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UNIQ HEAT BATTERIES REFERENCE MANUAL_V2.3
Where
V
E
= Total volume of the expansion vessel, [L]
V
HB
= Water content of the heat battery circuit used for DHW heating - From technical data tables, [L]
E
C
= Hot water expansion factor for standard heat batteries, E
C
= 0.03
P
1
= Absolute initial expansion vessel charge pressure,
[bar]
P
2
= Maximum absolute working pressure of the heat battery water circuit, [bar]
P
I
= Initial expansion vessel charge pressure = CW mains pressure, [bar]
P
F
= Maximum working pressure of heat battery water circuits = 10.0, [bar]
4.4.
Hot water secondary circulation and trace heating
Secondary circulation or trace heating should be provided when the length of hot water pipe work and its water content
becomes such that it would take an unreasonable length of time for hot water to reach the terminal fitting.
The Government guidance recommends that when opening a tap, or other outlet, the water should reach 50
o
C within 30
seconds.
The normal method for sizing the
secondary circulation pipework is to
calculate the heat loss from all the
‘flow’ and ‘return’ pipe circuits in the
system. From this data, the flow rate
required in each section to replace
the heat loss in that section.
The Institute of Plumbing (IOP) guide
states that as a ‘
rule of thumb’
, the
return pipe size for the secondary
circulation can be taken as two sizes
below the flow pipe as first estimate
for sizing the secondary return
system.
The schematic diagram of secondary
hot water circulation arrangement
with Sunamp UniQ range of hot water batteries is shown in figure 4.2.
Notes:
a)
All components in the secondary circulation loop (e.g. pump, expansion vessel, non-return valve) should have
WRAS approval.
b)
With PCM58 heat batteries, the hot water temperature in the secondary hot water circulation loop will be
between 50 and 55
o
C.
4.5.
Hard water areas
In hard water areas where mains water hardness can exceed 150 ppm Total Hardness, you must install a scale reducing
device in the cold water supply to the heat batteries to reduce the rate of accumulation of limescale. The limescale can
be controlled using one of the following devices:
a)
Chemical limescale inhibitors
b)
Polyphosphate dosing
c)
Electrolytic scale reducers
d)
Water softeners
Mains cold
water supply
3
2
Figure 4.2
1
Potable water expansion vessel
2
Thermostatic blending valve
3
Building hot water supply
4
Building cold water supply
5
Check valve
6
Secondary circulation pump
4
1
Heat battery
5
6
