emissions of oil and gas appliances and requirements in european standards
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Combustion AnalysisTRANSCRIPT
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Emissions of Oil and Gas Appliances and
Requirements in European Standards
Client
Austrian Standards InstituteConsumer Council
Vienna, Oktober 1998
C.Hübner
R.Boos
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0 SUMMARY 3
1 ADAPTATION OF THE EMISSION LIMITS TO THE STATE OF THE ART 6
1.1 Heating oil 71.1.1 Concepts for low emissions from oil heating systems 7
1.1.2 Market survey for Germany 8
1.1.3 Emissions of on-site heating systems 9
1.2 Gas 101.2.1 State of the art of the combustion technology 10
1.2.2 Emissions of on-site heating systems 11
1.3 Comparison of emission limits for oil- and gas-fired heating systems 12
1.4 Conclusions 17
2 HARMONIZATION AND STANDARDIZATION OF EMISSION VALUES AND
THEIR TESTING PROCEDURES 19
2.1 Heating oil 19
2.2 Gas 19
3 LABELLING 20
4 INCLUSION OF THE EFFICIENCY INTO EMISSIONS VALUES OF BOILERS 21
5 ADDITIONAL TESTING REQUIREMENTS FOR A REALISTIC EVALUATION OF
THE EMISSIONS OF HEATING SYSTEMS 21
5.1 Consideration of the emissions at starting and stopping 21
5.2 Testing at the CO-minimum 22
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0 Summary
In the area of oil and gas appliances a number of technical committees are working
on the draft and revision of European Standards and guidelines. An important focus
of this task is the settling of testing criteria according to the relevant directives of the
European Community. In these documents important aspects concerning
environmental protection have not been taken into consideration sufficiently. This
concerns above all the requirements affecting the quality of combustion, which does
not reflect the state of the art in the field of heating appliances.
On behalf of the Austrian Standards Institute Consumer Council the current
European Standards and drafts Standards concerning oil and gas heating appliances
were checked with regard to the environmental criteria they propose.
In summary, the following important aspects of the documents urgently require a
revision:
Short-term aims
��Adaptation of the emission limits to the state of the art
A fundamental goal of the normative work is to codify the current state of the art.
Concerning the requirements for emissions of oil and gas appliances this goal has
not been reached in any respect. Emission limits such as 250 mg NOx/kWh
respectively 125 mg CO/kWh for oil appliances and 260 mg NOx/kWh and
0,1 Vol% CO (� 1070 mg/kWh) for gas appliances are much to high and
correspond to the state of the art of the eighties.
On the other hand, producers have improved combustion technologies
considerably and field studies have shown that current emissions are much lower
than the highest emission limits of the relevant Standards. Furthermore, national
legislation for new appliances demand lower emissions without having lead to a
slump in sales.
� Therefore, an adaptation of the emission limits in these Standards should be
implemented as soon as possible, in order to meet the current state of the art.
� The requirements concerning the quality of combustion which should be taken into
account are shown in the table below. These proposed values take into
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consideration the state of the art of combustion technologies and national
regulations as well.
� The widely used or proposed concept of emission or performance classes should
be dropped anyway. This is owing to the fact that in some countries emission
limits are already effective which differ from the treshold values of the proposed
emission classes substantially. Furthermore, the definition of categories blurs the
differences between appliances, since classes do not show singular figures which
might be interesting for consumers.
tab. 1 Proposed requirements for the quality of combustion
Standard short title nominal CO NOx CxHy sootheat input mg/kWh mg/kWh ppm number
GasEN 303-3 Gas-fired central heating boilers -
Assembly boiler body / forced draught burner
<= 120 kW 90 100 - -
EN 676 Automatic forced draught burners for gaseous fuels
<= 120 kW 90 100 - -
EN 297 Gas-fired central heating boilers - Type B11 and B11BS (atmospheric burners)
<= 70 kW 90 100 - -
EN 483 Gas-fired central heating boilers - Type C
<= 70 kW 90 100 - -
Heating OilEN 303-2 Heating boilers with forced draught
burners - Boilers with atomizing oil burners
<=120 kW 90 120 10 1
EN 267 Forced draught oil burners <=120 kW 90 120 10 1
For gas-fired appliances intended to use only gases of the third family (propane/butane), the limit NOx value ismultiplied by a factor of 1,30.
