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Buderus efficiency
Jim Bergmann_2
Member Posts: 79
Testo analyzers like the 325M do not measure latent heat. I am sorry if someome gave you incorrect information. I have included a detailed explanation if you desire additional information below.
Combustion efficiency is a measurement of how well the fuel being burned is being utilized in the combustion process. This is different from the efficiency number produced on the analyzer, which is reflective of the total amount of heat available from the fuel minus the losses from the gasses going up the stack. Stack loss is a measure of the heat carried away by dry flue gases and the moisture loss. It is a good indicator of appliance efficiency. The stack temperature is the temperature of the combustion gases (dry and water vapor) leaving the appliance, and reflects the energy that did not transfer from the fuel to the heat exchanger. The lower the stack temperature, the more effective the heat exchanger design or heat transfer and the higher the fuel-to-air/water/steam efficiency is. The combustion efficiency calculation considers both the stack temperature and the net heat and moisture losses. This would include losses from dry gas plus losses from the moisture and losses from the production of CO.
Each type of fuel has specific measurable heat content. The maximum amount of heat that can be derived from a fuel is based on using pure oxygen as the oxidizer in the chemical reaction and maximizing the fuel gas mixture. In field practice, the oxygen is derived from the air which is 20.9% oxygen, 78% nitrogen and 1% other gasses. Because the oxygen is not separated from the air prior to combustion, there is a negative effect on the chemical reaction. Air is primarily nitrogen. While nitrogen is inert, and plays no role in the combustion process, it cools the chemical reaction (burning temperature) and lowers the maximum heat content deliverable by the fuel. Therefore, it is impossible to achieve combustion efficiencies above 95% for most fuels, including natural gas, when air is used as the oxidizer in the combustion process.
The combustion efficiency or maximum heat content of the fuel is then based upon the quality of the mixture of fuel and air, and the amount of air supplied to the burner in excess of what is required to produce complete combustion. The efficiency calculated by the combustion analyzer is a modified equation that considers combustion efficiency and stack losses. It is a part thermal, part combustion efficiency calculation. The equation is a reasonable estimation of the steady state operating efficiency of the appliance. This is true of all analyzers currently manufactured, and is not proprietary to Testo.
The entire system (furnace/boiler, ducting, and piping) must be evaluated to determine the true efficiency of the system. Combustion efficiency is a valuable part of the system evaluation, but it is only one part of the evaluation process and cannot be used as the sole reason or justification for keeping or replacing existing equipment.
If the excess air is carefully controlled, most furnaces are capable of performing at higher levels than their rated Annualized Fuel Utilization Efficiency or AFUE level, AFUE levels typically range from 80% to 95%
The ultimate thermal efficiency of the appliance is determined by dividing the heat output rate of the appliance by the rate of fuel input. During the combustion process, all furnaces that operate with the same combustion efficiency will produce the same amount of heat with the same fuel input. The combustion efficiency has no bearing on how well the appliance utilizes the heat produced after the combustion process has taken place. Heat exchanger design and its ability to transfer the sensible and possibly the latent heat to the room air determine how well the heat produced by the combustion process is utilized.
It should be noted that there is not a national industry standard for calculating measured efficiency with a combustion analyzer. Manufacturers of analyzers use differing calculations to derive efficiency values. Oftentimes this discrepancy is due to values that have been extrapolated into the condensing range.
Heat removed from the flue gasses on a condensing furnace is latent or hidden heat. A combustion analyzer that measures only temperature and not volume of condensate cannot measure the quantity of heat removed from the flue gas during the condensing process. Although terms of thermal and combustion efficiency are often used interchangeably on non-condensing units, they cannot be used in the same manor on condensing appliances.
The thermal efficiency of a condensing appliance and combustion efficiency will be different. The only way to calculate the actual thermal efficiency of an appliance is to measure the exact airflow across the heat exchanger, and the change in air temperature across the heat exchanger and input the measured values into the sensible heat formula to calculate the heat energy input into the conditioned air. There will be some minimal loss to the furnace cabinet by radiation and conduction. Depending on how much of the heat energy is extrapolated from the water in the flue gas, an average of 970 BTU per pound, the efficiency readings can differ by as much as 10%. This assumes that either all latent heat energy was extracted from the flue gasses after they reached the dew point or none of the latent heat energy was extracted.
