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7
Water to Water Heat Pump (WTW)
Sizing Expansion Vessels
Expansion vessel volume must fit the local system water
volume.
To size an expansion vessel for the heating circuit the
following formula and graph can be used. When the
necessary expansion vessel volume exceeds the volume of
an built-in expansion vessel, install an additional expansion
vessel so that the sum of the volumes of the expansion
vessels exceeds the necessary expansion vessel volume.
For installation of the heat pump unit, the installer MUST
provide and install a suitable primary-side expansion vessel
as the model DOES NOT come fitted with a primary-side
expansion vessel.
ε × G
V =
1 − P ¹ + 0.098
P ² + 0.098
Where;
V : Necessary expansion vessel volume [L]
ε : Water expansion coefficient
G : Total volume of water in the system [L]
P ¹ : Expansion vessel setting pressure [MPa]
P ² : Max. pressure during operation [MPa]
Graph to the right is for the following values
ε : at 70 °C = 0.0229
P ¹ : 0.1 MPa
P ² : 0.3 MPa
*A 30% safety margin has been added.
7.6.4 Water Circulation Pump Characteristics
1. Primary circuit
Pump speed can be selected by main remote controller setting
(see <Figure 7.6.5> ).
Adjust the pump speed setting so that the flow rate in the
primary circuit is appropriate for the Table 7.6.2. It may be
necessary to add an additional pump to the system depending
on the length and lift of the primary circuit.
<Second pump >
If a second pump is required for the installation please read the
following carefully.
If a second pump is used in the system it can be positioned in
2 ways.
The position of the pump influences which terminal of the FTC
the signal cable should be wired to. If the additional pump(s)
have current greater than 1A please use appropriate relay.
Pump signal cable can either be wired to TBO.1 1-2 or CNP1
but NOT both.
Option 1 (Space heating only)
If the second pump is being used for the heating circuit only
then the signal cable should be wired to TBO.1 terminals 3 and
4 (OUT2). In this position the pump can be run at a different
speed to the heat pump unit's in-built pump.
2. Sanitary circuit
Default setting: Speed 2
DHW circulation pump MUST be set to speed 2.
Immersion heater
When an immersion heater is fitted, do NOT energise the
heater until the DHW tank is full of water. Also do NOT energise
any immersion heater if any sterilisation chemicals remain in
the DHW tank as this will cause premature failure of the heater.
Expansion vessel sizing
25
20
15
10
5
0
0
50
100
150
System water volume [L]
<Figure 7.6.4>
Water flow rate range [L/min]
<Table 7.6.2>
* If the water flow rate is less than 7.1 L/min, the flow rate error
will be activated.
If the water flow rate exceeds 27.7 L/min, the flow speed will
be greater than 1.5 m/s, which could erode the pipes.
Water circulation pump characteristics
80
70
60
50
40
30
20
10
0
0
5
10
Flow rate [L/min]
<Figure 7.6.5>
200
250
300
350
400
7.1-27.7
Speed 1
Speed 2
Speed 3
Speed 4
Speed 5
15
20
25
30
B-229
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