Furthermore, emission limits should be introduced for appliances which at present
are not within the scope of the Standards discussed above, such as:
evaporative oil burners with and without fan
gas-fired air and space heaters, overhead radiant heaters
gas-fired water heaters (recirculated water heater, reservoir water heater)
gas-fired convection heaters
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��Harmonization and standardization of the emission limits and the
corresponding testing procedures (boiler and burner Standards)
The harmonization refers, in particular, to the :
- adaptation of EN 303-2 to the procedures and requirements of EN 267
(specification of the fuel, calculation of the NOx figures to standard
conditions)
- adaptation of EN 303-3 to the requirements of EN 676
(same CO emission limit value)
��Consistent labelling and specification of emission values
The current drafts for oil and gas appliances require an assignment of the
appliances to different NOx-, and in the case of oil-fired devices also to CO-,
emission classes by the producer. In the current version of the draft the
connection between such an assignment to a specific emission class and the
quality of combustion is not sufficiently clear.
Therefore and in view of the fact that consumers usually are not experts the
labelling should meet the following requirements:
1. Transparency for the consumers. This means that is has to be very clear if
a specific appliance has low, high or average emission levels. This could
be achieved by a figure.
2. The results from the type testing protocol should be shown on the data
plate.
A proposal for such a labelling is given in chapter 3.
� Goals to be achieved in the future
�� Inclusion of the efficiency into emission values
As a reference the emissions of oil and gas appliances are usually related to the
energy content of the fuel (mg/kWh). In order to make the comparison of heating
systems easier and more consistent, the efficiency should be included into the
evaluation of the emissions.
��Additional testing requirements for a realistic evaluation of the emissions of
heating systems
- Draft of a testing procedure for emissions during starting and stopping
- Testing of the NOx emission at the CO minimum
� These proposals are detailed in the following chapters 1-5.
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1 Adaptation of the emission limits to the state of the art
For heating systems issues related to environmental protection should be of the
same importance as the operational safety, the user-friendliness and the economic
efficiency. The usual approach in Europe during the harmonization of the Standards
is the description of testing procedures, in order to show the compliance with the
essential requirements, as laid down in the relevant documents of the European
Community. At present these requirements focus essentially on the operational
safety and the reliability of products, but do not promote efforts to improve the levels
of emission or the energy efficiency. Issues of environmental protection are largely
regulated at the national level and every state is free to lay down specific emission
limits by his own.
However, the European Standards are the basis of current and future markets for
heating systems and they should define the state of the art at the moment of their
publication. Unfortunately, the current standards for heating systems do not describe
the state of the art concerning the quality of combustion sufficiently.
Table 2 shows the emission limits for oil and gas appliances, as given in the
corresponding Standards of burners and boilers.
In some Standards or draft Standards emission classes are given for oil and gas
heating systems. These emission classes can be regarded as emission limits as well,
since they give a maximum value which can not be exceeded (e.g. 260 mg/kWh for
NOx in EN 297/prA5). The other values are thresholds of the respective class.
In practice, a producer defines a class for the appliance to be tested. The
compliance results from a type testing procedure, where the emission values are
measured and the classification by the producer is verified. The Standard drafts do
not make clear whether a classification into an other class results or is still possible
even if an emission value exceeds the corresponding class limit.
In prEN303-2 some classes for oil units are given. A unit is an appliance where a
specific burner type forms a unit with a specific boiler type, and the testing is
performed in this particular design. Usually such units rely on a good tuning of the
burner and the boiler with regard to their nominal output and their combustion
chamber volume. This tuning often results in lower emissions of pollutants.
