Checking The Water Volume And Expansion Vessel Prepressure; Setting The Pre-Pressure Of The Expansion Vessel - Rotex RKHBH008AA Manuel D'installation

Checking the water volume and expansion vessel pre-
pressure
The unit is equipped with an expansion vessel of 10 litre which has a
default pre-pressure of 1 bar.
To assure proper operation of the unit, the pre-pressure of the
expansion vessel might need to be adjusted and the minimum and
maximum water volume must be checked.
1 Check that the total water volume in the installation, excluding
the internal water volume of the indoor unit, is 10 l minimum.
Refer to "Technical specifications" on page 29 to know the
internal water volume of the indoor unit.
In most applications this minimum water volume will have a
satisfying result.
In critical processes or in rooms with a high heat load
though, extra water volume might be required.
When circulation in each space heating loop is controlled
by remotely controlled valves, it is important that this
minimum water volume is kept even if all the valves are
closed.
Example
1 2 3 4 5
7
1 Outdoor unit
2 Indoor unit
3 Heat exchanger
4 Pump
5 Shut-off valve
6 Collector (field supply)
7 Shut-off valve
2 Using the table below, determine if the expansion vessel pre-
pressure requires adjustment.
3 Using the table and instructions below, determine if the total
water volume in the installation is below the maximum allowed
water volume.
Installation Water volume
height
≤
(a)
280 l
difference
No pre-pressure adjustment
≤7 m
required.
Actions required:
• pre-pressure must be increased,
calculate according to "Calculating
the pre-pressure of the expansion
>7 m
vessel"
• check if the water volume is lower
than maximum allowed water volume
(use graph below)
(a) Installation height difference: height difference (m) between the highest point of
the water circuit and the indoor unit. If the indoor unit is located at the highest
point of the installation, the installation height is considered 0 m.
Installation manual
10
6 8
T1 T2 T3
M1 M2 M3
FHL1
FHL2
FHL3
8 By-pass valve
(field supply)
FHL1..3 Floor heating loop
(field supply)
T1..3 Individual room
thermostat (field supply)
M1..3 Individual motorised
valve to control loop
FHL1 (field supply)
>280 l
Actions required:
• pre-pressure must be decreased,
calculate according to "Calculating
the pre-pressure of the expansion
vessel"
• check if the water volume is lower
than maximum allowed water volume
(use graph below)
Expansion vessel of the unit
too small for the installation.
Calculating the pre-pressure of the expansion vessel
The pre-pressure (Pg) to be set depends on the maximum
installation height difference (H) and is calculated as below:
Pg=(H/10+0.3) bar
Checking the maximum allowed water volume
To determine the maximum allowed water volume in the entire circuit,
proceed as follows:
1 Determine for the calculated
corresponding maximum water volume using the graph below.
2 Check that the total water volume in the entire water circuit is
lower than this value.
If this is not the case, the expansion vessel inside the indoor unit is
too small for the installation.
2.5
2
1.5
1
0.5
0.3
0 10 50 100 150 200
maximum water volume [l]
= pre-pressure
= maximum water volume
Example 1
The indoor unit is installed 5 m below the highest point in the water
circuit. The total water volume in the water circuit is 100 l.
In this example, no action or adjustment is required.
Example 2
The indoor unit is installed at the highest point in the water circuit.
The total water volume in the water circuit is 350 l.
Result:
Since 350 l is higher than 280 l, the pre-pressure must be
decreased (see table above).
The required pre-pressure is:
Pg = (H/10 + 0.3) bar = (0/10 + 0.3) bar = 0.3 bar
The corresponding maximum water volume can be read from
the graph: approximately 410 l.
Since the total water volume (350 l) is below the maximum water
volume (410 l), the expansion vessel suffices for the installation.

Setting the pre-pressure of the expansion vessel

When it is required to change the default pre-pressure of the
expansion vessel (1 bar), keep in mind the following guidelines:
Use only dry nitrogen to set the expansion vessel pre-pressure.
Inappropriate setting of the expansion vessel pre-pressure will
lead to malfunction of the system. Therefore, the pre-pressure
should only be adjusted by a licensed installer.
Indoor unit for air to water heat pump system
pre-pressure (Pg) the
250 300 350 400 450
RKHBH/X008AA
4PW50203-1A