Vitodens with Hydroair

Paul Pollets

The Vitodens is best served when designing around a condensing load...such as radiant floors. Using the boiler to provide heat for (3) HW coils is not the best use of the appliance. The boiler should not be fired over 165. HW coils usually need a min of 140 to generate heat, or the AHU will be blowing cool air. The Vitodens works best when applied to 80-120 degree design loads.

The Vitodens will still work, providing the coils can be at design temp at 167 deg. Old school maybe, but I believe a cast iron boiler is better suited; I like taking advantage of the "casting lag" when using HW coils in the AHU. JMHO

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Dave_61

Vitodens with Hydroair

Sorry if I'm rehashing things....
I have been in the market for a new boiler and have heard great things about the Vitodens boiler in this forum. This has definitely risen to the top of my choices.
I just have a couple questions on our particular setup.
Our house was built in 2000. It is very well insulated with double pane windows, etc. It is approx 6000 sf on 3 levels. The calculated heat loss is about 200,000 BTU (rounding up).
We have 3 hydroair coils (One for each floor).
The first floor unit is a 20 x 25 double tubed coil rated at 80,000 BTU-not sure for what temp though. I think our first floor is about 3200 sf with 10 foot ceilings.
The second floor unit is the same (20 x 25 rated at 80,000 BTU). Our second floor is smaller than the first because our foyer and family room are 2 stories. I'd say our second floor is about 1500 sf with 8 foot ceilings.
Our third floor coil is 16 x 20 double tubed rated at 60,000 BTU. This floor is about 1300 sf with 8 foot ceilings.
Currently, they are being run on a boiler temp of 175 degrees.
With the Vitodens running at the lower water temps that you have described in different postings (so that its condensing most days), would these coils be adequate for heating the house? We live in Northern CT.
Thanks very much.
Dave

Nron_13

Vitodens

boiler has a max temp of 167 F and make sure that your fan coils are sized to handle the lower water temps at max output , you should try to make you designs to keep your boiler temp at 140 or lower to allow this boiler to give you the better energy savings ,

Constantin

Only a heat loss will tell

Here are a couple of things you can try:

1) Calculate yourself or have someone else calculate a heat loss for the building. Slant-Fin has one available on their web-site that you can download for free. Then see what heat you need vs. the capacity of the emitters you have.

2) Monitor the system and see how often the boiler fires on a cold, cold day (as close to a design day as possible). Then do the math to see how many BTUs per hour that approximately corresponds to.

3) Pull up past bills for your heating, some heating degree day data for your area and infer from there how much heat your home is losing.

If your home is well-built with little infiltration, etc. I would be surprised if you had more than 20BTU/(sq ft x hr) heat loss on a design day. That would make your emitter capacity about 2x of what your home is losing right now. In turn, that will allow lower temperatures to be run through your coils.

So, in the end it all depends on the output of your coils at lower water temperatures and the actual heat loss of the structure. Find a qualified contractor to do the heat loss, review the extant emitters, and then you should be able to know if the Vitodens will work well in this application. Ideally, the contractor will have a blower-door to test the infiltration on-site, as that number can vary quite a bit from structure to structure.

Ragu

Similar Situation Here

I'm looking into a 6,000 sq. ft. commercial job that is tailored for hydro air. I also crave the high 90's efficiency of the Vitodens, but at a maximum water temp of 167 degrees, I'm in the high 80's for efficiency. Unfortunately, my past experiences with fan coils here on the coast of Maine tell me that I want the availability of some seriously hot supply water when we get into the teeth of winter.

I went as far as I could with the design, and then asked for engineering assistance from our Viessmann reps who are outstanding.

At this point my gut tells me to go cast iron. We'll see.

Nron_13

boiler type

> Here are a couple of things you can try:

>

> 1)

> Calculate yourself or have someone else calculate

> a heat loss for the building. _a

> href="http://www.slantfin.com/he/"_Slant-Fin has

> one available on their web-site that you can

> download for free_/a_. Then see what heat you

> need vs. the capacity of the emitters you have.

> 2) Monitor the system and see how often the

> boiler fires on a cold, cold day (as close to a

> design day as possible). Then do the math to see

> how many BTUs per hour that approximately

> corresponds to.

>

> 3) Pull up past bills for your

> heating, some heating degree day data for your

> area and infer from there how much heat your home

> is losing.

>

> If your home is well-built with

> little infiltration, etc. I would be surprised if

> you had more than 20BTU/(sq ft x hr) heat loss on

> a design day. That would make your emitter

> capacity about 2x of what your home is losing

> right now. In turn, that will allow lower

> temperatures to be run through your coils.

