BS EN 777 3 2009 ICS 91 140 40 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BRITISH STANDARD Multi burner gas fired overhead radiant tube heater systems for non domestic use[.]
System and its constituent parts
An overhead radiant tube heater is a gas-fired appliance designed for installation above head level It effectively heats the space below through radiation, utilizing one or more tubes that are warmed by the internal flow of combustion products.
3.1.2 multi-burner systems those radiant tube heater systems which employ two or more burner units with each unit incorporating independent flame monitoring
The units can be found in various sections of tubing, and multiple fans may be utilized to aid in the removal of combustion byproducts or to provide combustion air.
System F: a system in which individual units with a fan are connected to a common duct with a fan
Only one burner unit is situated in each branch tube (see Annex B)
3.1.3 branch tube for the purposes of this part, a tube in which only one burner unit is situated and which only contains the products of combustion generated by this burner
3.1.4 common duct duct which receives products of combustion from two or more branch tubes for the purposes of evacuation to the outside
The individual burner unit consists of a main burner and, if necessary, an ignition burner This unit also includes essential components for igniting the burners, monitoring the flame, and controlling the gas supply to ensure efficient operation.
3.1.6 inlet connection part of the system intended to be connected to the gas supply
3.1.7 mechanical joint (mechanical means of obtaining soundness) means of ensuring the soundness of an assembly of several (generally metallic) parts without the use of liquids, pastes, tapes, etc
NOTE For example the following: a) metal to metal joints; b) conical joints; c) toroidal sealing rings (“O” rings); d) flat joints
3.1.8 gas circuit part of the burner unit that conveys or contains the gas between the burner unit gas inlet connection and the burner(s)
A restrictor device featuring an orifice is installed in the gas circuit to generate a pressure drop, effectively lowering the gas pressure at the burner to a specified level based on the supply pressure and flow rate.
3.1.10 gas rate adjuster component allowing an authorized person to set the gas rate of the burner to a predetermined value according to the supply conditions
NOTE 1 Adjustment can be progressive (screw adjuster) or in discrete steps (by changing restrictors)
NOTE 3 The action of adjusting this device is called “adjusting the gas rate”
NOTE 4 A factory sealed gas rate adjuster is considered to be non-existent
3.1.11 setting an adjuster immobilizing a gas rate adjuster by such means as e.g a screw after the gas rate has been adjusted by the manufacturer or installer
Sealing an adjuster refers to a method designed to prevent unauthorized changes to the adjustment This arrangement ensures that any attempt to alter the adjustment will damage the sealing device or material, making the interference clearly visible.
NOTE A factory sealed adjuster, i.e an adjuster sealed by the system manufacturer, is considered to be non-existent
A regulator is deemed non-existent if it has been factory sealed by the system manufacturer, rendering it inoperable within the normal supply pressure range for its system category.
When an adjuster or control, such as those regulating temperature or pressure, is "put out of service," it means that it has been deactivated and sealed in that position Consequently, the burner unit operates as if the device has been completely removed.
3.1.14 injector component that admits the gas into a burner
3.1.15 main burner burner that is intended to ensure the thermal function of the system and is generally called the burner
3.1.16 ignition device means (e.g flame, electrical ignition device or other device) used to ignite the gas at the ignition burner or at the main burner
NOTE This device can operate intermittently or permanently
3.1.17 ignition burner burner whose flame is intended to ignite another burner
3.1.18 primary aeration adjuster device enabling the primary air to be set at the desired value according to the supply conditions
3.1.19 combustion products circuit circuit consisting of:
3.1.19.1 combustion chamber enclosure inside which combustion of the air-gas mixture takes place
3.1.19.2 flue outlet part of a Type B system that connects with a flue to evacuate the products of combustion
3.1.19.3 draught diverter device placed in the combustion products circuit to reduce the influence of flue-pull and that of down- draught on the burner performance and combustion
The POCED combustion products evacuation duct is designed exclusively for use with a specific appliance or system, either provided with the appliance/system or detailed in the manufacturer's instructions.
The range-rating device on the burner unit allows installers to adjust the heat input according to the manufacturer's specified range, ensuring it meets the actual heat requirements of the installation.
This adjustment may be progressive (e.g by use of a screw adjuster) or in discrete steps (e.g by changing restrictors)
The zero regulator is a device designed to maintain a consistent downstream pressure at zero, regardless of fluctuations in upstream pressure or negative pressure downstream of the gas orifice, operating within fixed limits.
Adjusting, control and safety devices
3.2.1 automatic burner control system system comprising at least a programming unit and all the elements of a flame detector device
The various functions of an automatic burner control system may be in one or more housings
The programming unit device responds to signals from control and safety devices, issuing control commands and managing the start-up sequence It supervises burner operation, facilitates controlled shut-downs, and initiates safety shut-downs and lock-outs when necessary.
NOTE The programming unit follows a predetermined sequence of actions and always operates in conjunction with a flame detector device
3.2.3 programme sequence of control operations determined by the programming unit involving switching on, starting up, supervising and switching off the burner
3.2.4 flame detector device by which the presence of a flame is detected and signalled
A flame detection system typically includes a flame sensor, an amplifier, and a relay for signal transmission These components, except for the flame sensor, can often be integrated into a single housing to work alongside a programming unit.
