Vitodens 200 Turn down 3-1 ?

Mike T., Swampeast MO

Am positive that the circulator's logic is not simply linked to firing rate.

There are two distinct operating modes: boiler circuit mode (with low-loss header) and system circuit mode (w/o LLH).

In boiler circuit mode, the circulator varies its speed so that combined with the current firing rate the energy exiting the LLH is equal to the energy entering the LLH. The target temperature is maintained at the LLH--not necessarily the boiler--and the difference between the boiler temperature and LLH temperature certainly comes into play in the logic.

Secondary > primary flow is not desirable as it requires a higher boiler temperature to maintain the target in the low-loss header. Not much problem with high mass, low-temp emitters like nicely conductive radiant floors, but can be a serious problem with hydro air--especially if setback is used. In general try to keep secondary flow no more than 130% of the primary.

In system circuit mode with only the single circulator <I>under boiler control</I> driving the system, I can only speculate, but operation does not appear to based on such simple logic as boiler circuit mode.






In system circuit mode,

Big Will

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.

Uni R_2

IBC Technologies

If your jobs are all micro-zoned you really should check out the IBC.

http://www.ibcboiler.com/

15-150 MBH (or 45-225 MBH)

10:1

Big Will

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.

Andrew Hagen_2

HX

Is that similar to the ACV heat exchanger? Where can I get one?

trevor pierce, London Boiler Service

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.

Glen

viessmann model numbers

are ratings in KWs. 8-32 would be 4:1 turndown.

Constantin

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).

trevor pierce, London Boiler Service

playing with the public

Hi Constantin, Just thought I would let you know what I have been doing with very good results in London, but scarry! I have about 30 houses here that were gravity systems, well 2 are monoflow the rest are gravity that I have been running completely off outdoor control!!! I have room temp feedback sensors in stock and ready but haven't put any on yet! These houses are running with no room temp feedback! The boiler never seems to leave low fire, the heat in the house is very even, and after the first gas bill the customers dont want me to change a thing! I have a few in one section of town where the houses were hollow brick before and had massive radiators that I have set the system design temp at 120 degF, lots of return visits on the first couple! It is worth it though, these boilers are on low fire, and low temp! For everyone who doesn't know the efficiency of mod con boilers is relative to %firing rate and water temp, on the systems I just mentioned the Vitodens will normally run at 98% eff but if it goes to high fire this number will drop to about 90% The effects of water temp are much more drastic, One can make a mod con run in the low 80% very easily! Another thing I do Constantin is if I require indirect hot water heater I will size the tank for lower boiler temps and still meet domestic demand, I seem to be getting 150 supply 130 return so I am doing it relatively efficiently!

Thanks for Reading

scott markle_2

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?

Big Will

I called vittodens

Their tech help guy told me they are truely vairiable and not step down at all. Thats abig deal. My load is 90k btu and the model that fits runs as low as 18k btu. I asked spacificly if its a smooth ramp up to 100%. The answer was yes. That is impressive as far as I know this is the only mod/con that is truely vairiable not step down.

scott markle_2

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.

Big Will

the engineer

that specified the Vito 200 shows room sensors in seven locations and two primary thermostats. I don't think he really understands the way it works. Between this thread and the conversation with the Vito tech guy I think I have a handle on it. Keep in mind I have never built a constant circ system or used any Vito anything.

So between a outdoor sensor and an indoor sensor it will vary the circ speed and modulate the burner to meet the load. A indoor sensor is available that acts as a thermostat to give the customer temp control. This comes from the Vito tech guy but is reflected on their site. If I were to install zone valves and thermostats they would have to slave off of the sensors control.

Do I have it right? I have to put together a letter to go with the proposal that explains why the specified controls wont really work and why. Like I said before I really would like to keep my foot out of my mouth here. Thanks all so much for the help.

Side note: Trevor does that make your sprinter a Vitovan HA HA sorry kinda corn ball I know.

Uni R_2

tn4

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

Big Will

The vito likes it?

I looked at the tekmar web site and it looks like a good fit as long as it works well with the vito 200. It seems like anything that changes the control structure of the Vito 200 would change its efficiency by not allowing to run as a constant circ and load match as well.

trevor pierce, London Boiler Service

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

scott markle_2

Tn4 is a great system, I have some gaps in my understanding of how it interfaces with viesmann equipment. The attached tekmar service bulletin says it can be done which was not always the case. I don't understand why the control is set to stager mode if the interface is 0-10v modulating.


The only problem I have with this is that we are paying for controls on the vito 200 that we won't be using. The Tn4 has some advantages in responsiveness it will see the difference between desired and actual room temps and raise temps to speed recovery, zones that would overshoot as a result of this higher temp are put into a on-off "pulse mode" that is calculated to aviod room temp overshoots and sine wave bing bang feedback behavior.

While the tn4 will deliver the ultimate in responsiveness and high efficiency it's complicated and there is the potential in complicated systems like this that something is overlooked in commissioning and that the system is not operating to it's best. Recently fixed less complicated setup where the boiler contact had been wired to the argo relay instead of the Tekmar. This system was working fine but there was no ODR on supply as a result of this wiring error. After spending some time with this system I also noticed that the dhw demand was almost always on, turns out the sensor was in a shallow well that was not giving accurate reading the tank was set at 130 but was maintaining closer to 170.