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tab. 2 Emission limits of current Standards and draft Standards for oil and gas heatingsystems
Standard short title nominal date NOx CO CxHy soot
heat input mg/kWh mg/kWh ppm number
Gas
prEN 303-3 Gas-fired central heating boilers - Assembly boiler body / forced draught burner
<= 1 MW 05-97 - 1070
EN 676 Automatic forced draught burners for gaseous fuels
10-96 170 100
EN 297/prA5 Gas-fired central heating boilers - Type B11 and B11BS (atmospheric burners)
<= 70 kW 03-97 5 classes:260
200 / 150100 / 70
-
prEN 483 Gas-fired central heating boilers - Type C <= 70 kW 04-98 5 classes:260
200 / 150100 / 70
-
Heating Oil
prEN 303-4 Heating boilers with forced draught burners - Special requirements
<= 70 kW 02-98 - -
EN 304 Heating boilers - Test code for heating boilers for atomizing oil burners
09-92 - -
prEN 303-2 Heating boilers with forced draught burners - Boilers with atomizing oil burners
02-98 250 110 10 1
for units only3 classes: 185 / 120 /
120
3 classes: 110 / 80 / 60
prEN 267 Forced draught oil burners 09-97 4 classes:250 / 160120 / 70
4 classes:125 / 11060 / 30
10 1
1.1 Heating oil
1.1.1 Concepts for low emissions from oil heating systems
Low NOx emissions can be achieved by measures such as recirculation of flue gas,
pre-evaporation of the oil and optimal mixing with air. Depending on the design of the
burner, heating systems in use nowadays (yellow flame burners, blue flame burners
and burners with stabilized spin) achieve varying recirculation rates of the flue gas
and different rates of pre-evaporation at the site of the reaction. However, these
features are constrained by the requirement of a stable flame1.
1 Klausmann, W., Stock, R. (1998): Erfolgskonzepte für geringe Emissionen bei der Ölverbrennung.
Wärmetechnik 3/1998, pp.34
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With the specific burner systems different NOx emission levels can be reached.
Yellow flame burners usually are in a range of 110 - 180 mg NOx/kWh, but low NOx
appliances with flue gas recirculation can reach emission values below 120 mg/kWh.
Blue flame burners show, depending on their design, NOx levels between 70 and
120 mg/kWh. Using burners with a spin stabilisation NOx levels below 70 mg/kWh
can be reached owing to the high rate of recirculation.
1.1.2 Market survey for Germany
In a market survey for Germany, which was published lately in "Wärmetechnik"2 and
which takes into account the 1.BImSchV3, producers were consulted about their
products. Altogether 57 products by 18 producers were considered, all of them with a
thermal nominal output below 70 kW and in compliance with the 1.BImSchV
regarding the NOx emissions. This broad range of products shows, that many
producers already offer appliances with low-emission-burners and that a trend
towards blue flame burners is evident. This technology has improved in recent years
in such an extent, that its stability and the noise level are in the range of yellow flame
burners.
Fig.1 shows the NOx and CO emissions of burners and burner-boiler units as given
by the producers, tested according to EN 267 and in compliance with the 1.BImSchV
(NOx <= 120 mg/kWh).
Emission values which in the market survey are given as „lower as“, are quoted in
the figure with their respective numerical value.
2 Marktübersicht ´98: Öl-Druckzerstäuberbrenner kleiner Leistung (bis 70 kW). Wärmetechnik 4/1998,
pp.363 1.Bundesimmissionsschutzverordnung - Verordnung über Kleinfeuerungsanlagen. März 1997
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fig. 1 Evaluation of a market survey of oil-fired forced draught burners with NOx<=120 mg/kWh of 1998Classes according to prEN267 (Sept-97)
0
50
100
150
200
250
0 25 50 75 100 125
m g C O / kW h
mg
NO
x / k
Wh
C lass 2C lass 4 C lass 3 C lass 1
1.1.3 Emissions of on-site heating systems
Domestic oil-fired heating systems have been evaluated in a field test in Austria4, in
which emission measurements at approximately 200 light heating oil appliances with
low thermal nominal output were carried out. These measurements were performed
without any previous tuning of the appliances and therefore reflect the actual
emissions. The sample included heating facilities with new forced draught burners
and conventional yellow-flame burners as well. Owing to the age of the tested
appliances, this study represents the state of the art of the eighties and early
nineties.
