Chillers
ULTIMA FREECOOL
Chillers
Installation & Maintenance Manual : 903-125 IM E 05/04/A
23
Controls
Airedale recognises that all chiller applications are different but fall mainly into 2
application categories; Variable Supply Temperature and Constant Supply Temperature.
The onboard microprocessor has the capability of satisfying either control requirement as
illustrated below.
Using the Airedale Variable Supply Temperature control scheme,
energy savings are available when compared with previous schemes and that of the
Constant Supply Temperature application.
Variable Supply Temperature control schemes offer energy savings where the supply
water temperature is not critical to its operation and is recommended for free-
cooling applications.
Selection of the best application control scheme can be made via a software switch in the
microprocessor during initial commissioning.
CONTROL SCHEME
FEATURES
Examples based on Models UFC250 to UFC650 having 6 Stages of Cooling
Variable Supply
Temperature Control
6
7
8
9
10
11
12
13
14
WAT
ER T
EM
PE
R
A
TURE
°C
20%
40%
55%
70%
85%
100%
Chiller
Capacity %
Cooling Stage Sequence
1
2
3
4
5
6
Return Water Temperature
Supply Water Temperature
Compressor Off
Mean Value
Constant Supply
Temperature Control
6
7
8
9
10
11
12
13
14
0
2
4
6
8
10
12
14
Supply Water Temperature
Return Water Temperature
Chiller
Capacity %
Cooling Stage Sequence
20%
40%
55%
70%
85%
100%
1
2
3
4
5
6
W
A
TE
R T
EM
PE
RAT
UR
E °C
Factory set to Variable Supply Temperature Control unless otherwise stated
at order.
CAUTION
Only when the mode selection has been set can the unit be enabled.
In high ambients where free-cooling is not available the fan speed modulates in the
conventional manner to maintain a constant head pressure. Free-cooling is initiated
wherever the outdoor ambient is 1°C less than the return water temperature.
When free cooling and DX cooling are operating simultaneously the condenser fan speed
will operate at 100% maximising free cooling.
In ambients where the free cooling coil is capable of satisfying the full cooling demand,
the condenser fans are modulated to provide the desired duty. The condenser fans are
capable of being modulated between 25-100% of airflow to maintain the supply
water temperature.
Free-Cooling Operation
During periods where the condenser fan speed has been reduced to a minimum, the
supply water temperature will then be controlled by the 3 way valve.
