Hitachi UTOPIA R32 Series Technical Catalogue page 59

4 Capacities and selection data
System selection procedure
3 Pre-select the outdoor units that covers the installation's cooling load requirements
If the required loads will not be simultaneous (for example: the maximum required loads of room 1 (east zone) occurs
at the morning and the maximum required loads of room 2 (west zone) occurs at the afternoon.), select the outdoor
unit that cover the maximum simultaneous load on the installation and check that the total combination horsepower
must not be higher than the limits, using the following:
Total combination horsepower = (Total indoor unit horsepower / Outdoor unit horsepower) x 100
4 Calculation of f (Cooling piping length correction factor)
LC
The length of the refrigerant piping used and the height difference between the outdoor unit and the indoor units
directly affect the performance of the unit. This concept is quantified in the piping length correction factor.
To determine this value it is necessary refer to the piping length correction factor tables that are based on the
equivalent piping length in meter and height between outdoor and indoor units. For the equivalent one-way piping
length between indoor unit and outdoor unit (m) consider the following:
One 90º elbow is 0.5 m.
One 180º bend is 1.5 m.
One Multi-kit is 0.5 m.
5 Calculation of f (Correction factor according to altitude)
AL
The capacity is affected by the altitude of the installation location. When the altitude is above sea level, capacity must
be corrected with the altitude correction factor according to the "Correction factor due to altitude" table.
6 Cooling capacity correction (Q
The actual cooling capacity of the pre-selected unit must be calculated applying the necessary correction factors:
Q = Q x f x f
C MC LC AL
Q : Actual cooling capacity of the outdoor unit (kW).
C
Q : Maximum cooling capacity of the outdoor unit (kW).
MC
f : Cooling piping length correction factor.
LC
f : Corrections factor according to altitude.
AL
7 Cooling capacity correction of the outdoor unit (Q
The correction ratio due to humidity is the coefficient that corrects the sensible heat capacity of a unit according to
the relative humidity of the air entering the indoor unit. The greater the relative humidity the lower will be the sensible
heat capacity and vice versa.
The following formula is used to apply an adjustment to the cooling capacity showed in the tables due to the
difference between the real indoor air inlet dry bulb temperature vs the one used for calculate the nominal cooling
capacity data.
Q =Q + (CR x (DB - DB))
AC C R
Q : Actual cooling capacity of the outdoor unit (kW) (at given real % humidity)
AC
Q : Corrected cooling capacity of the outdoor unit by piping length (kW) (at given 50 % humidity)
C
CR: Correction ratio due to humidity.
DB : Real Dry Bulb evaporator temperature (ºC).
R
DB: Dry Bulb evaporator temperature (ºC) for each wet bulb temperature from the tables (HR = 50 %).
8 Actual indoor units capacity
Once it is known the actual outdoor units cooling capacity, it must be calculated the actual cooling capacity of each
indoor unit, according to the following formula:
Q = Q x (Q / Q )
CI AC NCI NCC
Q : Actual cooling capacity of the indoor unit (kW).
CI
Q : Actual cooling capacity of the outdoor unit (kW).
AC
Q : Nominal cooling capacity of the indoor unit (kW).
NCI
Q : Nominal cooling capacity of the combination (kW).
NCC
51 TCGB0136 rev.1 - 05/2021
) due to the piping length and altitude factor
C
) depending of the humidity of the indoor unit
AC
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