Exhaust gas measurement

The exhaust gas measurement in a heating system is used to determine the pollutants (carbon monoxide CO or soot number) emitted with the exhaust gas into the earth's atmosphere and the heating energy lost with the warm exhaust gas .

It is a legally required measure. This has two main goals: the atmosphere should be polluted as little as possible by pollutants; and energy should be used efficiently. Prescribed pollutant quantities per exhaust gas volume and energy losses ( exhaust gas losses , not more than about 10%) must not be exceeded.

Legal provision and implementation in Germany

The exhaust gas measurement (not to be confused with the examination of the engine management and exhaust gas cleaning system for the car) is a measurement to be carried out by the chimney sweep and which affects gas and oil boilers in the domestic heating system . Flue gas measurement is prescribed in Germany by the Federal Immission Control Act and the Ordinance on Small and Medium-sized Firing Systems (1st BImschV) and in Austria by the Clean Air Act . These regulations also regulate the legal limit values for exhaust gas losses.

For the results required by law in normal operation (the power with which the device is mainly operated), the measurement is made by means of a lambda probe (single-hole probe or multi-hole probe ) in the core flow of the connecting pipe (i.e. in the middle of the pipe cross-section, not on the edge) between the boiler and Chimney / exhaust pipe carried out. The measured values are recorded by a small computer and can be printed out.

The measurement is carried out once for boilers with a rated output of 4 kW to 11 kW four weeks after commissioning, and it is a recurring measurement for boilers from 11 kW and drinking water heaters from 28 kW. For drinking water heaters up to 28 kW and for combination heaters at maximum output (hot water preparation), only one CO measurement of the flue gas is required. If it is a pellet heating system , the dust and SO ₂ emissions are measured instead of the CO ₂ and CO content .

Changes due to the amendment of the 1st BImSchV

Since March 22, 2010, the 1st BImSchV provides for a mandatory inspection for all heating systems that are operated with liquid and gaseous fuels, from 4 kW. Devices that are only required for heating hot water (domestic water systems) are measured recurrently from a nominal heat output of 28 kW. There were also changes in the frequency of these measurements. Since March 22, 2010, the exhaust gas loss has been carried out every 3 years (for heaters that are younger than 12 years) or every 2 years (older than 12 years). Retrofitting obligations for solid fuel heating systems have been added in isolated cases.

Statutory determination and implementation in Austria

Exhaust gas and emission measurements are a matter for the federal states: In the case of heating devices, the emission limit values are regulated differently in the federal states in accordance with § 15a Agreement and federal law and must be measured in accordance with the rules and state of the art, as in the ÖNORM "Gas devices with atmospheric burners - emission values ”.

This measurement goes beyond a single measurement with a specified temperature pairing with a setting of 100% power and has to refer to the power at which the device is mainly operated (see e.g. § 2.1 Vienna Emission Limit Value Regulation 2004). Accordingly, measurements according to ÖNORM must be carried out for the statutory exhaust gas tests (e.g. M 7443/3 (= PG 307) Point 5.4.- Tests on gas devices for heating), which use the load factors specified for this (in% of the nominal load of the boiler) which were determined on the basis of representative heating requirements, meteorological data and average statistical heating load curves. In the case of gas heaters, this is 76% -58% -42% -27% -14%, with the measurement based on heating system conditions with flow / return at 40/30 ° C (condensing boiler) or 70/50 ° C (other devices) has taken place.

The result is therefore not simply a value measured at 100% nominal load, but the mean calculated from the defined standard load (= average from measurement at 5 load points).

According to ÖNORM, measurements on combination devices for heating and hot water preparation are to be weighted with 85% for calculating the heating component and 15% for hot water.

Officer measuring organs are Rauchfangkehrer ( Chimney Sweep ), installers and heating technicians, as well as factory customer services with approval by the Regional Authority.

Recorded measured values

When measuring will be

the exhaust gas loss q _A (according to Siegert's formula )
the concentrations of the exhaust gas components
- Carbon dioxide CO ₂ , carbon monoxide CO, oxygen O ₂ , as well
- In the case of oil heating, the smoke number and oil derivatives are also measured
as well as flue gas temperature, supply air temperature and combustion air temperature,
- Dew point temperature, excess air ratio ( combustion air ratio Lambda λ) and chimney draft.

