A.O. Smith 120 through 250 Series, Installation, User And Service Manual

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Instruction manual BFC 13
gis
2 Working principle of
the water heater
2.1 Introduction This chapter covers the following topics:
•
General working principle of the water heater;
• Water heater operating cycle;
• Protection for the water heater;
• Safety of the installation.
2.2 General working
principle of the water
heater
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 condens 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.