20
HOW TO SELECT THE UNIT
Beginning with the refrigerating power required by the given conditions of use and having checked the
Standard
performances
table, model IP 205 VB AB 7M5 can be selected as it provides a standard refrigerating power of
(171.4 kW).
The effective refrigerating power provided by the machine in the real conditions of use will be:
Where: P
f
= refrigerating power provided in the real operating conditions (kW)
P
f s
= refrigerating power provided in standard conditions (kW)
F
CH
= correction factor for the height above sea level
F
CP
= correction factor for the fouling factor
F
CD
= correction factor for the temperature difference
The available data and
tables 1, 2, 3
can be used to determine the values of correction factors F
CH
= 0.97, F
CP
=
0.98, F
CD
= 1, after which the refrigerating power supplied in the real operating conditions can be calculated, i.e.:
In the given conditions of use, the selected unit provides a 163 kW refrigerating power, which meets the cooling
requirements.
The flow rate of the water that passes through the evaporator will be:
with c = 4.186 kJ/kg C specific heat of the water.
A 27 kPa loss of head is given in the Loss of head graph, on a level with the determined water flow rate and the
curve of the selected model. This value is acceptable since it is within the limit values given in the Operating limits .
A 177 kPa useful head is given in the Useful head graph, on a level with the determined water flow rate and the
curve of the selected model.
Calculation of the maximum volume of water must also be used, as shown in the table of the maximum water volu-
me reference section, and the procedure for calculating the volume of the additional surge chamber adapted if
necessary (if the real volume of water in the system exceeds the maximum volume of the actual system itself).
Verification for operation in the heating mode:
With the data available for operation in the heating mode and considering the previously selected reversible unit IP
205 VB AB_7M2 , the standard heat output in the heating mode is P
rs
= 222.1 kW.
Considering the real conditions in which the machine is operated and using
tables 1, 2, 4
(
Tab.3
does not
apply in the heating mode), it is possible to calculate the values of corrective factors F
CH
=0.97, F
CP
=0.98,
F
cUr
=0.96 and, thus, the value of the heat output in the heating mode in the real conditions of use, i.e.:
As it exceeds requirements, this heat output value confirms that the selected unit is a valid choice: The flow rate of
the water that passes through the exchanger-evaporator will be:
which corresponds to a 41 kPa loss of head, thus within the limits of the exchanger.
A 144 kPa useful head is given in the
Useful head
graph, on a level with the determined water flow rate and the
curve of the selected model.
(l/s)
78
.
7
5
4.186
163
t
c
Pf
Q
=
⋅
=
Δ
⋅
=
(l/s)
9.68
5
4.186
202.7
t
c
Pf
Q
=
⋅
=
Δ
⋅
=
Fcd
Fcp
Fch
Pfs
Pf
⋅
⋅
⋅
=
kW
163
=
(1)
(0.98)
(0.97)
(171.4)
=
Pf
UR
D
H
Fc
Fc
Fc
Pfs
Pf
⋅
⋅
⋅
=
kW
7
.
202
)
96
.
0
)(
98
.
0
)(
97
.
0
)(
1
.
222
(
Pr
=
=
Summary of Contents for 150.4
Page 2: ...2...
