Emissions of Oil and Gas Appliances and Requirements in European Standards

Emissions of Oil and Gas Appliances and

Requirements in European Standards

Client

Austrian Standards InstituteConsumer Council

Vienna, Oktober 1998

C.Hübner

R.Boos

Emissions of Oil and Gas Appliances and Requirements in European Standards FTU GmbH

page 2 of 22

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


page 3 of 22

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


page 4 of 22

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


page 5 of 22

��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.


page 7 of 22

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


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


page 8 of 22

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


page 9 of 22

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).


page 10 of 22

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


page 11 of 22

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.


page 12 of 22

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.


page 13 of 22

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


page 14 of 22

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


page 15 of 22

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


Luftreinhalteverordnung NOx 4) 80 80 80 5) 80 5) 80Switzerland ( 1992) CO 4) 60 100 100 100 100


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)


page 16 of 22

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


page 17 of 22

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 - -


<= 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.


page 18 of 22

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


page 19 of 22

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


page 20 of 22

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.

Emissions of Oil and Gas Appliances and Requirements in European Standards

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