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5
COLD THERMOSTAT
Function
To bring the temperature of the cooled fluid as close as possible to the set point by adapting the number of
compressors in service to the heat load in operation.
Description
The thermostat THER controls the switching on and off of compressors.
It is determined in accordance with the following parameters :
TEEG ó Chilled water input temperature (°C)
CONSREG ó Active instruction for output of chilled water (°C)
This instruction is equal to CONSEA or CONSEB depending on the status of a logic
input associated with the variable CHPCONS.
Si CHPCONS = 0, CONSREG = CONSEA.
Si CHPCONS = 1, CONSREG = CONSEB.
(For regulation with air gradient, see page 7).
DELTAT ó Desired temperature difference between water input and output (°C)
ENCL ó Operating differential for a regulation stage (°C)
This variable is calculated as follows:
ENCL = ( DELTAT / No. Of compressors )
Example of a machine with 4 compressors:
With CONSREG = 7°C
et DELTAT = 5°C
⇒ ENCL = 1,25°C
Remarque : The thermostat is only authorised to increase by a stage if the following conditions are satisfied :
ð THER has not increased for at least 3 minutes.
ð The chilled water output temperature is greater than the set point.
ð The number of compressors in service is equal to the thermostat value.
THER
Compressor start-up Compressor stop
THER
TEEG (°C)
THER
TEEG (°C)
0 ð 1 8.25 4 ð 3 10.75
1 ð 2 9.5 3 ð 2 9.5
2 ð 3 10.75 2 ð 1 8.25
3 ð 4 12 1 ð 0 7
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