Emerson Liebert iCOM - Manual (Page 29)

Operation
23
GLYCOOL
™
Cooling—Free-Cooling
When GLYCOOL cooling is available, the temperature control will calculate a total cooling require-
ment of 200% rather than 100%. Assuming that full GLYCOOL capacity is available, the GLYCOOL
valve opens proportionally as the requirement for cooling rises from 0 to 100%. If more than 100%
cooling is required, then the compressors are activated at 150% and 200% respectively (133%, 163%,
180% and 200% for a four-step system). If full GLYCOOL capacity is not available, then the GLY-
COOL valve will be opened proportionally over a cooling requirement band equal to the available
GLYCOOL capacity. The compressors would be activated when the GLYCOOL capacity is exceeded.
For example, if the GLYCOOL capacity is 60%, then the GLYCOOL valve would be full open at 60%
cooling requirement and the compressors would activate at 110% and 160% cooling requirement. In
order to reduce compressor cycling and prevent hunting, GLYCOOL capacity first becomes available
when the entering glycol temperature is at least 8°F (4.4°C) (22% capacity) below the return air tem-
perature, or 3°F (1.7°C) below the return air temperature for two hours. GLYCOOL capacity is 100%
when the glycol temperature is 25°F (13.9°C) below the return air temperature. The system will con-
tinue to operate in Econ-O-Cool mode as necessary as long as the entering glycol temperature
remains at least 3°F (1.7°C) (0% capacity) below the return air temperature. If GLYCOOL is not
available, the temperature control will operate the compressors in the same manner as a two-step or
four-step system without GLYCOOL.
Dual Cooling Source
If dual cooling is available, the sensible cooling system operates in the same manner as a GLYCOOL
system, except that it is assumed that 100% chilled water capacity is available any time the chilled
water temperature is 3°F (1.7°C) below the return air temperature.
3.5 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 3.3.1 - Temperature Proportional
Band.
3.5.1 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 19. Your unit will have one of the nine reheat config-
uration types shown in Table 4.
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.