EWWQ090G ÷ EWWQ720L - R410A - Water-cooled scroll chillers
EWLQ090G ÷ EWLQ720L - R410A - Condenser less
EWHQ100G ÷ EWHQ400G - R410A - Heat pump scroll chillers
EWAQ-G 075
- R410A - Air-cooled scroll chillers
EWAQ-
- R410A - Air-cooled scroll chillers
EWYQ-
- R410A - Air-cooled scroll heat pumps
Air and Water cooled scroll chillers & heat pump
Operation
Manual
Operation Manual
56
EWWQ - EWLQ - EWHQ
EWAQ - EWYQ
Air or Water cooled scroll chiller &
heat pump
D-EOMHW00107-15EN
Superheat
The parameters mentioned below in italics can be set from the menu 4.3.1.3.
When the circuit is required to start, the EXV will go into the Pre-open with a fixed opening
Pre
Open %
for a fixed time
Pre Open Time
.
After that, the EXV can change to Start phase, in which it works always with a fixed opening
Start
%
and for a fixed time
Start Time
. The compressor will start synchronously with this transition.
Ended the Start phase the EXV switches in Pressure control to maintain the evaporating pressure
close to pressure target
Max Op Pressure
.
When the EXV works in pressure mode the transitions to Superheat mode is possible if the
following conditions are met:
SSH < SSH 1.5°C
or
Pressure control active for plus than 5 minutes
When the EXV works in Superheat mode the control maintains the superheat close to the
Cool
SSH target
or
Heat SSH target
depending on the actual operating mode.
The transition from Superheat Control to Pressure Control may happen only if the evaporating
pressure increases above the Maximum Operating Pressure (MOP) limit:
Evap Press > Max Op Press
Whenever the circuit is running, the EXV position is limited between 2% or 98% position.
Any time the circuit is in the Off or starts the shutdown procedure, the EXV shall be in the closed
position. In this case additional closing steps are commanded to guarantee a proper recovery of
the zero position.
5.8 Defrost (A/C only)
When the outside air become colder the circuit can start a defrost procedure. An algorithm is used
to determine the presence of ice on the air heat exchanger. The ice accumulation tends to degrade
the performances and for this reason a defrost may be needed to remove the ice layer.
Defrost is divided in phases. In each phase a specific status is forced to allow a proper execution
of the defrost. First of all the circuit is prepared for the 4 way valve change over to cool mode. To
do this smoothly one compressor is switched off and the exv prepared to manage the change over.
The 4 way valve is then changed to cool mode position and after a delay the other compressors
are also started. The defrost will finish when the discharge pressure reaches a pressure target that
has been determined to guarantee a complete deicing of all the coil surface.
Decreasing the Condensing Pressure limit may cause ice accumulation on the coils with
degradation of the unit performance. In case of need contact your local Daikin Service
reference.
