13
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Special requirements for R32 units
Installer and user reference guide
48
BS4~12A14AJV1B
VRV 5 branch selector unit
4P695527-1 – 2022.02
An extraction fan must be connected to the BS unit, see
88].
In order to size the fan, calculate the required pressure capacity. The total pressure
drop in the evacuation channel consists of multiple parts: the pressure drop
generated by the BS unit and the pressure drop generated by the components of
the ductwork.
Select an airflow rate for the evacuation that meets the legal requirements. This
means that the airflow rate is above the legally required minimum, and generates
sufficient pressure difference inside the BS unit when compared with the pressure
of the surroundings. The minimum required airflow rate (AFR
OUT
) is 18.8 m³/h, and
the pressure drop generated by the BS unit should lead to a pressure inside the BS
unit (P
internal
) that is more than 20 Pa below the pressure of the surroundings.
a
P
internal
AFR
OUT
a
BS unit
AFR
OUT
Airflow
P
internal
Internal pressure
It is advised to take a safety margin on these minimum values when designing the
evacuation channel in order to account for tolerances on parts, dirt and dust
building up in the evacuation channel over time, etc.
Note:
The internal pressure of the BS unit should not be more than 350 Pa below
the pressure of the surroundings.
Write down the pressure drop generated by all the components in the evacuation
channel for the selected airflow rate. For the BS unit, use the curve that presents
the pressure at the outlet (P
OUT
) in function of the airflow rate (AFR
OUT
). See the
latest version of the technical engineering data for the pressure drop curves of the
BS unit.
a
P
OUT
AFR
OUT
a
BS unit
AFR
OUT
Airflow
P
OUT
Outlet pressure
For the pressure drop caused by other components of the evacuation channel
(ducts, bends, etc.), use the curves of the manufacturer.
Use the airflow rate and the sum of the pressure drops to select a suitable fan.
Example
a
b
d
f
g
i
h
e
c
a
BS unit
b~h
Ductwork (duct, bend, reducer, expander, non-return valve, wall grill, etc.)
i
Extraction fan
In this example we use a BS12A unit. Use the curve of the internal pressure inside
the BS unit (P
internal
) in function of the airflow rate (AFR
OUT
). When an airflow rate of
115 m³/h is selected, the pressure inside the BS unit is 42.9 Pa below the pressure
of the surroundings. So this airflow rate is above the required 18.8 m³/h and the
