Should I install an Outside Air Thermostat for Viessmann Vitodens 100 B1HE-199?

erickyung

I recently had a contractor replace my 45 yo boiler with Viessmann Vitodens 100 B1HE-199. He did not install OAT based on his previous customers' experience where the outside temperature is at the borderline comfy but still chilly like in Spring - I live in MA. The heating temperature is hot enough based on the heat curve.

Does anyone have a different experience? I would like the contract to install the OAT because I have more control of the heat curve with ViCare app.

My current experience with the constant temperature (180F) is that it tends to overshoot and cause A.19-50 warning. Does anyone know a setting to get the boiler modulate tighter so that it does not overshoot often? One time it overshot many times and locked with a fault code F.62-50.

Redbaran

The B1HE199 is a modulating condensing boiler. Heating curves are adjustable throughout their full range of boiler operating temperatures. You need design temperatures on the design day: the coldest day of the year. Was a heatloss done? An accurate heatloss considering the design day for your area would be key to setting an effective curve. Additionally, the heat emitters and "tightness" of the home will indicate how to set the curve. The F62 fault is interesting - that's locking out on the fixed high limit. The boiler's control logic is very good - A 199 is a lot of boiler; load matching is important - it will fire at approximately 55% modulation and then start adjusting - if you have small loads connected and can't unload a low mass boiler (2.5gallons) you can hit the fixed high limit rather quickly.
That being said - the heating curve is adjustable; and you can always re commission the boiler as fixed set point if you don't like the operation; but a modulating condensing boiler isn't well served by fixed set point operation.

erickyung

That's what I am thinking. B1HE-199 is good and efficient if it's used with OAT, and I can adjust the heat curve from ViCare app. Constant set point does appeal in a way that I don't need to muck around with temperature adjustments - pretty much like a traditional boiler.

@Redbaran You are absolutely right on the point that there is a dedicated small zone to the sunroom - it's adjacent to the living room that is right above the boiler. The sunroom is normally colder than the rest of the house but the boiler can definitely overwhelm it even at the minimum 10% modulation. What I did to reduce the chance of A.19-50 is program its thermostat to call for heat exactly the same time as the first floor zone which I believe to be the biggest zone. Finger-crossed, I have not seen A.19-50 since. Plan B if plan A did not get rid of A.19-50 would be to tie the sunroom's thermostat and the first floor's thermostat together so that either one can call for heat for both zones and they can maintain their own schedules. Both are programmable (not smart) thermostats. But I have not had to go there yet.

I have another question somewhat related to this topic. When I stay with constant set point, I can lower the set point to 160F or 170F to avoid A.19-50. I had it at 180F, that's when it got a series of A.19-50 then F62.50. With lower set point, the boiler will run longer on colder days like 3 or 4 hours for each heat call. Is it ok? Is it better for the boiler to start fewer times but each time run longer? I am just worrying about wear and tear of the internal fan and pumps.

Redbaran

Eric, what you did makes sense; you've increased the load on the boiler by timing the thermostats together; however it does take away from the advantages of independent zones. Lowering your fixed setpoint would give the boiler more time to unload before "stacking" (hitting the fixed high limit). You may find that you do not need 180 at all (depends on the heatloss analysis and how cold it actually gets this season)
Low mass boilers (low water content relative to Btu input) tend to cycle more than high mass (high water content boilers). One is not necessarily better than another; just different design philosophies. Longer run times are preferable: Short cycles are hard on boilers - starting and stopping fans and gas valves present the toughest conditions for the equipment (compare a car that typically runs on the interstate vs a city cab) Additionally on the heat exchange side; more cycles means more heat ups and cool downs over the lifespan of the equipment (think expansion/contraction cycles) Longer run cycles are preferred - Viessmann and many European manufacturer's have long been proponents of heating circuits (running the circulator once it gets below a defined outdoor temperature) and modulating individual thermostatic valves at every panel radiator (for example). I'm not a circulator expert; but I think the industry would agree that a circulator that runs for longer cycles will outlast one that is cycling on and off often. Additionally really short cycles can be tough on ideal combustion - the boiler will calibrate combustion but short bursts can be a challenge.

erickyung

Thank you for you insights! I will find any optimal setting to let it run longer. I've noticed the boiler fire up a dozen plus times throughout the day up to this point - normal?!

I've set the temperature set point at 160F since it hit a series of A.19-50, then the high limit F.62-50 last week when the temperature set point was at 180F. It's been running ok at 160F and the heat is comfortable given the outdoor temperature is around 30F to 50F. The next few days will be a test and see if it can raise the indoor temperature to 68F within 4-ish hours with the outdoor temperature around 20s to 30s and possibly high teens.

I may consider doing a heatloss next season.

Redbaran

Eric, thanks. It's difficult to define "normal" cycles; the easy answer is: "it depends". Heat Loss of the building changes as it gets colder out. Your system is zoned with DHW so there are a number of possible combinations of demands on the boilers from 1 to several. By lowering the operating temperature, you are more or less proving that an outdoor reset curve will work. Your process is essentially finding the correct boiler temperature for a given outdoor temperature. Going out on a limb here, I think your boiler is probably a bit oversized to the load; an accurate heatloss will tell the tale for sure. If you find that your boiler can heat the house at say 150 when it's 40 outside and you have to go to say 170 when it's 20 outside you have essentially found 2 points on a heating curve that will define an effective curve for your home. Don't get too hung up on how often the boiler is cycling. Just know that longer circulator run times with the lowest temperature water that will keep your house comfortable (comfortable is personal - we are all different) will reduce cycle compared to a high fixed setpoint whenever a themostat calls on the boiler.

erickyung

I contacted my contractor and he said he would send me the outside temperature sensor immediately. Hopefully it's already been on the way. With all carriers busy delivering holiday packages, I need to wait a bit longer for it to arrive.

