BS 4876:1984 pdf free download.Specification for Performance requirements for domestic flued oil burning appliances (including test procedures)
Section 1. General
1.1 Scope
BS 4876 specifics performance requirements for flued oil burning appliances, up to and including 44 kW capacity, used for hot water supply and for space heating purposes. Test procedures and measurement methods are also described.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
1.2 Definitions
For the purposes of BS 4876, the following definitions apply.
1.2.1
performance requirements
the range of stipulated performance values (maximum and minimum) between which the tested value achieved by an appliance should lie (see section 2)
1.2.2
test procedure
the procedure to determine a particular overall aspect of an appliance’s performance which usually involves several parameters, e.g. its thermal efficiency (see Table 2)
1.2.3
measurement method
the method for determining each parameter. e.g. draught: several methods are normally required for each test procedure (see Table 2)
1.2.4
declared output
the output specified by the manufacturer of the appliance
1.2.5
smoke index
the product of the average smoke number and the time in minutes during which the average smoke number exceeds 2 during transient operating conditions of the appliance, e.g. during sart.up (see 4.1)
1.2.9
integral draught diverter
a device for preventing conditions in a secondary flue from interfering with the combustion performance of an appliance
1.2.10
poor conductor
a conductor fabricated from material possessing a thermal conductivity not in excess of 0.3 W/(m K)
NOTE Requirements for condutivity ar only pocifid for control knoh.
1.2.11 air heaters
1.2.11.1
indirect impelled convection air heater
an air heating flued appliance in which the products of combustion are primarily passed through a water heater. The air to be heated is forced by an integral fan to traverse a wawrlair heat exchanger
1.2.1 1.2
direct impelled convection air heater
an air heating flued appliance consisting of one or more heat exchangers with air circulating past these. The heated air movement is dependent on an integral power.driven fan
1.2.11.3
direct natural convection air heater
an air heating flued appliance consisting of one or more heat exchangers with air circulated past these by natural convection. The combustion gases do not come into contact with the air being heated
1.2.11.4
combined unit
any one of the air heaters defined in 1.2.11.1 to 1.2.11.3 incorporating a domestic hot water heating device
1.3 Marking
Each flued oil burning appliance complying with BS 4876 shall be durably and clearly marked with:
a) the manufacturer’s name and type designation:
b) the number of this British Standard. i.e. BS 487&.
NOTE BS 4876 speciflea performance requirementa of the appliance: addit,onal marking in reipect of conatructional or other nqtIIremvnts may be required.
The procedure is formulated to provide data which will be employed to assess the conduct of the appliance under two headings:
a) Control timings. Control timings where simulated failure of the burner to ignite and failure of flame are employed to assess the function and adequacy of the control system.
NOTE It si expected that all electrically operated control boxea embodying timing mechanim will be type teated for function at the extremea of temperaturea declared by the control manufacturer.
b) Combustion performance. Combustion performance where measurements of emissions of carbon dioxide, carbon monoxide, smoke and where applicable of the degree of incomplete combustion are taken. Additionally, surface temperatures are measured as well as the effectiveness of any guards.
3.1.2 Control timings
3.1.2.1 Outline of procedure. The appliance is operated under specified environmental conditions and when temperature stability is achieved the control box surface temperature is measured. Following this the burner and its controls are subjected to simulated failure. i.e. sham failure to ignite and a flame failure teat. During these tests the timings of the control sequence to effect safe conditions are checked. It is essential that a minimum of 15 mm elapses before repent of tests on controls incorporating thermal timing elements.
3.1.2.2 Apparatus. The following apparatus is required:
a) electrically operated stopclocks;
b) relays, suitable for circuit voltages;
c) low capacitance switches;
d) portable contact thermometer;
e) a prepared electrical circuit appropriate to the control system undergoing test.
3.1.2.3 Preparation of apparatus. The underlying principle of the test is the same for all classes of appliance employing electrically operated controls, although design differences may demand different test circuitry arrangements. When preparing for the test procedure, appropriate test circuits (e.g. Figure 1 and Figure 2) employing means to alter the circuit of specific actuating components are frequently necessary. Such test circuits include electric stopclocks so connected or operated that they are actuated (stopped or started) simultaneously with burner control functions.
Where a burner is dependent on an electrically driven motor to supply oil fuel to the combustion zone (e.g. pressure jet and waliflame) an electric stopclock is connected in parallel to the circuit so that the clock is actuated simultaneously with the motor when the circuit is energized or interrupted.
Where, however, the fuel supply to the combustion zone of a burner is interrupted and governed by a magnetic valve (e.g. some forced draught vaporizing burners) an electric stopclock is connected in parallel to the circuit so that the clock and valve are actuated simultaneously when the circuit is (de)energized. A suitable tapping is taken from the lock-out switch mechanism to actuate a stopclock.
3.18.3 Apparatus. Apparatus is required for the determination of:
a) smoke number (method 1);
b) flue gas composition (method 2);
c) flue gas temperature (method 3);
d) flue draught (method 4);
e) degree of incomplete combustion and combustible gas index (method 5);
fi fuel flow rate (method 7).
A stopwatch or stopclock is also required.
3.18.4 Preparation of apparatus
3.18.4.1 Test hearth for air hecxteronlv. The unit is installed on the test hearth in accordance with the manufacturer’s recommendations and fitted to the correct declared flue system. A suitable supply of the required test fuel incorporating a continuous fuel metering system is fitted. Where appropriate (i.e. with appliances designed to discharge hot air through ducts) the manufacturer’s declared duct resistance should be applied.
3.18.4.2 Test hearth for combined unit. The appliance is mounted on the test hearth as described in 3.18.4.1. In addition, a suitable water cooling and circulation system is used so that the unit can be supplied with water at a rate such that the normal maximum temperature of the out.going water is 83 ± 3°C with a water inlet temperature of 60 ± 3 °C. The water system is so arranged that the water inlet temperature can be set at 19 °C to 24 °C for part of the cycle (see Figure 17). Water temperature measurement at the appliance inlet and outlet is by the use of mercury in glass thermometers in thermometer pockets or resistance thermometers.
3.18.4.3 Timer control. A continuous operating timer is used which gives the following sequences:
a) Automatic appliances
l)2hoff;
2) 1 h on;
3) 6 cycles of 10 mm on. 10 mm off.
This sequence is repeated three times. The fourth sequence is:
1) 6 h off;
2) 1 h on;