23
CONNECTIONS
Hydraulic connections
To design properly the hydraulic system respect the local safety
regulations in force.
It is always necessary to guarantee an appropriate water flow
through the plate heat exchangers of the unit even if on both
the hydraulic circuits (source side and plant side) is installed, as
standard, a flow switch that stops the unit if the water flow rate
is too low.
To adjust the water flow rate through the heat exchangers modify
the speed of the pump by means of the 3 speed selector. For a
more accurate adjustment it is reccomended the installation of a
valve on the outlet of each circuit.
It is also reccomended to install a filter on the inlet of each circuit
in order to avoid the entrance of foreign substances.
The hydraulic circuit on the plant side is equipped with safety
valve and expansion vessel. To mantain the circuit under
pressure a self-filling group, that automatically fills the circuit,
can be installed.
If the hydraulic circuit on the source side is used as a closed
circuit it is necessary to install an expansion vessel and an
adequate safety valve (maximum setting 3 bar).
Suggestions for the hydraulic plant realization
Prepare the pipes with the minimum possible number of bends
in order to minimize pressure losses, and suitably support them
to prevent excessive stresses at the connections of the unit.
Install shut-off valves near the components that need
maintenance, to allow their replacement without having to drain
the system.
Provide manual or automatic valves in the highest part of the
circuit to vent the air.
Make sure there are no leaks before insulating the pipes and
filling the system.
In order to avoid condensate generation insulate all the pipes on
the source side (and also on the plant side for reversible heat
pumps) using steam barrier type material.
Brine solutions
When the unit is used as a brine-water heat pump, the source
side hydraulic circuit must be filled with a brine solution able
to guarantee a freezing temperature lower than the minimum
expected operating temperature. In order to guarantee the unit
to work inside the whole operating range declared, a freezing
temperature not higher than -15°C is required.
The brine solution must be mixed before filling the circuit.
All the components used on the source side hydraulic circuit
must be suitable to work with the brine solution adopted.
Galvanized steel pipes are not to be used.
Expansion vessels setting
All the units are equipped with expansion vessels on the plant
side.
The precharge pressure of the expansion vessel must be
adequate to the total volume of the hydraulic circuit at which the
unit is connected.
The factory setting (p
VE-std
= 0,5 bar g) is the minimum value
necessary to avoid the presence of zones with a negative
relative pressure inside the hydraulic circuit and the risk of pump
cavitation, supposing that no parts of the plant are placed at a
higher level than the one at which the unit is installed. In that
case the precharge pressure must be increased proportionally
to the elevation of the highest part of the plant according to the
following relation :
p
VE
= p
VE-std
+ H
max
/ 9,81
p
VE
: expansion vessel precharge pressure [bar g]
H
max
elevation of the highest part of the plant referred to
the unit installation level [m]
The maximum value of the precharge pressure is equal to the
safety valve pressure set.
Increasing the precharge pressure, the maximum plant volume
supported by the expansion vessel of the unit is reduced :
V
I
= V
VE
· C
e
· [ 1 - ( 1 + p
VE
) / ( 1 + p
VS
) ]
V
I
: plant volume supported by the expansion vessel [l]
V
VE
: expansion vessel volume [l]
C
e
: expansion coefficient
p
VS
: safety valve pressure set [bar g]
If the real plant volume is higher than such calculated volume,
it is necessary to install an additional expansion vessel of
appropriate volume.
Once the hydraulic circuit has been filled, the pressure at the
expansion vessel must be slightly higher than the precharge
pressure.
If parts of the plant are placed at a lower level than the one
at which the unit is installed, verify that the components can
withstand the maximum pressure that can be present.
Acqua
Ethylene glycol
(percentage by volume)
Propylene glycol
(percentage by volume)
10%
20%
30%
40%
10%
20%
30%
40%
Freezing temperature [°C]
0
-3,8
-8,9
-15,7
-24,9
-3,4
-7,4
-13,1
-21,5
C
e
Plant side (T
min
= 5°C , T
max
= 60°C)
58,63
47,80
45,24
42,82
40,61
45,47
39,96
35,82
32,88
Source side (T
min
= 5°C , T
max
= 45°C)
101,46
73,28
68,84
64,77
61,08
69,42
60,41
53,91
49,03
Source side (T
min
= -10°C , T
max
= 45°C)
-
-
-
51,85
48,57
-
-
42,67
38,50
