AK-PC 781A Capacity controller RS8HE202 © Danfoss 2017-07 115
2. Offset of the condensing pressure
Reference
Regulation is done using a heat exchanger temperature/receiver
temperature of e.g. 40°C, the value is adjustable. A temperature
sensor Shr is installed in the receiver and the temperature is main-
tained in a band around the selected value.
When the temperature goes above the reference plus the half
band, the gas is routed around the heat exchanger.
The reference can be displaced variably using an external 0-10 V
signal. 0 V results in no displacement. 10 V results in a displace-
ment indicated by the set value.
Regulation
The following can be used as a regulation sensor:
- Shr8
- Shr4
- Delta T via the heat exchanger (Shr4-Shr3) of e.g. 4K, but still us-
ing Shr8 as the thermostat sensor.
The pump can be controlled on/off or variably. For Shr4 or DeltaT
regulation it must be variably controlled. During variable opera-
tion the pump will stop when the regulation request a lower
capacity than the selected min. speed capacity for the pump. .
Increasing the condensing pressure
When the temperature is below the reference and heat recovery is
carried out, the condensation pressure may be increased.
The pressure is measured using the pressure transmitter Pgc and
the controller at the valve Vhp.
How much the pressure shall be increased by is determined using
a setting and an analogue voltage signal. The signal must be a
0-10 V signal or a 0-5 V signal.
During heat recovery and a signal of 0 V, the pressure is increased
to "Pgc HR min."
At max. signal (e.g. 10 V) the pressure will increase according to
the setting "Pgc HR offset".
.
Up to 5 signals can be received from external regulations. They
can all increase the pressure, and the controller will use the signal
that requires the largest offset. The signal employed is filtered
over a time period. The length of the period can be set.
Relay output
A relay can be reserved that will pull in if the received signal ex-
ceeds 9.5 V (4.75 V) for more than 10 minutes.
The relay is defined in the function: "Additional heat output".
Remember the isolation amplifier
If signals are received from different controls, e.g. heat recovery
for one of the inputs, a galvanically insulated module should be
inserted.
Reference
Band
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