Vitola Biferal

Rocky_3

Scenario: 6300' all radiant home. Hot water maker. Vitola Biferral was initial thought. However, since boiler will at times be making DHW, the boiler will be at between 167 and 180 degrees. Cannot send that out to radiant system untempered. Hence, Viessman recommends a mixing valve. If I now have to mix my water, why use the Vitola Biferral anyway? Isn't the main reason I would use this boiler the fact that it IS the mixing valve? If I now have to temper the water anyway, why spend the premium on the Viessman and not just go with a Buderus, or, God forbid, an EK-2 with buffer tank? some will say to install a high limit on the system pump to kill it if the radiant system is too hot. But simply installing a high limit on the radiant system that kills the system pump if the water temp is too high seams like hit-and-miss to me. As soon as the system pump kicks on and draws DHW-production temp water out of the boiler (ie: 180 degree), the high limit will kill the system pump. Now it must just sit there and cool off by radiation before the high limit allows it to try again. How long will that be? Who knows?! Then, because the 50 gallons of super insulated boiler water, (because these Euro-boilers don't scrimp on the insulation)hasn't dropped but about 2 degrees during this time, as soon as the high limit allows it to try again, we now send 178 degree water across the high limit, once again killing the system pump. We now wait another undetermined amount of time for the pipe the high limit is strapped to to cool off so that the system pump can try again. How long would we like our heat to be off at -45 below? And so on and so on until we finally waste enough of that 50 gallons of superinsulated boiler water up the stack to where the boiler has cooled down enough to fianlly allow the high limit to keep the system pump on . Am I making sense yet? So, untempered radiant supply sounds like it is un-doable, and a high limit on the supply doesn't really seem like it really fixes the problem. So, we are back to having to temper the supply water somehow after DHW. Now I know the Viessman purges excess heat into the DHW tank after a call for DHW to "fix" this problem (Hey, much like an EK boiler!), but that is only a pre-timed delay. It doesn't go off boiler temp to stop the DHW purge, only a predetermined amount of time. So while it will help, you cannot be sure you won't damage radiant system because you really don't know what temp the boiler is at after the DHW purge. So now we are back to making sure by adding a mixing valve. Why not use any boiler then if we have to add a mixing device? Why pay the premium for a Viessman in this instance if you cannot run it at low temps. Then, if you DO add a mixing device, how do you size it? For a boiler temp determined by the outdoor reset control? Or, for a boiler temp determined by the DHW production limits? I mean, if I size a mixing valve to deliver 23 gpm to the system utilizing boiler water temp of 110 (ie: outdoor reset), then I most certainly am oversized for boiler water temp of 170 or 180 after DHW call. I now lose rangeability and the mixer is "hunting". However, I must size it for the Outdoor reset temp because that is where the boiler is running for most of the time. It take 1gpm of 110 degree boiler water to make 1gpm of 110 degree system water. So I must size my mixing device based on this one-to-one ratio. but that ratio dramatically changes when the delta T is widened such as after a DHW call. What to do, what to do. Perhaps I am making a mountain out of a mole-hill and I would appreciate any info on this situation by experience Viessman installers. Otherwise, I'm going with a Buderus and tekmar system.
Regards,
Rocky

heatboy

Personally...........

......I have never done a residential radiant system without a mixing device ,regardless of the boiler chosen, ie Vitola, Vitodens, etc.. Using a three way motorized valves does not hurt overall efficiencies. With a Vitola or Vitodens, the boiler may be 10°F above your mixed temp, but when it comes out of the higher temp DHW production it will save your floors. Residential radiant should always have a mixing device regardless of the boiler. The mixing device (valve or injection) allows fine tuning of water temperatures for the floor and increases the occupant comfort level.

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Paul Pollets

VBC boiler

I agree with HB. The Vitola is the better boiler. The Vitotronic 200 control is matched for the boiler, the boiler is extremely easy to clean, maintain and install...it has 2 sets of tappings off the rear for DHWTank and system supply & return. The oil chassis burner outperforms all others...I'd install a mixing valve, for sure. The mixing valve must be sized for desired flow rate. Don't oversize the mixing valve.

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Steve Ebels_3

Let's see...............

6,300 sq ft would normally equate to roughly 90,000-110,000 btu heat loss, (assuming a whole bunch of variable stuff.) What about the domestic load? Any human car wash type showers? Did I miss whether you said oil or gas fired?

