Douwe Egberts Cafitesse 700, Back Office Manual

Page: 218 / 265

July 2004
5F - 16
Functions - cooling system
Principle of thermoelectric cooling
• In order to keep the BIBs chilled, the
dispenser is equipped with a thermoelectric
cooling system. The element in this type of
system is called Peltier element (4). (Fig. 1)
• The Peltier element (4) consists of a row of
thermoelectric cooling cells The elements of
which consist of two semiconductor bridges
made of bismuth and tellurium material of
various degrees of doping. (Fig. 1)
• The transported heat quantity is proportional
to the electric current as well as to the
amount of cooling cells in the element.
• More than 100 cells are series-connected
electrically in the element of the dispenser.
In terms of thermal technology, these cells
are parallel-connected. The typical electric
current value (in stable cooled state of the
system) amounts to 2.7–3.1 A.
• Like a heat pump, the Peltier element (4)
transports the heat energy from the cold
cooling compartment side to the warm heat
sink side. In addition to the refrigerating
capacity (typically 10 W) transported out of
the cooling compartment (1), the electric
loss capacity of the element (typically 55
watts) is also transferred to the warm side.
(Fig. 1)
Structure – cooling system
• The structure of the cooling system is
shown in Fig. 1:
Cooling compartment (1)
• The cooling compartment (1) consists of a
pressure-cast aluminium container with two
cast-on areas for fastening the cooling
modules. In the container wall, the heat
penetrating from the outside is collected
and conducted to the cooling modules.
(Fig. 1)
Aluminium plate (3)
• The aluminium plate (3) is installed on the
heat sink and covers the Peltier elements.
(Fig. 1)
• This provides a self-contained cooling
module that is easily replaced in case of
repair.
F.3.2 Function: cooling system
Peltier element (4)
• The structure of the Peltier element in-
cludes two small ceramic plates. The actual
cooling elements are located in between
these small ceramic plates.
• To ensure the correct functioning of the
system, it is particularly important that the
Peltier element (4) has very good thermal
contact to both sides. This is achieved by
means of face-milled contact surfaces on
the aluminium plate (3) and on the heat
sink (6) and by means of thermal com-
pound as contact material. Since the ther-
mal compound possesses very low thermal
conductivity, it is very important to spread a
mere minimum of thermal compound evenly
onto the peltiers. (Fig. 1)
ATTENTION: During the assembly proce-
dure, dust particles must never
get in between these surfaces.
Seal on the Peltier element
• Any condensation water on the cold side of
the Peltier element, would result in corro-
sion and could shorten the service life of
the element considerably. As a means of
protection against this corrosion process,
the internal parts of the elements have
been coated with a thin layer of epoxy
resin.
Insulation (5, 6)
• Polyurethane foam insulation is used to
reduce the heating-up effect caused by the
surroundings.
• Due to the relatively low refrigerating ca-
pacity of Peltier cooling systems, thick-
walled insulation is required resulting in
very low power consumption of the cooling
system.
Cafitesse 700 - Functions - cooling system