3.2.5 flame signal signal given by the flame detector device, normally when the flame sensor senses a flame
3.2.6 flame simulation condition which occurs when the flame signal indicates the presence of a flame when in reality no flame is present
3.2.7 pressure regulator 1 device which maintains the outlet pressure constant independent of the variations in inlet pressure within defined limits
3.2.8 adjustable pressure regulator regulator provided with means for changing the outlet pressure setting
3.2.9 flame supervision device device that, in response to a signal from the flame detector, keeps the gas supply open and shuts it off in the absence of the supervised flame
3.2.10 automatic shut-off valve device that automatically opens, closes or varies the gas rate on a signal from the control circuit and/or the safety circuit
System operation
Q quantity of energy used in unit time corresponding to the volumetric or mass flow rates; the calorific value used being the net or gross calorific value
NOTE The heat input is expressed in kilowatts (kW) [EN 437:2003]
Q n value of the heat input (kW) declared by the manufacturer
V volume of gas consumed by the appliance in unit time during continuous operation
NOTE The volume flow rate is expressed in m 3 /h, l/min, dm 3 /h or dm 3 /s [EN 437:2003]
M mass of gas consumed by the appliance in unit time during continuous operation
1 The term “regulator” is used in this case and for a volume regulator
NOTE The mass flow rate is expressed in kg/h or g/h [EN 437:2003]
3.3.5 flame stability characteristic of flames which remain on the burner ports or in the flame reception zone intended by the construction
3.3.6 flame lift total or partial lifting of the base of the flame away from the burner port or the flame reception zone provided by the design
Flame lift may cause the flame to blow out, i.e extinction of the air-gas mixture
3.3.7 light-back entry of a flame into the body of the burner
Light-back at the injector refers to the ignition of gas at the injector, which can occur due to flame propagation from the burner or backflow of flame into the burner itself.
3.3.9 sooting phenomenon appearing during incomplete combustion and characterized by deposits of soot on the surfaces or parts in contact with the combustion products or with the flame
3.3.10 yellow tipping yellowing of the tip of the blue cone of an aerated flame
Purge refers to the forced introduction of air through the combustion chamber and flue passages to eliminate any residual fuel/air mixture or combustion products This process includes two phases: a) pre-purge, which occurs between the start signal and the activation of the ignition device, and b) post-purge, which takes place immediately after the system is shut down.
The first safety time interval refers to the duration between the activation of the ignition burner valve, start gas valve, or main gas valve, and their subsequent deactivation if the flame detector indicates that no flame is present at the end of this interval.
The second safety time is defined as the duration between the energization and de-energization of the main gas valve, specifically when there is an initial safety time for either an ignition burner or start gas flame This interval is crucial as it occurs if the flame detector indicates that there is no flame present at the conclusion of this period.
2 Where there is no second safety time, this is called the safety time
Extinction safety time refers to the duration that passes from the moment the supervised flame is extinguished until the automatic burner control system activates the shutdown process by cutting power to the automatic gas shut-off valves.
3.3.15 start-gas flame flame established at the start-gas rate either at the main burner or at a separate ignition burner
3.3.16 running condition of the system condition in which the burner is in normal operation under the supervision of the programming unit and its flame detector device
3.3.17 controlled shut-down process by which the power to the gas shut-off valve(s) is removed immediately, e.g as a result of the action of a controlling function
The safety shut-down process is activated immediately after a safety control or sensor responds to a fault in the burner control system This process ensures the burner unit is taken out of operation by promptly cutting power to the gas shut-off valve(s) and the ignition device.
The burner unit features a non-volatile lock-out safety shut-down condition, ensuring that a restart can only be achieved through a manual reset of the unit, preventing any alternative methods.
A volatile lock-out is a safety shut-down condition for the burner unit, requiring a manual reset or a restoration of the mains electrical supply for a restart.
3.3.21 spark restoration process by which, following the loss of the flame signal, the ignition device will be switched on again without the total interruption of the gas supply
This process concludes with either the restoration of the running condition or, in the absence of a flame signal after the safety time, a volatile or non-volatile lockout.
3.3.22 automatic recycling process by which, after a safety shut-down, a full start up sequence is automatically repeated
This process concludes with either the restoration of normal operation or, if a flame signal is not detected after the safety time, a volatile or non-volatile lockout occurs if the cause of the interruption persists.
Gases
The calorific value refers to the amount of heat generated by the complete combustion of a unit volume or mass of gas at a constant pressure of 1,013.25 mbar This measurement is based on the combustible mixture's constituents under reference conditions, with the combustion products also returned to the same conditions.
The gross calorific value (H_s) refers to the total energy released when combustion occurs, assuming that the water produced is condensed In contrast, the net calorific value (H_i) represents the energy available when the water produced remains in the vapor state.
NOTE The calorific value is expressed:
1) either in MJ/m 3 of dry gas at the reference conditions; or
2) in MJ/kg of dry gas [EN 437:2003].
3.4.2 relative density d ratio of the masses of equal volumes of dry gas and dry air at the same conditions of temperature and pressure
The Wobbe index, represented as the gross Wobbe index (W_s) and the net Wobbe index (W_i), measures the calorific value of a gas per unit volume relative to the square root of its relative density under consistent reference conditions It is classified as gross or net based on whether the calorific value utilized is the gross or net calorific value.
