Best settings for Vitotrol and a prog. thermostat?

sunlight33

Hi everyone, I have a Viessmann Vitodens 200 boiler with baseboard heating. A Vitotrol 300 is installed on one level of the house (one heating zone), there is also a programming thermostat a couple of feet away from the Vitotrol. This is how the system works: the Vitotrol controls the pump on the primary loop, and the thermostat controls the pump on the secondary loop. The issue is that if the Vitotrol is on but the thermostat is off, the primary pump would circulate water within the primary loop that's not going anywhere, which would cause boiler to short cycle. If the Vitotrol is off but the thermostat is on, it would just have lukewarm water circulating in the baseboards and not doing much in terms of heating up the zone, but it has no negative effect on the boiler itself. One interesting thing I noticed with the Vitotrol 300 is that it only displays room temperature by every 2 degrees (66, 68, etc.), I am not sure if the internal mechanism can recognize a difference of one degree, I am sure it can. Another thing is that the room temperature displayed on the thermostat is usually 2 degrees higher than that on the Vitotrol. How would you suggest me to set these two to achieve the highest heating efficiency?

CMadatMe

You don't even need the thermostat. The Vitotrol can control the secondary/zone pump as long as that pump is wired to the 28/20 Programmable pump output.

Change Coding 2 General Address 51:0 to 51:1 so primary/boiler pump starts with burner.

In Coding 2 Heating Circuit 1 Change Coding address B0:0 to B0:3 B5:0 to B5:5. Pump will be turned off when Vitotrol reaches setpoint.

Vitotrol is programmable like a stat.

As far as overshooting, sounds like you need a shift change not a curve change. Change shift to -3 run for a while and see if that helps.

sunlight33

Thank you for your suggestions.

Regarding B2 in Coding 2, what exactly is "Room influencing factor"? The default is 8. This is somewhat unrelated to your comments but I am just curious as to how it would affect the heating.

I will take a look at the rest when I get home tonight. Cheers!

sunlight33

I went through the coding level 2 list and have a question about address 90, which is the time constant for calculating the adjusted outdoor temperature. The default is 128, which is equal to 1280 minutes (21.3 hours), does it mean the boiler takes 21.3 hours to adjust its supply temperature to a change of outdoor temperature? Seems totally absurb to me, I figure there has to be something wrong with my thinking.
I am clear on every other settings besides B2 (I figured out B5, the manual made a typo, ON means OFF) as I mentioned in the last post. I am still unclear on those two.
Thanks!

CMadatMe

No. Doesn't take that long to adjust supply. Time constant means it's going to adjust the low loss header temp every 10 minutes to match the requirement of the reset curve.

128x10 = 1280/60 = 21.3 hrs. You can change that to a 24 hour clock if you wanted. 24x60/10 = 144 So 90:144

Coding 51:0 change to 51:1 will only allow the boiler pump to start when the burner fires instead of running 24/7 until you hit warm weather shut down, ie Set Point.

Leave the room influence factor alone. Change the shift not the curve to that -3 and you should grab that 2 degree difference you spoke about.

Have to remember across the pond, this boiler runs on constant circulation so get that shift right and that zone pump should rarely shut off. Goal is too put a btu into the room as a btu is leaving the room.

sunlight33

Gotcha! So the time constant of 21.3 hrs means the boiler does the adjustment 21.3 hrs over a 24-hr day.
Right now I set the thermostat of this zone a few degrees higher to force a constant circulation, then have the burner on/off controlled by the Vitotrol, I guess it doesn't get any better than an ODR + indoor temp feedback!

CMadatMe

Basically boiler supply temp sensor (LLH sensor) only adjusts water temp between 9:30pm-Midnight based on that 9:30pm reading. Remember at 10:30pm boiler is looking at the "reduced room temp setpoint" not room temp setpoint. Vitotrol will shut down burner cycle but not the boiler pump unless you change 51:0 to 51:1. Trick is to recycle system side return water temp, not both boiler side and system side. If you do that then you don't have to program for the 28/20 and just let it fly.