>

> So,

> in the end it all depends on the output of your

> coils at lower water temperatures and the actual

> heat loss of the structure. Find a qualified

> contractor to do the heat loss, review the extant

> emitters, and then you should be able to know if

> the Vitodens will work well in this application.

> Ideally, the contractor will have a blower-door

> to test the infiltration on-site, as that number

> can vary quite a bit from structure to structure.

Nron_13

boiler type

Look at viessmanns vitola or vitogas 100 instead of the vitdens for the fan coils sysems , I have a vitola running 2 unico systems and raadiant floor inbasement with domestic with indirect and another one with a vito gas 100 and 79 gal indirect with 2 solar panels as a complment that were in the midddle of installing now

jerry scharf_3

heat loss doesn't sound right

Dave,

I've been saying this alot recently. A 6000 sqft well insulated house should not be using 30 BTUs/sqft in CT. I would expect more like 15-20. So it's time to do the heat loss calc again. Don't round anything up, just run the numbers and get room by room loss.

As for using a condensing boiler vs a atmospheric with gas, you're talking someting like 80% vs 90% efficiency. So it still saves money. Someone also posted about a noncondensing gas boiler that had 86% efficiency. Like people said, make sure that the boiler can deliver the design water temps.

Another thing, check/improve the insulation and pressure test for leaks in the air ducts. Poorly installed systems can lose a whole lot of heat this way.

good luck

jerry

Jed_2

Ragu

What do the HWC curves tell you? You can put out some serious btu's with 167ºF HWS temp, appropriate GPM, and CFM volume with the right sized AHU. Volume is important.

Jed

Dave_61

So, say I get the Buderus GB 142 or Vitodens and find that we need to run it at higher temps. Will we still get big savings if we are only running one zone (say 80,000 BTU on a 200,000 BTU boiler) by modulating the flame?
In other words, even if we're not condensing so we're running the boiler at high temp, will it decrease the flame so only 80,000 BTU is used on the one zone?
Thanks.
Dave

Mike T., Swampeast MO

In other words, even if we're not condensing so we're running the boiler at high temp, will it decrease the flame so only 80,000 BTU is used on the one zone?

Yes. That's the entire point of modulation. As Jerry mentioned however, your heat loss does seem quite high for a well-constructed and insulated modern home. Does it have an extremely irregular footprint with LOTS of glass?

Dave_76

I sent for the Slant Fin Heat Loss calc CD, so I will be doing my own calcs. I also had someone come last week and take measurements to do their own.
I never saw the original calcs that the first contractor supposedly did before the house was built in 2000. That was before I knew anything about this subject.
Say that the heat loss calcs show a total loss of 120,000 BTU on a design day.
If I understand correctly, I can get say a 150,000 BTU boiler and then even if we run the boiler temp at 180 degrees on the colder days, the burner can "turn itself down" to say 70,000 BTU if just the first floor air handler needs to run at 180 degrees, and then increase the burner strength to say 120,000 BTU if the second floor also calls?
I spoke with a Buderus rep yesterday, and he thought we'd be better served by their GA244 cast iron boiler (over the GB142) since we have hydroair, so I'm confused.
dave

Mike T., Swampeast MO

I presume you currently have a boiler? If so, why are you replacing after only 5 years?

Dave_76

We have a 5 year old low mass copper tube Lochinvar 300,000 BTU boiler (yes that's 300,000 BTU's)!. It has been nothing but a hassle, and I don't want to even consider doing anymore work trying to get it to work properly (buffer tanks, etc).
So, would the modulation on either a Vitodens or GB142 allow bringing the output of the boiler down to say 50,000 BTU if only one zone were calling, even if the boiler temp is way above the normal condensing range (say keeping it around 170-180 degrees) for the hydroair?
Or would I be better served with a cast iron one like the GA244?

S Ebels

Answers for Dave

As to whether a Vito will work on Hydro-air, read the post now on the Wall titled Vitodens power. It was posted last March and Steamhead was kind enough to put it back up here. Sounds like nearly the same situation that you have.

Mike T., Swampeast MO

Was actually thinking of suggesting a properly sized, staged fire low-mass copper tube boiler!

Vitodens for certain (and I suspect nearly any) modulating boiler strives to exactly meet the current load. The "Viessmann way" of primary/secondary (the low-loss header) ensures that this is achievable.

Their 11-44 model has an output range of 49,000 - 153,000 btu; the 15-60 range is 71,000 - 205,000 btu.

I'm honestly not comfortable saying which boiler (or even which type) would be best for your application. I love my own Vitodens, but it's connected to a fully proportional system with quite low temperature requirement.