Daikin EWAQ016CAW - Formula to Calculate the Expansion Vessel Pre-Pressure; To Check the Water Volume and Expansion Vessel Pre-Pressure

4 Preparation
Installation and operation manual
7
EWAQ016~064CAW + EWYQ016~064CAW
Packaged air-cooled water chiller
4P489435-1B – 2017.10
Capacity class Water piping diameter
040~064 2"
NOTICE
It is strongly recommended to install an additional filter on
the water circuit. Especially to remove metallic particles
from the field water piping, it is advised to use a magnetic
or cyclone filter which can remove small particles. Small
particles can damage the unit and will not be removed by
the standard filter of the unit.
▪ Water pressure. Take care that the components installed in the
field piping can withstand the water pressure (maximum 3 bar +
static pressure of the pump).
4.2.2 Formula to calculate the expansion vessel
pre-pressure
The pre-pressure (Pg) of the vessel depends on the installation
height difference (H):
Pg=0.3+(H/10) (bar)
4.2.3 To check the water volume and expansion
vessel pre-pressure
The unit has an expansion vessel of 12 litre with a default pre-
pressure of 1bar.
See the installer and user reference guide for more information.
To make sure that the unit operates properly:
▪ You must check the minimum and maximum water volume.
▪ You might need to adjust the pre-pressure of the expansion
vessel.
Minimum water volume
Cooling only model Minimum total water volume (l)
016~032 33
040~064 66
Heat pump model Minimum total water volume (l)
016~025 76
032 110
040+050 152
064 220
INFORMATION
In critical processes, or in rooms with a high heat load,
extra water might be required.
INFORMATION
The temperature step difference can be modified using
settings [A‑02] and [F‑00]. This has an impact on the
minimum water volume required when the unit operates in
cooling.
By default, the unit is set to have a water temperature
difference of 3.5 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
values of setting [F‑00] (for cooling mode), 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.
Example:
To illustrate the impact on the system when modifying the setting
[F‑00], we will consider a unit with a minimum allowable water
volume of 66l. The unit is installed 5 m below the highest point in
the water circuit and is charged with 30% of ethylene glycol.
Assuming that the setting [F‑00] is changed from 5°C (default value)
to 0°C. From the below table we see that 5°C corresponds to a
temperature differential of 3.5K and 0°C to 1K, which is actually the
lowest value we can set.
[F‑00] value (°C) Temperature differential (K)
0 1
1 1.5
2 2
3 2.5
4 3
5 3.5
6 4
7 4.5
8 5
9 5.5
10 6
11 6.5
12 7
13 7.5
14 8
15 8.5
The water volume correction factor according to the curve shown in
the below graph is 3.5; this means that the minimum volume will be
3.5 times larger.
Correction factor curve for minimum water volume
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5
9
a
b
a Water volume correction factor
b Temperature differential (K)
When multiplying 64 l by the correction factor, we get 224l, which
will be the minimum water volume allowed in the installation if a
temperature differential of 1K is used.
Now it is very important to check that for the height difference of the
system, the volume in the system is less than the maximum allowed
value at that pre-pressure (Pg). If we take a look at the ethylene
glycol concentration curve of 30%, for 1 bar of pre-pressure the
maximum volume allowed is 240l.
The total volume in the system will definitely be larger after adding
the internal volume of the unit. In this case, some pre-pressure can
be applied or an additional expansion vessel or buffer tank must be
installed in the field piping.
Maximum water volume
Use the following graph to determine the maximum water volume for
the calculated pre-pressure.