That's why changing 51:0 to 51:1 and using a Grundfos Alpha for a system pump is the bomb. Just recycle that system side return water. Be surprise how much you cut down on burner hours over the course of a heating season.

Vitotrols aren't used by contractors as much as they should be. They make a similar control "Comfortrol" for the Vitodens 100 and I've only had one guy that uses them consistently.

sunlight33

Got an issue here. After making the changes in coding 2 I noticed that the burner would now turn on then off after a minute or two and run at significantly higher temp than before. I set heating curve to 1.2 and the outside temp is 39F. Based on the graph this should produce ~110F water, but the boiler temperature now ramps up to 145-160F, then the burner shuts down a minute later. I remember the temperature had been much lower when it was running based on ODR. What could have freaked it out?

Edit: On one occasion, I turned off the thermostat, then a few minutes later the burner kicked in, ramped to 160F, then shut off a minute later, while the room temperature had been stable all along, weird. I will keep a close eye on its behavior.

CMadatMe

You have a low loss header sensor!!!! Boiler not looking at what it's making looking at the temp inside the LLH. What's the common supply temp?

Boiler pump should also be on Speed 3 if a Grundy 15-58. If not, reason why you are spiking.

sunlight33

Common supply temp is 120-124.

Paul Pollets

Yes, the pump speed to the LLH needs to be set at "3"!!!

CMadatMe

Max flow rate across the HX is 6.2gpm - Boiler pump exceeds that at settings 1 or 2. At speed 3 5.7gpm across HX. You're working with a 40 boiler side delta-t (Rise). BH2HA35 is 114,000 Btu/hr output same as the WB2B-35.

5.7 x (40 x500) = 114,000 Btu/hr output

Can't get the full load otherwise.

You'll also spike due to not pulling out the 5.7GPM on the boiler side out to the system side. If the system side is only taking 2 gpm or 20,000 Btu/hr as an example that means 3.7gpm of boiler side water is flying up the boiler return.

sunlight33

I read the graph again, yes speed 3 can give a delta close to 40. Does this mean the DHW pump should also be set to 3?

CMadatMe

No. Because you have to calculate the pressure drop (head loss) of the indirect into the equation. At speed 3 you're sitting at 5.7gpm overcoming approx 14' of head in the HX which maxes out the pump. Pump curve is on Page 62. What's the brand and model of the indirect? What is the boiler supply and return temps entering and leaving the indirect?

https://us.grundfos.com/content/dam/GPU/Products/up10/98532861_0614_UP Series_DB_US_Internet.pdf

sunlight33

It's a Vitocell 100-V

CMadatMe

How many gallons? a CVA45, CVA53,CVA79?

sunlight33

53

CMadatMe

Pressure drop across the tank is nothing so I'd leave it on speed 3 as well.

sunlight33

Thank you so much! I had both at speed 1, now changed to speed 3!

sunlight33

Chris said:

Max flow rate across the HX is 6.2gpm - Boiler pump exceeds that at settings 1 or 2. At speed 3 5.7gpm across HX. You're working with a 40 boiler side delta-t (Rise). BH2HA35 is 114,000 Btu/hr output same as the WB2B-35.

5.7 x (40 x500) = 114,000 Btu/hr output

Suppose the heat loss of my house is around 50,000 Btu/hr, this means a flow of 2.5 gpm would satisfy the 40 delta-t, right? So in this case speed 1 would be sufficient, am I right? In other words is the 5.7 gpm aimed at the high end of the modulation?

Second question: should 9F in coding 2 be left in default or can tweaking squeeze more efficiency?

GW

Chris, for a while I've been trying to understand the 40 degree temp rise. Everytime I attempt to ask the question I get what seems to be a nun around answer, I just want to know if I'm nuts or maybe i can't do basic math.

If you have a traditional usa high temp hw sysyem, the typical temp at the return is generally 20 degrees less, gosh I hope no one will argue that one.

