Airedale Ultima Compact FreeCool 30kW - 450kW - Manual (Page 9)

Chillers ULTIMA COMPACT
Chillers
9
Technical Manual : Part No 6259543 TM E_1.3.0 04/2013
Design Features & Information
ELECTRONIC EXPANSION VALVES
Thermostatic Expansion
Valves Whilst offering versatile control at the full design duty of the chiller, standard TEVs do not
automatically optimise themselves to all operating conditions. Therefore, if the chiller 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.
Electronic Expansion
Valves Using an EEV allows for good refrigeration control with the chiller operating at part load
and lower ambient conditions with a reduced condensing pressure. By fitting an EEV and
adjusting the head pressure control setting, reduction in energy running values of up
to 27% can be achieved. 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 below 30% rated capacity.
Pr
ess
u
re
(B
a
ra)
Enthalpy
(kJ/kg)
Reduced
Condensing
Pressure
Evaporating
Pressure
Bubble Dew
Reduction in
Compressor
Input Power Increase in
Cooling Duty
Ex
p
a
n
s
io
n
Heat of Rejection
Cooling
Key
Cooling Cycle @ 22°C ambient with a conventional TEV fitted.
Cooling cycle @ 22°C ambient, demonstrating a typical EEV
condensing temperature taking full advantage of lower ambient air
temperatures (below 30°C).