May have figured out this efficiency thing...Boilerpro

Darin Cook_2

that the calculated efficiency numbers on the analyzer are going by stoichiometric combustion which does not happen here. so the numbers are a little skewed. I do not know to what percentage but it is less than the number displayed on the screen. This is according to Jim Davis. But never the less it sounds like you have a well tuned piece of equipment.


Darin

Boilerpro_3

Hmmmm.....

Just tuned in my boiler yesterday and ran a combustion test with a recently calibrated Bachrach 125.

Here's the numbers:

Water supply 120F
Water return (estimated) 105F
Ambient(intake) 46F
Stack 82F
Efficiency 99.2%
CO2 8.6%
O2 5.6%
Air free CO 56 PPM
Excess air 32.6%

Now the boiler is running about 103,000 input and at 99.2 % efficiency, this gives you abaout 102,176 output.

However, I don't believe combustion analyzers take into account the condensate production, so we need to add these btu's. This boiler makes a little under a gallon per hour of condensate. So thats about 8,000 btu/hr from the phase change from steam to water (heat of vaporization) and another 1,000 btu/hr from that water cooling from 212F to 82F. The condensate is probably a little hotter coming off the recuperative heat exchanger, so lets say we get 700 btu/hr.
So at 103,000 input, we are getting 102,176 + 8,000 + 700 =
111, 176 btu/hr or 108% efficiency.

This seems to jive with the real life energy savings of 25% to 40% reported here when replacing an 80% AFUE boiler with a 92% AFUE model.

103,000 x 80% =82,400.... figure some stack losses during off cycle and pre and post purge and if you're lucky you probably get about 80,000.
With 103,000 in a condensing + recuperataive unit you get about 111,000 with some losses, so lets say 110,000.
Overall you gain about 30,000 btu/hr more usable heat.

If you take the overall efficiencies of these two boilers you get a savings percentage of:

100% -(80/103 / 110/103)= 1- .7766/ 1.068 =.27 or 27% savings. This is much greater that the 15% or so savings that the AFUE numbers indicate.

Boilerpro

thp_8

Less than

Unless your unit employs the refrigeration cycle somewhere in the system. Rest assured you are running less than 99%. If not you are gaining extra output from some other heat source.

db_6

That seems to...

Square with the min./temp. efficiency ratings published
by many, yet they all seem to leave the actual mechanics out.

Having hard data to put in front of a customer and explained the way you have may help them understand
how the extra efficiency is achieved.

(i.e.; ACV Prestige Solo 97/107% @ min./temp.)

Course having a 187.5% increase in their gas bill has many
taking notice.

Whether or not it comes out exactly that much pickup
from the recuperative cycle is science lost on most
regular folk, a 25 to 40% reduction in their bill isn't.


Nice work Dave, Regards, db

Boilerpro_3

refrig cycle...sort of

The secondary recuperatiave heat exchanger pulls heat from the exhaust and preheats the intake...that's how the exhaust temp is well below the return water temp. There is also a small condensate pump (.43 amp)running to move the water through the heat exchangers, so you pick up a few btu's here. You loose about 5 points of efficiency when only running the condensing heat exchanger and not the recuperative, according the boiler manufacturer.

Boilerpro

Boilerpro_3

Prestiges

So you have a few of those going, Just put in my first 3 in the last 2 months, and have alot more interested. FYI, Natural gas prices here in Northern ILL have gone up about 350% in the last 5 years. Yes, 25 to 40 % is getting thier attention, however, some won't believe it because the AFUE numbers are so much closer. I suspect the extra observed savings beyond 28% are due to improvements in system efficiency..... reduction of hot air at ceilings, reduction in air infiltration due to less stack effect, and reduced piping losses.

Boilerpro

thp_8

100%

> The secondary recuperatiave heat exchanger pulls

> heat from the exhaust and preheats the

> intake...that's how the exhaust temp is well

> below the return water temp. There is also a

> small condensate pump (.43 amp)running to move

> the water through the heat exchangers, so you

> pick up a few btu's here. You loose about 5

> points of efficiency when only running the

> condensing heat exchanger and not the

> recuperative, according the boiler manufacturer.

> Boilerpro

thp_8

100%

You would need an intake and exhaust temp. the same and all condensate accounted for. All heat extracted from condensate
and you would be close to 100%. Supply and return temps. only tell half the story. Now if you had say 200*F outside air for combustion air then we could exceed 100%.

TK03

Curious

What btu input was the old boiler and what size was the new boiler?

Boilerpro_3

Old and New

My old boiler was(is still, as back up)a 270,000 input American Standard G series. It would fire at about 75% efficiency, even with the pins now resembling nubs after decades of operation without return temp protection. I still have yet to see one fail, except rotting out at the waterline after many years. However, this is not the boiler I am using in my comparison. The new boiler is a 100,000 btu/hr input Dunkirk Quantum Leap (no longer being produced, I believe), which is still oversized to heat our 2800 sq ft 1906 home here in northern Ill with 700 sq ft of windows. Heat load is calculated at about 50,000 btu/hr at -4 outdoor, and it appears the house is starting to perform better than that with some weatherstripping and insulation improvements this past fall (I am keeping boiler about 20F colder than last year and maintaining same indoor temp).

Boilerpro