Tandem Digital Compressor Annunciation Criteria And Unit Behavior; Tandem Operation; Temperature Control-Reheat; Figure 25 Digital Scroll Ramping Example With Two Tandem Digital Scroll Compressors - Emerson Liebert iCOM Manual

The digital compressor within the tandem compressor set will be activated upon a call for cooling.
This compressor can ramp between 20% and 100% capacity to meet the room load. If the call for
cooling increases above its available capacity the fixed compressor within that tandem compressor set
will be activated and the digital compressor ramps down to its minimum speed.The Liebert DSE
activates the compressors in the following manner based on the amount of cooling needed.

Figure 25 Digital scroll ramping example with two tandem digital scroll compressors

100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
NOTE
Special operation for suction pressure management and compressor-related alarms may alter
stage definitions.
As shown in Figure 25, the Digital Compressor loading for both C1A and C2A can be determined for
any CFC value, as long as the Cooling Stage is known. For example, if the CFC is 50%, and the
cooling stage is 2, then only compressors C1A and C2A will be On, and each will both be loaded at
about 82%. This is because each operates from Ramp 2 during this cooling stage. If the CFC is 50%
when the Cooling Stage is 3, then compressors C1A, C2A, and C1B will be On, with C1A loaded about
23%, and with C2A loaded about 82%; C1A operates from ramp 3, and C2A operates from Ramp 2.
3.3.2

Tandem Digital Compressor Annunciation Criteria and Unit Behavior

For each of the tandem specific alarms (see Table 21), the following rules dictate their annunciation
conditions and control behavior.
3.3.3

Tandem Operation

If alarms that require lead-lag changes are present in both tandem banks, then Tandem Bank 1 must
be set as the lead bank.
Once a compressor alarm is reset, the affected compressors may be reactivated, and the actual tandem
activation sequence will be reset to match what is indicated on line S402 ("Compressor Sequence").
3.4 Temperature Control—Reheat
If the room air temperature becomes too cold, the control will call for heating. Heating mode is
controlled by the Temperature Proportional Band (see Figure 21). The Liebert DSE is qualified for
heating-only operation at return temperatures not exceeding 80°F (27°C).
NOTE
Some reheat limitations may apply during dehumidification depending on model unit
installed. See 3.5.3 - Dehumidification for more information. Reheat operation is not
permitted on units equipped with Liebert EconoPhase while the EconoPhase cycle is active.
Ramp 1
Stage 1: C1A
Ramp 2
Stage 2: C1A & C2A
Stage 3: C2A
0% 10% 20% 30%
Ramp 3
Stage 3: C1A
Stage 4: C1A
40% 50% 60% 70%
Call For Cooling
31
Ramp 4
Stage 4: C2A
Stage Definitions
Stage 1: C1A
Stage 2: C1A, C2A
Stage 3: C1A, C2A, C1B
Stage 4: C1A, C2A, C1B, C2B
80% 90% 100%
® ®
Liebert iCOM for Liebert DSE
Operation
™