If gas is an option, I'd be thinking about a Vitodens. The 200 model. Personally I have never used a mix valve on one unless it was for a second temperature. Just set circuit A to the slope and shift as you would on a mixing valve and let it rip. The low mass of the boiler allows very quick dissipation of the temps used to make DHW.

If your customer wants the M1 Abrams tank of the boiler world, then of course it's the Vitola. Not as efficient as some of the newer condensing designs but it'll still be plugging away long after you and I are gone.

EDIT:....... 189,000...........you're in Alyeska, right?

Rocky

oil fired

heat loss is 189,000. Just seems to me that if I add a mixing valve or device of some kind, the inherent advantage of the VB is lost. Might as well use some other high temp boiler like the Buderus which can still run down to around 122 degrees and not pay the premium for the VB. I mean the Buderus is as easy to clean, as efficient as far as AFUE goes, and, you can use whomevers controls you want. Am thinking of going with the Buderus LT300 water tank for about $1800 less than the Vitocell tank. Just seems like a better fit overall.
Thanks,
Rocky

The Wire Nut

I have both...

... a Vitola, and the mixing valve. Here is what I would consider:

1) How often do you run the boiler for domestic hot water? If the DHW demand is constant, consider a separate heating source.

2) If the DHW use is intermittent (as most of them are), then the boiler can, and will, run most of the time at much lower temperatures.

3) Why are the very high temperatures required for DHW in the first place? I maintain 120°F in the tank most of the time and set the Vitotronic to pasturize the IDWH every 4 heating cycles. With the right IDWH, you don't need to run at very high temperatures to get good heat transfer performance.

4) Consider boiler temperature minimums. In a well-insulated home, the RFH supply temperature will frequently stay below the boiler temperature minimum imposed by the manufacturer.

So, to me, the mixing valve makes perfect sense.

Kevin__Flynn

Vitola with Mixing Valve

Rocky,

The reason for the mixing valve in the case of the Vitola is more for the radiant than the boiler. Usually the addition of a mixing valve such as a 4-way valve is thought to protect the boiler as well. With the Vitola you can also use the 3-way valve. The 3-way will still provide the same effect on the radiant side but still sends the coldest water back to the boiler, raising combustion efficiency.

Could you go mix-less if you didn't have DHW? Sure. However, the stand-by losses would be increased out to the heating system. The Vitola is a large mass boiler and like any boiler it operates off of a burner switching differential. The mixing valve will insure that you maintain a setpoint within about 1 degree out to the radiant system. This cuts down on stand-by losses and eliminates any overshooting or the fly-wheel effect.

Kevin Flynn

Rocky

Yep, Bearflanks alaska

Good 'ol Bearflanks...uhh..Fairbanks Alaska. Home of design temp of -47 below and 14,000 degree days.
Rocky

Rocky

sounds like the mixing valve...

doesn't really affect the efficiency of the system as a whole, (detrimentally). Just had always heard the VB could act as the mixer, but what I wasn't considering was the "overshoot" of the boiler even during low temp applications where the boiler was sending out the radiant temperature water. There is bound to be some sort of differential on the boiler, so even though it is targeting maybe 110 degree water, it still may be sending out 120 depending on the boiler control differential. So in order to protect the radiant, better have a mixer. Mixing valve not so much adversely affecting the heating system's efficiency, but gaining radiant protection. thanks for all the replies. So, in order to size the mixing valve, what would you recommend I do? If I size for the outdoor reset temp on the boiler, ie: say 120 degrees on design day, the mixing valve would need to be able to send 23 gpm to system. That means, the mixing valve would need 23 gpm of 120 boiler water to make 23 gpm of 120 system water, right? So, I would probably need a 1-1/4 or 1-1/2 mixing valve, depending on respective CV. But, if the boiler is in post DHW temp, then I would need considerably less gpm of 160 or 170 degree boiler water to make 23 gpm of 120 system water. Size for worst case scenario? In this instance, size the mixer so that it can flow 23 gpm boiler water at 120 degrees to make 23 gpm system flow at 120 degrees.
Thanks for all the inputs,
Regards,
Rocky
P.S. Don't know why I am even working on this. It is 84 out today and still blindingly bright at 7:00 pm. Am sitting outside in shorts and no shirt with my shades on doing bids on my laptop. Summers in Fairbanks ROCK!

American plumber

DHW Priority

A feature of the vitotronic 200/300 that you may find useful in such an extreme winter climate is "reduced DHW priority" coding address A2:2. By changing this you can allow the radiant system to receive "some" heat during long DHW heating cycles.