NOTE The Wobbe index is expressed either in MJ/m 3 of dry gas at the reference conditions or in MJ/kg of dry gas [EN437:2003]
3.4.4 test pressure gas pressures used to verify the operational characteristics of appliances using combustible gases; they consist of normal and limit pressures
NOTE Test pressures are expressed in mbar 1 mbar = 10 2 Pa [EN 437:2003]
3.4.5 normal pressure p n pressure under which the appliances operate in nominal conditions when they are supplied with the corresponding reference gas
3.4.6 limit pressure maximum limit pressure p max and minimum limit pressure p min pressures representative of the extreme variations in the appliance supply conditions
A pressure couple refers to the combination of two different gas distribution pressures resulting from a notable difference in Wobbe indices within a specific family or group of gases In this context, the higher pressure is associated exclusively with gases that have a low Wobbe index, while the lower pressure is linked to gases that possess a high Wobbe index.
Conditions of operation and measurement
3.5.1 reference conditions in this standard the following reference conditions apply: a) for calorific values, temperature: 15 °C b) for gas and air volumes dry, brought to 15 °C and to an absolute pressure of 1 013,25 mbar
3.5.2 cold condition condition of the installation required for some tests and obtained by allowing the unlit burner unit to attain thermal equilibrium at room temperature
3.5.3 hot condition condition of the installation required for some tests and obtained by heating to thermal equilibrium at the nominal heat input
3.5.4 equivalent resistance resistance to flow in millibar, measured at the outlet of the system, which is equivalent to that of the actual flue
Thermal equilibrium refers to the operating state of a system where the flue gas temperature remains stable, fluctuating by no more than ±2% (in °C) over a duration of 10 minutes, corresponding to a specific input setting.
Country of destination
The direct country of destination refers to the specific country for which the system has been certified and designated by the manufacturer Upon market release or installation, the system must operate seamlessly, without any adjustments or modifications, using one of the gases available in that country at the correct supply pressure.
More than one country can be specified if the system, in its current state of adjustment, can be used in each of these countries
The indirect country of destination refers to a country for which the system has received certification; however, it is currently not suitable for use in its present state Necessary modifications or adjustments must be implemented to ensure safe and correct utilization in that country.
Classification according to the nature of the gases used (categories)
Gases are categorized into three main families, which can be further divided into groups based on their Wobbe index values Table 1 outlines the specific families and groups of gas referenced in this standard.
Gas family Gas Group Gross Wobbe index
Classification according to the gases capable of being used
Systems of category I are designed exclusively for the use of gases of a single family or of a single group: a) Systems designed for use on first family gases only:
Category I 1a : systems using only gases of Group A of the first family at the prescribed pressure (this category is not used) b) Systems designed for use on second family gases only:
Category I 2H : systems using only gases of Group H of the second family at the prescribed supply pressures
Category I 2L : systems using only gases of Group L of the second family at the prescribed pressures
Category I 2E : systems using only gases of Group E of the second family at the prescribed pressures
Category I 2E+ systems utilize only gases from Group E of the second family and operate with a pressure couple that does not require adjustment In these systems, any gas regulator present is inactive within the two normal pressure ranges of the pressure couple Additionally, there are systems specifically designed for use with third family gases only.
Category I 3B/P : systems capable of using the third family gases (propane and butane) at the prescribed supply pressure
Category I 3+ systems are designed to utilize third family gases, specifically propane and butane, and operate at a fixed pressure without the need for system adjustments However, certain systems may allow for the adjustment of primary combustion air when switching between propane and butane, as specified in particular standards Importantly, these systems do not permit the use of gas pressure regulating devices.
Category I 3P : systems using only gases of Group P of the third family (propane) at the prescribed pressure
Systems of category II are designed for use on gases of two families: a) Systems designed for use on gases of the first and second families:
Category II 1a2H systems are designed to utilize gases from Group A of the first family and gases from Group H of the second family The gases from the first family are employed under the same conditions as those for Category I1a.
The second family gases are used under the same conditions as for category I2H b) Systems designed for use on gases of the second and third families:
Category II 2H3B/P systems are designed to utilize gases from Group H of the second and third families The second family gases are employed under the same conditions as those for category I2H, while the third family gases are used under conditions similar to those for category I3B/P.
Category II 2H3+ systems are designed to utilize gases from Group H of the second and third families The gases from the second family are employed under the same conditions as those for category I2H, while the third family gases are used under conditions similar to those for category I3+.
Category II 2H3P : systems capable of using gases of Group H of the second family and gases of Group
P of the third family The second family gases are used under the same conditions as for category I2H
The third family gases are used under the same conditions as for category I3P
Category II 2L3B/P systems are designed to utilize gases from Group L of the second family and gases from the third family The second family gases are employed under conditions similar to those of category I2L, while the third family gases are used under conditions akin to those of category I3B/P.
Category II 2L3P : systems capable of using gases of Group L of the second family and gases of Group
P of the third family The second family gases are used under the same conditions as for category I2L
The third family gases are used under the same conditions as for category I3P
Category II 2E3B/P systems are designed to utilize gases from Group E of the second family, as well as gases from the third family The second family gases are employed under conditions similar to those of category I2E, while the third family gases are used under conditions akin to those of category I3B/P.
Category II 2E+3+ systems are designed to utilize gases from Group E of the second family, as well as gases from the third family The second family gases are employed under the same conditions as those for category I2E+, while the third family gases are used under conditions similar to those for category I3+.
Category II 2E+3P systems are designed to utilize gases from Group E of the second family, as well as gases from the third family The second family gases are employed under the same conditions as those for category I2E+, while the third family gases are used under conditions similar to those for category I3P.
