Survey of Vitodens 200 heating curve settings?

Simply Rad_2

Andrew
I might have you beat....just barely. Design temp -20 supply temp 98 degrees heating curve .5 indoor temp a balmy 72. The system have 4" poured concrete floors so it is an outstanding candidate for radiant. I do have one other system with a design supply temp of 96 degrees. FOr the most part I am running the systems at a .7 curve with a 110 degree supply@-20 design temp. That's using Warmboard and slab.
Jeffrey

Dave_4

heating curve settings

I was wondering if anyone has a survey of what heating curve settings worked for them or their customers?

The sweet spot for my house was slope of 0.9 with a +2 offset. This keeps the house (mostly oversized CI rads) at 72F so far up to 5F weather. I assume even though the supplied diagram ends at -4F that the curve continues down to -40F?

With the setting I don't think I'll ever hit 140F supply which means I'm always going to be well into the condensing zone.

Unknown

curve

on my own vito w/panel rads i'm at 1.1 with a +2 shift. i designed the system for 140 deg. F but the basement is unfinished & uninsulated (soon to change) so the design temp is a little more than 140. still, 80% of the year it's in condensing mode.

one i just finished for a customer is at 0.6 with a 0 shift so far! in-slab radiant all 3 floors, they're still doing finishing work in the house but the indoor temp is at 69 deg F all the time.

ALH_4

curve

I think that's the lowest I have seen. 0.6 w/0° shift in Big Sky, MT, urethane spray foam, above floor Thermofin @ 6" oc. The owner tweaks the Vitodens curve via the internet. I witnessed it heating to 68°F indoor temp with 96°F supply water @ -24°F outdoor temp.

Steven Gronski

Curves

My house is set at 1.0 and it is baseboard heat and panal rads, set up on a constant circulation, My wife loves it, I think its to warm, but i like it cold anyway. I just finished a job in Charlestown, all radiant,set on a .8 and the customer thinks it is still to warm. This house is 2x6 construction with R-19 in the walls, R-38 in the floor that carrys an exposure to out door temp, R-13 in the ceiling of the first floor for second floor heat, and R-45 in the attic, sprayed on the roof and trusses its self. The whole house was sprayed with that close cell spray foam.

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Steve Gates_2

the lowest one I've got out there is .03/-4. Yep. They do however like a cool house.

Uni R_3

Translation?

How is the curve calculated? Is it range of water temp over range of outdoor temp?

Dave_4

its provided by Viessmann

I think the details of quadratic equation used by Viessmann are proprietary (as is everything else about the Vitodens) but Viessmann does provide a graph of the curves under different slope settings in the manual which I'm including below. Most try to approximate the first heating curve setting but afterwards its a matter of tweaking over time.

Ron Gillen

Haven't seen design this winter but.....

1700 sq. ft. walkout bungalow. Logix icf, r-50 ceilings, 2" foam under slab, -25F design, Edmonton, Alberta. Heating circuit A, main floor, Quiktrac, slope .2, shift -6, supply 95F, room 70F @-5F. Heating circuit B, basement, slope .2, shift -3,supply 75F, room 70F @-5F. Except when heating up the Vitocell have never seen it run above low fire which clocks at 22,800 Btuh. Hardly ever find it off when temps are below 14F.

Perry_3

Mine varies between 1.2 and 1.0

I have cast iron baseboard on a single loop monoflow T system, 1700 Sq Ft house, Mid 50's, some insulation, etc.... I also have a Low Loss Header installed with constant secondary circulation.

I have the RS sensor installed in addition to the outdoor temp sensor - and it feedsbacks houshold temp to the vitodens so that the curve can be shifted depending on the situation.

The outlet from the Low Loss Header Varies between the 1.0 and 1.2 curve depending on wind and sun. I once looked at what the boiler was running and noted that it was running at a 1.6 curve to meet a 1.2 curve outlet from the Low Loss Header.

Hope that helps.

Perry

Brad White_9

Perry, I suspect

that if you are running a 1.6 curve (practially a conventional boiler) to get a 1.2 radiation curve, then your radiation loop is being over-pumped. Too much system side flow and you get a wider T-Mix at the LLH outlet than you would want; the Vitodens then compensates.

What delta-T are you getting on your radiation loop? You might be able to get away with half the flow, just so long as it is not less than your boiler flow to prevent mixing and raising the boiler return.

