The Appliance's Heating Cycle; Protection For The Appliance - A.O. Smith ADM - 40 Installation, User And Service Manual

2
2.3 The appliance's
heating cycle
2.4 Protection for the
appliance
2.4.1
2.4.2
12
Working principle of the appliance
In this appliance, the cold water enters the bottom of the tank through the cold
water inlet (14). The heat of combustion is conducted to the water by the
combustion chamber (8) and heat exchanger (11). The heated tap water leaves
the tank through the hot water outlet (2). Once the appliance is completely filled
with water, it will constantly be under mains water pressure. When hot water is
drawn from the appliance, it is immediately replenished with cold water.
The gas required for combustion flows via the gas control (16) into the manifold.
Orifices are mounted in the manifold. The gas is injected into the burner bars at
pressure from these orifices (36). The burner bars together form the burner tray.
The injection of gas into the burner bars also draws in the primary air required
for combustion. The narrow opening in the orifice causes the gas flow to
accelerate. This in turn causes a partial vacuum. It is this partial vacuum that
draws in the air (the Venturi effect). Additional air is drawn in through the
opening in the burner tray.
The hot surface igniter (20) ensures ignition of the gas/air mixture.
The flue gases released by this combustion are led through the flue tubes (part
of 11). Flue baffles (part of 11) are mounted in the flue tubes. These retard the
flow of the flue gases, thereby increasing the thermal efficiency of the appliance.
The flue gases are vented from the appliance via the draught diverter (33).
A radiation shield/condensation tray (35) is mounted below the burner tray. This
prevents overheating of the floor area below the appliance, as well as serving
as a collection tray for condensation water.
The insulation layer (24) prevents heat loss. The inside of the tank is enamelled
to protect against corrosion. The anodes (9) offer extra protection.
The entire appliance is controlled by the burner control (40) and the control
thermostat (41) or frost thermostat (44). The control thermostat and frost
thermostat both independently measure the water temperature (T
appliance's heating cycle is activated as soon as T
value (T ). The value of T
set
appliance (8.2 "Operating modes"). When the appliance is in OFF mode (frost
protection), this value is determined by the frost thermostat (threshold value =
20 °C). When the appliance is in 'ON mode', the threshold value can be set via
the control thermostat (±40 °C - ±70 °C).
As soon as T falls below T
water
close, and the burner control will register demand. The gas control (16) is
opened, and the gas is mixed with air. This mixture is ignited by the hot surface
igniter (20) and the water is heated. As soon as T
thermostat opens again. The demand will cease, and the burner control will stop
the heating cycle.
The thermostats have a certain margin both when closing and opening. We refer
to this margin as the hysteresis. The hysteresis cannot be adjusted.
Introduction
The burner control monitors the water temperature by means of thermostats
and ensures safe combustion. This takes place using:
• the Water temperature protection;
• the Flue gas backflow safeguard;
• the Flame probe.
Water temperature protection
By means of the frost, high-limit and safety thermostats, the burner control
monitors three temperatures that are important for safety. The table explains the
working principle of the thermostats with sensors.
water
depends on the selected mode of the
set
, the relevant thermostat (control or frost) will
set
gets higher than T
water
Instruction manual ADM
gis
). The
water
falls below the threshold
, the
set