Liebert TM-10098 service manual Stage Compressorized Cooling – No Dead Band

iCOM Controls Training and Service Manual

The temperature controller deactivates the second stage of cooling (lag compressor) when the return air temperature decreases to 50% of the cooling proportional control band value. The first cooling stage (lead compressor) is deactivated when the return air temperature decreases to the temperature set point value or 0% of the cooling proportional control band value.

2 Stage Compressorized Cooling – No Dead Band

Temp Set Point + (1/2 Proportional Band)
Temp Set Point: 70°F
Proportional Band: 8°F
		Cool 1 On		Cool 2 On
70	71	72	73	74	75
Cool 1 Off		Cool 2 Off
			Increasing Temperature

Note: in the above example that the control band begins at the 70°F temperature set point and has a length of 4°F, which is ½ of the programmed temperature proportional band value.

As the return air temperature increases Cooling 1 (lead compressor) is activated at 72°F or 50% of the cooling control band. If the return air temperature continues to increase Cooling 2 (lag compressor) will activate at 74°F or 100% of the cooling control band.

When the return air temperature starts to decrease, Cooling 2 (lag compressor) is deactivated at 72°F or 50% of the cooling control band and Cooling 1 (lead compressor) is deactivated at the temperature set point of 70°F or 0% of the cooling control band.

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