Whole home viessmann boiler

Mn1985

mattmia2 said:

Looking at the manual it could be controlled with a 0-10 v signal on what they call the "open therm" terminal from a building management system.

On the 100-W b1he? 

mattmia2

You could potentially make the air handler and the DHW make a DHW call and set that to a fixed higher temp and set a reset curve for the DH call for the radiant but I would push them to provide something closer to what they bid and refund the difference.

GGross

The DHW circuit is separated from the space heating circuit via a diverting valve inside the boiler. While you can get tricky with that it is not advised. I would push them to provide something closer to what you were quoted. The CU3A that was quoted would do what you want it to, and the 200 series would as well. I agree @Mn1985 that if the floor heat will be running the most you want the boiler to make that low temperature the majority of the time.

mattmia2

GGross said:

The DHW circuit is separated from the space heating circuit via a diverting valve inside the boiler. While you can get tricky with that it is not advised. I would push them to provide something closer to what you were quoted. The CU3A that was quoted would do what you want it to, and the 200 series would as well. I agree @Mn1985 that if the floor heat will be running the most you want the boiler to make that low temperature the majority of the time.

oh, so you must do dhw priority, you can't set it up however your system needs to be?

GGross

You could set it up to not use the separate tappings for DHW, but it's nice to keep that high temp separate from your low temp circuits if possible so I like to use the separate tappings. I see where you are going with this though, that you maybe could set the tank up as a zone, and if either the air handler or DHW calls the boiler would make high temp. It might work but I would not recommend it, because we are kind of fooling the control. One other quirk to point out, Viessmann uses a DHW tank sensor, and that helps the boiler fire as low as it needs to for DHW, if you just hook an aquastat to it, the boiler will fire at 194 F. We have actually used these for sanitizing lines at a dairy operation due to that extremely high temp. This is a feature I believe is only found in the current series boilers.

Mn1985

I think i found a solution. swap to 200 b2he and add thermostatic mixing valves to the radiant zones. put the house radiant on zone relay since they will all be same curve and has 3 separate zones and allows odr and thermostat control, put the air handler on non- mixed zone with thermostat, and garage radiant on heating circuit.

Any thoughts on this setup?

Paul Pollets

are you exactly sure that the heatloss is identical on each zone? If it varies by more than 5-8 degrees, you should be using another mixing valve. And you'll get better performance using the Alpha 15-55 pumps, which can modulate to demand load. The DHWT can be a fixed rate pump, depending on tank size

Mn1985

Paul Pollets said:

are you exactly sure that the heatloss is identical on each zone? If it varies by more than 5-8 degrees, you should be using another mixing valve. And you'll get better performance using the Alpha 15-55 pumps, which can modulate to demand load. The DHWT can be a fixed rate pump, depending on tank size

no, how would I calculate heat loss for each radiant zone?

Paul Pollets

This leaves HC1 as the air handler, HC2 the mixing valve and the DHWT as the circuits after the Low Loss Header

Mn1985

Paul Pollets said:

This leaves HC1 as the air handler, HC2 the mixing valve and the DHWT as the circuits after the Low Loss Header

dhwt direct from internal diverter valve.

Paul Pollets

Each circuit would have its own curve and the DHWT the temperature setpoint. If the piping and wiring diagram is followed that Viessmann provides in the installation manual, it will work with high accuracy. There will be a sensor in the LLH, the mixing valve, the DHWT and outdoors

Paul Pollets

Advanced heat loss calcs use proprietary software designed for radiant applications. LoopCad works well (and has a cost). The slantFin software is really for baseboard, not a radiant floor zone

Mn1985

Update, boiler being switched to the 200 model and low loss header put in place. Thanks for everyone’s help in solving this 

Allislandradiant

Send photos of the finished job.

tim smith

Definitely a credit is in order for the downgrade of lesser boiler, no llh. Absolutely need of reset. I too if was doing viessmann would go the 200 not the 100 as Paul said, it has more capability. Bit sketchy not actually talking to you about contract change.
Good luck

Paul Pollets

The #100 is the economy model with no bells and whistles. It works best with 1 temperature. The #200 is designed for multiple circuit temperatures and has many features in the integral computer control

Mn1985

Still working on it. Should be finished tomorrow. Have not seen any mixing valves yet so should be interesting to see how they intend to have multiple temperatures if no mixing valves are added. 

Mn1985

Update. Looks like instead of using mixing valves they just put the air handler zone on priority over the radiant zones. Thoughts? 

Paul Pollets

The boiler can only make different temperatures if a mixing valve is installed and integrated to the boiler computer.

Mn1985

Here is the layout 

Paul Pollets

You're in Minnesota. You'll find any issues with the design and installation sooner, rather than later. Unfortunately, they occur on the colder days of the year. If the heating curve is set for the air handler, the radiant zones will be too warm. If the curve is set for the radiant floors, the airhandler will be too cool. The boiler only recognizes different heating circuits and their respective temperatures by using a mixing valve proprietary to the boiler computer. It will also do an Indirect DHW tank with sensor on priority.

Mn1985

Boiler does have different heating curves the for floor zones and air handler. Floor zones won’t run if air handler is calling for heat. 

