Checking The Water Volume And Expansion Vessel Pre-Pressure - Rotex RKHBH008BB3V3 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 "12. Technical specifications" on page 49 to know the
internal water volume of the indoor unit.
INFORMATION
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.
NOTICE
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
1 Outdoor unit
2 Indoor unit
3 Heat exchanger
4 Backup heater
5 Pump
6 Shut-off valve
7 Collector (field supply)
8 By-pass valve (field supply)
FHL1...3 Floor heating loop
T1...3 Individual room thermostat (optional)
M1...3 Individual motorised valve to control the floor
heating loop (field supply)
2 Using the table below, determine if the expansion vessel pre-
pressure requires adjustment.
RKHBH/X008BB
Indoor unit for air to water heat pump system
4PW62574-1 – 10.2010
5 6 7
T1 T2 T3
M1 M2 M3
6
FHL1
FHL2
FHL3
3 Using the table and instructions below, determine if the total
water volume in the installation is below the maximum allowed
water volume.
Installation
height
(a)
difference
No pre-pressure adjustment
≤
7 m
required.
Actions required:
• pre-pressure must be
increased, calculate
according to "Calculating the
pre-pressure of the
>7 m
expansion 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.
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
8
To determine the maximum allowed water volume in the entire circuit,
proceed as follows:
1 Determine for
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 50 100
1 0
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.
Water volume
≤
280 l >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.
the calculated pre-pressure
150 200 250 300 350
maximum water volume [l]
= pre-pressure
= maximum water volume
Installation manual
(Pg) the
400 450
16