Personally I think it's a good idea to question complexity. Vito style full reset ODR (maby even piped direct) and some trv's can be the basis of a very good system, additional indoor feedback is optional. The sun moon interface can also be located remotely in a more convenient location than the boiler if desired.

Big Will

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.

scott markle_2

Tn4 is a great system, I have some gaps in my understanding of how it interfaces with viesmann equipment. The attached tekmar service bulletin says it can be done which was not always the case. I don't understand why the control is set to stager mode if the interface is 0-10v modulating.


The Tn4 has some advantages in responsiveness as it will see the difference between desired and actual room temps and raise temps to speed recovery, zones that would overshoot as a result of this higher temp are put into a on-off "pulse mode" that is calculated to avoid overshoots and sine wave bing bang feedback behavior.


Personally I think it's a good idea to question complexity. Vito style full reset ODR (maby even piped direct) and some trv's can be the basis of a very good system, additional indoor feedback is optional. The sun moon interface can be located remotely in a more convenient location (than the boiler) if desired. If indoor feedback (curve shift) is used it must be located in an area that has no trv's or other thermostatic control. If your going to strap third party stuff on the boiler (tn4) I'd take a look at the 100. Why pay for controls you would essentially be bypassing on the 200?

scott markle_2

IIRC

Constantin, what is a Vitodens IIRC?

trevor pierce, London Boiler Service

will hanson

I would have any sensor in the most neutral part of the house, or none at all! I have many houses in London, ON running with no room temperature feedback at all, just outdoor temp control! They are working great but it was many visits and came out of personal interest! Zoning is a big issue for me if done with valves or pumps in the traditional form! I do like the tn4 system also! My concern is with zoning and tstats the customer has an expectation of a reaction when adjusting these things, they must react therefore requiring higher boiler temps and more fuel! My aproach would be different on different systems, if it were all infloor heating and relatively equal temps I would take say the area with carpet and highest water temps and adjust the slope/curve to accomadate this area then use mixing by (balancing before panels, injection,or valve) the big advantage to this is you justify the computer hanging off the 200 and if the customer ever has a problem it is convenient because it is all Viessmann, or triangle tube or whatever! tweaking can be done by flow controls etc! I personally like balancing valves for flow control to control temps, this only seems to be mainstream in hospitals and schools though! This is just me though, Im not a fan of tstats and many zones, I believe zones controling the boiler have there place, just not with mod cons this powerfull! Hay, if I have time I will sketch something, there are many good control systems out there, Tekmar has done very good and are reliable, if the customer is set on control this will do it just fine!

Big Will

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

Mike T., Swampeast MO

Exactly what I've done in my house in Missouri Trevor. Works wonderfully and the Vitodens 6-24 thrives without the LLH and the single variable speed circulator. And yes, am essentially running only on outdoor control with the only feedback being the TRVs throttling for solar or occupation gain.

Uni R

hahaha

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

By "over there", do you mean England?

Brad White_185

IIRC

Is an acronym for "If I Recall (or Remember) Correctly".

Mike T., Swampeast MO

Not simply temperature related--if anything reducing the target temperature will reduce the tendency to go into pulse or batch mode. With an 80 mbh Manual J loss, such could be common in certain weather.

Unknown

Thanks Brad, I can stop wondering about the new IIRC Vitodens!

The 200 lights somwhere in the mid to upper modulation range. I'm told that the 100 lights at low fire. Budarus gb is a throttle up design as well.

I only wish that when the Vito had loads that were below minimum modulation it would expand it's differential to avoid this "pulse mode". Seeing how well my system works with the steam control and fixed min modulation I see no reason for such a narrow differential in these low load conditions. One nice feature of the Tekmar is automatic variable differential. I wish a similar logic or even just an fixed adjustable differential was part of the comfortrol.

The tn4 will establish near constant circ. (with lowest required water temp) for the zone with the highest demand. The other zones will run in a predictive on/off mode, additionally these on off cycles are synchronized with each other to keep an even load on the boiler. I don't think this system has any adverse effect on efficiency. It just adds complexity.

Big Will

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.

Unknown

direct observation

Mike,

Secondary greater than or equal to would be more accurate on the P/S issue. If primary is greater than secondary we have a warming of return, not ideal.

I don't understand how the low loss sensor and boiler supply sensor could provide enough information for the variable speed logic you assume to be present. Seems to me system and boiler return sensors would be required to provide a basis for adjusting boiler flow rate. If boiler return temp is greater than system return this would indicate a need to lower boiler flow rates.

Direct observation (living with) has shown that "pulse mode" is directly related to low target temps. I have no problem with 1 or 2 minute burns. But what drove me crazy were conditions when the boiler would not even have time to modulate down before shutting off. It takes about 20 sec. to reach min modulation. My house only needs maybe 105 at design and as a result I was seeing a lot of 5-10 second cycles.

Running the boiler at a fixed minimum modulation has been an interesting exercise. Basically with the structure at room temp supply temps peek at about 113. My shortest run time is one min. every 38 min. An indoor sensor on the Tekmar will shift the curve or shut off the heat if room temps exceed target. At design (0 f) I'm seeing near constant combustion at min modulation. Initially deltas are over 30deg. and even with sustained burns they never go below 20.

I feel that I am getting the highest possible efficiency thru this unorthodox control strategy. And I was thrilled to loose the unnecessary low loss header that the local rep convinced me I needed. Any one need one of these?