18
SLS/SLH 10/06
7
CONDENSER FAN CONTROL
(IN COOLING MODE
WITH FAN SPEED CONTROL)
Parameter used: Minimum Fan Speed, Max Fan Speed,
Discharge Pressure Set (DPSET), Max Discharge Pressure,
MINDP, Condensation type Control (STEP or FSC)
Control uses one digital output to power on one fans
relay and an analogue output 0-10Vdc to drive a Fan
Speed Controller (FSC). The fans try to maintain a con-
stant condenser pressure equal to the programmed set
point by varying fan speed.
As soon as the first compressor starts, the fan relay will
turn on, and it will stay on until the all compressors turn
off. For the first 10 seconds the fans will begin at an out-
put level proportional to the ambient temperature. The
hotter it is out, the faster the fans will start. Below is a
chart showing the correlation.
Table 1 – Startup Fan Values
There is one high pressure transducer each system. If
only one compressor is running, the fans control to its
discharge pressure. If two compressors are running, the
fans control the pressure of the 1st system started, or the
one which is running at 100% capacity if the other one
is running at lower capacity as long as neither pressure
exceeds the maximum discharge pressure.
Once on, the fan speed is recalculated every second
according to the below basic rules:
If DPSET-1 < DP < DPSET+1 then no change in AO
If (DPSET+1 < DP < DPSET+2) AND (DP IS NOT DECREASING) then AO = AO + 1 %
If (DP > DPSET + 2) AND (DP IS NOT DECREASING) then AO = AO + 5 %
If (DPSET-2 < DP < DPSET-1) AND (DP IS NOT INCREASING) then AO = AO -1%
If (DPSET-2 < DP < 10.5) AND (DP IS NOT INCREASING) then AO = AO -2%
If (DP < MINDP) then AO = AO - 2 %
To check if DP is increasing or decreasing, value
q
DP = ± 0.2 bar/sec is used.