The NOx emission were, depending on the type of technology, within the range of
100 - 180 mg/kWh and only very few appliances had emissions higher than 200
mg/kWh.
4 Hübner,C., Herger,M., Heger,F., Zobl,P., Hackl,A. (1996): Exhaust Emissions of Heating Fuel Fired
Plants during Stationary Operation Phase. Part 1: Plants up to 350 kW with Domestic Heating Fuel.Erdöl, Erdgas, Kohle 112/4, pp. 170 (in German).
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Considering those appliances which were in proper conditions with regard to their
maintenance and tuning, most of them had CO emissions below 20 mg/kWh. Only
these figures can reasonably be compared with the results of type testings with
appliances, which are usually tested under optimal conditions.
As the results of this field study in Austria have shown, NOx emissions about 200
mg/kWh and below can be achieved simultaneously with low CO emissions by
appliances which reflect the state of the art of the late eighties and early nineties.
These levels were reached at a moment when the stricter emissions limits of the
Austrian Kleinfeuerungsanlagenverordnung (120 mg NOx/kWh for appliances with oil
fan burner) did not yet had come into effect5.
Surprisingly, the draft Standards prEN267 and prEN303-2 from 1998 still have an
emission limit of 250 mg NOx /kWh.
1.2 Gas
1.2.1 State of the art of the combustion technology
1.2.1.1 Atmospheric burners
A atmospheric burner consists in principle of a nozzle, where the flowing gasstream
exerts a suction by which the combustion air is totally or partially drawn in (full or
partial premixing). The mixture of fuel and combustion air is therefore formed without
any additional mechanical devices.
Partial premixing atmospheric burners, which have dominated the market in the last
decades, will in future only be employed for some kinds of special gas boilers. In the
area of domestic fireplaces this type of burner with nominal outputs between 10 and
30 kW emitts approximately 150-200 mg/kWh NOx and 50-100 mg/kWh CO6.
In the field of small scale combustion facilities the full premixing burners have
meanwhile become widespread owing to their lower emissions. In this type of
appliances the mixing of gas and air is carried out with an excess of oxygen before
the ignition takes place. Therefore, there is no need of a secondary air supply as it is
the case in partially premixing devices7.
5 Art. 15a Vereinbarung über Schutzmaßnahmen betreffend Kleinfeuerungsanlagen (1995).6 Gia My,T., Bosch,J., Lenze,B. (1996): Einfluß von Vormischung, Strömung und Wärmebelastung auf
die Stickoxidbildung in Haushaltsbrennern. GWF Gas, Erdgas 137, Nr.2, pp.89.7 Jantzer,M., Bienzle,M., Frieling,Th. (1997): Zum Stand der Brennertechnik bei Gas-
Umlaufwasserheizern. GWF Gas, Erdgas 138, Nr.11, pp.627
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The level of emission in this type of appliances is dependent on the air number and
the heat input. If the air number is sufficiently high and the premixing is good as well,
a stable combustion and low CO emissions can be achieved.
Moreover, a series of measures can be implemented in order to reduce the NOx
emissions, such as cooling of the flame by special devices, reduction of the heat
input by enlargement or stretching of the combustion zone or by the use of
catalytically active surfaces.
The emission levels which can be reached during continuous combustion are in a
range below 60 mg CO/kWh and, depending on the heat input, between 60 and
80 mg NOx/kWh.
1.2.1.2 Gas-fired forced draught burners
In contrast to the atmospheric burners for gas-fired forced draught burners the
combustion air is supplied by a fan. Depending on the design of the burner NOx
emission levels reach about 80 mg/kWh.