Perry_3

I would agree that I am getting more pumpage than the past

I typically run a system drop of about 5 to 8 F, with a primary raise twice that. I have looked at the system several times and feel that the vitodens is running a primary flow of 1/2 of the secondary system.

I have a Taco 007 installed (which replaced a Series 100). The Taco 007 has the capability to pump more water at the head lose I beleive I was in.

A Taco 005 might work better for system temp drop; but I'd have to buy it and pay to have it installed (unless I install it myself). Is the new system going to perform that much better (from a money standpoint) to justify the change?

For now, I'm just watching.

Perry

ALH_4

pumps

Too bad it wasn't a 3-speed UP 15-58. Incidentally, the pumps are interchangable dimensionally. Rotometers on the primary and secondary and thermometers on the supply and return are always fun.

Perry_3

I requested that from the heating contractor... but...

He was not interested in installing it. Too expensive down the road.... He dosn't stock or like to deal with that company as their parts are too expensive...

He thought the Taco 007 would be the best match, and indicated that he carries Taco 007's on the trucks should anything go wrong with it.

Someday I may put in a 005; but not now.

Perry

Brad White_9

I agree with Andrew

A Grundfos 15-58 on low speed does my Susan's house to perfection, running about 4.5 GPM. Still I get about an 8-10 degree delta-T most times I have checked. I have reduced the flow by throttling the balancing valve but as it is, it works so I left it at 4.5 GPM, a theoretical 20 degree drop for a 46 MBH heat loss. When it gets colder that may be seen yet. The next day or two will tell me plenty.

The money you speak of saving by motor savings (if that is the case you are thinking of), pales before what you are spending on gas by running the Vito at an artificial 1.6 curve just because you are mixing down water.

Sure, you are just watching- but paying too.

Perry_3

Brad - I'm not so sure about that

"The money you speak of saving by motor savings (if that is the case you are thinking of), pales before what you are spending on gas by running the Vito at an artificial 1.6 curve just because you are mixing down water.

Sure, you are just watching- but paying too."

Break -------

I'm not so sure that there is that much money involved.

The boiler is operating at least most of the time - if not all of the time in the condensing mode. The vast majority of the time the boiler outlet is 110 F or less.

If my seconday pumpage was less - I'm not so sure that my boiler outlet temperature would change much - or the exhaust gas outlet would change much.

I've already got about 45% reducting in fuel usage, while there might be another percent or two there... I'm not sure that is such a large number compared to the cost of buying and paying for the installation of another pump (if my new gas bill averages $900 per year, 2% savings would be $18 per year).

Tell you what, though. We'll see if we can squeeze it into say the summer service call on the boiler when they will alrady be here; and then I can compare next winter to this one.

Perry

ALH_4

savings

As Brad mentioned, you might try throttling the system pump until your system supply matches your boiler supply temp and see how low the heating curve can go. That way it doesn't cost you anything to lower your heating curve. If it doesnt make any difference, you can just open the valve again. No harm done.

Mike T., Swampeast MO

0.6 ratio with +7°C shift gives a very comfortable 66°F max room temp (TRVs on standing iron rads). 103 year-old home with a hyper-abundance of original windows and glazed doors to the outside.

mac

Rads at 0.7 and the radiant floor at..

0.5. Initially set a huge 8*C negative shift w/sundial at 65*, but now I just keep 2* neg shift and the sundial at 54*F and the house is a wonderfully comfortable 66*F. I've really had a ball screwing this control all over the place. Bottom line, the house needs like 45,000 btu at design, so anything milder than 30*F, the Vitodens is too big, even on low fire...All constant circ, rads have TRV's, but right now their all wide open.

Both wife and I like it a touch cool 66-68* For us 70*F is smokin hot..

Small home 1200 sq.ft, foamed walls, 5.5 Stars on Energy Star Home scale. Blower door said house tight as a drum. We have all casements, so anytime outdoor temp above 30*F, we crack a few windows cuz we can.

Sorry for the ramble..!!

Perry_3

Savings.... What savings?

That 1.6 was a one time spot check. With the RS controller I am sure that it changes at will.

I have never seen the boiler outlet temperature reach 150 F. I have seen it reach the low 140's on the coldest weather with windy days. It is obvious that if the boiler was fixed on the 1.6 curve that it would have exceeded 160 F during our coldest weather.

