) that low turndown operation tends to have disproportionate gas/air blends.

One needs higher pressure drops to amplify the burner's ability to measure and meter the flow of each.

Lurkin' Murkin'

O.K. - I've never seen this boiler or it's literature, only what's discussed here. It is a residential unit we're talking about, right? And whatever differential pressure we're talking about must be pretty low when it modulates down to the lowest firing rate (less than 1/4" w.c.?). Is this pressure used to control the gas flow rate, through a transducer or other detection method, as the other thread suggests? Is this the most accurate way to correlate the appropriate gas flow to the combustion air flow, as opposed to a venturi directly mounted to the gas valve?

Mike T., Swampeast MO

Quote from Vitodens "Start-Up/Service Instructions"

The MatriX burner blower and the combination gas valve are factory calibrated and pre-adjusted for optimum boiler performance at all firing rates through a non-mechanical, pneumatic modulating link between combustion air and gas flows. Blower speed is automatically increased or decreased based on heat demand and venting system resistances, thereby regulating the amount of combustion air drawn. The pneumatic modulating link between air and gas introduces the required amount of gas for correct combustion to meet the current heat demand, based on a linear relationship between delta-P air and delta-P gas.

Optimum combustion air flow rate is recognized and monitored by the differential air pressure sensor (transducer). The output voltate signal of the transducer is analyzed for logic by the LGM 29.22 burner control unit. The LGM 29.22 burner control contains pre-programmed performance curves and operational safety parameters unique for every boiler model.

Flue gas adaptation function

The Vitodens employs a flue gas adaptation function. This function records, processes, and reacts in real time to fluctuations in pressure drops in the vent air-intake pipe during normal operation caused by partial pipe blockages due to ice formation on the vent termination, debris and/or sudden high winds. Such increase in pressure drop, if not promptly corrected, will reduce the combustion air flow rate, and hence lead to unstable combustion. The differential air pressure sensor (transducer) records such pressure drops and supplies voltage signals to the LGM 29.22 burner control unit which, in turn (based on stored performance curves and safety parameters), initiates prompt adjustment of the blower rotational speed, thus readjusting the combustion air flow rate for optimum combustion. The same automatic adaption logic applies if combustion air is reduced (or increased) due to slower (or faster) blower speed resulting from line voltage drops (or increases) below (or above) the threshold of 85% (or 110%).

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

Really slick, and I believe still unique. Remember that combustion analysis for the Vitodens is for verification only--air/fuel mix is not adjustable by the user.

See what I mean about everything being proportional?

A given amount of combustion air results in a given amount of fuel virtually regardless of the pressure of either the air or the fuel. BUT there is no assumption that X voltage supplied to the fan always results in Y amount of combustion air. The voltage applied to the fan is first adjusted to compensate for the static pressure drop in the flue of each individual installation, it then self-modifies in real time to compensate for "unusual" conditions in the flue and gas supply that would change the pressure of either.

VERY important to note how the process begins: "Blower speed is automatically increased or decreased based on heat demand..."

This would appear to be a completely separate feedback mechanism from the proportional pneumatic link that provides continuous self-adjustment.

Put the two together and I can better understand how the Vitodens does what it does with only the one (supply temp) sensor. Unless demand changes it knows that fuel consumption won't change. While it may not know the exact amount of air/fuel being consumed at any given moment, I suspect that it has a very good idea...even though there appears to be no actual measurement device for either combustion air or fuel.

Actually it's elegantly simple in theory, but probably MUCH more difficult to turn that theory into reality.

Perry_3

This is not a unique approach...

An old fashion carborator in a car does the same thing.

You throttle the air flow, and the air flow automatically picks up the right amount of gasoline as it passes through the carborator for engine operation at that power level.

All kinds of fancy things were added - such as a small gas pump to prefeed in some extra gas when you depress the gas pedal. If you did not need a quick speed boost the engine would get there as the airflow slowly picks up more fuel and the engine speed (or load) increases.

Of course, Fuel injection is all the rage now because keeping a carborator precisly tuned is difficult as they age. However, note that you still throttle the air with the gas pedal - and then fuel is mixed proportional to the air flow....

The vacuum created by the pistons is the motive force for the air flow to increase when you open the throttle.

All Viessman has done with the Vitodens is essentially copy the same principals and build a sensitive valve to do the same thing - input gas proportional to the air flow.

Perry

Lurkin' Murkin'

Thanks for the clarity on the method used, guys - I think something in the other thread confused me. The gas flow follows the air flow, like with the venturi system - but an extra feature of the combustion air pressure being monitored can correct the air flow to try to maintain the desired input rate. Seems like this would make the terminal cage plate not really necessary, but if everyone including the mailman likes it...