AFUE, attn Boilerpro

Mike T., Swampeast MO

Whew! That's some hefty oversizing assumption--but (sorry to say) likely quite accurate for CONVENTIONAL EQUIPMENT.

What I consider even MORE interesting is that ASHRAE calls two-stage equipment "MODULATING."

Modulate: "to pass gradually from one state to another" How on earth can they call a two-STAGE piece of equipment "modulating"? No wonder even trained heating engineers in the US tend to pooh-pooh TRUE modulation--they don't even know what it is!!!!!!!!!!

To make it worse yet, those boilers that REALLY DO MODULATE will be considered STAGED and STILL QUITE OVERSIZED A SIGNIFICANT AMOUNT OF THE TIME.

I've got to dig through that math, but it also appears that there is a "penalty" for on-off (digital) cycling that is nearly eliminated when a modulating burner is teamed with modulating control.

While I guess it's "fair" to consider the EQUIPMENT ONLY for such ratings, it seems rather "unfair" to lump hydronics with air.

When compared to hydronics, forced air WILL have greater transmission loss and it WILL result in pressure imbalances that affect air infiltration into and out of the structure. If they can assume such great oversizing of equipment, I have a hard time believing they can't make some reasonable "assumption" for these factors when comparing air with water!

EGAD!!! You don't even have to be good at math to see that boilers in general and TRULY modulating boilers in particular are not realistically portrayed IN OPERATION AS COMPARED TO FORCED AIR!!! Either ratings are unrealistically HIGH for forced air or unrealistically LOW for hydronics--likely both at the same time with TRULY moduulating boilers!!!!

Will try to get up really early tomorrow and play with some of those equations to see what happens with a boiler that FULLY MODULATES delivering through a modulating control system with continual circulation. It will be VERY interesting if I have to "divide by zero" to do it!!!!

Unknown

I have FINALLY located it....

http://fire.nist.gov/bfrlpubs/build02/PDF/b02022.pdf

On page "2" (actually page 16 in the PDF document) in this publication, under "Background", it explains the testing process, including the part where they consider boilers installed in residences are oversized by a factor of 0.7, or 70%.

I've been looking everywhere for this....and it was right here the whole time.

Mike T., Swampeast MO

Manual J (ASHRAE Residential)

There is something REALLY strange in a set of "rules" that defines the sizing standard yet still seems to assume that installed equipment it 70% above what is required!

I wonder how much of that 70% is REALLY there to address typical "ductmanship"!!!

Maybe they should just quit pretending and rename themselves ASFAHRAE!

Mike T., Swampeast MO

a (alpha) = oversize factor, rated heating capacity to design heating requirement

Can you find any ambiguity in this [ASHRAE] nomenclature?

[Deleted User]

All I know is...

the formulas made me go cross eyed. Mike, if you can "run the numbers", you're a much better man than I....

Looks like some pretty serious engineering to me.

I'm in the process of "base loading" a large city housing heating system with three Viessmann Vitodens boilers and displacing two each 2.5 mill 2 stage each boilers. I'm also doing DOMESTIC HOT WATER ECTOMY. This is the reason the 2 2.5 millers are there. The three V's will be tied to 3 new DHW tanks. Should be interesting to see what happens to their gas bill. Funny thing is, these big 2.5 mill boilers are so inefficient, they don't even think about trying to establish an AFUE for them.

Stay tuned.

Good Stuff from THe Wall! Thanks guys!

ME

Mike T., Swampeast MO

READ THE COVER

IMPORTANT

These are PROPOSED revisions.

The 70% factor DOES though seem to come from the status quo.

Calling staged equipment "modulating" seems UTTERLY WRONG.

Doesn't ASHRAE post these things for the purpose of receiving criticism?

Mike T., Swampeast MO

Compared to formulas for computing radiation--or much worse forced convection--they're not too bad... You just have to keep referring back to "nomenclature".