Flue gas loss measured value

The exhaust gas loss q _A indicates what percentage of the nominal heating output is lost with the exhaust gas. The lower the exhaust gas temperature and the greater the CO ₂ content of the exhaust gas, the smaller it is, which is associated with a small excess air ratio. From November 1, 2004, the flue gas loss may be 11% for boilers up to 25 kW, 10% for boilers over 25 to 50 kW and only 9% for boilers over 50 kW. If these limit values are exceeded, the boilers must be replaced with new ones or, if necessary, cleaned and adjusted by a competent person.

Concentrations of the exhaust gas components

carbon dioxide

So that the exhaust gas loss q _{A is} low, the CO ₂ content in the exhaust gas must be as high as possible (see below, Siegert formula ). With ideal mixing of the fuel with the supply air, the CO ₂ content in the exhaust gas is LL max. 11.8% and with natural gas E 12%, with heating oil EL a maximum of 15.4%. Since this mixture preparation is practically impossible to achieve, an excess of air is required, which increases the exhaust gas loss (heated air).

Carbon monoxide

Carbon monoxide CO can be fatal even in small amounts and still has a calorific value, which is why not too much of it should be blown out of the chimney. It occurs in the event of a lack of oxygen (lack of air), which on the one hand results from insufficient air excess, from contaminated burners or from insufficient fresh air supply at the installation location of the boiler. The CO content in the undiluted exhaust gas (calculated with lambda) should be below 80 ppm (0.008%), at 500 ppm (0.05%) an inspection is urgently recommended. Exceeding the limit value of 1000 ppm (0.1%) carbon monoxide initially results in a complaint by the district chimney sweep and a re-measurement must be carried out after a period of 10 days. If the CO content is high and the exhaust gas is backing up in the installation room, the fireplace is shut down with the cooperation of the municipal utility (gas supplier) (hazard prevention).

oxygen

The oxygen content O ₂ goes hand in hand with the excess air ratio lambda and should be as low as possible, depending on the boiler and operating mode, it assumes the values below.

Soot number for oil heaters

In addition, the possible carbon content C in the exhaust gas with oil heating is determined according to Bacharach and specified as the soot number, the max. 1, for old systems before 1988 2 may be. Soot is unburned carbon that is created when the mixture is insufficiently mixed. Reasons can be a lack of air, an incorrectly selected oil nozzle (spray angle) or an atomization pressure that is too low. Oil derivatives (unburned oil), which show up as yellow deposits on a filter paper sample, must not be present in the exhaust gas.

Nitrogen oxides

In Germany, it is not part of the exhaust gas measurement, but the device manufacturer must provide evidence of nitrogen oxides (NO _x ), which are formed from the nitrogen in the supply air at too hot combustion temperatures. In general, the combustion temperature and thus the amount of nitrogen oxides can be lowered by cooling the burner or, more simply, by partially returning the hot exhaust gases from the tip to the root of the flame ( internal recirculation, blue burner ) or by using pore burners .

In Switzerland, the nitrogen oxides are subject to verification and for oil max. 120 mg / m³.

The formation of nitrogen oxide is an endothermic reaction and the latent energy that is avoided in the reaction enthalpies is then available as thermal energy. However, the heat that can be achieved is negligible. The standard enthalpy of formation of NO ₂ is 33 kJ / mol (mol = 46 g) and of NO 90 kJ / mol (mol = 30 g), for the formation of these 120 mg NO _x an amount of heat between 86 (for NO ₂ ) and 360 would be Y or Ws (with NO) necessary. Converted into kWh results in a negligibly low value between 0.00002 and 0.0001 kWh / 120 mg / NO _x or 0.00002-0.0001 kWh / m³ exhaust gas. If these 120 mg NO _{x were} generated from natural gas (with a calorific value H _s 8.2 - 11.1 kWh / m³ with a gas-air ratio of 1:10), that would result in an "additional heating cost" of just 0.01%. . A reduction in the nitrogen oxide content in the exhaust gas therefore only corresponds to a negligible gain in heat.

Exhaust gas temperature

The flue gas temperature is around 60–140 ° C for gas boilers , 120–180 ° C for oil heating and approx. 40–50 ° C for calorific value. Lower flue gas temperatures worsen the chimney draft and, if they are below the dew point temperature , can lead to condensation of the water vapor in the flue gas, which can lead to sooting of the chimney or corrosion of the flue system. This can be prevented by renovating the chimney (e.g. pulling in a stainless steel exhaust pipe). High exhaust gas temperatures indicate poor heat transfer at the heat exchangers, which can be the result of soot deposits and can be remedied by cleaning the boiler.

