AK-PC
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Manual RS8EL402 © Danfoss 03-2010
5
Linear/non-linear capacity curve for fans
The first fan step provides relatively more capacity than the subse-
quent capacity steps. The increase in capacity that an extra step/
speed will generate falls gradually, as more and more steps are
connected/the speed is increased.
The fan regulation therefore has a crooked capacity curve, which
provides optimal reinforcement at both high and low capacities.
However, for some systems a straight curve is required for capacity
regulation, e.g. if the analogue signal is used for more than con-
trolling fans. In this instance the capacity curve can be set at linear.
(The capacity curve for the three-way valve will always be straight.)
Step-by-step coupling of fans
The fans can either be connected in the sequence defined for
them (sequentially) or they can be connected in rotation (sequen-
tially with alternating start).
In sequential operation all fans are enabled at least once every 24
hours, so no fan rusts up due to being inactive for a longer period
of time.
In rotation the various fans take turns in being first.
Monitoring fans
The controller must receive a signal of the status of each defined
condenser step’s safety circuit. The signal is taken directly from the
safety circuit and connected to a “DI” input.
If the safety circuit is broken, the controller will lose the signal and
emit an alarm.
The associated relay output will not be disconnected. The reason
is that fans are often connected in pairs, but with one single safety
circuit. If there is a fault in one fan, the other will continue to oper-
ate.
If no monitoring is desired, the input must be permanently wired
at 24 V.
Reference
Regulation reference
The regulation reference can be defined in one of the following
two ways:
• Fixed setting
The set point for the regulation sensor is set in °C.
If displacement is required, the reference can be displaced
with a 0-10 V signal. During setup you define how great the
displacement is to be at the signal’s max. and min. value.
• Floating reference according to outdoor temperature
This function allows the reference to vary according to the
outdoor temperature within a defined range.
The outdoor temperature is measured with the Sc3 sensor,
and the reference will always fall within a fixed value (min. tm)
above the measured outdoor temperature.
Heat recovery
When heat recovery is enabled via the digital input, the reference
will switch to another set point “Heat SP”, although this too can
be overridden via the external 0-10 V signal. At the same time the
relay for heat recovery is enabled, which then transmits a signal to
either a pump or a valve. The reference's max. value (r30) is over-
riden from the set value to 99.9° C.
If heat recovery is in progress and the temperature by the regula-
tion sensor is lower than the reference’s set minimum value, the
following happens (see also the following section on limiting the
reference):
