System Performance With Advanced Microprocessor Controls; Temperature Control; Cooling/Heating Required, In Percent (%); Response To Control Types - Liebert Himod Operation & Maintenance Manual

Precision cooling for business-critical continuity

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Service manual (36 pages)

Table Of Contents

Table of Contents

4.0

YSTEM

ERFORMANCE WITH

This section provides details on how your Himod unit responds to user inputs and room conditions.

Refer to this section when you need specific information. This section includes details on control.

4.1

Temperature Control

4.1.1

Cooling/Heating Required, in Percent (%)

The temperature control program for the advanced microprocessor is based on a calculated % require-

ment for cooling/ heating.

4.1.2

Response to Control Types

Proportional Control

The % requirement is determined by the difference between the return air temperature and the tem-

perature setpoint. As the return air temperature rises above the temperature setpoint, the % cooling

required increases proportionally (from 0 to 100%) over a temperature band equal to the temperature

sensitivity plus 1 degree F. The % heating requirement is determined the same way as the tempera-

ture decreases below the setpoint. With this type of control the temperature at which the room is con-

trolled increases as the room cooling load increases. At full cooling load the room would be controlled

at a temperature equal to the setpoint plus the sensitivity.

4.1.3

Cooling Operation

One-Step Cooling, Compressorized Direct Expansion (DX) Systems

Cooling activates when the temperature control calculates a requirement for cooling of 100%. It is

deactivated when the cooling requirement drops below 50%. The hot gas bypass is energized on a call

for cooling.

To aid in lubricating the compressor, the hot gas bypass solenoid is delayed for 30 seconds on the initial

call for cooling and de-energized for 30 seconds during every 60 minutes of continuous operation.

Table 13

Cooling/dehumidification load status response

1-Step Cooling Only

Dehumidifying Only

1-Step Cooling w/ Dehumidifying

* See 4.2.3 - Dehumidification Operation.

GLYCOOL 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 compressor is activated at 200%. If full GLYCOOL capacity is not avail-

able, then the GLYCOOL valve will be opened proportionally over a cooling requirement band equal

to the available GLYCOOL capacity. The compressor would be activated at a cooling requirement of

100% above the available GLYCOOL capacity.

For example, if the GLYCOOL capacity is 60%, then the GLYCOOL valve would be full open at 60%

cooling requirement and the compressor would be in full cooling at 160%. In order to reduce compres-

sor cycling and prevent hunting, GLYCOOL capacity first becomes available when the entering glycol

temperature is at least 8°F (22% capacity) below the return air temperature, or 3°F below the return

air temperature for 2 hours. GLYCOOL capacity approaches 100% when the glycol temperature is 25

degrees F below the return air temperature. The system will continue to Econ-O-Cool as necessary as

long as the entering glycol temperature remains at least 3°F (0% capacity) below the return air tem-

perature. If GLYCOOL is not available, the temperature control will operate the compressor in the

same manner as a 1-step or 2-step system without GLYCOOL.