New Boiler Optimization, Prevent / Minimize Short Cycling.

mrhemi

Short history. Last winter the combi heating boiler (Triangle Tube 125CC) was replaced due to failure. The replacement is a Triangle Tube Instinct 155CC. They came good for the replacement minus the install labor. The new boiler has far more tuning capability so I wish to optimize operation for both efficiency and longevity.
System is 4 zone:
Zone 1 (CH1) is high temp coil air handler forced air for main dwelling (2800 sq. ft.) @ 70 deg.
Zone 2 (CH2) is in floor radiant, basement (1800 sq. ft.) @ 71 deg.
Zone 3 (CH2) is in floor radiant, garage / work shop (1100 sq. ft.) @ 55 deg.
Zone 4 is DHW (combi with storage tank).

My concern is short cycling the boiler on CH1 calls. The boiler will fire for 7-8 mins. then the call is satisfied. It never reaches set point (OTR is being utilized). The next CH1 call may not be for 20 mins. Is this considered "short cycling"?

Located in SW. Ontario, so excessive weather fluctuations are the norm.

Any insight and / or questions welcomed.

Cheers,

Mr. Mike

Daveinscranton

Try going into the menu and turning down the max fire percent.  The actual fire 🔥 will be the minimum plus X percent of boiler max minus minimum.  Lower the X as far as you can while maintaining comfort.   The look back function on the screen will allow you to see what is going on for the last 30 hours.  Triangle Tube tech support is wonderful BTW.  Until I got a feel for what was going on, I used a bucket and hose to get a handle on it while watching flue temperature, supply and return temperatures.

Best wishes 

Daveinscranton

You can lower your set point too.  Looks like a few options in curve choices.  You can select different curves for CH1 and CH2.  The menu tries to herd you back to factory defaults.  Probably a good thing until familiar with it.  I think you will like it once you get it dialed in.

Daveinscranton

A very fast way of getting a feel for what outdoor temperature (outdoor reset) versus boiler set point looks like is to wire about 20-30 K ohms of fixed resistance in series with a 50 K ohm linear (variable) potentiometer.  Or just use a 100K linear (not audio taper) potentiometer.  And try it in lieu of outdoor reset.  

In my application, it looks like lowering max fire rate takes care of the cold winter end of the curve.  We have had design day weather which helped sort it out.  I think that the outdoor reset will take care of the shoulder seasons.  

It was faster than getting into the programming to make each change.  Quick experiment.  $5 worth of parts.

You want very low flue temperature if possible in condensing mode, which is where the bucket and condensate hose method had some instructive value.  With the caveat that condensing in the stack will look just like condensing in the boiler (condensing in the boiler is what you want).

Best wishes 

mrhemi

Reducing the boiler max fire rate is not a viable option as there are certain times when full rate is required to meet demand (CH1 & CH2 simultaneous call).

Adjustment of the demand temperatures as well as fan and pump speeds through the air handler has helped somewhat.

CH1 call, which is the fan coil air handler and main heat source for the dwelling cannot operate in condensing mode due to the temperature requirements of the unit (140 - 180 deg.). CH2 calls which are radiant are not at issue.

Question is, are the 7-8 min. fire times considered short cycling for burner?

hot_rod

One rule of thumb is for a 10 minute minimum run. cycle. There really is no standard or even manufacturers suggested run time.
I'd say 8 minutes is still reasonable. It's the multiple firing times a minute that really is tough on all the components.

Daveinscranton

Less than 10 minutes is short.  Might not matter. The unit is robust.  

I would try dropping the max firing rate anyhow. If your new boiler is larger than the last one, you are essentially telling the new boiler that it is smaller.

In the end you will juggle efficiency and comfort.

mrhemi

After that 8 min. firing, it might not fire for 30 min. The home is very thermal efficient. The burner lock out feature is being utilized (@ 2 min.) to help with successive zone calls.

Keep in mind that because this is a combi boiler, the entire 155,000btu capacity is not available for central heating.

Yes, this is much more robust than the Challenger it replaced. An aluminum exchanger in a condensing flue gas path (Challenger design) is "planned obsolescence".

Hot_water_fan

Reducing the boiler max fire rate is not a viable option as there are certain times when full rate is required to meet demand (CH1 & CH2 simultaneous call).

I highly doubt that, usually boilers are way oversized. If you're on 8/off 30 minutes for a larger, above ground space, I don't think you'll need the full capacity for that plus a smaller basement.

mrhemi

The 8/30 is not during very cold outside conditions. Still waiting for some sustained colder weather at my location. Also, that is for the above ground air handler zone only. There is an additional 1100 sq. ft. above ground radiant zone that can come into play as well. There were times with the previous 125,000 btu boiler, during sustained cold weather that it would not keep up with all zones simultaneously and I had to temporarily intervene with the 1100 sq. ft. space to allow catch up.

Daveinscranton

It too early to think of a buffer tank.  You may get there but not soon.  The Instinct appears to have a lot of flexibility built in.  It took me awhile to figure out the options built into it.  Used up a few gallons of propane experimenting.  It was worth it.

Best wishes with your project.  I actually enjoyed the process.  It appears that I am heating 2300 square feet of living space and a 2300 square foot shop in the basement on roughly 42,000 btu/hr at sub ten degrees weather at night with an Instinct 110.  Daytime is way different because of my solar gain.

mrhemi

I have large solar gain during the day as well. Not the best situation during A/C season though.

Daveinscranton

One last thought.  You could set up a series of voltage dividers and make them variable.  One voltage divider per zone.  Pretty sure it would work.  And use each thermostat to control its own 0-10 volt divider, set individually.  You would specify a max temp limit (essentially your only control internal to the boiler) in the boiler menu for 0-10 volt modulation demand. The max would only be reached if you turned up your biggest load all the way.  (Or if you made a mistake and turned up your radiant floor voltage divider by error.  Ouch).   If your radiant got too hot (supply) you could put a high limit circuit interrupter switch/relay in series with that zone control.

Someone must make a software and hardware package to do it.  Of which I know nothing.

Triangle Tube tech support probably has a solution for you.  They would also be able to tell you if 2 volts from one would have any effect on 7.7 volts from another.  Seems like the boiler would only see the max.  It should respond to the max.  You would want the internal resistance of your voltage dividers to be high I think. If low internal resistance, and high amperage they may want to fight.  Ohm’s law.  I would be inclined to run each divider on its each 10 volt wall wart as an experiment.  I would start with 1, and add a second and so on.  DC volt meters would be your friend.

This solution is simple enough that it absolutely positively has to be fatally flawed so Triangle Tube should have an opinion.  And I would trust them.

I think maximizing what is built into the boiler is a better solution than the above.  Just a thought.

Best wishes