Mod-Con Boiler and system questions???

@Paul48 the Ahu you see has the same water running through coil as your faucets.
I would assume the coil is designed for a 40 degree delta t

njtommy...........That scenario is un-desirable as far as I'm concerned.

@Paul48 - SWT 114F, return temp 109F, boiler fire rate 20%.

Mixing heating and DHW?

DanHolohan said:

For everyone's consideration. Often overlooked.

That will be an interesting formula.

Provided you can get the necessary heat at somewhat closer to design temp, you don't have to worry about DT. With a low mass, fin-tube system, the buffer tank will delay the inevitable once we get into the arctic conditions.

Gordy said:

The spirit of the discussions is overall system efficiency, there are many micro, and macro efficiencies in a system that all come together to produce the big picture. Boiler,pumping,heat transfer,emitter,envelope to name a few. What efficiencies can take a hit to make others shine . System cost to achieve that goal, and create an exceptable ROI while providing ultimate comfort at cheap operating costs.

That sums it up nicely.

The challenge is for installers, designers and customers to wade through all the choices and options. Where to go to get accurate non-biased info to make comparisons.

Remembering back 20- 30 years the first "perfect" radiant boiler was presented to us as the copper tube design. Basically a swimming pool heater morphed into a hydronic boiler.

Manufacturers and reps promoted them as long lasting, a solid track record in pool use. Able to handle low return temperatures all day, excellent heat transfer material copper (that one is true) but in reality they were not so ideal. So they added staging gas valves to try and minimize short cycling and over-shooting temperatures. Then bypass piping was built in with a manual valve to adjust return, to help keep them from condensing to death. Then a pump was added to help blend return temperature. Then electronic controls.

One of the big copper tube manufacturers told me "they would never build a mod con, no need the copper tube will do everything better" Never say never!

Next were the coiled tube type mod cons, with about the same exact story. But they did in fact bring modulating, and a microprocessor to the table, and that was worth some of the pain and price the early adopters paid.

Then the tank guys got into the picture, Polaris, HydroPulse, Voyager, and a few others. Those too were presented as the "perfect" hydronic boiler.

Now on to mid mass. What exactly is the definition of mid-mass? Over 5 gallon, or more than 200 lbs of "mass" When does mid-mass turn into high mass? At 50 gallon or more fluid capacity?

Regardless, every one of these has pros and cons, chose accordingly.

You may be onto something . Did you know the firetube heat exchanger was originally developed as a condensing component by moonshiners in WV? More liquor quicker !

Appreciate all the thoughts/input on the various factors that impact hydronic heating efficiencies....Good Stuff!

Ziggy presents a graph of Modcon boiler efficiency vs inlet/return water temperature at two different burner firing rates (25% and 100%). see attached pix. While the need to keep return water below ~125F to gain condensing efficiencies is often discussed, the efficiency differences at the 25% firing rate vs 100% firing rate with sub 100F return water is quite large. From the graph, the boiler efficiency drops by~ 5%, so 1/2 of the efficiencies of modcon is lost over a CI boiler when operating at 100% ouput ?

Couple of questions:

1) is the graph correct? Is it valid for both the TT style "firetube" heat exchanges and the spiral "honeycomb" style?
2) If the graph is correct, how can most modcon boilers be rated as 95% efficient, when even under the most favorable conditions, they are operating around 90% efficient at full fire?
Maybe the efficiency ratings are determined at 50% output?...a weighed average?

That Hatterasguy is perty darned smaht . LMAO

Copy that!

Chester........Some of the finest heating contractors in the country come here. None of them were born with innate knowledge of heating systems (maybe 1 or 2). You are to be commended for what you have been able to teach yourself.

If more customers were like me you guys would be happy because a well-educated consumer is likely willing (should definitely be willing) to pay more for a higher quality installation :-)

I'm glad I was able to learn that quality of the install is probably more important than brand of equipment. Even then I had no idea what really goes into it until my contractor was on site and I saw the craftsmanship.

Honestly, @Chester is representative of a lot of us homeowners on here, trying to learn as much as possible and appreciating a trade that isn't nearly recognized as much as it should be due to the very visible "bad apples" that most people are used to complaining about.

Knowledge is power, but as I've said before, sometimes it sucks having "inside info" and then having so called professionals dismiss what you know because you're an idiot customer that doesn't really know what he wants (I see that a lot in my own line of work, IT). Fortunately Dan runs a great site here that allows a great exchange of information in BOTH directions, homeowners to pros and vice versa.