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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 from a traditional
system using a boiler, a much larger
coil is required inside the cylinder to
transfer the heat efficiently.
Grant has a range of seven single coil
(from 120 to 400 litres) and five twin coil
(from 170 to 400 litres) unvented
stainless steel heat pump cylinders
These cylinder have been specifically
designed to match the output from the
Grant Aerona heat pumps. These are
fitted with larger coils (up to 4m² area)
for maximum efficiency and faster
re-heat times when compared to
standard type indirect cylinders.
Gr
Br
Bl
O
Heating
Off
Zone Valve
Fuse Isolator
L
L
N
CH HW
Programmer
L
N
230V 50Hz
The HW boost pack contains a power relay and an additional 2-pole isolator.
Figure 9-1: Connection diagram for HW booster system
26
Visit www.grantuk.com for more
information.
In order to ensure that a minimum of at
least 5K temperature difference is
maintained between cylinder flow and
return, the correct Grant single coil
cylinder must be selected to match the
heat pump output, as in the following
table:
Heat
Pump
Model
HPAW65
HPAW85
HPAW110 11.0
HPAW130 13.0
HPAW155 15.5
Failure to use the correct cylinder can
result in a reduced heat transfer in the
cylinder and a lower temperature
differential, causing the high pressure
cut-out to operate and the heat pump
to shut down.
230V/24 Vac
Transformer
N 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
PCH
Compressor
Controller
Output
Grant Single
(kW) Coil HP Cylinder
Size (litres)
Min.
Max.
6.5
125
250
8.5
200
300
250
300
300
400
300
400
Return
sensor
Supply sensor
Outdoor
sensor
Gr
Br
Heat pump
Bl
3 2
1
S-Plan controls
HW CH C
connections
O
HW
Off
Zone Valve
To domestic hot water
boost kit relay coil
(see Figure 9-2)
Relay 2 in heat
pump control
panel
Earth connections
have been excluded
for clarity. Ensure all
earth connections
are made prior to
energising.
For twin coil installations, where the
heat pump is used in conjunction with
solar thermal, the same minimum and
maximum surface area requirement
applies to the upper coil of the cylinder.
Thus, the correct Grant HP twin coil
cylinder should be used, as follows.
Heat
Output
Pump
(kW) Coil HP Cylinder
Model
Min.
HPAW65
6.5
170
HPAW85
8.5
200
HPAW110 11.0
250
HPAW130 13.0
300
HPAW155 15.5
300
9.3 Temperature Boost
It is possible to use the heat pump to
raise the HW cylinder to 60°C. During
the summer, when the external ambient
air temperature is high, this may be
preferable. However, during the winter it
would not be economical for any heat
pump to try and raise the water
temperature in the cylinder to
this level. As the heat pump
12
23
works more efficiently when
11
24
heating water to a lower
10
22
temperature Grant has
9
21
BTC
developed a control system
8
20
7
19
that will automatically take the
6
18
temperature of the water in
5
17
the cylinder from around 45 -
4
16
50°C up to 60°C, after the
3
15
2
14
cylinder thermostat has
1
13
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 a
relay and 'by-pass' 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 'by-pass'
switch, to manually boost the
hot water cylinder temperature
– irrespective of the
programmer or cylinder
thermostat setting or whether
the heat pump is operating.
NB. Setting this 'by-pass'
switch to OFF does NOT stop
Grant Twin
Size (litres)
Max.
250
300
300
400
400
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