58
ARTC-SVX007A-EN
Sequence of Operations
When chiller starts (from ‘Idle’ state):
1. Enable signal sent from BAS sets digital input on chiller
control to true. Chiller controller waits for (adjustable)
low urgency zone (LUZ) timer before acting on BAS
enable.
2. If the LCHWT is greater or equal than the chiller
temperature setpoint plus the “ΔT over set point” and
there are compressors available to run, the chiller is set
to ‘Start’ state.
3. If compressor is available, the adjustable Start Demand
(default 65%) is sent to the compressor and the
compressor starts.
4. This software is capable of staging multiple
compressors (up to 6) but Thermafit TACW is a single
compressor chiller only. Therefore, this chiller should
not go to state 'Stage-in' or 'Stage-out'.
5. Once the compressor state becomes 'Operational' the
chiller state also goes to 'Operational', the PID loop
takes control supplying demand to the compressors
based on the error between the set point and leaving
chilled water temperature.
a. If the chilled water temperature drops below the set
point temperature for a period longer than the
adjustable stage out timer, the chiller controller will
determine if it should shutdown a compressor.
Chiller goes in shutdown state.
• The inlet guide vane must have remained at a
position lower than the chiller controller IGV
STAGE DOWN, % for the adjustable Stage Out
Timer.
(OR)
• The chiller demand has reduced to less than
the adjustable minimum demand for last
compressor.
Chiller Operational States
Figure 44. Chiller Operational States Flow Chart
Idle State
The chiller is standing idle (zero capacity) but is ready for
start of the first compressor.
Start State
The pressure ratio must be kept low while one or more
compressors are in the process of starting. The start state
maintains the low-pressure ratio until all running
compressors have reached sufficient speed to operate
without risk of surging. At that point, the state is changed
into the operational state.
Operational State
The chiller is in normal operation.
Stage-In State
Note: Not needed on Thermafit™ TACW.
Starting a compressor when other compressors are already
running requires some care because the pressure ratio has
to be low enough to start a compressor.
This is the purpose of the stage-in state. The system is
instructed to lower the pressure ratio and the rack controller
contributes by instructing all running compressors to
reduce their capacity (the retreating and hold states of the
individual compressor states below. As soon as the
pressure ratio has reached the threshold, the new
compressor is instructed to start and the state changes into
start state.
To Next Page
Loading...
