Dunham-Bush ACDX, Инструкции по установке, эксплуатации и обслуживанию, Страница: 22 / 44

4.3. Compressor Current Limiting 4.6. Compressor Start Delay
The amp limit B setpoint on the unit control A compressor start delay of one or two minutes
data sheet is the amp value at which the is incorporated into the computer to prevent two
compressor will be prevented from loading. compressors from starting at the same time and
The amp limit A setpoint is the amp value at insure that the system load requires another
which the compressor will be given an unload compressor. The compressor control point will
command until the current drops below the A display COFF ("clock off") during this timing.
setpoint.
If the values are changed, the difference This function allows the customer the option of
between the hold and unload points should automatic or manual reset of the computer after
not be decreased below 10% of compressor a power loss to the computer. The power loss
RLA so that oscillations will not occur. could be from the UVR or control switch. For
4.4. Ramp Control loss B setpoint. For manual reset after power
Ramp control can be implemented with the failure, a 1.0 is stored in the setpoint. A power
microcomputer. Whenever the unit starts with loss alarm is also recorded by the computer.
leaving water temperature greater than 5
E
F
above setpoint, a ramp up is generated. The 4.8. Anti-Recycle Timing
ramp start B setpoint specifies the percent At the start of a compressor, a 15 minute timer
capacity target at which the ramp begins on is initiated during which the compressor cannot
the first compressor. This can be set between start. If cooling is called for during this time, a
25 and 100 percent. The ramp rate A COFF is displayed in the compressor control
setpoint specifies the maximum amount that point.
can be added to the target each compressor
control interval. Thus a ramp rate of 0.1
CAUTION: This timer is bypassed by manual
produces the longest ramp rate. Table 1 gives control of compressors. DO NOT manually start
sample ramp times for various ramp rate a compressor more than once every 15
setpoints and start points for a minutes.
two-compressor machine.
4.9. Low Pressure Safety
TABLE 1 When the evaporator pressure of a given
Sample Ramp Times (Minutes) For a Two- pressure B setpoint, a time delay is initiated. If
Compressor Unit with a 2 Second Compressor the pressure stays below the setpoint during the
Control Interval time period, all compressors on the circuit will
Ramp 25% 50% 75% recorded by the computer.
Rate Start Pt. Start Pt. Start Pt.
Setpoint Setpoint Setpoint Setpoint For an air-cooled unit, the time delay is two
minutes when ambient temperature is above
.1 58 50 42 40
E
F. If ambient temperature drops below
.2 29 25 21 40
E
F, the delay on compressor start up is
.3 19 17 14 extended to 4 minutes. After start-up, the low
.4 15 12 10 pressure delay is two minutes.
A formula for calculating ramp time in minutes is 4.10 High Pressure Safety
T = [(# compressors x 100) - start pt.] x If the condensing pressure of a refrigeration
Compressor Control Interval/(Ramp rate x 60)] circuit exceeds the high pressure A setpoint, all
The compressor control interval can be high pressure alarm will be recorded by the
determined by timing the frequency of load/unload computer. Typical setpoint value is 360 psig.
pulses given to a compressor. It is typically 2
seconds.
4.11 Freeze Safety
4.5. Manual Lead/Lag Selection drops below the freeze B setpoint, all of the
The lead compressor can be selected by the compressors will be locked off. The freeze
lead B setpoint. The number stored in this alarm will be recorded by the computer. Press
setpoint should be one less than the desired RESET to clear the lockout.
compressor number. So a 0.0 in the setpoint
specifies compressor 1 as the lead, a 1.0 puts
4.12 High Oil Temp Safety
compressor 2 as lead, etc. It is preferable to If the oil temperature switch of a compressor
have compressor 1 as the lead. If a opens, the oil temperature digital input turns
compressor is locked off, the next compressor ON. If the compressor is operating, the
will automatically take its place in the lead/lag compressor will be locked off. The high oil
sequence. temperature alarm will be recorded by the
21
4.7. Power Loss Reset
automatic reset, a 0.0 is stored in the power
refrigeration circuit drops below the low
be locked off and the low pressure alarm will be
compressors on the circuit are locked off. The
If the leaving water temperature of a chiller
computer and RESET must be pressed after the
problem is resolved.