Most of the time the boiler outlet temperature is about 5 to 7 F higher than the system temperature. That is not the worst match - and anyone with a LLH with a secondary system that pumps more water than the primary system is going to have the same situation.

I note that I don't have throttle valves - or flowmeters installed.

I do have isolation ball valves installed; but I also know that they can degrade if throttled. The cost of draining down the system and replacing leaking isolation valves far exceeds any energy savings that I could concieve of because my boiler oultet is a few degrees higher than my system temp.

Throttling the valve also raises system head and increases pumping cost.

I know some would say that is only a dollar or so in the year... So lets look at the potential gain.

The potential offsetting savings would be by recovering more heat by cooling the condensate a few more degrees (when possible). So if I range from 1 to 5 gallons of condensate a day, - and using the 5 gallons @ 8.5 lb per gallon you get 42.5 Lb of water a day. I am ignoring the potential energy gains from cooling the exhaust gases as they will be on the order of 10 times less than what you can get from the water.

Let us assume that I match my my secondary system flow to my primary system flow so that essentially all system water is flowing through the boiler. This will provide a system drop temperature about twice what I have now. 20 - 30 F (with the 30 F comming on the coldest - windiest day); this compares to my current 10 - 15 F drop (with the 15 F drop on the coldest - windiest day). However, most of the time it is at the lower range so I use a 20 F system drop for cutting my system flow in half.

That would potentially lower my condensate temperature by another 10 F because the boiler inlet water would now be 10 F cooler.

The most potential energy savings is thus 425 BTU (42.5 Lb times 10 F) per day. Over a 200 day heating season this would be a maximum possible savings of about 8,5000 Btu's.

Now on most of those days - you will not be getting 5 gallons of condensate. A better esimate might be half of that over the 200 days (say 4,250 Btu).

Anyway. 1 Therm of natural gas is 100,000 Btu's and cost me about $1.25.

So, I'm susposed to spend a couple hundred - or chance damaging my isolation valves to save much much less than a dollar a year (8,500 Btu ought to cost about a 10 Cents)? Are you sure I won't spend more than that by incresing pumping cost when I throttle the system to reduce flow?

There is no actual energy loss by mixing down the boiler outlet temperature in the LLH. An increase in entropy - but no energy loss. The gazins = the gozouts.

In the end it is great to talk about how in theory you should do everything reasonable to reduce your fuel usage. And I did that. I installed a highly efficient Vitodens boiler - that rarely (if ever) gets off of idle at my house. The thing lives in condensing mode, and I would be very surprised to find that it ever reaches a non-condensing mode situation - and it autoajust the heating curve to account for wind loses and solar gain where needed.

But at some point theory needs to be checked against what is practical and cost effective.

Once you condense the exhaust in a proper mod-con boiler... there are only slight to modest gains by using colder temperatures. Not saying that using colder temperauteres does not have advantages. Just that if you are at other temperatures then you need to check carefully to see if any improvments is actually worth doing.

I don't see the value in spending a couple hundred dollars for a new pump or more to try to get my boiler to notch down a heating curve - so that I might save perhaps a few dollars - or less. Nor do I see the value in spending my time and potentially damaging my installed isolation valves for gains that might be measured in a few pennies (and might be negative due to increased pumping cost).

Now if my math is wrong - show me a better analysis of the situation.

Perry

Uni R_3

Brad, don't forget...

Monoflo's need a minimum velocity. If Perry slows down his flow, his heat at some point will become unpredictable and erratic. For my monoflo-fintube system that is speed 1 on a 15-58.

Personally, I don't think there are any tangible savings by slowing down the flow of the heating circuit from the current 007.

ALH_4

what savings

Forgive me for not knowing the intricacies of your system, Perry. I did not know you had the RS installed. A little experimentation was all that I suggested. It takes far more than a few days of the sort of velocity a 007 is capable of producing to damage your isolation valve. You mentioned your boiler was at 1.6 to meet a 1.2, this could easily be 20°F difference in supply temperature at design. You dont know where it might run until you try. Shift is one thing, slope is another.

Dave_4

what benefit is the RS?

Perry, is the reason that you have an RS sensor because of the monoflow system? I have two pipe system with LLH and it seems the RS would just complicate the controls needlessly.

