APC INROOM ACPSC3000 Operations Instructions download pdf (Page 15)

InRoom CW/DX – Operating Instructions 15

2.4 Basic components/function of refrigerant circuit

The refrigeration circuit consists of a compressor, a condenser, an expansion valve and an evaporator.

In units of the G, GCW or GE version, these components are connected by pipelines to a sealed refrigerant

circuit. In units of the A or ACW version, an external air-cooled condenser must be connected to the open

refrigerant circuit of the unit.

The pressure and temperatures values stated in the following paragraph are valid when the standard refri-

gerant R407C is used.

The compressor is used to compress the refrigerant and maintain the refrigerant ﬂ o w. The gaseous refrige-

rant is compressed in the compressor to approximately 20 bar (290 psi) at approximately 70°C (158°F) and

enters the condenser. The condenser gives up the heat absorbed and liqueﬁ es the refrigerant which is under

high pressure. The refrigerant temperature drops down to approximately 40°C (104°F) in the condenser.

The liquid refrigerant enters the expansion valve and is from there conducted back to the evaporator at low

pressure (about 6 bar (87 psi)) and low temperature (about 10 °C (50°F)). The heat of the air is absorbed

by the gaseous low temperature refrigerant in the evaporator at an evaporation temperature of about 10°C

(50°F).

All components of the refrigerant circuit are designed for a maximum operating pressure of 28 bar (406 psi).

Electronic expansion valve

The suction gas pressure and temperature are measured by two individual sensors. These values are used

by the controller to calculate the opening degree of the expansion valve.

Dehumidifying circuit

To achieve dehumidiﬁ cation, the electronic expansion valve is partially closed in the ﬁ rst step. The reduction

of the refrigerant mass ﬂ ow makes the evaporation temperature drop, which lets the surface temperature in

a part of the evaporator fall below the dew point of the air. This causes dehumidiﬁ cation.

For an increased dehumidiﬁ cation, the fan speed is reduced. With a constant cooling capacity, the tem-

perature of the air which ﬂ ows through the heat exchanger coil passes below the dew point. The moisture

contained in the air condenses on the heat exchanger, gathers in the condensate pan, and is carried away

by the drain.

Safety features

The cooling units have various safety devices to avoid malfunctions. In the liquid line there is a ﬁ l ter drier

to separate humidity and a sight glass to check the sufﬁ cient charge of refrigerant.

The refrigerant circuit is protected against insufﬁ cient operating pressure by a safety pressure limiter

(low-pressure (LP) switch). If the operating pressure falls below the low pressure threshold of the pressu-

re switch, a warning signal appears on the display and the unit is put out of operation. A safety pressure

cut-out (high-pressure (HP) switch) is triggered at 365 psi (25,2 bar) and switches off the compressor. A

warning signal on the display of the controller appears. A liquid receiver and a safety valve, which releases

refrigerant at 406 psi (28 bar), are ﬁ tted on A/ACW-units as further protection.

Adjustment of the pressure switches:

LP switch:

releases at: 14.5 psi (1,0 bar)

automatic reset at: 43.5 psi (3,0 bar)

HP switch:

releases at: 365 psi (25,2 bar)

manual reset possible at: 261 psi (18,0 bar)

Safety valve: 406 psi (28 bar)

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APC INROOM ACPSC3000 Operations Instructions Page 15

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