102
Aquarea air / water heat pump – design handbook 07 / 2014
Project Design
Hydraulics
Expansion vessel
With the exception of the mini Monobloc units with a heating capacity of
5, 6 and 9 kW respectively (see note), the Aquarea heat pumps have an
internal expansion vessel with a capacity of 10 litres and an initial pres-
sure of 1 bar.
This expansion vessel can be used for heating systems with an overall
quantity of water in the system of under 200 litres and a static head
of not more than 7 metres (difference between the highest point of the
system to the expansion vessel).
When the overall quantity of water is greater than 200 litres or greater
static heads are required, the pressure must be sustained by means of
an expansion vessel that is installed in the building itself. In general the
pressure limit of the pressure relief valve must be observed. This may be
derived from the technical data and is maximum 3 bar.
5.13.6 Expansion vessel
Note
Unlike the other units, the mini Monobloc units WH-MDC05F3E5,
WH-MDF06E3E5 and WH-MDF09E3E5 with a heating capacity of 5,
6 and 9 kW respectively have an expansion vessel with only 6 litres
capacity. Accordingly, these units can only be used in heating systems
with a total water volume of less than 150 litres. The other conditions
correspond to those of the other units.
The required expansion vessel is designed according to the nominal volume VN taking into account:
1. The expansion volume Ve is based on the system volume, the maxi-
mum temperature and the expansion coefficient 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
2. The volume of the water header VV can be calculated by a simplified
method:
V
V
= 0.2 × V
N
(with a nominal volume of VN < 15 litres) or
V
V
= 0.005 × V
A
(with a nominal volume of VN > 15 litres,
whereby VV ≥ 3 litres)
System volume
V
A
(Total volume of the heating system)
Maximum temperature
T
max
(Highest temperature in the system, e.g. 60 °C)
Final pressure of the pressure relief valve p
e
(Depends on the pressure relief valve, max. 2.5 bar)
Admission pressure expansion vessel
p
0
(Initial pressure 1 bar)
V
N
= (V
e
+ V
V
) p
e
+ 1
p
e
- p
0
V
e
= V
A
n
100