So I have started reading the installation booklet for how to install the outside temperature sensor, which needs to be 2.5m above ground in north or northwest direction. It specifies 16awg wire with the maximum length of 35m. I guess I cannot use the normal thermostat wire which is 18awg. I believe I can meet those requirements without difficulties.

I have a few thoughts. Currently the boiler says outside temperature sensor is missing. If I install it and have a switch to turn it on/off (switch off the boiler first), it would be ok right? I am just thinking in case it does not work out well, I can turn it off and go back to what it is now. The other thought is if the outside temperature sensor goes bad, would it mess up anything? With a switch, I can isolate it from the system. Lastly, does it matter which wire go to which terminal on the boiler circuit board?

lanem2494

@erickyung I was in a very similar situation as you with my boiler and heating set up. Three years ago I converted to natural gas and my contractor installed a Vitodens 100W (B1HA) boiler with no outdoor reset temp sensor. He opted not to install the sensor based on his "experience" with them (looking back, I think he just didn't fully understand the concept of outdoor reset and its benefits). Anyways, fast forward three years, and after some thorough research of my own I finally installed a sensor myself to utilize the outdoor reset capabilities. I ended up using regular 18awg thermostat wire with no issues.

I've only been heating with outdoor reset for a little over a month, so I'll need some more time to determine the gas usage and monetary savings, but I can say that I've noticed that my house is much more comfortable with consistent heat when compared to how I was operating the system in the past with up and down temperature adjustments, nightly setbacks followed by overshoots, etc (however, I never had the boiler throw a fault code). I've been playing with the curve ever since utilizing outdoor reset, but I think I finally found the sweet spot of a 1.0 curve (I've also come to believe that my boiler is oversized for my house, but that's another story...) that has worked for the varying winter weather so far (I am also located in MA).

GGross

erickyung said:

I contacted my contractor and he said he would send me the outside temperature sensor immediately. Hopefully it's already been on the way. With all carriers busy delivering holiday packages, I need to wait a bit longer for it to arrive.

So I have started reading the installation booklet for how to install the outside temperature sensor, which needs to be 2.5m above ground in north or northwest direction. It specifies 16awg wire with the maximum length of 35m. I guess I cannot use the normal thermostat wire which is 18awg. I believe I can meet those requirements without difficulties.

I have a few thoughts. Currently the boiler says outside temperature sensor is missing. If I install it and have a switch to turn it on/off (switch off the boiler first), it would be ok right? I am just thinking in case it does not work out well, I can turn it off and go back to what it is now. The other thought is if the outside temperature sensor goes bad, would it mess up anything? With a switch, I can isolate it from the system. Lastly, does it matter which wire go to which terminal on the boiler circuit board?

1+2 terminals on the digital input terminals, from left to right there should be 6 terminals. it does not matter which terminal each wire goes to as long as it is 1+2




Once you plug in the sensor you may need to reprogram the boiler, but it sounds like they had it set up or ODR since you are getting an error. once you bring the boiler back online check to see if it lets you adjust the heating curve. If not you may need to go back through the commissioning assistant to set the sensor

If the boiler loses connection to the outdoor sensor it will give a soft non-lockout fault and the boiler should assume it is 32 and run in freeze protection mode until you either re-program it to a setpoint or replace the faulty sensor

erickyung

Thank you, @lanem2494 and @GGross!

My installer did commission the boiler with ODR but did not actually install the ODR. What I've been doing for the past 3 months is adjust the heat curve slope and level in ViCare app manually based on the outdoor temperature and eventually find the heat curve slope (0.8) and level (22) to be the sweet spot. 140F temperature setpoint lines up with 32F on that heat curve + level. That's the temperature my boiler has been operating at for the past month or more (even when the outdoor temperature drops to teen), and it's quite comfortable.


I have the ODR on hand but am waiting for a good day to install it so I don't have to adjust the slope and level manually in ViCare app when the outdoor temperature changes drastically on a daily basis.


I've also replaced 3 basic HoneyWell Home thermostats with RobertShaw ProSeries because RobertShaw thermostats allow me to set the swing. I set the temperature on the thermostat to 67 with the swing of 1 degree. With this setup, when the temperature in the room drops to 66, it will call for heat until the room temperature rises to 68 - and it takes a few hours to raise 2F with boiler water temperature at 140F. I didn't like the HoneyWell Home thermostat because the swing is set at 0.25F - that made the boiler run more frequently but shorter.

I've also decided to tie the 3 thermostats in parallel at the Taco zone controller so any thermostat calls for heat, all 3 zones get heat. No more overshoot with warnings and fault codes. Surprisingly the entire house is quite comfortable - no zone gets overheated so far.

@lanem2494 Please keep updating and I will do the same so others can learn. My next challenge is the first service call on the first year anniversary. I don't believe my installer wants to do regular maintenance so I have to find a Viessmann Pro near my home area soon.