This extrapolation of values is distorted, and has led manufacturers of appliances to inadvertently post higher than actual thermal efficiency numbers. Due to the readings achieved on their analyzer. (NOTE: This calculation does not affect the AFUE numbers, which are derived by a different means.) By not taking this discrepancy into account, some in the industry have suggested that fuels are being delivered with low BTU levels. This leads them to suggest that fuel pressures be raised to provide the net heat output that the manufacturer has published. For this reason, Testo is recommending that the fuel pressure be set per the manufacturers instructions. The combustion efficiency will then be a function of the actual dry flue gas and not of the thermal efficiency of a condensing appliance. This avoids use of a calculated rather than a measured parameter. Testo has chosen to use a combustion calculation that does not extrapolate the thermal efficiency values of flue gasses below the dew point, as those values are not representative of the heat that is removed from the flue gasses during the condensing process. Although this may result in the appearance of a lower thermal efficiency of the appliance, the science used for measuring combustion efficiency is not artificially high. Once differences in combustion and appliance thermal efficiency are understood, the methodology of scientific measurement verses extrapolation of measured values can be appreciated and applied, allowing manufacturers to publish combustion and thermal efficiencies that are representative of the actual efficiency of their appliance, thereby creating a standard that is based upon actual measurement rather than an extrapolation.
Jim Bergmann
Testo Technical Specialist
330-618-3472
Combustion efficiency is a measurement of how well the fuel being burned is being utilized in the combustion process. This is different from the efficiency number produced on the analyzer, which is reflective of the total amount of heat available from the fuel minus the losses from the gasses going up the stack. Stack loss is a measure of the heat carried away by dry flue gases and the moisture loss. It is a good indicator of appliance efficiency. The stack temperature is the temperature of the combustion gases (dry and water vapor) leaving the appliance, and reflects the energy that did not transfer from the fuel to the heat exchanger. The lower the stack temperature, the more effective the heat exchanger design or heat transfer and the higher the fuel-to-air/water/steam efficiency is. The combustion efficiency calculation considers both the stack temperature and the net heat and moisture losses. This would include losses from dry gas plus losses from the moisture and losses from the production of CO.
Each type of fuel has specific measurable heat content. The maximum amount of heat that can be derived from a fuel is based on using pure oxygen as the oxidizer in the chemical reaction and maximizing the fuel gas mixture. In field practice, the oxygen is derived from the air which is 20.9% oxygen, 78% nitrogen and 1% other gasses. Because the oxygen is not separated from the air prior to combustion, there is a negative effect on the chemical reaction. Air is primarily nitrogen. While nitrogen is inert, and plays no role in the combustion process, it cools the chemical reaction (burning temperature) and lowers the maximum heat content deliverable by the fuel. Therefore, it is impossible to achieve combustion efficiencies above 95% for most fuels, including natural gas, when air is used as the oxidizer in the combustion process.
The combustion efficiency or maximum heat content of the fuel is then based upon the quality of the mixture of fuel and air, and the amount of air supplied to the burner in excess of what is required to produce complete combustion. The efficiency calculated by the combustion analyzer is a modified equation that considers combustion efficiency and stack losses. It is a part thermal, part combustion efficiency calculation. The equation is a reasonable estimation of the steady state operating efficiency of the appliance. This is true of all analyzers currently manufactured, and is not proprietary to Testo.
The entire system (furnace/boiler, ducting, and piping) must be evaluated to determine the true efficiency of the system. Combustion efficiency is a valuable part of the system evaluation, but it is only one part of the evaluation process and cannot be used as the sole reason or justification for keeping or replacing existing equipment.
If the excess air is carefully controlled, most furnaces are capable of performing at higher levels than their rated Annualized Fuel Utilization Efficiency or AFUE level, AFUE levels typically range from 80% to 95%
The ultimate thermal efficiency of the appliance is determined by dividing the heat output rate of the appliance by the rate of fuel input. During the combustion process, all furnaces that operate with the same combustion efficiency will produce the same amount of heat with the same fuel input. The combustion efficiency has no bearing on how well the appliance utilizes the heat produced after the combustion process has taken place. Heat exchanger design and its ability to transfer the sensible and possibly the latent heat to the room air determine how well the heat produced by the combustion process is utilized.
It should be noted that there is not a national industry standard for calculating measured efficiency with a combustion analyzer. Manufacturers of analyzers use differing calculations to derive efficiency values. Oftentimes this discrepancy is due to values that have been extrapolated into the condensing range.
