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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:
Example:
To illustrate the impact on the system when modifying the setting, we will consider a unit with a minimum allowable water
volume of 100l. Assuming that the setting is changed from Delta T 2.5 K (default) to 1.5 K. The correction factor to be
2,5
applied is �� =
= 1,67, and so to calculate the minimum water content in the system for a 21 kW unit all we need to do
1,5
is multiple the default minimum volume by this correction factor to obtain the new minimum volume, 167l.
4.15. Water flow limits
To ensure correct operation of the unit, the value of the water flow in the evaporator must be within the declared range for
that unit. A water flow lower than the minimum value shown in the following table could cause problems with freezing,
fouling and poor control. A water flow rate higher than the maximum value shown in Table 13 will result in an unacceptable
load loss and excessive erosion of the pipes, with vibrations that can cause breakage.
4.16. 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:
•
Pi 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 litres expansion vessel with an initial pressure of 1 bar.
�� ∙ �� = 2.5
Figure 19 – Minimum water volume correction factor
Unit flow limits
MODEL
Min flow [l/s]
EWYT021CZI-A1
EWYT032CZI-A1
EWYT040CZI-A1
EWYT064CZI-A2
Table 13 – Operating limits
P
=0.3+(H/10) (bar)
i
Max flow [l/s]
0.84
1.90
1.01
2.66
1.01
2.66
1.41
5.50
D-EIMHP01505-22_00EN 27/59
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