If the exhaust gas temperatures are still too high even with cleaned heat exchangers, this indicates that the heat exchanger surfaces are overloaded. Since the set combustion outputs are usually considerably higher than the actual heat demand of the house, this can very often be corrected by reducing the output of the burner. A reduction in output is only possible if the new, reduced burner output is still within the output range of the burner used. In the case of gas burners, the gas throughput is reduced, with oil burners either the atomization pressure is reduced or the size of the atomization nozzle is reduced. However, the manufacturer's instructions for the burner and heat generator must always be observed. After each reduction in output, the burners must be readjusted using the flue gas measuring device, just like when starting up again.

Supply air temperature

The supply air temperature corresponds to the room temperature of the boiler installation room, provided that it is heating oil or gas devices that draw the air from the installation room. Gas devices and heating oil devices that work independently of the ambient air and draw in fresh air from the outside are equipped with an air-exhaust system (LAS), which diverts exhaust gas in a pipe-in-pipe system and draws in fresh air in countercurrent. This preheated fresh air is included in the exhaust gas loss calculation as the combustion air temperature.

Dew point temperature

The dew point temperature of the water vapor in the exhaust gas can be used to estimate whether water is condensing in the chimney or exhaust pipe. It is assumed that the flue gases cool down by 5 ° C per meter of chimney height. If you subtract the cooling related to the chimney height from the flue gas temperature, you get a flue gas temperature that can be present at the chimney outlet. If this temperature is below the dew point temperature, water vapor condensation is possible; if it is higher, water formation is unlikely.

The sulfuric acid dew point is comparable to the dew point of water. However, sulfuric acid is considered to be the condensate. The carrier medium is mostly exhaust gas / flue gas from the combustion of fuels containing sulfur. The resulting SO ₂ and SO ₃ react further with the water vapor in the exhaust gas to form sulphurous acid and sulfuric acid.

Excess air ratio

The excess air ratio lambda indicates the ratio of the actual to the theoretically necessary amount of air, which is equivalent to the ratio of CO ₂ max. to CO ₂ . Atmospheric burners work with an excess air ratio of around 1.8; Fixed fan burners with around 1.2 to 1.4. Regulated forced draft burners (measurement with an integrated lambda probe ) achieve λ = 1.03. The excess air is therefore 3% to 80% depending on the burner type.

A small excess of air reduces the exhaust gas loss and improves efficiency.

Chimney draft

The chimney draft has the task of removing the hot flue gas produced during the combustion and at the same time drawing in the cold combustion air required. Leakages on the flue gas side have a positive or negative influence on the combustion, as the chimney draft is reduced by secondary air. Excessively high flue gas temperatures are also measured when the chimney draft is too high, but the excess air during combustion is normal. The installation of a secondary air flap can help here.

Modified Siegert formula according to BImschV to calculate the exhaust gas loss.

The numerical equation used is:

{\ displaystyle q_ {A} = (\ theta _ {A} - \ theta _ {L}) \ cdot \ left ({\ frac {A1} {CO_ {2}}} + B \ right)}

or.

{\ displaystyle q_ {A} = (\ theta _ {A} - \ theta _ {L}) \ cdot \ left ({\ frac {A2} {21-O_ {2}}} + B \ right)}

With:

{\ displaystyle q_ {A}}

Exhaust gas loss [%]

{\ displaystyle \ theta _ {A}}

Exhaust gas temperature [° C]

{\ displaystyle \ theta _ {L}}

Supply air temperature / combustion air temperature [° C]

{\ displaystyle CO_ {2}}

Carbon dioxide content of the exhaust gas [% by volume] or

{\ displaystyle O_ {2}}

Oxygen content of the exhaust gas [% by volume]

Fuel parameters for fuels according to Siegert
	Constants:
	NATG, natural gas	PROP, propane, LPG	OIL2, light heating oil	OIL6, heavy fuel oil	TGAS, town gas	CGAS, coke oven gas
A1	0.37	0.42	0.50	0.50	0.35	0.29
A2	0.66	0.63	0.68	0.68	0.63	0.60
B.	0.009	0.008	0.007	0.007	0.011	0.011

Note: The information relates to the calorific value , only the calorific value describes the full amount of energy contained .

