Emerson Liebert ICOM-DO User Manual download pdf (Page 31)

100

Operation

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.

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

Table 4 Reheat configuration types

Type A B C D E F G H I

Stage 1 Electric 1 Electric 1 Electric 1 Hot Gas Hot Gas Hot Gas Hot Water Hot Water Hot Water

Stage 2 - Electric 2 Electric 2 - Electric 1 Electric 1 - Electric 1 Electric 1

Stage 3 - - Electric 3 - - Electric 2 - - Electric 2

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.

Heating

65 70

Heat 3

½ Dead-

band

66 67 68 69

Heat 2

Heat 1

Heat 3

Off

Heat 2

Off

Heat 1

Off

-100 %

Heating

½ Proportional Band

Decreasing Temperature

Temp Setpoint: 70°F

Proportional Band: 8°F

Deadband: 2°F

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 99 100

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Emerson Liebert ICOM-DO User Manual Page 31

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