Systems of Category III are designed for use on gases of the three families
This category is not in general use
Categories III Systems which are in use in certain countries are given in Annex B.3.
Classification according to the mode of evacuation of the combustion products
Systems are classified into several types according to the method of evacuation of the combustion products and admission of the combustion air
This standard pertains to Type B systems, which are designed to connect to a flue that expels combustion products outside the room housing the system, with combustion air sourced directly from the room Additionally, it includes Type B5 appliances, which are Type B systems that lack a draught diverter and connect directly to their flue terminal through a flue duct.
For systems in which the combustion air is supplied and/or in which the products of combustion are evacuated by mechanical means, two types are identified (see Annex A): c) Type B52x
3: a Type B5 system incorporating a fan downstream of the combustion chamber/heat exchanger; d) Type B53x 3: a Type B5 system incorporating a fan upstream of the combustion chamber/heat exchanger
General
When converting gases between different groups or families, or adjusting to varying gas distribution pressures, only specific operations are permissible for each category.
It is recommended that these operations should be possible without disconnecting the system
In Category I systems, modifications vary based on specific subcategories: for I 2H, I 2L, I 2E, and I 2E+, no system modifications are required; similarly, Category I 3B/P also mandates no changes However, Category I 3+ allows for the replacement of injectors or calibrated orifices solely to convert between different pressure couples, such as from 28-30/37 mbar to 50/67 mbar In contrast, Category I 3P permits no modifications for gas type changes, but does require injector replacements and gas rate adjustments when altering pressure.
5.1.1.2.1 Categories of system designed for use with gases of the first and second families
Adjustment of the gas rate with, if necessary, a change of injector, restrictor or regulator
To optimize the gas rate of the ignition burner, adjustments can be made using an adjuster, or by replacing the injector or restrictor If needed, consider changing the entire ignition burner or specific components to ensure efficient operation.
Putting the regulator out of service under the conditions of 5.2.6
Putting the gas rate adjuster(s) out of service under the conditions of 5.2.1 and 5.2.2, if applicable
The adjustments or component changes are only acceptable when converting from a gas of the first family to a gas of the second family or vice versa
5.1.1.2.2 Categories of system designed for use with gases of the second and third families
Adjustment of the gas rate with, if necessary, a change of injector, restrictor or regulator
To optimize the gas rate of the ignition burner, adjustments can be made using an adjuster, or by replacing the injector or restrictor If needed, consider changing the entire ignition burner or specific components to ensure efficient operation.
Putting the regulator out of service under the conditions of 5.2.6
Putting the gas rate adjuster(s) out of service under the conditions given in 5.2.1 and 5.2.2 if applicable
Adjustments or component changes are permissible only in specific cases: a) when converting between second family gases and third family gases; b) when switching from one butane/propane pressure couple to another, such as from 28-30 mbar to 37 mbar.
Category III systems which are in use in certain countries are given in Annex A (see A.3.2.3)
5.1.2 Materials and method of construction
The materials used in constructing a system, including its POCED, must be of high quality and appropriate thickness to maintain safe operation under normal usage and maintenance conditions Additionally, these materials should guarantee a reasonable operating lifespan.
When installed as per the manufacturer's guidelines, all components of the system are designed to endure the expected mechanical, chemical, and thermal conditions during normal use.
Copper shall not be used for gas carrying parts where the temperature is likely to exceed 100 °C
Asbestos or materials containing asbestos shall not be used
Solder that has a melting point below 450 °C after application shall not be used for gas carrying parts
5.1.3 Accessibility for maintenance and use
Components and controls must be organized to allow for easy adjustments, maintenance, or replacements without the need to remove the radiant tube from its installed position Access doors or removable panels should be included where necessary.
Removable parts designed for maintenance or cleaning must be easily accessible and straightforward to assemble correctly, while also being challenging to assemble incorrectly This is crucial to prevent hazardous conditions or potential damage to the system and its controls.
Components of the system that are not designed for user removal and whose removal could compromise safety must only be detachable with the use of tools.
5.1.4.1 Soundness of the gas circuit
Screw and stud holes for component assembly must not extend into gasways Additionally, the wall thickness separating these holes, including any threads, from the gasways must be at least a specified minimum.
To ensure the integrity of components and assemblies linked to the gas circuit that may require routine maintenance at consumer locations, mechanical joints such as metal-to-metal joints, O-ring joints, and packing must be utilized, while avoiding sealing compounds like tape, mastic, and paste It is essential that the soundness of these joints is preserved even after dismantling and reassembly.
Sealing compounds may be used for permanent threaded assemblies The sealing material shall remain effective under normal conditions of system use
5.1.4.2 Soundness of the combustion circuit
The combustion circuit's integrity must be maintained solely through mechanical means, except for components that do not need disconnection during routine maintenance These parts can be securely joined with mastic or paste to ensure lasting soundness under normal operating conditions.
5.1.5 Supply of combustion air and evacuation of combustion products
All air supply openings in the system must be effectively safeguarded against unintentional blockage and should prevent the entry of a 16 mm diameter ball when subjected to a force of 5 N Furthermore, the cross-section of the air passageways must remain fixed and non-adjustable.
The combustion circuit's cross-section can be adjusted using one or more dampers, allowing for the fine-tuning of individual sections within the manufacturer's specified suction limits to ensure optimal system performance.
