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9 Domestic Hot Water
9.1 Temperature Control
The desired hot water temperature
stored in the cylinder can be adjusted
on the BTC controller. As already
mentioned, the heat pump works most
efficiently at lower temperatures but
these temperatures are not suitable for
domestic hot water which should
always be stored at about 60ºC.
9.2 Heat Pump Cylinders
As the water temperature from the heat
pump is lower than traditional systems,
a much larger coil is required inside the
cylinder to transfer the heat efficiently.
Grant Engineering has a range of 7
stainless steel cylinders from 90 litres to
300 litres with coil areas of up to 3.5m².
Visit www.grantuk.com for more
Gr
Br
Bl
O
Off
HIg
Zone Valve
Fuse
L
N
Programmer
L
N
230V 50Hz
The DHW boost pack contains a power relay and an additional 2-pole isolator.
Figure 9-1: Connection diagram for DHW booster system
26
information. These cylinder have
been designed to match the output
from the Grant Aerona heat pumps for
maximum efficiency and faster re-heat
times when compared to standard type
indirect cylinders.
9.3 Temperature Boost
It is possible to use the heat pump to
raise the DHW temperature to 60ºC.
During the summer, this may be
preferable, when the external ambient
air temperature is high. However, during
the winter, it would not be economical
for any heat pump to try to raise the
water temperature to this level.
230V/24 Vac
Transformer
L N
E
4 5
6 7 8 9 10
2
HW
CH
1
3
Room
Thermostat
Compressor
Return
sensor
Supply sensor
Outdoor
sensor
Gr
Br
Bl
O
Off
DHW
Zone Valve
Limit
Control
1
2
1
2
c
c
Cylinder Thermostat
Heat Pump
PCH
Controller
As a result, Grant has developed a
control system that will take the
temperature of the existing cylinder
from 45°C to 60°C, after the cylinder
thermostat has switched off the hot
water operation of the heat pump.
This system uses both the existing
cylinder immersion element and cylinder
thermostat, but operated via an 'add-
on' relay and override switch enclosed
in a separate unit to be mounted next
to the cylinder. This system is fully
automatic but can be overridden by the
user if required, i.e. the user can switch
on the immersion element using the
override switch to manually boost the
hot water cylinder temperature.
12
11
10
9
8
BTC
7
6
5
4
3
2
1
Heat pump
3 2 1
S-Plan controls
HW CH C
connections
To domestic hot water booster
relay coil (see Figure 9-2)
Relay 2 in heat
pump control
panel
24
23
22
21
20
19
18
17
16
15
14
13
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