I used to have a Grundfos UP15-42F which I felt was overpumping the system since the boiler temp needed to be 2 to 3 degrees C above the target in the LLH. When the pump died I had it replaced with the 15-58F 3 speed and found the medium speed closely matches the flow from the primary circuit of the Vitodens. Not sure what the efficency difference is but the hum from the water moving through the rads is now much softer. The problem I see with a high flow is with the delta tee. As you increase the flow, the difference between the supply and return gets lower so to get the same radiation out of your emitters you need to have your supply water at a higher temp and your return temp will also be higher. The effiency diagrams of the vitodens show that the boiler is more efficient with lower return temperatures.

Perry_3

The RS Sensor...

Acts like a house thermostate.... Kinda.

In the classic "best case" setup of a Vitodens you would use TRV's on the radiators to individually control room temperature. Then the Vitodens curve would be set so that it supplied water just high enough so that the TRV's could keep each room just warm enough... In reality - this means that the circulating water temperature is just a tad high for some of the house - but it does work very very well; and I will conceed that it is the most efficient use of a Vitodens where you have radiators.

However, not all raiators and systems can be so easily converted to TRV's. In my case with cast iron baseboard I would have to remove the end cover on all of my radiators to install the TRV's (and the covers would not go back on). This would not look the best.

Also, in a case of a monflo T system - the monoflo loop depends on water flowing through most if not all of the radiators (it is the lowest pressure route). Installing TRV's that could throttle down a lot at times may make heating other parts of the house more difficult.

Finally, my house is not nearly as wind tight as many - and will not be easily or cheaply improved a lot more. Also, I can have considerable solar gain on certain days. So I needed a way to feedback the actual house temperature to the boiler. Just like the old thermostate system.

The RS sensor does that - and it works well on my kind of system. The house is rather open for air movement so one well placed in the house works well.

Instead of outright turing the boiler off and on which is what the classic thermostate does; the RS sensor first shifts which curve the Vitodens is on, up or down, depending on the house needs. That way the boiler is always operating on a highly efficient curve - and the house temperature stays rock steady. All without modifying the existing monoflo T system or retrofitting TRV's onto the baseboard radiators.

It is my understanding that the RS sensor is not the best choice for a radiant floor; and obviously this system would not work well where you had several clearly different heating zones.

Of course for the Vitodens purest the RS controller is heresy... I have had more than one person tell me that I just had to retrofit TRV's - regardless of the looks issue (or cost) on all of my radiators (not to mention the risk of piping issues and having to tear into walls to fix piping that did not cooperate on comming apart). No matter, some have said, even if I had to tear into all the walls and ceiings to fix piping that did not want to come apart cleanly, even if I spilled black water all over my floors, even if they looked "bad" -- I just had to install TRV's to reach "optimal" efficiency with the Vitodens.

I guess I'm not that much of a purest...

In many cases the RS controller can be installed where the old house thermostate was and operate well when a boiler is replaced as a very practical solution to "how do you control the house temp" question. Be sure to run all new wire.

While I agree that the boiler is more efficient when the water temperature gets lower. You also need sufficient water temperature to heat the house. In my case my house was designed for 140 F water; and the heat loss study I did modeled my existing radiation as adequate and not that excessive at 140 F water for the "desing day" (-15 F).

However, on most days when the outdoor temperature is above say 25 F the heating water runs 110 F or below (and as it gets warmer I have seen heating water at 95 F). So the system works. My observations are that depending on outdoor temperature, wind, and solar gain that the Vitodens with the RS sensor shifts the secondary circuit between curves 1.0 and 1.2. That is actually what you would expect given the type of system installed.

So I am getting the efficiency. Now because of the LLH and differences in primary & secondary flow - the boiler actually runs on a higher curve as it must. But I have believe the highest I have ever seen the boiler output was at 143F Still fairly efficient.

Hope that answers the question.

Perry

Dave_4

Just want to say that you don't need TRVs to make use of the heating curve on the Vitodens. I don't have a single TRV on any of my 16 CI rads heated by the Vitodens and the system works really well controlled by the outdoor reset. Of course the EDR in each room happens to be balanced and even if a rad is slightly bigger than needed there's usually a valve that you can manually adjust to restrict flow if needed.

I don't have much experience with baseboard radiation but it would seem hard to balance as the runs along the walls are not always proportional to the heat loss and the water in the early part of the loop would be a lot hotter than at the end causing further imbalance.