A.O. Smith BFC Cyclone 28, Installation, User And Service Manual

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5 Introduction
5.1 About the water heater
The BFC water heater is intended for heating water for sanitary purposes.
The BFC is a condensing gas–fired storage water heater with a fan in the air intake. The
flue gasses transfer their heat to the water through an efficient heat exchanger. The water
heater has a concentric venting connector and can function as an open or as a room-
sealed water heater.
5.2 The appliance's heating cycle
The appliance's heating cycle is activated when the measured water temperature (T
1
) falls
below the threshold value (T
set
). This threshold value depends on the currently selected
appliance operating mode. For example, if the appliance is in OFF mode (frost
protection), then this value is 5°C. If the appliance is in ON mode, this threshold value is
adjustable, for example to 65°C.
The heating cycle runs successively through the following states:
HEAT DEMAND;
PRE-PURGE;
PRESSURE SWITCH;
PRE-GLOW;
IGNITION;
RUNNING;
POST-PURGE.
5.3 Working principle
The water heater is fitted with a modulating premix burner system with 1:1 gas-to-air
ratio regulation. The air required for combustion is delivered by the fan (18). The gas is
supplied via the gas control valve (16) and the venturi (30) on the intake side of the fan.
The 1:1 gas-to-air ratio always guarantees the most efficient gas/air mixture.
In this water heater, the cold water enters the bottom of the tank through the cold water
inlet (14). The tap water, heated by the combustion chamber (8) and heat exchanger
(11), leaves the tank through the hot water outlet (2). Once the water heater is
completely filled with water, it will constantly be under mains water pressure. As hot water
is drawn from the water heater, cold water is immediately added.
The special design of the heat exchanger (11) ensures that the flue gases are first led
downwards via the combustion chamber, then upwards via the heat exchanger, and
downwards again alongside the water in the tank. The flue gases gradually become cooler
in the process. Because the cooled flue gases flow alongside the cold water lower down in
the tank, they start to condense. This condensation causes latent heat energy to be
transferred to the cooler water, thereby increasing the performance of the unit. The
condensate yielded by this process is discharged via the condense trap (23).
The insulation layer (24) prevents heat loss. The inside of the tank is enamelled to protect
against corrosion. The anodes (9) provide extra protection against corrosion.
The water heater has an inspection and cleaning opening (12) for maintenance.
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0311704_BFC_28-120_III_
ENEN_V2.4, 2022-10-17
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