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ters, gaskets, droplet eliminators etc. close to electric heater may become dam-
aged or even catch fire. This could lead to the spread of fire and significant dam-
ages to the wider building.
In order to avoid the above mentioned risks, TRANE provides, as standard, electric heaters with 2
independent safety thermostats.
7.4.1
AHUs equipped from TRANE with control
Units, which are supplied from TRANE with control, are limiting the supply air temperature to a de-
fault value of 35 °C.
The execution and function, as specified below, is supplied by TRANE.
Control-side limitation of the air temperature beyond the electric heater
The control of the electric heater always regulates the temperature of the air passing through the
heater so that it never exceeds the permitted air temperature in the AHU (40 °C, if not differently
specified in the technical data). This item must be especially observed, when the AHU is only oper-
ated with a partial air flow (e.g. in times of reduced use of the building).
As the heat output of an electric heater is generated very quickly and at full ca-
pacity at ON-OFF operation, there is a significant risk of overheating of the AHU,
which contributes to the damage of several components. This risk occurs espe-
cially at low air flows.
For this purpose, the air handling unit is equipped with a supply air sensor, which directly measures
and monitors the air temperature generated by the electric heater. The control engineering is used
to ensure that the heating power of the electric heater is controlled so that the temperature remains
within the permitted air temperature in the AHU.
Avoid overheating of AHU components by residual heat of electric heater
In order to avoid excessive heating of components by residual heat of electric heater control en-
sures that fan motor keeps on running for at least 5 min after cutting off of electric heater! By using
an enabling contact (see Figure 73) the control engineering also ensures that the electric heater
can only start its operation when the fan is running.
If in case of main power failure (for example lightning stroke) this automatic run
cannot be ensured, AHU may become damaged by the residual heat of the elec-
tric heater.
In order to avoid damages, an uninterrupted power supply is recommended. If the AHU is not oper-
ated by an uninterrupted power supply after every main power failure an AHU inspection is required
as indicated in chapter 9 (Maintenance).
Safety concept
Electric heater power supply is equipped with 2 contactors in serial connection!
The 2 safety thermostats protect the AHU in two independent ways:
Firstly: By hardware via contactors in the power supply.
Secondly: By software via controlling. In case of failure contactors immediately cut off the electric
heater from power supply.
-
The 2 safety thermostats are connected in serial connection.
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