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8.8 Bivalent Systems
For the connection of a boiler for a
bivalent system it is necessary to
disconnect the immersion element from
the relay in the heat pump.
Take the live for the boiler from this
relay. The neutral for the boiler must be
taken from the heating controls wiring
centre. Refer to Figure 8-13.
Isolate this supply via a fused double
pole isolator switch and mark on the
switch that the supply comes from the
heat pump.
Follow the wiring diagram as shown in
Figure 8-13 for a bivalent system.
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.
Gr
Br
Bl
O
Heating
G/Y
Zone Valve
Fused Isolator
L N
L
N
CH HW
Programmer
230V
50Hz
Figure 8-14: Connection diagram for Grant solar thermal system
8.9 Solar Thermal
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 8-14 below will give
the solar thermal system a priority over
the heat pump when there is a demand
for HW only.
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.
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
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.
8.10 Buffer Tanks
When using a buffer tank with the heat
pump, the weather compensation
function of the built-in BTC controller is
NOT used.
A cylinder thermostat (with immersion
probe) should be fitted to the buffer
tank. This must be wired to switch
between terminals 1 & 3 (the Common
and HW terminals) on the S-Plan
controls terminal block in the heat
pump control panel. Refer to Figure
8.15 in Section 8 for wiring diagram.
The BTC setting for 'HW BOIL
TARGET' should be set to 48˚C.
Refer to Fig 8-15 for connection details.
Solar controller
L
N
In
E
E
Relay 3
N
Out
L
Gr
Br
Earth connections have
Bl
been excluded for clarity.
O
Ensure all earth
HW
G/Y
connections are made
Zone Valve
prior to energising.
C
1
1
Figure 8-15: Buffer tank thermostat
Panel
sensor
Cylinder
sensor
Solar
pump
CH
HW
Heat pump
S-Plan controls
connections
2
3
2
Cylinder
Thermostat
c
25
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