Temperature Control-Reheat; Three-Stage Electric, Hot Gas And Hot Water Reheat; Scr Reheat; Figure 21 Three-Stage Heating - Emerson Liebert Challenger 3000 User Manual

3.4 Temperature Control—Reheat
If the room air temperature becomes too cold, the control will call for heating. Heating mode is con-
trolled by the Temperature Proportional Band, explained in 3.2.1 - Temperature Proportional
Band.
3.4.1

Three-Stage Electric, Hot Gas and Hot Water Reheat

The Reheat Proportional Band is divided into three equal parts, each representing one reheat stage.
As the Temperature Proportional Band increases the call for heating from 0% to -100%, stages 1
through 3 are switched On, as shown in Figure 21. Your unit will have one of the nine reheat config-
uration types shown in Table 4.
Table 4 Reheat configuration types
Type A
Stage 1 Electric 1
Stage 2 -
Stage 3 -
NOTE
1. Hot gas / hot water are not influenced by the setting of electric reheat during
dehumidification.
2. Hot gas output will be set only if the selected compressor is in operation.

Figure 21 Three-stage heating

3.4.2

SCR Reheat

SCR reheat is a type of electric reheat that provides tighter temperature control than staged electric
reheat. SCR reheat capacity modulation is achieved by pulsing the reheat On and Off. Full capacity is
achieved by constantly energizing the reheat. Units equipped with SCR reheat can operate in Tight or
Standard mode. By default, cooling units with SCR reheat are factory-set to operate in Tight mode.
The mode of operation can be set by adjusting the SCR Control Type parameter (Service Menu, Set-
points).
Tight Mode
In Tight mode, the compressors and reheats are operated at the same time to provide maximum tem-
perature control. The temperature deadband is set to zero at the factory. In a cooling unit with SCR
reheat and two single-step compressors, the first single-step compressor is started and full reheat
B C
Electric 1 Electric 1
Electric 2 Electric 2
- Electric 3
Temp Setpoint: 70°F
Proportional Band: 8°F
Deadband: 2°F
Heat 3
On Heat 2
On
65 66
-100 %
Heat 3
Heating
Off
½ Proportional Band
Decreasing Temperature
D E F
Hot Gas Hot Gas Hot Gas
- Electric 1 Electric 1
- - Electric 2
Heat 1
On ½ Dead-
band
67 68 69
Heat 2 Heat 1
Off Off
25
G H
Hot Water Hot Water
- Electric 1
- -
70
0%
Heating
Operation
I
Hot Water
Electric 1
Electric 2