Panasonic Aquarea WH-UX12HE5 - Page 114

114 Aquarea air-to-water heat pumps - Planning and installation manual - 02/2022
Planning
5
Model-specic limit values for the integrated expansion vessel
WH-MDC05J3E5
WH-MDC07J3E5
WH-MDC09J3E5
All other models
Expansion vessel volume l 6 10
Initial pressure bar 1 1
Total water quantity in the heating system (max.) l 150 200
Static height m 7 7
Pressure stage safety valve (max.) bar 3 3
In case the total quantity of water is greater than 150 or 200 litres, or greater static heights are
required, it is necessary to maintain the pressure by means of an expansion vessel to be installed
on site. Generally, pay attention to the pressure stage of the safety valve. This is given in the
technical data and is maximum 3 bar.
The following criteria must be taken into consideration when designing the necessary expansion
vessel nominal volume V
N
.
Nominal volume V
N
(nominal volume of the expansion vessel)
Expansion volume V
e
(expansion volume of the expansion vessel)
System volume V
A
(total volume of the heating system)
Water reserve V
V
(volume of the water reserve)
Maximum temperature T
max
(highest temperature in the system e.g. 60 °C)
Final pressure of the safety valve p
e
(depends on the safety valve, max. 2.5 bar)
Initial pressure of expansion vessel p
0
(initial pressure 1 bar)
V
N
= (V
e
+ V
V
)
p
e
+ 1
p
e
– p
0
1. The expansion volume V
e
is obtained from the system volume, and the maximum
temperature is obtained from the coe󰀩cient of expansion of water according to the
following table:
T
max
(°C) 40 50 60 70 80 90 100
n (%) 0.93 1.29 1.71 2.22 2.81 3.47 4.21
Percentage expansion of water:
V
e
= V
A
n
100
2. The volume of the water reserve V
V
can be calculated in a simplied manner as
follows:
V
V
= 0.2 × V
N
(for a nominal volume V
N
< 15 litres) or
V
V
= 0.005 × V
A
(for a nominal volume V
N
> 15 litres, where V
V
≥ 3 litres)
3. The nal pressure of the safety valve p
e
is obtained from the response pressure of the
safety valve minus a tolerance of 0.5 bar:
p
e
= Safety valve response pressure – 0.5 bar
4. Select the initial pressure p
0
such that it corresponds to the static height of the heating
system plus a supplement factor of max. 0.5 bar. 10 metres static height corresponds
to 1 bar. Adjust the initial pressure of the Aquarea expansion vessel, if necessary.