Daikin EKHBHE008BA3V3 Installation Manual page 17

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 A minimum water volume is required to prevent that the water
temperature drops too much during defrost (low ambient
temperature).
If the water volume is too low, two problems can occur:
1 The water temperature drops too much during defrost and
defrost stops to protect the plate heat exchanger against
freezing.
2 The compressor does not start up after the defrost cycle
because the water temperature is too low.
In both cases the backup heater will operate instead of the
compressor to increase the water temperature.
When the water temperature is high enough, the backup heater
stops and the compressor restarts.
If the heating load is higher than the backup heater
capacity, the water temperature can not increase. In
this case refer to
temperatures" on page 22
Repeated forced defrost stops can in some cases
cause severe ice build-up on the outdoor unit. This will
lead to reduced unit performance.
The minimum required water volume in the system is 20 l.
However, to minimize emergency backup heater operation it is
highly recommended to have a water volume of 40 l.
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.
EKHBH/XE008BA
Indoor unit for air to water heat pump system
4PW56301-1A
"Re-start at low outdoor ambient
NOTE 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
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.
4 5 6
T1 T2 T3
M1 M2 M3
7 FHL1
FHL2
FHL3
8 By-pass valve (field
supply)
FHL1..3 Floor heating loop
(field supply)
T1..3 Individual room
thermostat
(optional)
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.
Installation manual
8
15