Disappointing efficiancy w/ Alpine ALP 150?

rich_b

Hi. I recently had an ALP150 (AFUE 96) installed, air intake and exhaust piped up the chimney. They did flue gas analysis and the combustion efficiency of 87% seemed rather disappointing. Here are the numbers, from a Wohler A 400



Cal date 9/21/2012



Low fire

O2.....4.2%

CO....4ppm

Effc....87.9%

CO2...9.4%

TS.....148.4F (stack temp)

TA.....64.7F (air temp)

EA....25% (excess air)

SL.....12.1% (stack loss)

Dpt....131.1F (dew point)

COc...5ppm



High Fire

O2.....5.9%

CO....28ppm

Effc....87.4%

CO2...8.5%

TS.....163.4F (stack temp)

TA.....64.7F (air temp)

EA....39% (excess air)

SL.....12.6% (stack loss)

Dpt....127.9F (dew point)

COc...39ppm



Is this the expected efficiency on a condensing boiler w/ AFUE 96? Anything that can be tweaked based on these numbers to improve efficiency? Thanks in advance for your input.

CMadatMe

AFUE is Dependent

On return water temp and condensing. If your not in the condensing range then yup that's what your going to get. You stack temps show return water temps 140 or so on high fire and 130 or so at low fire. So that tells me your not condensing for the most part. 134 degree return water temp gets you to where you start condensing but that number is also at the mercy of your CO2. Dew point can change..

Jim Davis_3

efficiency

Believe it or not it is the analyzers calculations that might be off.  Older analyzers did not add percent of condensation into their calculations.  No such thing as a real 95% but you are running closer to 90%+ than the analzyer is calculating.

The 95% counts point for when the boiler isn't running and adds them on to the other number.  Your readings are good, don't be disappointed, you should be saving some big bucks.

CMadatMe

Huh?

Attached is a running boiler at 98.6%

Aaron_in_Maine

Baseboard

I bet that's not hooked up to baseboard. I bet his is. On baseboard systems between 88-92% is common depending on the season. The savings come in modulation and having outdoor reset.

CMadatMe

Cast Iron

You are correct. Good ole fashion radiators...I posted it because I was questioning Mr Davis' post. Can you guess the return water temps this boiler was seeing? Boiler was running for 10 minutes when this test was taken. It was 15 degrees outside.

Jim Davis_3

efficiency printout

Perfect example of how analyzers mis-calculate efficiency.  Normally every percent of O2 in the flue gas is a 1% loss of efficiency.  5.2% = 94.8%   HOwever once the flue temperature gets to 100 degrees, they seem to ignor the O2 reading. 

The combustion efficiency calculation is based on conditions that normally don't exist. 

1. Equipment is operating at full input

2. Equipment is operating at full temperature and at design load.

Any firing rate lower than maximum and any load less than maximum makes the calculations more bogus than they are normally.

I spent many hours when I first started using and selling analyzers trying to figure out why calculated efficiencies went down when equipment was tuned and yet people were saving considerable energy.  It was because of the two things I mentioned above.

Unfortunately even when those are met there are some additional assumptions that are made such as the btus value of the fuel and percent of energy is converted from potential energy to kinetic energy.   Analyzers assume 100% under all conditions and assume they are perfect.  Not!