A.O. Smith TWI 35-130, Installation, User And Service Manual

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12 Instruction manual TWI 35-130 G/TWI 45-190 G
Operation of the device
2
2.3 Heating cycle of
the device
2.4 Security of the device
In this device the cold water is supplied through the cold water inlet (16) at the
bottom of the tank. The tap water heated by the combustion chamber (15) and
heat exchanger (13) leaves the tank at the hot water outlet (12). If the device
is maximally filled with water, there is a constant water piping pressure. When
tapping hot water from the device, cold water is immediately added again.
The device has been provided with an e premix burner (4) with 1:1 gas/air ratio
control. The fan (10) sucks in the air that is required for the combustion. The
gas is supplied through the gas control (7) and the venturi on the suction side of
the fan. The 1:1 gas/air coupling always ensures an optimum gas/air ratio.
Because of the special construction of the heat exchanger (13), the flue gasses
are first led up through the combustion chamber and then down through the
heat exchanger along the water. This gradually cools down the flue gasses. As
the cooled down flue gasses are finally led along the cold water at the bottom
of the tank as well, the flue gasses start condensating. Condensation causes
release of energy (heat) that is also transferred to the water, which improves the
output. The condensate that is formed with this heating is discharged through
the siphon (20). The insulating layer (2) prevents loss of heat.
The temperature sensor (1) measures the water temperature. As soon as
the measured temperature is below the set water temperature, the electronic
control observes a ‘heat demand’. The gas control (7) opens after about half
a minute and the gas mixes with the air. The hot surface igniter (9) ignites
this mixture and the water is heated. As soon as the measured temperature
is above the set water temperature, the heat demand ends and the electronic
control stops the heating cycle.
2.4.1 Introduction
The electronic control monitors the water temperature and ensures safe combustion.
This is done by:
• the Security of the water temperature ;
• the Gas control ;
• the Fan ;
• the Air pressure switch;
• the Ionisation detection .