803 B – 04/11 D – pag. 4/24
Servo Controlled modulating liquid level regulators
PFS are equipped with a modulating servo-controlled main expansion valve type controlled by a pilot float valve
type to perfectly modulate refrigerant flow to the evaporator, proportionally to the required capacity. This ensures a
stable regulation and economic operation, because pressure and temperature variations are strongly reduced.
Electrical panel
Power and control are located into two sections of the main panel that is manufactured to insure protection for all
weather conditions.
The power panel is fitted with a interlocked door main isolator to prevent access while power supply is on.
Electrical panel is IP43.
Power section includes -
The power section includes contactors, all compressors fuses, and control circuit
transformer. Additional space is provided for an easy installation of the various optional accessories provided to
enhance the PFS units capabilities.
Certifications
All the PFS units are CE marked (89/392). McQuay Italia obtained ISO 9001:2000.
Water content in cooling circuits
The cooled water distribution circuits should have a minimum water content to avoid excessive compressors start
and stop.
In fact, each time the compressor starts up, an excessive quantity of oil goes from the compressor sump and
simultaneously there is a rise in the temperature of the compressor motor’s stator due to the inrush current during
the start-up. To prevent damage to the compressors, McQuay has envisaged the application of a device to limit
frequent stops and restarts.
During the span of one hour there will be no more than 6 starts of the compressor. The plant side should therefore
ensure that the overall water content allows a more constant functioning of the unit and consequently greater
environmental comfort. The minimum installation water content envisaged should be calculated with a certain
approximation using this simplified formula:
(1)
Q = 35,83 X
)
C
(
T
(kW)
P
°
∆
X
N
1
where:
Q = Minimum content of the plant expressed in litres
P = Cooling capacity of the plant expressed in kW
∆
T = Entering/leaving water temperature difference of the evaporator expressed in °C
N = Number of compressors.
For a more accurate determination of the quantity of water, it is advisable to contact the designer of the plant.
