Determining The Required Volume Of Resin; Resin Exchange Capacity And Capacity Of The Unit - Pentair Siata V132 SFE Installer Manual

4.2.2. Determining the required volume of resin

When sizing a softener, make sure that the volume of resin in the tank (bed volume) will be sufficient
so that even when the peak flow rate is reached, the velocity is still between the above values
depending on the hardness. When sizing a softener, always choose the resin volume and tank size
based on the peak flow rate but not on the nominal flow rate.
A
Note
Sizing on the nominal flow rate without taking the peak flow rate into account would result
in choosing smaller tank size and resin volume, and may lead in severe hardness leakage
during the service cycle when the peak flow is reached.
The maximum softened water flow rate that can produce a softener is given by the following formula:
Q = Fs
service max service
Knowing this required volume of resin, it is possible now determine the tank you need. Note that at
least a third of the total volume of the tank must de kept as free space so that the bed expansion
during backwash is sufficient to ensure correct cleaning of the resin.

4.2.3. Resin exchange capacity and capacity of the unit

The resin exchange capacity and capacity of the unit are two different things and should not be
confused. The resin exchange capacity is the amount of Ca
which will depend on the resin type and salt dosage, whereas the capacity of the unit is the capacity
of the system which will depend on the volume of resin and resin exchange capacity.
Knowing the required volume of resin and the tank size, you can determine the exchange capacity of
the unit. The capacity of the unit can be expressed in a different way:
• The mass capacity, which corresponds to the weight in equivalent CaCO
resin, expressed in kg as CaCO
• The volume capacity, which represents the maximum amount of water that can be treated
between 2 regenerations. This last capacity takes into account the hardness of the water to be
treated and is expressed in m
• The combined capacity, which represents the volume of water that can be treated between 2
regenerations if the inlet hardness is 1 °f or ° dH. This capacity is expressed in °f.m
The unit exchange capacity depends on the amount of salt to be injected in the resin bed during the
regeneration. This amount of salt is given in grams per liter of resin. The 2 tables on the following
pages show the resin exchange capacity based on the amount of salt for a system with standard
efficiency regeneration and for a system with high efficiency regeneration.
Ref. MKT-IM-003 / B - 19.04.2017
x BV
;
3
3
or liters;
Installer manual Siata V132 - SFE - System sizing
with:
Q : service flow rate [m
service max
Fs : service velocity [BV/h]
service
BV : bed volume of resin [m
2+ 2+
and Mg that 1 liter of resin can retain,
3
/h]
3
]
that can be fixed on the
3
3
or °dH.m
25 / 88
3
.