Danfoss AK-PC 420 User Manual page 6

The heat recovery relay is disconnected and can only be re-ena-
bled once the temperature by the regulation sensor has reached 2
K above the reference's minimum setting.
Ramp function
To avoid overswing and underswing of the reference, a ramp
function has been included to guarantee that the reference cannot
change more quickly than the preset ramp in Kelvin/minute.
Limitation of reference
To protect against regulation reference that is too high or too low,
a limit must be set for the reference. The limit is valid under normal
regulation, but is increased during heat recovery to 99.9° C.
The upper limit is always an absolute value. The lower limit can
either be an absolute value or it can vary in accordance with the
outside temperature Sc3 whereby the limit has a fixed value ("r56,
Min tm") above the outside temperature. This means that a refer-
ence below the minimum value, making all fans run continuously,
can be avoided.
P or PI regulation with floating or fixed reference
See appendix.
Safety functions
Monitoring of condensation pressure
The controller has a safety function that provides protection
against the condensation pressure being too high.
The function can be enabled in two ways.
• Digital input - HP safety
When the digital input is connected, full capacity is cut in to
both fans and three-way valve. An alarm is emitted at the same
time.
The capacity remains cut in until the digital input is inter-
rupted, at which point the alarm is also cancelled. The digital
input can possibly be connected to an external safety pressure
control.
• Measuring the Pc/S7 temperature
This function always uses condensation pressure Pc if the
pressure signal is connected. If Pc is not fitted, brine return
temperature S7 is used instead.
The function cuts in all condenser steps and emits an alarm
if the measured temperature is higher than 3 K below the set
limit "S7/Pc max".
Normal capacity regulation is restored when the temperature
(pressure) has once more fallen to 3 K below the limit, and a
delay time of 60 seconds has passed.
Pump controL
The controller can control and monitor one or two pumps that
circulates the brine.
If two pumps are used and operating time equalisation is selected,
the controller can also execute a switch between the two pumps if
operating alarms occur.
Pump selection is performed using the following settings:
0: Both pumps are stopped
1: Pump 1 is started
2: Pump 2 is started
3: Both pumps are started
4: Automatic switch between the pumps is permitted. Start before
stop
5: Automatic switch between the pumps is permitted. Stop before
start
6 Manual RS8EL402 © Danfoss 03-2010
Ref. Max.
Ref. Min.
Ref. Max.
Ref. Min.
AK-PC 420