Each damper shall be supplied by the manufacturer and once adjusted shall be capable of being locked and sealed in position
Requirements for adjusting, control and safety devices
The functioning of any safety device shall not be overruled by that of any control device
The system shall not incorporate any controls which need to be manipulated by the user when the system is in normal operation
Systems categorized as I 2H, I 2L, I 2E, I 2E+, I 3B/P, I 3P, II 2H3B/P, II 2H3+, II 2H3P, II 2L3B/P, II 2E3B/P, II 2E+3+, and II 2E+3P are prohibited from being equipped with a gas rate adjuster However, all regulated systems within these categories, with the exception of II 2E+3+, may include a gas rate adjuster that features an adjusting screw on the gas regulator.
Systems in category II1a2H shall have a gas rate adjuster for first family gases
In systems categorized as II2H3+ with a gas rate adjuster, it is permissible to deactivate these devices when supplied with third family gas This regulation also extends to category II1a2H systems when they utilize second family gas Additionally, for systems classified as II2E+3P with a gas rate adjuster, these devices can be completely or partially taken out of service.
(see 5.2.6) when these systems are supplied with a second family gas
The adjusters shall be adjustable only with a tool and they shall be capable of being set in the operating position
A range-rating device on a system is optional
In category II1a2H systems, the gas rate adjuster can also function as the range-rating device However, if the gas rate adjuster must be sealed, either fully or partially, when using a second family gas, the installer must not use the gas rate adjuster or its sealed portion as a range-rating device.
Aeration adjusters are not permitted
Manual valves, push buttons, and electrical switches are crucial for the proper operation and commissioning of the system, and they should either be included with the system or detailed in the manufacturer's installation instructions.
Manual valves shall be of the 90° turn type
Manual valves must be designed and positioned to avoid accidental operation while ensuring ease of use when needed Their design should clearly distinguish between the OPEN and CLOSED positions during operation.
A system isolating valve must be an integral component of the system, capable of operating at a pressure of 1.5 times the maximum supply pressure, and it should be easily accessible.
Manual valves used solely for OPEN/CLOSED operation shall be provided with positive stops at the OPEN and CLOSED positions
Regulators shall comply with EN 88-1:2007
For systems using first or second family gases, it is essential to have an integral regulator installed upstream of the automatic shut-off valves to control the gas supply to the burner and ignition burner, unless a zero regulator is used or the regulator is part of a multifunctional control system.
For a system burning third family gases, the fitting of a regulator is optional
The regulator's design must ensure easy adjustment or deactivation for use with different gases, while implementing measures to prevent unauthorized modifications to its settings.
For systems categorized as I2E+, II2E+3+, and II2E+3P, the gas regulator must not operate within the normal pressure range of the second family pressure couple, specifically between 20 mbar and 25 mbar Additionally, in systems classified as II2E+3+ and II2E+3P, it is essential to allow the regulator to be partially out of service when using second family gases, ensuring it remains non-operational within the same pressure range.
Multifunctional controls shall comply with EN 126:2004
Automatic shut-off valves shall comply with EN 161:2007
The gas supply to the main burner is regulated by two automatic shut-off valves installed in series One valve must be of Class A or Class B, while the other must be of Class A.
When using a Class J valve, it is essential to install a strainer that prevents the passage of a 0.2 mm pin gauge, ensuring proper filtration This strainer must be positioned upstream of the Class J valve to maintain optimal performance.
The start gas supply shall be under the control of one automatic shut-off valve of either Class A or Class B
The upstream valve in the gas supply to the main burner, classified as Class B, controls the start gas supply taken from immediately downstream When a single automatic shut-off valve regulates the start gas supply, the heat input during ignition must not exceed 1 kW or 5% of the main burner heat input, whichever is lower.
The arrangements shown in Figure 1 are given as examples Any other arrangement giving at least an equivalent level of safety is permissible
B a) Systems with an ignition burner of heat input not exceeding 1 kW or 5 % of the main burner heat input
B J b) Systems with direct ignition of the main burner
Figure 1 — Automatic shut-off valve configuration 5.2.9 Gas strainers
To ensure the protection of burner units with automatic shut-off valves, a strainer must be installed at the inlet to prevent foreign matter from entering This strainer can be integrated with the upstream automatic shut-off valve, and it is essential that the maximum hole size of the strainer does not exceed 1.5 mm, while the mesh should be fine enough to block a 1 mm pin gauge.
In gas circuits incorporating more than one automatic shut-off valve, only one strainer needs to be fitted, provided it gives adequate protection to all valves
For valves incorporating a shearing action (self-cleaning) and for valves of size ẵ (or DN15) and below, the strainer may be omitted
Where a regulator is fitted upstream of the automatic shut-off valve(s), the strainer may be fitted upstream of the regulator
Integral mechanical thermostats shall comply with EN 257
The system shall incorporate an air-proving device within the common duct and separate air-proving system on each burner unit
The common duct shall be fitted with a suitable device for proving adequate air-flow during the pre- purge, ignition and operation of the system (see 6.6.1 e and 6.7)
The sensor shall be located at a specified point in the common duct and shall not rely on static pressure measurement
Before starting the system, it is essential to verify the air-proving device in a no air-flow condition If the device is not proven in this state, the system will not be allowed to start.
