Ao-smith BFC - 28 User Manual download pdf (Page 14)

Functioning of the appliance

14 Instruction Manual BFC

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.

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Ao-smith BFC - 28 User Manual Page 14

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