20 TGZ 040A through TGZ 190A OMM TGZ-1
Sequence of Operation
The following sequence of operation is typical for TGZ Templifier models when in the
heating mode. The sequence can vary slightly depending upon options.
Start-up/Compressor Staging (when compressors start and stop)
Stage Up Temperature (displayed on ‘VIEW UNIT TEMP (3)’ screen) is the Condenser
Leaving Water Temperature by which the next compressor to start will stage up (start) after at
least one compressor on the unit has started and is running.
Start Up Temperature (displayed on ‘VIEW UNIT TEMP (3)’ screen) is the Condenser
Leaving Water Temperature by which the first compressor starts. The start up temperature
equals the Stage Up Temperature minus the Start Delta Temperature set point. A higher Start
Delta Temperature set point value will keep the unit off longer and reduce unit cycling at low
loads. However, this high Start Delta Temperature set point will cause a larger excursion from
the Active Heat Leaving Water Temperature set point before the unit starts. Stated another
way, the Start Delta Temperature set point is the number of degrees below the Active Heat
Leaving Water Temperature set point, minus ½ the Control Band, that determines when the
first compressor starts. The Start Delta is in effect for only the first start after all compressors
have been off. Additional compressor starts and stops are determined by the Condenser
Leaving Water Temperature (LWT) with respect to the Control Band only. The Control Band
is automatically set based upon the number of stages (compressors) for the unit. A four (4)
compressor unit will have a Control Band that is 30% of the CondDeltaT set point. A six (6)
compressor unit will have a Control Band that is 20% of the CondDeltaT set point.
The following sequence would occur for the settings shown below for a four compressor unit:
CondDelta T set point = 10.0°F
StartDelta set point = 5.0°F
StopDelta set point = 2.0°F
Heat LWT set point = 140.0°F
The calculated Control Band will be 30% of 10ºF (Cond Delta T) which is 3ºF.
For a cold start-up (no compressors running), the first compressor will start at any temperature
below 133.5°F. Each subsequent compressor will start after the Stage Up Timer has timed out and if
the temperature is below the Control Band, 138.5°F in this case.
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