Really thinking it should have computer controlled mixing valve on radiant but thinking maybe just a mixing valve on them to limit temp to radiant and not have air handler on priority 

mattmia2

Mn1985 said:

Really thinking it should have computer controlled mixing valve on radiant but thinking maybe just a mixing valve on them to limit temp to radiant and not have air handler on priority

That is how it has to be set up. The mixing valve has to limit the temp to the radiant zone. Turning the setpoint of the boiler down doesn't instantly make the water in the system a safe temp for the radiant. Priority won't work for the air handlers because both zones will be calling for long periods of time if the curve is set up right. Priority for dhw only works because dhw calls are short and infrequent.

GGross

I thought in the previous photos there was a manual style mixing valve installed? is that not there anymore? Forgive me it has been awhile and maybe this mixing valve serves another purpose. systems set up with a motorized valve are often ideal, I do like the manual style valves as an easier to deal with option if something were to break.

Mn1985

GGross said:

I thought in the previous photos there was a manual style mixing valve installed? is that not there anymore? Forgive me it has been awhile and maybe this mixing valve serves another purpose. systems set up with a motorized valve are often ideal, I do like the manual style valves as an easier to deal with option if something were to break.  Correct. That is for the garage radiant zone. They removed that and have not finished that portion yet. 

You made a good point of not running on priority because I’m afraid the radiant will never run. These are decisions of the contractor. 

hot_rod

You can do a proportional mix control with manual mix valved. Set the boiler up for the highest temperature load, on ODR

then set the manual  valves at design temperature, so their temperature floats along the odr curve at the mixed down temperature

Sn actuator could be added later if you want tighter control.

for actuators you just need to know what signal the boiler sends out, 0-10vds or PWM for example

one limitation is the mixed down circuits need to be a single zone, you could not add zone valves on the low temperature as it is a flow control mixing

it is an inexpensive way to get a 3 temperature system all on odr

GGross

As a bonus the boiler you have will accept up to three separate calls for heat, each with their own setpoint temp or ODR heating curve. The boiler will only be able to make the highest temp that is called for at any given time, but if you only have a call for low temp the boiler will only fire at the set temperature for that low temp call

heathead

Gross,

That is a great option I hadn't thought about. One could set it up with a two stage thermostat to make the boiler run the lowest curve most of the time, the low end of things and if it was too low the upper curve could take over to catchup in stage two. Or use one set for a vacation heating curve and one for a regular heating curve. That would save the most money by lowering the curve to match required load when it drops, when the house is not occupied for long periods of time.

Mn1985

I asked them about no mixing valves and this is what I was told. 

That boiler is a multi temp boiler.Air handler is set as priority with high temp.Floor zones are secondary at low temp.Nick from Viesmann set this up for us and all was working well when he left.

For garage zone,plate exchanger is here,manifold should be here any day.Does Thursday the 25th work for this week?

Thank you,

Paul Pollets

Let us know if you're able to get the system to respond at the right temps required without further modifications.

mattmia2

you might want to have a little private conversation with nick from viessman about if the boiler is installed as recommended

Paul Pollets

I'd be very surprised if this doesn't become a boondogle. I've worked on hundreds of Vitodens boilers and know that if manufacturer's design specs for near-boiler piping and controls are not followed for multi temp systems, problems can be expected. I hate to be a downer but something's wrong with this setup.

Mn1985

Paul Pollets said:

I'd be very surprised if this doesn't become a boondogle. I've worked on hundreds of Vitodens boilers and know that if manufacturer's design specs for near-boiler piping and controls are not followed for multi temp systems, problems can be expected. I hate to be a downer but something's wrong with this setup.

This is why I turned to this site to get additional recommendations. Waiting to hear the reps explanation.

every piece of literature from viessmann shows mixing valves when multi temps are used, even the tech seminar on the boiler explains it in detail. 

Allislandradiant

I be be late to the party, but how are you controlling the low temperature zones? Air temperature or slab temperature?

hot_rod

Call Viessmann tech support and ask for Bruce Faul or Pete the Heat. They are both long time contractors and reps in Colorado with V experience and they are tech support for Viessmann now.

As I understand the Lochinvar 3 temperature you can only do one temperature at a time. Unless you add mixing devices. I don't see how the Viessmann would differ.,

Mn1985

Allislandradiant said:

I be be late to the party, but how are you controlling the low temperature zones? Air temperature or slab temperature?

Air temp 

Mn1985

Here is local rep 

Not certain who recommended it, but it was the way I programmed & currently would be the most efficient way to operate the boiler as you are not producing hotter water and mixing down for your low temperature zones.  Radiant floor can be without heat for around 45min-1 hour without noticing a difference in temperature, typical AHU call last 6-8 min.

 

GGross

I'm sorry that rep is mistaken. The low temp zone in this case needs to have a mixing valve, it doesn't have to be a motorized mixing valve, but it must have a mixing valve (motorized is best). So it sounds like they are turning off the pump to the low temp zone while the high temp zone is calling? This is not the correct way to set up this system. This is either a case of the rep actually not understanding how this system should function, or they are afraid to tell the contractor to fix it.

How do they know the typical AHU call is 6-8 minutes when the system hasn't been started up yet?

dko

The rep sounds like he is under the impression the AHU and radiant are running at the same temperature.

Mn1985

Additional info from rep 

The AHU would have never shutoff would only be the way your RFH would get starved, typical AHU/Furnace run around 6-8 min then it will switch to your RFH should be a great system, this is how I program all our IBC Boilers too and have never had an issue.