Daikin GYEQ20AN Service Manual page 102

Control Overview
The basic cooling control function keeps the compressor intake pressure (low pressure side) at
a constant level by controlling the compressor capacity. It controls the compressor capacity
through controlling the engine speed and switching the number of compressors operating.
If the low-side pressure cannot be controlled solely through controlling the compressor,
however, additional control is performed to keep the low-side pressure constant.
Fig. 3.2/ Basic cooling control: Flow chart
Table 3.1/ Engine speed range (cooling) (min
Full range
2 compressors
2 compressors
1 compressor
(compressor 2)
1 compressor
(compressor 1)
∗ 1. For GYEQ30AN, variable capacity SV = ON
91
Basic cooling control
Normal control
<Compressor control>
Low-side pressure constant control
Engine speed
&
Yes
Evaporation energy secured
<Waste heat recovery capacity control>
EV5 (Sub evaporation outlet SH control)
EV5 (Upper limit control)*
EV5=Lower limit opening degree
&
Yes
Outdoor units
∗1
∗1
<Avoid low-side pressure
No decline during transition>
High/low-side pressure
bypasses (EV3) Open
No
*EV5 (Upper limit control)
023270-00E01
-1
)
Model
Maximum revolution
Minimum revolution
Maximum revolution
Minimum revolution
Maximum revolution
Minimum revolution
Maximum revolution
Minimum revolution
Maximum revolution
Minimum revolution
SiAUY361411EA
(Cooling) "Avoid Low-Side
Pressure Drop during
Transition" control function
When the low-side pressure
significantly drops for such a reason
as many indoor units stop operating
almost simultaneously, this function is
activated to prevent the low-side
pressure from rapidly dropping by
opening the high/low pressure bypass
(EV3).
(Cooling) "Waste Heat Recovery
Capacity" control function
When the low-side pressure on the
compressor intake side is lower than
the target low-side pressure, this
function is activated to adjust the low-
side pressure to the normal low-side
pressure target level and retain it at
that level by utilizing the engine
cooling water heat via the waste heat
recovery device to heat the intake
side refrigerant gas (partially liquefied
refrigerant). This control function is
triggered when the engine speed is at
the lowest level and yet the low-side
pressure is lower than the target low-
side pressure. The function controls
the superheating degree of EV4 at
the waste heat recovery device outlet
and restricts its opening degree upper
limit so that the appropriate amount of
refrigerant passes through the waste
heat recovery device, thereby
optimizing the recovered heat quantity.
GYEQ20AN GYEQ30AN
2200
650
2100
700
-
-
2000
700
2200
650
Control and Functionality
2300
650
2300
725
-
-
2300
650
2300
650