Vitodens 200 Turn down 3-1 ?

Today my vendor

told me that the Vitodens 200 was 3-1 turn down. I have never used Viessmann but hear enough positive here to form a good opinion. However I use Knight boilers all the time and they have 5-1 turn down. Most of my jobs are Zoned very small and this one is no different. This makes me want to advise the homeowner to go with the Knight because it would be more able to load match. I looked on the Viessmann site and couldn't find the answer. It almost sounds like they have a variable gas valve. I really don't want to put my foot in my mouth here. I have had hoofinmouth before and don't want to catch it again.

That is cool

I have never heard of IBC boilers before but 10-1 turn down is great. No more buffer tanks. I will look into that tommorow.

the vitodens 200 also has a variable speed pump! input 25to91, 37-124, 55to172, 80to230 btu! And a control computer that seems to learn the system! Mind you, i usually run these with TRV's, gravity cast systems or infloor and normally don't do much zoning, condensing boilers love the high mass systems! I have also had good luck installing multiple Vitodens 100 boilers 30-200 btu with 2! I use a Tekmar control.

With a lot of microzones...

... you might be better off with a small buffer tank that you could also use as a LLH. Whatever boiler you use can then take advantage of the mass in the tank to fire longer. This is especially true for the systems that start on a high fire and then ramp down. The Vitodens, IIRC can start off on low-fire.

Like Trevor, I'd investigate TRVs if I were you. Very simple mechanicals, excellent comfort. Combine it with a variable-speed pump like the Wilo series and you have amazing energy savings. In those kinds of scenarios, a buffer tank may well be avoidable, since you could have a lot more mass to play with in the system (depends on the emitter).

The Vitodens 8-32 I was involved with in ME has no buffer tank, just a standard LLH. The RFH system has enough mass where a buffer tank is not needed, particularly as the Vitodens is very good at "micro-firing" or whatever term Mike T. invented for the low-fire mode. The owner reports a 46% fuel cost savings over the cast-iron 83% AFUE atmospheric system that predated the Vitodens (to be fair, there were some near-boiler piping issues also).

Pulse mode

Constantin, I believe Mike's term for this is "pulse mode" I love the vito but still think this is another word for short cycle, regardless of how well equipped the unit is to handle these cycles.

While the variable speed pump on the vito is a nice feature, it remains unclear to me the exact nature of it's logic. I believe it is simply linked to firing rate, more than any sort of A.I. "learning".

The ramp down firing is a real issue for small low temperature systems. it's very difficult for the 6-24 to provide sub 95 constant circ. temperatures at the flow rates appropriate to smaller systems. Target is simply reached before min modulation is established.

I think the sort of micro zoning that we see in conventional systems is not ideal for condensing boilers. The other design issue being that maintaining secondary>primary flow rates is difficult in these sort of multi zone systems.

Some manufactures are not concerned by this and actually want the primary loop to be over pumped (knight) they need consistent high flows across heat exchanger.To me this seems like a waste of electricity and a detriment to achieving lowest possible return temps.

What is the vitodens IIRC?

6-24

Will, I hope my comments didn't create any confusion for you. The burner is indeed fluidly variable as opposed to stepped. If the heating load is within the range of modulation the boiler and control has a very impressive ability to maintain accurate supply temperatures. So precise in-fact that it is possible to deliver very stable room temperatures with no more control feedback than the outdoor sensor. Finding the curve that matches the structures heat loss can take some time though. Viessmann is probably the only manufacturer that respects the intelligence of the user (home owner) enough to include instructions for these adjustments in the users manual. Although in reality this is beyond what most americans want to know about their heating equipment.

The thing about the vitodens and it's controls is that it's really designed for constant circulation. Multiple on/off zones kind don't integrate with the elegance of this approach in my opinion. I hate to see an boiler like this grafted onto a conventional heating system. Take a look at trv's and panel radiators. If you design for low head in your pipe work you might even be able to move all the water in the system with the single built in circulator.

The problem I was discussing is specific to my own very low temp low load structure. The ignition sequence of the boiler is such that it lights at a relatively high firing rate and then modulates up or down accordingly. In my case most of the heating season requires supply temps so low that by the time the boiler throttles down to min modulation it has exceeded target temp and shuts down. This behavior assured short cycle operation for far to much of the heating season. This is really only an issue for ultra low temp applications. The boiler which is designed to handle the punishing cycles of tankless dhw production (combi unit) is capable of operating this way, but it bugged the hell out of me. I ended up using a ODR interval timer (tekmar 269) to work around this. Keep in mind my heat loss is around 20k at design

The vitodens-200 is a great machine. It's at it's best when connected to a european style system or a gravity conversion.

If you working with natural gas, have a look at the new vito 100. A more competitively priced unit with TT contacts that's probably more suitable for connection to a american style multi zone system.

tn4

Could be a win win. The scenes buttons have James Bond bling, and it is what was spec'd out... right? ;-)

hahaha

I gues it does , yeah, the vitodens 200 is an amazing piece of equipment! The remote room control works well too! It isn't a thermostat as we know it, what it does is shift up or down the the curve and slope and doesn't do the on off thing! I know the vitodens 200 can run multiple temp zones with mixing etc but I think it can only handle one remote mounted control, things change though! The 100 is not even close to the same, however, $2200 for a 100 alows me to put multiple units in appartment buildings pretty efficiently! I wonder if I can get vitovan licence plates you have me thinking of this now!

Trevor

Treavor

Do i still need the indoor sensor to help regulate the running temp. I am thinking the vitodens sensor goes in the coldest area of the home and the zone control system is a separate system. I am jealous I know that thing are done differently on your side of the water. I was over their for a month when I was younger. At that time I was a dry guy working in new construction retrofit forced air. I would look at different things now. I was in London in January it was cold but beautiful of all the places I went on that trip London felt the most like home. Like San Fransisco without the hills.

IIRC

Constantin, what is a Vitodens IIRC?

Treavor

I really have to thank you. Having never used a vito 200 your help is invaluable. Now I can go to the customer with real understanding of how the 200 works and how the controls will affect it. I hope some day I can return the favor. If I ever make it back over their I will buy you a beer. Thanks again. Will

hahaha

As someone who grew up in London (Ontario, Canada) I got used to that confusion.

By "over there", do you mean England?

not really

when I went over their in my late teens it was all over the place. London, to Ireland, to London, to France , to Italy, back to London. All in all About five days total in England mostly London. Two friends and I, Eurail passes, and backpacks. Oh and lots of rain It was late January. I would think if I was In Europe again London would have to be part of it. Although now that I am married vacations involve less wandering. I would guess I will need more than $800 in my pocket and I don't think my wife will go for hostels.