Mod-Con Boiler and system questions???

DanHolohan

For everyone's consideration. Often overlooked.

Rich_49

If the boiler does not see those low return temps it's all for nothing

njtommy

@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

Paul48

Define your system as well as Chester did, and we could answer that question.

Paul48

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

njtommy

Why's that @Paul48?

Brewbeer

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

Gordy

Brewbeer said:

Along the lines of efficiency, I'd like echo one of Chester's comments a few posts up:



"Do I really care what my [boiler] Delta T is if I have low return temps and long run times?"

The boiler efficiency is where one of the biggest potential savings are. Along with less hardware to make that happen. Like @Rich said........

Paul48

Mixing heating and DHW?

Brewbeer

Just heat.

Gordy

DanHolohan said:

For everyone's consideration. Often overlooked.

That will be an interesting formula.

Rich_49

@Paul48 . Don't really need a FPHX for hydro air , you can exercise the pump for 3 minutes a day to prevent contamination issues . Versa Hydro stores at up to 160* and WILL provide 160* temps if you need them , remember the sensor location is critical , the water above will be hotter than at that location . VS pump for tank / FPHX senses supply and return temps based on the programmed odr , return water is put back to the bottom of the tank .

Paul48

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.

Rich_49

@Dan Holohan Too often forgotten . The HOUSE as a SYSTEM . Firing on all cylinders is BEST .

hot_rod

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.

Paul48

Don't really need a FPHX for hydro air , you can exercise the pump for 3 minutes a day to prevent contamination issues .


That validates the beliefs of every backwoods installation ever done. All I gots to do, is excersize my pump. And I didn't even know it was possessed.

Rich_49

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 !

Paul48

They had to catch them early in the day, to explain its construction. With all the sampling , by the end of the day, you'd never understand them.

vicbrick

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?

Chester

As I recall the video webinar posted above describes the laboratory conditions used to measure AFUE. The test doesn't seem to be based on anything resembling real-world conditions as much as it is a way to measure one unit against another based on some standard criteria. It was pretty revealing, especially the part about how the relatively high humidity required for the test creates "free" condensate that wouldn't necessarily be there with dry winter air. I think I recall they way they measure efficiency is simply by measuring the amount of condensate the unit spits out based on a given level of fuel burn.

This certainly reinforces Hatterasguy's ongoing comments about how unfortunate it is that consumers buy (or are sold) "95% efficient" boilers just because that's what the AFUE sticker says, without regard to return water temps, etc. That's not to say that modcons can't be 95% efficient in a proper design, though.

Rich_49

That Hatterasguy is perty darned smaht . LMAO

Paul48

Better question....what's Chester's background? Contractor? Homeowner? Either way, you're among the few that have a clue about mod/cons.

Gordy

Copy that!

Rich_49

Sound alot like Chester Birchwood . Is it ?

Chester

Chester is a dog. I'm just a homeowner who's really just spitting back what I've learned on this and other boards. I kind of got obsessed because we had natgas installed in our neighborhood this year and there were lots of us that were talking with contractors and trying to figure out what made sense relative to upfront cost, rebates, performance, etc. Most homeowners obviously don't have a clue and probably haven't ever made a heating system decision in their life, or they just depend on their trusted contractor to tell them what they need. I did that 20 years ago and ended up with a 140,000 Btu boiler for a small house. Then once I started talking to contractors the range of recommendations was pretty dramatic and I realized I had to educate myself. Then once I had a heat loss calc in hand two contractors basically refused to install the smaller size unit I wanted. The Bosch-certified contractor I went with has installed a whole bunch of Greenstars but never a 57,000. And even though they did a great-looking installation, per the book, they left everything on default settings. So I think there's a lot of work to be done.

This is a great resource and it's fun to pretend I'm contributing somehow to the effort.

DanHolohan

You're contributing a lot, Chester. We need to hear stories like yours. Thanks for taking the time to tell it.

Paul48

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.

Gordy

What if they were all like Chester, and not the dog.

Chester

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.

Canucker

Well said @Chester That's why I'm here, just a homeowner trying to learn. As a plus, its helped me at work.

vr608

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.

Paul48

I've spent my whole life learning to do things I couldn't afford to pay someone else to do wrong.