Cooler Freeze Protection — The control will try to prevent shutting the chiller down on a Cooler Freeze Protection alarm by removing stages of capacity. If the cooler fluid selected is Water, the freeze point is 34 F (1.1 C). If the cooler fluid selected is Brine, the freeze point is the Brine Freeze Point (Set Points→FRZ→BR.FZ). This alarm condition (A207) only references leaving fluid temperature and NOT Brine Freeze point. If the cooler leaving fluid temperature is less than the freeze point plus 2.0° F (1.1° C), the control will immediately remove one stage of capacity. This can be repeated once every 30 seconds.
Low Saturated Suction Protection — The control will try to prevent shutting a circuit down due to low saturated suction conditions by removing stages of capacity. These circuit alert conditions (T116, T117) compare saturated suction tempera- ture to the configured Brine Freeze Point (Set Points→FRZ→BR.FZ). The Brine Freeze point is a user- configurable value that must be left at 34 F (1.1 C) for 100% water systems. A lower value may be entered for systems with brine solutions, but this value should be set according to the freeze protection level of the brine mixture. Failure to properly set this brine freeze point value may permanently damage the brazed plate heat exchanger. The control will initiate Mode 7 (Circuit A) or Mode 8 (Circuit B) to indicate a circuit’s capaci- ty is limited and that eventually the circuit may shut down.
Head Pressure Control — The main base board (MBB) controls the condenser fans to maintain the lowest condensing temperature possible, and thus the highest unit efficiency. The MBB uses the saturated condensing tempera- ture input from the discharge pressure transducer and outside air temperature sensor to control the fans. If OAT is greater than 70 F before a circuit is starting, then all condenser fan stages will be energized. A fan stage is increased based on SCT (saturated condensing temperature). When the highest SCT is greater than the Fan On Set Point (Set Points→HEAD→F.ON), then an additional stage of fan will
be added to the current fan stage. Fan On Set Point (F.ON) equals Head Set Point (Set Points→HEAD→H.DP) except after a fan stage increase when the Head Set Point is increased by Fan Stage Delta (Set Points→HEAD→F.DLT). A fan stage is decreased when the SCTs of both circuits are less than the Fan Off Set Point (Set Points→HEAD →F.OFF) for two minutes. Table 20 shows the number of fan stages, contac- tors energized and the fans that are on during the fan stage. Unit sizes 035 to 060 have common fan control. Figure 14 shows the location of each fan and compressor within the unit.
MOTORMASTER® V OPTION — Motormaster V is stan- dard on 30RAP010 and 015 size units. For all other units that need
Operation of Machine Based on Control
Method and Cooling Set Point Selection Set- tings — Machine On/Off control is determined by the
configuration of the Control Method (Configura- tion→OPT2→CTRL) and Cooling Set Point Select (Config- uration→SLCT→CLSP) variables. All units are factory configured with Cooling Set Point Select set to 0 (single set point). With the control method set to 0, simply switching the Enable/Off/Remote Contact switch to the Enable or Remote Contact position (external contacts closed) will put the chiller in an occupied state. The control mode (Operating Modes→MODE) will be 1 (OFF LOCAL) when the switch is Off and will be 5 (ON LOCAL) when in the Enable position or Remote Contact position with external contacts closed.
CTS (F)
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 |
| SST (F) |
LEGEND |
|
SCT — Saturated Condensing Temperature | |
SST — Saturated Suction Temperature |
|
Fig. 14 — Operating Envelope for R-410A Compressor
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