1.2.1.3 Fan assisted surface burners
This type of burner also has a fan to ensure a thorough mixing of the fuel and the air.
The gas/air mixture passes a perforated sheet and the combustion is carried out on
a metallic or ceramic surface.
These burners are very common in appliances characterized by a low heat input.
Owing to the intense radiation and the low thermal stress at the surface the
temperature of the flame is lower as in other types of burners. NOx emissions below
40 mg/kWh are therefore feasible8. Burners with catalitically active surfaces have
even lower NOx emissions.
1.2.2 Emissions of on-site heating systems
Between 1990 and 1995 an extensive field study with emission testings on gas-fired
heating systems was carried out in Austria9. 500 domestic appliances with a nominal
heat input below 350 kW were tested. The selection of the sample was
representative for gas heating systems on-site in Austria.
8 Hüppelshäuser,H., Berg,H., Altfeld,K. (1994): Schadstoffarme Gas-Vormischbrenner für kleine
Leistungen. GWF Gas, Erdgas 135, Nr.4, pp.2299 Brötzenberger,H., Kreft,N. (1997): GF 24 Emissionen von Gasgeräten in Österreich -
Emissionsfaktoren und Einsparpotentiale. ÖVGW Forschung Gas, Österreichische Vereinigung fürdas Gas- und Wasserfach.
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A trend towards lower NOx emissions is evident, if older and newer appliances are
compared (table 3).
tab. 3 NOx and CO emissions of on-site heating systems depending on year of manufacture.Mean values for all types of appliances with an actual heat input of not more than 10% of thenominal heat input. (Source: Brötzenberger & Kreft, 1997)
Year of manufacture NOx emissions(mg/kWh)
CO emissions(mg/kWh)
1980 - 84 220 148
1985 - 89 176 61
1990 - 96 115 68
In this report no separate emission data were provided for different types of burners
or appliances for different years of manufacture. Therefore, a separate evaluation of
forced-draught burners and atmospheric burners with regard to the year of
manufacture is not possible.
Nevertheless, it can be shown on the basis of these data which emissions are to be
expected from gas-fired heating systems on-site. Moreover, a trend becomes
apparent due to the increased use of Low-NOx-burners and improved combustion
technologies in the last 15 years. This trend has not been taken into account in the
European body of Standards.
1.3 Comparison of emission limits for oil- and gas-fired heating systems
In many European countries national legislation exists concerning the emissions of
small scale combustion facilities, e.g. 1.BImSchV in Germany,
Kleinfeuerungsanlagenverordnung in Austria (by the §15a Vereinbarung),
Luftreinhalteverordnung in Switzerland and VLARM II in Belgium.
Moreover plans for measures exist in Netherlands and Denmark, which are based on
the Swiss Luftreinhalteverordnung.
In the following figures and tables the national emission limits and those of
Standards and draft Standards are compared.
The scopes of the regulations in the different countries and of the Standards are not
identical. This applies for example to the range of heat input. In addition, some
national legislations apply the emission limits to the heating system as a whole and
not to the burner or the boiler separately as in the Standards. Some specific
restrictions and remarks are not detailed in the table in order to make the comparison
easier.
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tab. 4 Oil-fired heating systems
Heating oil appliances(emission limits in mg/kWh)
Atomizing oil burner Heating boilers with atomizing
oil burners
Heating boilers with atomizing
oil burners - Units
European Standard Standard prEN 267 prEN 303-2 prEN 303-2NOx 250/160/120/70 250 185/120/120CO 125/110/60/30 110 110/80/60
CxHy 1) - 19 19RZ - 1 1
remarks <= 1000 kW <= 70 kW (?)
