A.O. Smith BFC - 28 - Manual (Page 14)

Functioning of the appliance
14 Instruction Manual BFC
2
gis
In this appliance the cold water enters the bottom of the tank via the cold water
inlet n. The tap water, heated by the combustion chamber h and heat
exchanger k, leaves the tank through the hot water outlet b. Once the
appliance is completely filled with water, it remains constantly under water
supply pressure. As hot water is drawn from the appliance, cold water is
immediately added.
The air required for combustion is forcibly delivered to the burner q by the
fan r. The gas is fed to the burner q via the gas control p. Thanks to the
modulated supply of gas and air, the optimum gas/air mixture is always
achieved. The special construction of the burner causes the mixture to form a
vortex (the cyclone effect), before it becomes ignited. Because of this vorticity,
ignition at the glow igniter t is improved, and the combustion efficiency is also
optimised. Through the special design of the heat exchanger k, the flue gases
are first led downwards via the combustion chamber, then upwards again via the
heat exchanger, then once more downwards beside the water in the tank. In this
process, the flue gases gradually become cooler. Because the cooled flue
gases flow alongside the cold water below in the tank, they start to condense.
This condensation causes latent heat energy to be released, which is
transferred to the cooler water, and thereby increases the performance of the
unit. The water of condensation yielded by this process is discharged via the
siphon w.
The PU insulation layer x prevents heat loss. The inside of the tank is
enamelled to protect against corrosion. The magnesium anodes i provide
extra protection against corrosion.
For use during maintenance, the appliance has a inspection and cleaning
opening l.
2.3 The appliance’s
heating cycle The entire appliance is controlled (and monitored) by theThermoControl d. The
temperature sensor T1 g (in the top of the tank j) and the temperature sensor
T2 m (in the bottom of the tank) measure the water temperature. These
temperatures are sent to the ThermoControl. Based on these two observations,
the ThermoControl calculates a net water temperature: T
net
. The value of T
net
lies between the temperatures measured at the top and bottom of the tank. As
soon as T
net
falls below the set water temperature (T
set
), the ThermoControl
registers a ‘heat demand’. The gas control p is opened, and the gas is mixed
with air. This mixture is ignited by the glow igniter t and the water becomes
heated. As soon as T
net
rises above T
set
, the heat demand ends, and the
ThermoControl stops the heating cycle.
Both when registering and ending the heat demand, the ThermoControl
assumes a certain margin. We refer to this margin as the hysteresis (see
paragraph
’9.2 Setting the hysteresis’ ).
2.4 Protection for the
appliance The ThermoControl monitors the water temperature and ensures safe
combustion. This is achieved by:
•
the Water temperature protection ;
• the Gas control ;
• the Fan ;
• the Pressure switch ;
• the Ionisation rod .