So on the coldest day of the year, we need 180, amd there's 160 coming back. Now my confusion lies with the 40 degree drop in the boiler and/or llh. How does that make sense from a math standpoint? How can the boiler be returning colder water than the sysyem is returning?

Of course if there's some lower temp stuff going on, I am no longer confused with the math.

Thanks, Gary

sunlight33

I am guessing because the boiler supply temp and system supply temp are not going to be same? Once the LLH is in place you essentially have two separate systems. If you want the system to run at 160F, then the boiler would supply 180F to meet the 20 degree drop in the system and end up with 140F return, thus 40 delta T.

GW

That's the only math that makes sense, running the boiler 20f higher than the systems temp. Who would do that though?

Still don't understand

sunlight33

Because the boiler (use Viessmann as an example) does not see the system side, it only knows how much heat it needs to deliver to LLH based on the outside temperature. It doesn't care how the system is taking all the heat away. I think this design principle is what makes the boiler side and system side temperature different (like you said, otherwise the math would not work out). Please correct me if I wrong.

GW

I agree with the theory but I don't know how it's possible to fully heat a system that's designed to unload 20 degrees (I'm speaking retrofit here, old school boiler replacement). If you require 180 on a cold day and you send back 160, I'm still confused this works unless you crank up the boiler's supply temp 40 degrees above the systems return temp.

If you have the Vitotrol that's scoping room temp, should the boiler be Modulating to keep the Vitotrol happy?

The LLH is just a bigger brother to the close space tee, there's no magic. I use them on occasion but more often use a simpler 2" x 1" Alberta tee.

Still searching for the answer

sunlight33

Unlike a regular boiler, a Vitodens has no thermostat, it simply looks at the ODR sensor to determine the water temperature at LLH, then it will heat up the boiler water to whatever temperature necessary to achieve the proper temperature at LLH. By monitoring the temperature change at LLH (and a few other parameters) the boiler will modulate accordingly. But it has no knowledge of the room temperature.

So this is when Vitotrol comes in, it provides a room temperature feedback, so the boiler has an even better picture of when to start and when to stop.

As for the 40 delta T, where is Chris when we need him?

GW

Hatterasguy I admit I forgot about that discussion. I'm just a stubborn man, refusing to buy stuff I don't need. If I could understand why I need it, then I buy it. I get sideways when I'm told I must buy something I don't need.

Sunlight, I've installed 125 vitodens boilers, I know the basics.

Anyway, did you remove that thermostat or did you remove the Vitotrol?

sunlight33

Neither, I just set the thermostat a couple of degrees higher to force a constant circulation. I could have configured the Vitotrol to let it control the zone valve but I figure this is simpler.

GW said:

Sunlight, I've installed 125 vitodens boilers, I know the basics.

Absolutely, that's 125 more vitodens than what I have installed.

CMadatMe

Was away all weekend but will post a reply this evening. Reverse the math around of system side flow rate greater then boiler side to find boiler temp required. Remember this is for 114,000 btu/hr in the case of a B2HB35. Use 140 as your design day water temp. You'll find the boiler side return water temp because at design day your are exhausting the full 5.7gpm fixed boiler flow rate into the secondary side which would need to be 11.4 gpm. (11.4 x 10,000 = 114,000 bth/hr) Without doing the math here you should see something like this. Boiler supply 160 - (LLH)System Side Supply 140 - System side return 120. 160-120 = 40 Rise.

5.7 x (40 x 500) = 114,000

Now how often do you think this happens? Prob never, slim to none. Because Vitodens 200 requires the use of a LLH sensor the boiler is looking to satisfy the system heating curve not the boiler itself so to speak. So while yes the boiler return side can never be lower then the system return side, the boiler supply side can be higher then the system supply. That's how you get the increased rise and thus the reason why Viessmann sizes boiler pumps for lower flow rates then most others.

sunlight33

Chris: After making the coding 2 changes you recommended, the number of cycles dropped from 70 to 40. Great! I am guessing to bring it down further would require something more than programming, right?

