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8.8 Bivalent Systems
For bivalent systems, it is necessary to
disconnect the internal immersion
element from the relay inside the heat
pump control panel. Taking the live and
neutral outputs from this relay extend
this wire to the boiler. Isolate this cable
through a fused double pole spur
switch and mark on the switch that the
supply comes from the heat pump.
IMPORTANT
Do not take the Neutral from the heat pump to feed the boiler circuit. This will create
an imbalance at the MCB and cause nuisance tripping. Always take the neutral
supply from the existing S-Plan wiring centre.
Follow the wiring diagram as shown in
Figure 8-11 for a bivalent system.
Gr
Br
Bl
O
Off
Heating
zone
valve
Fuse
L N
L
N
CH HW
Programmer
230V
50Hz
Figure 8-14: Connection diagram for Grant solar thermal system
8.9 Extending the Electrics
It may be part of the system design to
incorporate Solar Thermal into the
design.
This is easily done with the use of an
additional two-pole relay. Following the
diagram in Figure 8-13 below will give
the solar thermal system a priority over
the heat pump when there is a demand
for DHW only.
E 4 5 6 7 8 9 10
Limit
Control
1
2
1
2
c
c
2
1
3
Cylinder Thermostat
Room
Thermostat
Heat pump
1 2 3
S-Plan controls
C CH HW
connections
This can, of course be added to both
monovalent and bivalent systems. It is
much easier to carry out all these types
of systems based on S-plan type
controls only.
Y and W type plans can be used, but
the need for additional relays is not
practical. It is much easier to convert Y
and W type plans to S types from the
start.
L
N
E
E
Relay 3
N
L
Gr
Br
Bl
O
Off
DHW
Zone Valve
Solar controller
In
Out
Solar
pump
Panel
sensor
Cylinder
sensor
25
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