Air-flow failure in the common duct at any time during the pre-purge, ignition and operation of the burner shall cause non-volatile lock-out of the system
The system control shall be designed such that there is at least one check of the pressure switch in the no air-flow state every 24 h
Each burner unit must be equipped with an appropriate device to ensure sufficient air flow in its branch duct during pre-purge, ignition, and operational phases.
The sensor shall be located at each burner unit and shall not rely on static pressure measurement
Ignition devices
When properly installed according to the manufacturer's guidelines, the system can be ignited from a conveniently accessible location using an integrated electrical or other ignition device.
Ignition burners and devices must be strategically designed and positioned to prevent issues such as draughts, combustion byproducts, overheating, condensation, corrosion, and falling debris, which could lead to their reduction in effectiveness or complete failure.
Ignition burners and devices, along with their mountings, must be engineered to ensure rigid and accurate positioning in relation to all components and burners they are intended to work with.
5.3.2 Ignition device for the main burner
Each main burner shall be fitted with an ignition burner or other ignition device for direct ignition
When converting a system from one gas to another, it is essential that different ignition burners are clearly marked, interchangeable, and easy to install The same requirements apply to injectors, which must be replaced as needed Additionally, injectors should feature a permanent identification method and can only be removed using a tool.
Ignition burners shall be protected against blockage by gas-borne particulate matter.
Main burners
The cross-sectional area of the flame ports shall not be adjustable
The burners shall be so located and arranged that misalignment cannot occur It shall not be possible to remove the burner assembly without the use of tools.
Pressure test points
Each burner unit must include a minimum of two pressure test points: one located upstream of the first control and safety device, and the other positioned downstream of the final gas flow rate control These test points should be strategically placed to facilitate accurate measurements.
The test points must feature an external diameter of (9 − 0 0 , 5 ) mm and a minimum useful length of 10 mm to accommodate a tube Additionally, the bore's minimum diameter should not exceed 1 mm.
In addition, a pressure test point shall be fitted for the measurement of suction in each branch tube
Injectors
All injectors and removable restrictors must have a permanent identification method They should be designed for easy replacement without relocating the tube assembly from its installed position However, the removal of injectors requires the use of a tool.
Soundness
6.1.1 Soundness of the gas circuit
The gas circuit must be airtight, defined as having an air leakage not exceeding 100 cm³/h under the conditions specified in section 7.3.1.1, regardless of the number of components installed in series or parallel on the burner unit.
6.1.2 Soundness of the combustion circuit
The soundness of the combustion circuit upstream of the fan in the common duct shall be verified in accordance with the requirements in 6.8
Under the conditions specified in section 7.3.1.2, the air leakage rate from any part of the combustion circuit, including the POCED downstream of the fan in the common duct, must not exceed 0.10 m³/h per kW of nominal heat input.
Heat inputs
When measured under the conditions described in 7.3.2.2, the heat input obtained at the normal pressure shall be within ± 5 % of the nominal heat input
When measured under the conditions described in 7.3.2.3 the heat input obtained at normal pressure shall be within ± 5 % of the start gas heat input declared by the manufacturer
However, this tolerance is extended to within ± 10 % where the injector has a diameter of 0,5 mm or less
6.2.3 Effectiveness of the range-rating device
For burner units equipped with a range-rating device separate from a gas rate adjuster, it is essential to verify that, under the conditions outlined in section 7.3.2.4, the nominal heat input is achieved within ± 5% when the range-rating device is set to maximum Additionally, when set to the minimum rate, the heat input must also fall within ± 5% of the manufacturer's specified minimum heat input.
Limiting temperatures
When the system is tested under the conditions described in 7.3.1.1, the wall and ceiling temperatures shall not exceed the ambient temperature by more than 50 K
When the system is tested under the conditions described in 7.3.3.2 the maximum temperature of the system components shall not exceed the maximum temperature specified by the individual component manufacturer
When tested according to section 7.3.3.3.1, the external temperature of any part of the POCED, when installed as per the manufacturer's guidelines and positioned within 25 mm of combustible building materials, must not exceed the ambient temperature by more than 50 K.
When installing the POCED as per the manufacturer's guidelines, it must be enclosed within another duct, sleeve, or insulation when it traverses a combustible wall or ceiling It is crucial that the external temperatures of this enclosure do not exceed the ambient temperature by more than 50 K, in accordance with the conditions outlined in section 7.3.3.3.2.
Ignition, cross-lighting and flame stability
Under the test conditions described in 7.3.4.1.1, correct and smooth ignition and cross-lighting shall be assured
Reducing the gas rate of an ignition burner to the minimum necessary for maintaining the gas supply to the main burner, as outlined in section 7.3.4.1.2, ensures reliable and smooth ignition of the main burner while minimizing noise.
The gas line supplying the ignition burner must be positioned between the main burner gas valves, and it is essential to confirm that igniting the ignition burner under the specified test conditions does not create a hazardous situation.
Under the specified test conditions, ignition of any ignition burner or the main burner, when ignited directly, must occur safely and without excessive noise, even if ignition is delayed.
50 % longer than the safety time declared by the manufacturer
Under the specified test conditions, flames must remain stable during normal operation, with only a minor tendency to lift at the moment of ignition being permissible.
Pressure regulator
When tested in accordance with the conditions given in 7.3.5 the rate shall not differ by more than
+ 7,5 % and - 10 % for first family gases, and by more than ± 5 % for second and third family gases, from the initial rate obtained under those conditions.