1.BImSchV NOx 120 120 120Germany (1.1.1998) CO - - -
CxHy - - -RZ - - -
remarks <= 120 kW <= 120 kW <= 120 kW
KFA-Verordnung (§15a) NOx 2) 126 126 126Austria (1995, 1998) CO 2) 72 72 72
CxHy 2) 21,6 21,6 21,6RZ 1 1 1
remarks 4-400 kW 4-400 kW 4-400 kW
Luftreinhalteverordnung NOx 3) 124 124 124Switzerland (1-1-92) CO 3) 62 83 62
CxHy 3) 31 - -RZ 0,5 1 1
remarks <= 350 kW <= 350 kW <= 350 kW
Blauer Engel NOx 120 110Germany (1998) CO 60 60
remarks <= 120 kW <= 70 kW
1) converted values: ppm (3%O2) into mgC/kWh2) converted values: mg/MJ into mg/kWh 3) converted values: mg/m³ (3%O2) into mg/kWhRZ = Soot numberCxHy = volatile organic compounds
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fig. 2 Oil-fired heating systems
NOx emission limits and state of art
0
30
60
90
120
150
180
210
240
270
prEN267 prEN303-2 1.BImSchV §15a CH-LRV state of art
mg/
kWh
CO emission limits and state of art
0
30
60
90
120
150
prEN267 prEN303-2 1.BImSchV §15a CH-LRV state of art
mg/
kWh
no li
mit
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tab. 5 Gas-fired heating systems
Gas appliances(emission limits in mg/kWh)
Forced draught burners for
gaseous fuels
Gas-fired heating boilers with
forced draught burner
Gas-fired central heating boilers fitted with atmospheric burners
Condensing boilers
European Standards EN 676 prEN 303-3 EN 297/prA5 prEN 483 EN 677NOx 170 - 260/200/150/100/70CO 100 1070 1)
remarks <= 70 kW <= 70 kW <= 70 kW
1.BImSchV NOx 80 80 80 80 80Germany (1998) CO
remarks <= 120 kW <= 120 kW <= 120 kW <= 120 kW <= 120 kW
KFA-Verordnung (§15a) NOx 2) 108 108 108 3) 108 3) 108Austria (1995, 1998) CO 2) 72 72 72 72 72
remarks <= 350 kW <= 350 kW <= 350 kW <= 350 kW <= 350 kW
Luftreinhalteverordnung NOx 4) 80 80 80 5) 80 5) 80Switzerland ( 1992) CO 4) 60 100 100 100 100
remarks <= 350 kW <= 350 kW <= 350 kW <= 350 kW <= 350 kW
Blauer Engel NOx 70 70 70 70 (60 6)) 60Germany (1998) CO 60 60 60 60 50
remarks <= 120 kW Units <= 70 kW <= 70 kW <= 70 kW Units <= 70 kW
1) converted values: ppm (0%O2) into mg/kWh 2) converted values: mg/MJ into mg/kWh 3) for gas-fired recirculated water heater, reservoir water heater and single stove: 216 mg/kWh4) converted values: mg/m³ (3%O2) into mg/kWh5) for atmospheric burners up to 12 kW nominal heat input: 120 mg/kWh6) for special kinds of water heaters (Kombiwasserheizer, Umlaufwasserheizer)
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fig. 3 Gas-fired heating systems
NOx emission limits and state of art
0
30
60
90
120
150
180
210
240
270
EN676 EN297/EN483 1.BImSchV §15a CH-LRV state of art
mg/
kWh
CO emission limits and state of art
0
100
200
300
400
500
600
700
800
900
1000
1100
EN676 prEN303-3 1.BImSchV §15a CH-LRV state of art
mg/
kWh
no li
mit
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1.4 Conclusions
�� Combustion technologies for oil- and gas-fired appliances are available, which
have much lower emission levels than the emissions limits of the current
Standards or draft Standards for burners and boilers.
�� As a result of the technological development, which was strongly reinforced by
national regulations and measures for environmental protection, a range of
producers offer oil and gas appliances with low emissions. This state of the art has
not been taken into account by the Standards at issue.
�� Even on-site heating facilities, which reflect the state of the art of the eighties and
early nineties, have shown emissions below the threshold limits proposed by the
Standards for oil- and gas-fired appliances.
