Daikin EWAT016CZN-A1, Installation, Maintenance And Operation Manual

Page: 15 / 30

EWYT~CZ / EWAT~CZ DEIMHP0140521_00EN
15
4.12. Operating stability and minimum water content in
the system
For the correct functioning of the machines it is important to guarantee
a minimum water content inside the system, avoiding an excessive
number of compressor startups and stops. In fact, every time the
compressor starts working, an excessive amount of oil from the
compressor enters the circulation in the refrigerant circuit and at the
same time there is an increase in the temperature of the compressor
stator, generated by the inrush current of the starting. In order to
prevent damage to the compressor, the control system will therefore
permit no more than 10 startups per hour. The plant where the unit is
installed must therefore ensure that the overall water content allows
constant operation of the unit and consequently also greater
environmental comfort.
As a general indication the water content should not be less than the
values in the following table:
HeatPump
Suggested
L/kW
Min water
content [L]
EWYT016CZ(N/P/H)-A1 5.7 90
EWYT021CZ(N/P/H)-A1 5.0 100
EWYT025CZ(N/P/H)-A1 4.4 110
EWYT032CZ(N/P/H)-A1 4.9 160
EWYT040CZ(N/P/H)-A1 4.6 180
EWYT040CZ(N/P/H)-A2 3.0 120
EWYT050CZ(N/P/H)-A2 2.6 130
EWYT064CZ(N/P/H)-A2 2.7 170
EWYT090CZ(N/P/H)-A2 2.7 230
CoolingOnly
Suggested
L/kW
Min water
content [L]
EWAT016CZ(N/P/H)-A1 3.7 58
EWAT021CZ(N/P/H)-A1 2.8 58
EWAT025CZ(N/P/H)-A1 2.3 58
EWAT032CZ(N/P/H)-A1 2.8 90
EWAT040CZ(N/P/H)-A1 2.3 90
EWAT040CZ(N/P/H)-A2 1.5 60
EWAT050CZ(N/P/H)-A2 1.2 60
EWAT064CZ(N/P/H)-A2 1.1 73
EWAT090CZ(N/P/H)-A2 1.0 90
Table 7 – Minimum water content in the system
NOTE Extra water may be required in critical processes or in
spaces with a high thermal load.
The difference in startup temperature may vary from 1 to 5 K. This has
an impact on the minimum water volume required when the unit is
functioning in cooling mode. The unit is preset for a startup
temperature difference of 2.5 K.
The Thermo ON condition is shown below:
EWT > Se startup ∆T
Default Max Min
startup ∆T (K) 2.5 5 1
By default, the unit is set to have a water temperature difference of 2.5
K which allows it to operate with the minimum volume mentioned in
the previous table. However, if a smaller temperature differential is
set, as in the case of process cooling applications where temperature
fluctuations must be avoided, a larger minimum water volume will be
required.
To ensure proper operation of the unit when changing the value of
setting, the minimum water volume has to be corrected. If this volume
exceeds the range allowed in the unit, an additional expansion vessel
or a buffer tank must be installed in the field piping.
Minimum water volume correction factor
A water volume correction factor “a” is introduced on the basis of the
difference in startup temperature “b”, the function of which is:
a · d = 2,5
0
0,5
1
1,5
2
2,5
3
0 1 2 3 4 5 6
a Min volume correction factor
b Delta T Startup (K)
Minimum water volume correction factor
Figure 15 – Minimum water volume correction factor
Example:
To illustrate the impact on the system when modifying the setting, we
will consider a unit with a minimum allowable water volume of 58 L.
Assuming that the setting is changed from Delta T 2.5K (default) to
1.5K. The correction factor to be applied is
a =
2,5
1,5
= 1,67 , and so to
calculate the minimum water content in the system for a 25 kW unit, in
cooling mode, all we need to do is multiple the default minimum
volume by this correction factor to obtain the new minimum
volume, 97l.
4.13. Calibrating the expansion vessel
The expansion vessel’s starting pressure depends on the difference
between the level at which the unit is installed and the highest point in
the water circuit, and is calculated as follows:
P
i
=0.3+(H/10) (bar)
• P
i
Initial pressure
• H Difference between the level at which the unit is installed
and the highest point in the circuit
A unit with an onboard pump has a 12 liters expansion vessel with an
initial pressure of 1 bar.
Maximum water volume
Refer to the graph below to determine the maximum water volume in
order to calibrate the expansion vessel:
0
0
0,5
1
1,5
2
2,5
3
50 33 100 150 200 250 300 350 400 450 500 550 600
a
b
A
F
E
D
B
C
Figure 16 – Initial expansion vessel pressure on the basis of
maximum water volume
a
Initial pressure of the expansion vessel [bar]