Combustion
6.6.1 All systems (still air conditions)
In accordance with section 7.3.6.2, the testing results indicate that for Test No 1, the carbon monoxide (CO) concentration in the dry, air-free combustion products must not exceed 0.1% For Test No 2 and Test No 3, the CO concentration limit is set at 0.2% for both tests.
Under consistent conditions, when the sooting limit gas is used, the system should operate for three cycles of 30 minutes on and 30 minutes off without significant soot deposits inside the radiant tube and fan Additionally, for Test No 4, the carbon monoxide (CO) concentration in the dry, air-free combustion products must not exceed 0.2%.
The system must be verified to ignite and operate continuously under specified conditions For Test No 5, the concentration of carbon monoxide (CO) in the dry, air-free combustion products must not exceed 0.2%.
6.6.2 Supplementary tests under special conditions
When supplied with reference gas under the conditions described in 7.3.6.3, the CO concentration in the dry air-free products of combustion shall not exceed 0,2 %
Under the conditions specified in sections 7.3.6.3 a) and 7.3.6.3 1, the pressure increase at the outlet of the installation must be at least 0.75 mbar for systems with a wall termination and 0.5 mbar for systems featuring a vertical flue at the shut-off point.
Air-proving device in the common duct
Under the conditions described in 7.3.7, the air-proving device in the common duct shall operate to cut off the electricity supply to the burner units
Under the conditions specified in sections 7.3.6.3 a) and 7.3.6.3 l), the pressure increase at the outlet of the installation must be at least 0.75 mbar and 0.5 mbar, respectively, at the shut-off point (refer to section 6.6.2).
Prolonged performance
After testing the system as outlined in section 7.3.8, it is essential to meet several requirements: compliance with section 6.6.1 a), no significant soot deposition or disturbance of flames during verification, absence of combustion product leakage from the combustion chamber and flue connections, no breakdown or distortion affecting safety, no significant deterioration of the radiant tube's external surface such as flaking or excessive oxidation, no signs of corrosion that could compromise the system's lifespan, and no evidence of corrosion at the outlet following the inspection at the test's conclusion.
Measurements of oxides of Nitrogen, NO x
The manufacturer shall declare the NO x class in Table 2 that is applicable to the system
According to the testing method outlined in section 7.4.1, the concentration of NOx in the dry, air-free combustion products must ensure that the weighted NOx value, calculated as specified in section 7.4.2, remains within the maximum NOx concentration limits set by the manufacturer for the declared NOx class.
Class Maximum NO x concentration mg/kWh
General
7.1.1 Characteristics of test gases: reference and limit gases
Systems are designed to operate with various gas qualities A key objective of this standard is to ensure that the system's performance meets satisfactory levels for each specific gas family or group, as well as for the intended pressure, utilizing adjusting devices when necessary.
The test gases, test pressures and system categories given here are in accordance with those specified in EN 437:2003
The characteristics of the reference and limit gases are given in Tables 4 and 5 The values in Table 4, measured and expressed at 15 °C, are derived from ISO 6976:1995
7.1.2 Conditions for preparation of the test gases
The gases used for testing must closely match the compositions listed in Table 4 Specifically, the Wobbe index of the gas should remain within ± 2% of the specified value in Table 4, accounting for measurement errors Additionally, the components used to create the gas mixtures must meet or exceed the purity levels indicated in Table 3.
Methane (CH4) 95 a) Propene (C3H6) 95 a) Propane (C3H8) 95 a) Butane 4 (C4H10) 95 a) a) With a total concentration of H 2 , CO and O 2 below 1 % and a total concentration of N 2 and CO 2 below 2 %.
The requirements for each component are not mandatory as long as the final mixture matches the composition of a mixture made from components that meet the conditions outlined in Table 3 Thus, it is possible to begin with a gas that already contains several constituents of the final mixture in appropriate proportions to create the desired mixture.
For second family gases, tests using reference gases G 20 or G 25 allow for the use of a gas from Group H, L, or E, even if its composition does not meet specified conditions This is acceptable as long as the final mixture, after adding propane or nitrogen as needed, achieves a Wobbe index within ± 2% of the value listed in Table 4 for the corresponding reference gas Additionally, when preparing limit gases, an alternative base gas may be used instead of methane.
1) for limit gases G 21, G 222 and G 23 a natural gas of Group H may be used;
2) for limit gases G 27 and G 231 a natural gas of Group H or of Group L or of Group E may be used;
3) for the limit gas G 26 a natural gas of Group L may be used
The final mixture achieved by incorporating propane or nitrogen must maintain a Wobbe index within ± 2% of the specified value in Table 4 for the corresponding limit gas Additionally, the hydrogen content of the final mixture should align with the values provided in Table 4, where applicable.