�� Many national regulations stipulate much lower emission limits, which can be
reached by available technologies.
�� A revision of the Standards concerned is therefore indispensable, in order to
adapt the proposed emission limit values to the state of the art and to the national
legislation.
The emission limits should be as follows:
tab. 6 Proposed emission limits
Standard short title nominal CO NOx CxHy sootheat input mg/kWh mg/kWh ppm number
GasEN 303-3 Gas-fired central heating boilers -
Assembly boiler body / forced draught burner
<= 120 kW 90 100 - -
EN 676 Automatic forced draught burners for gaseous fuels
<= 120 kW 90 100 - -
EN 297 Gas-fired central heating boilers - Type B11 and B11BS (atmospheric burners)
<= 70 kW 90 100 - -
EN 483 Gas-fired central heating boilers - Type C
<= 70 kW 90 100 - -
Heating OilEN 303-2 Heating boilers with forced draught
burners - Boilers with atomizing oil burners
<=120 kW 90 120 10 1
EN 267 Forced draught oil burners <=120 kW 90 120 10 1
For gas-fired appliances intended to use only gases of the third family (propane/butane), the limit NOx value ismultiplied by a factor of 1,30.
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Furthermore, emission limits should be introduced for appliances which at present
are not within the scope of the Standards discussed above, such as:
evaporative oil burners with and without fan
gas-fired air and space heaters, overhead radiant heaters
gas-fired water heaters (recirculated water heater, reservoir water heater)
gas-fired convection heaters
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2 Harmonization and standardization of emission values and their
testing procedures
2.1 Heating oil
In prEN 303-2 (heating boilers with forced draught burners) emission classes for CO
and NOx are only proposed for units, but these are not consistent with the respective
classes of prEN 267 (forced draught oil burners). According to prEN 267 the testing
of the forced draught burners is carried out at a test combustion chamber or,
alternatively, with a boiler suited for the burner. This means that at a test of a boiler-
burner-unit the thresholds of prEN 303-2 and prEN 267 have to be met
simultaneously. In this respect the classes for units in prEN 303-2 are irrelevant.
Furthermore, prEN 303-2 does not specify the nitrogen content of the fuel. Also, the
calculation of the measured NOx to standard conditions is not taken into account
(nitrogen content of the heating oil, humidity and temperature of the combustion air).
In this respect an adaptation of EN 303-2 to the testing requirements of EN 267 is
necessary.
2.2 Gas
The current drafts of prEN 303-3 (assembly gas-fired forced draught burner and
boiler) and EN 676 (automatic forced draught burners for gaseous fuels) differ with
respect to the CO emissions by one order of magnitude. According to EN 676 a
emission limit for gas-fired forced draught burner of 100 mg CO/kWh has to be
reached. The testing after the assembly of boiler and burner according to prEN 303-3
requires CO emissions below 0,1 Vol% (� 1070 mg/kWh). This discrepancy has no
technical foundation, since a CO threshold of 0,1% might be sufficient for personal
safety, but does not meet the requirements of a modern combustion system.
Furthermore it is not logical at all, that a burner tested at a test combustion chamber
can have higher CO emissions after having been assembled with a boiler, to which it
must be adjusted anyway. Requirements concerning the NOx emissions were
omitted completely, in the foreword of prEN 303-3 only a reference to EN 676 is
given.
An adaptation of prEN 303-3 to the requirements of EN 676 is absolutely necessary
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3 Labelling
As required by the current draft standards for oil-fired heating systems (prEN 303-2,
prEN 267) and gas-fired boilers for atmospheric burners (EN 297/prA5, prEN 483),
producers have to assign their products to a NOx- ,and in the case of oil-fired
appliances, to a CO-emission class as well. The introduction of emission classes
shows at the first time, that more stress was put on the environmental issues than
previously. On the other hand, it implies that by using different technologies different
levels of emission can be reached. This procedure is basically a reasonable
approach, if the limits of the emission classes reflect the state of the art (see
above/see Pos.1). Moreover, an appropriate labelling is a prerequisite for a
consumer to decide if an appliance has low emissions or not.
