Airedale EasiCool 6kW 64kW - Manual (Page 14)

EasiCool™EZE Precision Air Conditioning
1 Compression
2 Condensation
3 Expansion
4 Evaporation
Key:
(1) Cooling Cycle @ 22°C ambient with a conventional TEV fitted.
(2) Cooling cycle @ 22°C ambient, demonstrating a typical EEV condensing temperature taking full advantage of lower
ambient air temperatures (below 35°C).
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 significant 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 microprocessor display.
Whilst offering versatile control at the full design duty of the unit, TEVs 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 artificially 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 fitting an EEV and adjusting
the head pressure control setting an increase in the system EER (Energy Efficiency Ratio)
of up to 30% can typically be seen. The Mollier diagram shown below helps to illustrate
how this increase in efficiency is achieved.
EEV’s differ to normal thermostatic expansion valves in their ability to maintain control
of refrigerant flow and the suction superheat at reduced head pressures. The turn-down
rate of a typical EEV is superior to that of it’s 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 zero to 100%, there will not be a problem with turn
down, even down to 10% of the valves rated capacity.
Heat of Rejection
Reduction in
Compressor Input
Power
Enthalpy kJ/kg Increase in
Cooling Duty
Evaporating
Pressure
Reduced
Condensing
Pressure
Presssure
Bara
Thermostatic Expansion Valve (1)
Electronic Expansion Valve (2)
1
2
3
4
14
Introduction
EasiCool™ EZE Technical Manual 7588163 V1.1.0_02_2013