Table of Contents
Advertisement
54
Installation Electrical
CCAF - Fan Control
On air cooled chillers, heat is removed from the evaporator water loop and released to
ambient air by the condenser. In order to control condensing conditions, the volume
of airflow is changed to compensate for ambient air temperature and cooling load.
Starting and stopping condensing fans controls airflow.
Outdoor Air Temperature Control
Condenser fan staging is on a per circuit basis and is a function of outdoor ambient
temperature and load. The load parameter used is the number of compressors
running per circuit. Fans for the various units are staged as shown in the following
figures. In the chart, there are areas where more than 1 choice is possible, 1 or 2 fans
for example. These are areas of hysteresis in which the current number of fans
running is maintained. The number of fans running will depend upon the direction
entered. When the circuit is not running the number of fans running will be initialized
to 0. When the first compressor starts on a circuit, the minimum number of fans shall
be started based on the outdoor air temperature, i.e. if outdoor air temperature is in a
hysteresis range, use the smallest number for that range. There should always be at
least one fan running when a compressor is running. Staging compressors is a
horizontal movement on the fan control charts. If this movement is into a hysteresis
area, then the previous number of fan stages is used.
Each refrigeration circuit has two relay outputs for fan control. Depending upon how
many fans are connected to each circuit, there may be either two or three air flow
levels. The number of fan stages is shown on the following table for each unit size.
Table 16
Fan Configuration
Tons
# of Fans/chiller
20
2
25 - 30
3
40
4
50 - 60
6
For 20 and 40 ton chillers, the first fan relay will be on whenever a compressor is
running. The second relay will be energized when more condenser cooling is required
and de-energized when less cooling is required. The 25, 30, 50, and 60 ton chillers
have 3 stages of fan flow. The first relay will be connected to one fan. The second
relay will be connected to two fans. For these chillers the first relay will not always be
energized. When two fans are needed the first relay will be de-energized at the same
time the second relay will be energized. Energizing both relays turns on 3 fans.
There is a 5 second delay between turning the fans on and starting the first
compressor.
# Relays/chiller
#Fan Steps/ Circuit
2
2
2
3
4
2
4
3
CGWF-SVX01A-EN
Hide quick links:
Advertisement
Table of Contents
