A.O. Smith ADMR-115, Installation, User And Service Manual

Page: 14 / 98

Working principle of the appliance
14 Instruction manual ADMR
2
gis
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 exhausted from the appliance via the draught diverter (33).
An energy-saving flue damper (32) is mounted in the draught diverter. The flue
damper opens before the burner tray ignites, and closes as soon as the flame
is extinguished.
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.
2.3 The appliance's
heating cycle
<The entire appliance is controlled and monitored by the ThermoControl
(electronic controller).The water temperature is measured by temperature
sensors T1 (7) in the top of the tank (10) and T2 (13) at the bottom of the tank.
These temperatures are sent to the electronic controller. Based on these two
observations, the electronic controller calculates a net water temperature: T
net
.
The value of T
net
lies between the temperatures at the top and bottom of the
tank. As soon as
Tnet
falls below the set water temperature (T
set
), the electronic
controller registers a "heat 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 becomes heated. As soon as
Tnet
rises above T
set
the heat demand
ends, and the electronic controller stops the heating cycle.
The electronic controller assumes a certain margin both when registering and
ending heat demand. We refer to this margin as the hysteresis
(12.2 "Setting
the hysteresis") .
2.4 Protection for the
appliance
2.4.1 Introduction
The electronic controller monitors the water temperature and ensures safe
combustion. This is achieved by:
•
the Water temperature protection ;
• the Flue gas backflow safeguard ;
• the Flame probe .