Paul Pollets

GW, remember the Vitodens will only achieve a 167 degree max temperature, not 180. Usually it will never climb to 167 unless recovering the indirect tank.

GW

Paul, the wb2b went hotter than that, the wb1b had a lower high limit you mention. I just got by with the skin of my teeth only once on a job where I needed more temp (true, most jobs don't need the full 180, but when you need it, you need it). The B2HA only goes to 167?

Once my local vendor starts to stock parts I'll start installing them again. They bang me on shipping and a higher cost, so i get double wammied for them not sticking much stuff. Doesn't seem right.

CMadatMe

What parts? An electrode, ionization rod, maybe an outdoor sensor. Those combined cost less then 2 Zones valves. If you're an installer I would take it you'd have those on your shelf or at the min include them in the install and leave them there.

The biggest issue I have with stocking Viessmann Blowers, Gas Valves, Controls/electronics is that they sit there and collect dust. In case of an emergency would rather pull them off a boiler then hand a customer a part that's been sitting around for a year.

CMadatMe

sunlight33 said:

Chris: After making the coding 2 changes you recommended, the number of cycles dropped from 70 to 40. Great! I am guessing to bring it down further would require something more than programming, right?

Yea, a buffer tank.

sunlight33

I was on the phone with a Viessmann technician regarding the address 90 and B2, and this is what he said:
90: The duration which the boiler uses to calculate the supply water temperature. With the default of 21.3 hours, the boiler looks at the average temperature in the past 21.3 hours to calculate the supply water temperature.
This would probably not work in my town where sometimes the high and low of the day can differ by over 30 degrees. I'll have to change it to a less value, something like 36 so the boiler can adjust more readily to falling temperature at evening.

B2: This number refers to the tightness of the room, the tigher the room (less air infiltration) the lower the number should be set, but there was no explanatin to what the number actually means, like how it is related to ACH of the house, if there is any relationship at all.

Update: I found an article on the room influence factor (last page): http://www.kwe-tech.com/files/vitotalk/VitotalkIssue1.pdf

GW

Chris said:

What parts?

What parts??? gee wiz, I've replaced much more than what you indicated. Yes i do have parts on my shelf. I'd have slightly less $ tied up if the local supplier (who sells the boilers) actually stocked parts for the boilers they sell. Or, is it your assertion the vendor shouldn't stock stuff?

sunlight33

It's 13F outside, here are the water temps I measured:
LLH boiler supply: 153, return 140
LLH system supply: 149, return 140
I actually have both the boiler and system pumps on speed 1, is there a way to get more delta T to drop the return temp to 130 or lower?

GW

sunlight33 said:

It's 13F outside, here are the water temps I measured:
LLH boiler supply: 153, return 140
LLH system supply: 149, return 140
I actually have both the boiler and system pumps on speed 1, is there a way to get more delta T to drop the return temp to 130 or lower?

was the boiler running? it's hard to get steady numbers unless the boiler is purring. more pump equals less drop (delta t). it was mentioned earlier you should be at 3 for the boiler. You must be in good shape if your able to heat with speed 1 when it's 13 out. your system seems good with speed 1, very nice.

what model vitodens do you have? I didn't see the size or model indicated in your earlier posts.

sunlight33

it's a 200 Wb2b-35, I took those measurements while the burner was on.
I just measured those temperatures again, I am getting 157-159 on the supply side and 147 on the return side, again while the burner was on and this lasted for about less than 10 minutes, then the boiler shuts off for 15-20 minutes. It cycles about twice per hour. The heating curve was set at 1.2, no shift, and OT is 12F. The supply temp should be around 140 according to the manual. Not sure what's making it overshoot to high 150s.

Update: Changed curve to 1.0, now supply is 148, return is 137.

Paul Pollets

Turn the boiler pump up to speed 3. It will make a huge difference.

sunlight33

Wouldn't speed 3 make delta T even smaller? The small delta T with speed 1 indicates that the boiler is over-producing heat.