Examples of exhaust gas measurement

Flue gas measurement on an atmospheric burner

(Kombi-Therme, natural gas LL , CO ₂ max. = 11.8%)

		Start gas	12 kW heating load	Max load
Exhaust gas temperature	° C	80.6	90.2	113.9
Supply air temperature	° C	26.4	26.4	26.4
Dew point temperature	° C	35.7	41.3	48.8
CO ₂	%	2.8	4.1	6.6
O ₂	%	16.0	13.6	9.3
Exhaust gas loss q _A	%	7.6	6.2	5.7
CO	ppm	24	12	14th
CO un.	ppm	99	35	25th
Lambda	-	4.21	2.88	1.79
Chimney draft	hPa	−0.02	−0.02	−0.03

The exhaust gas values q _{A of} the heating load (middle column) must meet the requirements of the 1st BImschV (regulation on small combustion systems), which is based on the BImSchG . The max. Load (right column) is required for the provision of hot water, which is why only the CO content has to be verified. The starting gas behavior is not subject to any review. The relevant measured values in the table, the exhaust gas loss q _A and the CO concentration, meet the requirements. The chimney sweep then certifies this with a so-called measurement certificate.

Flue gas measurement on a permanently set forced draft burner

(Boiler, EL heating oil , CO ₂ max. = 15.4%, according to in undisturbed continuous operation)

		Full load
Exhaust gas temperature	° C	140.0
Supply air temperature	° C	20,
Dew point temperature	° C	48
CO ₂	%	11.9
O ₂	%	4.8
Exhaust gas loss q _A	%	5.8
CO	ppm	5
CO un.	ppm	6th
Lambda	-	1.29
Chimney draft	hPa	−0.1

The exhaust gas loss q _A and the carbon monoxide concentration CO are below the limit values, the filter sample did not reveal any residues, which means that the measurement meets the requirements of the BimSchV.

Flue gas measurement on a regulated forced draft burner (condensing boiler)

(Boiler, EL heating oil , CO ₂ max. = 15.4%, based on continuous operation under different weather conditions)

Get lost
		Full load
Flue gas temperature ( condensing boiler )	° C	77
Supply air temperature	° C	20th
Dew point temperature	° C	48
CO ₂	%	15.2
O ₂	%	0.6
Exhaust gas loss q _A	%	2.0
CO	ppm	15th
Lambda	-	1.03
Chimney draft	hPa	−0.08

The carbon monoxide concentration CO is below the limit values, the filter sample did not reveal any residues, which means that the measurement meets the requirements of the BimSchV. Flue gas loss is not subject to any control in condensing boilers.

Current status

All deadlines and transition periods granted by the legislator have expired since November 1, 2004. If the heating system does not comply with the legal requirements within the scope of a flue gas measurement and the chimney sweep as the authoritative examiner determines this in writing, the operator of the system must remedy the situation by, for example, replacing the old boiler or modifying it by replacing the burner or the like. If he does not want to do this, he is committing an administrative offense and must expect sanctions from the environmental agency. In the worst case, a fine will be imposed on him and the heating will be forcibly shut down. Under certain conditions, such as undue hardship , the environmental agency can temporarily override the requirements for the heating system in individual cases.

Web links

How to read the certificate according to the 1st BImSchV
Comparison: Situation in Austria ( Memento from April 20, 2015 in the Internet Archive )

Individual evidence

↑ FAQ of the BMU (PDF; 178 kB) ( Memento from March 17, 2016 in the Internet Archive )
↑ Type of burner, yellow or blue burner? . Heiz-tipp.de. Retrieved July 3, 2010.
↑ Clean Air Ordinance . Waltermeier.com. Archived from the original on June 18, 2010. Retrieved July 3, 2010.
↑ Günther Cerbe et al .: Fundamentals of Gas Technology. Gas procurement, gas distribution, gas use. 7th, completely revised edition. Hasner, Munich et al. 2008, ISBN 978-3-446-41352-8 .

[1] FAQ of the BMU (PDF; 178 kB) ( Memento from March 17, 2016 in the Internet Archive )

[2] Type of burner, yellow or blue burner? . Heiz-tipp.de. Retrieved July 3, 2010.

[3] Clean Air Ordinance . Waltermeier.com. Archived from the original on June 18, 2010. Retrieved July 3, 2010.

[test-4] Günther Cerbe et al .: Fundamentals of Gas Technology. Gas procurement, gas distribution, gas use. 7th, completely revised edition. Hasner, Munich et al. 2008, ISBN 978-3-446-41352-8 .