Table 4 — Test gas characteristics a) (gas dry at 15 °C and 1 013,25 mbar)
% MJ/m 3 MJ/m 3 MJ/m 3 MJ/m 3 Gases of the first family b)
CH4 = 26 combustion flame lift and H2 = 50 21,76 13,95 24,75 15,87 0,411
N2 = 24 Gases of the second family
Reference gas G 20 CH4 = 100 45,67 34,02 50,72 37,78 0,555 Incomplete combustion G 21 CH4 = 87
Sooting limit gas C3H8 = 13 49,60 41,01 54,76 45,28 0,684 Light back limit gas G 222 CH4 = 77 42,87 28,53 47,87 31,86 0,443
H2 = 23 Flame lift limit gas G 23 CH4 = 92,5 41,11 31,46 45,66 34,95 0,586
Reference gas and light back
N2 = 13 Flame lift limit gas G 27 CH4 = 82 35,17 27,89 39,06 30,98 0,629
Reference gas G 20 CH4 = 100 45,67 34,02 50,72 37,78 0,555 Incomplete combustion G 21 CH4 = 87 49,60 41,01 54,76 45,28 0,684 Sooting limit gas C3H8 = 13
Light back limit gas G 222 CH4 = 77 42,87 28,53 47,87 31,86 0,443
H2 = 23 Flame lift limit gas G 231 CH4 = 85 36,82 28,91 40,90 32,11 0,617
N2 = 15 Gases of the third family c)
80,58 116,09 87,33 125,81 2,075 combustion and sooting limit gas iC4H10 = 50
Flame lift limit gas G 31 C3H8 = 100 70,69 88,00 76,84 95,65 1,550 Light back limit gas G 32 C3H6 = 100 68,14 82,78 72,86 88,52 1,476
Incomplete combustion Sooting 4) and flame lift limit gas
Light back and Sooting limit gas d) G 32 C3H6 = 100 68,14 82,78 72,86 88,52 1,476 a) For gases used nationally or locally, see Annex B.4 b) For other groups, see Annex B.4 c) See also Table 5 d) See 7.1.2 footnote 3)
Table 5 — Calorific values of the test gases of the third family
Test gas H i H s designation MJ/kg MJ/kg
7.1.3 Practical application of test gases
Gases required for the tests described in 7.3.2, 7.3.3, 7.3.4 and 7.3.6 shall be as specified in 7.1.1 and made up in accordance with 7.1.2
To facilitate testing for the specified tests, it is allowed to substitute the reference gas with a distributed gas, as long as its Wobbe index is within ± 5% of the reference gas's Wobbe index.
When a system is capable of utilizing gases from multiple groups or families, test gases are chosen from those specified in Table 2 and in accordance with section 7.1.5.1 The gases selected for each system category are detailed in Table 4.
7.1.3.2 Conditions of supply and adjustment of the burner unit
7.1.3.2.1 Initial adjustment of burner units
Before conducting the necessary tests, the burner unit must be equipped with the correct injector(s) that match the gas family or group of the specified test gas, as outlined in Table 2 Additionally, any gas rate adjusters should be configured according to the manufacturer's guidelines, utilizing the appropriate reference gas(es) and the normal pressure(s) specified in section 7.1.4.
This initial adjustment of the burner unit is subject to the limitations given in 5.1.1
For testing purposes, the normal, minimum, and maximum supply pressures must comply with section 7.1.4, unless an adjustment of the supply pressure is required as outlined in sections 7.1.3.2.3 and 7.1.3.2.4.
Unless otherwise specified, the initial adjustment of the burner unit shall not be altered
For tests that necessitate adjusting the burner to the specified nominal heat input, it is crucial to maintain the upstream pressure of the injector(s) within a range that ensures the heat input remains within ± 2% of the manufacturer's specifications This can be achieved by modifying the pre-set adjuster(s), the burner unit regulator (if adjustable), or the supply pressure of the burner unit.
The specified heat input shall be determined in accordance with 7.3.2 and with the burner unit supplied with the appropriate reference gas(es)
To achieve a nominal heat input within ± 2%, it is essential to adjust the burner unit inlet pressure, p, from the normal pressure, p_n Consequently, tests typically conducted at the minimum or maximum test pressures, p_min and p_max, must instead be performed at the corrected test pressures, p′_min and p′_max.
Table 6 — Test gases corresponding to the system categories
Tests involving limit gases are conducted using the injector and adjustments that correspond to the reference gas of the respective group to which the limit gas belongs.
The corrected test pressures are determined using the formula \$p' = \frac{p_{max} - p_{min}}{p} \cdot p_n\$, where \$p_n\$ represents the normal test pressure, \$p_{min}\$ is the minimum test pressure, \$p_{max}\$ is the maximum test pressure, and \$p\$ denotes the burner unit inlet pressure The corrected minimum and maximum test pressures are denoted as \$p'_{min}\$ and \$p'_{max}\$, respectively.
The test pressures (i.e the pressures required at the gas inlet connection of the burner unit) are given in
These pressures and the corresponding injectors are used in accordance with special conditions given in
Annex B, for the country in which the system is to be installed (see Annex F and Annex I for national conditions)
In specific situations, the system manufacturer may designate a different normal pressure at the system inlet than what is listed in Tables 7 and 8 In such instances, the alternative pressure and the relevant injector(s) will be utilized for system testing, and the values of \$p_{min}\$ and \$p_{max}\$ will be established according to section 7.1.3.2.4.
Table 7 — Test pressures where no pressure couple exists a)
System categories having as index Test gas p n p min p max mbar mbar mbar
The third family of gases includes G 30, G 31, and G 32, with specific test pressures outlined in Table B.4 Systems in this category can operate without adjustments at supply pressures ranging from 28 mbar to 30 mbar Testing for G 31 and G 32 is conducted at a normal pressure of 29 mbar, ensuring that these test gases are more stringent than any gas from Group 3B, thereby accommodating normal fluctuations in gas supply.
Table 8 — Test pressures where a pressure couple exists
System categories having as index
Test gas p n p min p max mbar mbar mbar