Electronic Expansion Valves (EEV)
Electronic expansion valves differ to the normal thermostatic expansion valves in their ability to
maintain control of the suction superheat at reduced head pressures. This can lead to signicant
energy savings particularly at reduced loading and low ambient temperatures.
EEV step position, superheat setpoint, head pressure set point and other features can be viewed
and adjusted via the microcontroller display.
Whilst offering versatile control at the full design duty of the unit, Thermostatic Expansion
Valve’s (TEV) do not automatically optimise themselves to all operating conditions. Therefore,
if the refrigeration system is operating at 40% or 50% of full load, especially at a lower ambient
temperature than that for which the valve was sized, the conventional TEV must have the
design head pressure available to ensure good refrigerant control. Maintaining an articially high
condensing pressure is normal in conventional systems.
Using an EEV allows for good refrigeration control whilst operating at part load and lower ambient
conditions with a reduced condensing pressure. By tting an EEV and adjusting the head pressure
control setting an increase in the system EER (Energy Efciency Ratio) of up to 30% can typically
Heat of Rejection
Reduction in
Compressor Input
Power
Enthalpy kJ/kgIncrease in
Cooling Duty
Evaporating
Pressure
Reduced
Condensing
Pressure
Presssure
Bara
Thermostatic Expansion Valve (1)
Electronic Expansion Valve (2)
1
2
3
4
be seen. The Mollier diagram shown below helps to illustrate how this increase in efciency is achieved.
EEVs differ to normal thermostatic expansion valves in their ability to maintain control of refrigerant ow and the
suction superheat at reduced head pressures. The turn-down rate of a typical EEV is superior to that of its thermostatic
equivalent, such that a reduced optimum condensing pressure can be maintained at low compressor load. However low
the load is on the compressor, from 10 to 100%, there will not be a problem with turn down, even down to 10% of the
valve’s rated capacity.
Key:
(1) Cooling Cycle @ 22°C ambient with a conventional TEV tted.
(2) Cooling cycle @ 22°C ambient, demonstrating a typical EEV condensing temperature taking full advantage of lower
ambient air temperatures (below 35°C).
Refrigerant Leak Detection
If the leak detector reaches the alarm set point, a leak alarm will be set and a message displayed (if display is tted). By
default after detecting a leak, the unit will give an alarm and will disable the mechanical cooling. Freecooling will then be
enabled if available.
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