Heat removed from the flue gasses on a condensing furnace is latent or hidden heat. A combustion analyzer that measures only temperature and not volume of condensate cannot measure the quantity of heat removed from the flue gas during the condensing process. Although terms of thermal and combustion efficiency are often used interchangeably on non-condensing units, they cannot be used in the same manor on condensing appliances.
The thermal efficiency of a condensing appliance and combustion efficiency will be different. The only way to calculate the actual thermal efficiency of an appliance is to measure the exact airflow across the heat exchanger, and the change in air temperature across the heat exchanger and input the measured values into the sensible heat formula to calculate the heat energy input into the conditioned air. There will be some minimal loss to the furnace cabinet by radiation and conduction. Depending on how much of the heat energy is extrapolated from the water in the flue gas, an average of 970 BTU per pound, the efficiency readings can differ by as much as 10%. This assumes that either all latent heat energy was extracted from the flue gasses after they reached the dew point or none of the latent heat energy was extracted.
This extrapolation of values is distorted, and has led manufacturers of appliances to inadvertently post higher than actual thermal efficiency numbers. Due to the readings achieved on their analyzer. (NOTE: This calculation does not affect the AFUE numbers, which are derived by a different means.) By not taking this discrepancy into account, some in the industry have suggested that fuels are being delivered with low BTU levels. This leads them to suggest that fuel pressures be raised to provide the net heat output that the manufacturer has published. For this reason, Testo is recommending that the fuel pressure be set per the manufacturers instructions. The combustion efficiency will then be a function of the actual dry flue gas and not of the thermal efficiency of a condensing appliance. This avoids use of a calculated rather than a measured parameter. Testo has chosen to use a combustion calculation that does not extrapolate the thermal efficiency values of flue gasses below the dew point, as those values are not representative of the heat that is removed from the flue gasses during the condensing process. Although this may result in the appearance of a lower thermal efficiency of the appliance, the science used for measuring combustion efficiency is not artificially high. Once differences in combustion and appliance thermal efficiency are understood, the methodology of scientific measurement verses extrapolation of measured values can be appreciated and applied, allowing manufacturers to publish combustion and thermal efficiencies that are representative of the actual efficiency of their appliance, thereby creating a standard that is based upon actual measurement rather than an extrapolation.
Jim Bergmann
Testo Technical Specialist
330-618-3472
0
Comments
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Buderus efficiency
I have the Testo 325 analyzer. I've installed a few GB142 Buderus's lately and I'm not getting the 98% efficiency they claim. I know water temp effects this but when the rep for Buderus sticks his analyzer in the exhaust and reads 99.1% and the Testo reads 90% for the same boiler, which one is right? The rep says it is because the Testo doesn't read latent heat but Testo says B.S. it sure does!!!!!
Does anyone have a good explanation for this?????0 -
If the Buderus is...
getting all combustion air from outdoors, make sure to zero in the analyzer before actually doing the test, by GOING OUTSIDE TO TAKE THE ZERO-ING sample to properly setup the analyzer's parameters.
The reason I know this phase is often overlooked?
I made that mistake, not once; but twice!
0 -
yeah
I used to be guilty of that myself.
Pays to take a combustion testing class using your analyzer.There was an error rendering this rich post.
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Combustion efficiency
I'm not sure that it's possible for any combustion analyzer to effectively measure latent heat. In order to do this it would have to measure the amount of condensate that is leaving the boiler (not the flue however). The "combustion" efficiency of Natural Gas can't really be higher that 88%-89%. The extra efficiency comes from the amount of heat that can be reclaimed from the condensate as it passes through the heat exchanger. So the only way the true efficiency can be gathered is by taking the measured combustion efficiency and measuring the amount of condensate that is leaving the boiler. Then apply the following formula.There was an error rendering this rich post.
0 -
Combustion efficiency
I'm not sure that it's possible for any combustion analyzer to effectively measure latent heat. In order to do this it would have to measure the amount of condensate that is leaving the boiler (not the flue however). The "combustion" efficiency of Natural Gas can't really be higher that 88%-89%. The extra efficiency comes from the amount of heat that can be reclaimed from the condensate as it passes through the heat exchanger. So the only way the true efficiency can be gathered is by taking the measured combustion efficiency and measuring the amount of condensate that is leaving the boiler. Then apply the following formula.
Kevin FlynnThere was an error rendering this rich post.
0
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