The classification and the labelling into the classes 1-4 respectively. 1-5 which is
discussed at present, can not be accepted. The connection between a certain class
and the level of emission is not clear for a consumer in the current version. Most
likely, central European consumers would regard a class 1 appliance as a low
emission product, whereas a French consumer might expect an appliance with high
emissions, according to their respective school rating systems.
A minimum requirement for a future labelling of heating systems is the expression of
the emission values, which were determined at the type testing. Furthermore, the
labelling should enable the consumer to compare and to asses the emission levels of
heating appliances (preferably by a figure as proposed below).
fig. 4 Proposal for a labelling for oil-fired appliances
NOxNOxNOx
NOx: 84 mg/kWhNOx: 84 mg/kWhNOx: 84 mg/kWh120120120
202020
707070
000
COCOCO
CO: 50 mg/kWhCO: 50 mg/kWhCO: 50 mg/kWh909090
606060
303030
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fig. 5 Proposal for a labelling for gas-fired appliances
NOxNOxNOx
NOx: 36 mg/kWhNOx: 36 mg/kWhNOx: 36 mg/kWh100100100
202020
606060
000
COCOCO
CO: 50 mg/kWhCO: 50 mg/kWhCO: 50 mg/kWh909090
606060
303030
4 Inclusion of the efficiency into emissions values of boilers
As a reference the emissions are usually related to the energy content of the fuel
(mg/kWh). However, at an efficient heating appliance emissions are lower taking into
account that smaller amounts of fuel are necessary for a defined heat output. An
accurate figure for the energy output of a heating appliance is the useful efficiency.
As a criterion the inclusion of the efficiency into the emission values would ensure
comparable and standardized assessments of heating appliances.
5 Additional testing requirements for a realistic evaluation of the
emissions of heating systems
5.1 Consideration of the emissions at starting and stopping
Emission limits apply to the continuous operation and therefore only cover a part of
the total emissions. Little attention was paid to the emissions during the starting and
stopping which can be considerable, such as the CO- an CxHy-emissions,
respectively the methane emissions of gas-fired appliances. These emissions are
relevant when the operation time of the burner is short. The operation time is usually
in the range of 3 to 10 minutes. Short operation times are to be expected, if the
storage capacity of the boiler/heating system is low and/or the output of the burner is
much higher than the demand of heat.
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The Standard on oil-fired forced draught burners (prEN267) only contains
requirements for a fast transition to a continuous operation after the start, which has
to be controlled by testing the fluctuation of the pressure in the combustion chamber.
The emissions of CxHy can be higher than 10 ppm within the first 20 seconds. There
are no limitations for CO.
The Standards on gas-fired appliances do not take into consideration this aspect at
all.
The testing of emission during the starting and stopping is often rejected, because it
is supposed to require great technical efforts giving results with a low reproducibility.
On the other hand, it has been the norm in other areas (as the automobile industry)
since many years, to monitor stop-and-go periods of operation or test cycles in order
to get realistic emission values.
The corresponding working groups and technical committees are required to
formulate proposals as how to monitor emissions during the starting and stopping
and to develop an adequate testing procedure.
5.2 Testing at the CO-minimum
The testing of emissions at a type testing control does not necessarily lead to a
realistic assessment of a heating appliance. In practice, very often higher combustion
air volumes (higher air numbers) are chosen at the start up or at maintenance, in
order to achieve a higher operational safety. At type tests it is possible, to attain
lower NOx emissions at the expense of higher CO levels, by varying the operational
conditions (e.g. the air number). The measurement of the NOx emissions in a range
of the air number where the CO level is at its minimum, would reproduce realistic
conditions much better. The quality of a (forced draught) burner-boiler-system
becomes evident, when the burner can be operated in a wide range, without leading
to a relevant increase of the CO and CxHy emissions and, in the case of the oil-fired
burners, of the soot number.