Hitachi RWM-(H)FSN3E Technical Catalogue page 71

4 Capacity and selection
data
N O T E
In case of working with an ambient temperature value not included in the Maximum heating capacity tables of
section Maximum heating capacity
above and below the ambient temperature.
• Step 2: Heating capacity correction for defrost and piping length
The actual heating capacity of the pre-selected unit must be calculated applying the necessary correction factors:
Q : Actual heating capacity (kW)
H
Q : Maximum heating capacity (kW)
MH
f : Defrost correction factor
D
f : Heating piping length correction factor
LH
The maximum heating capacity (Q
- Calculation of f :
D
In situations where the ambient temperature is lower than 7 ºC DB, frost may build up on the heat ex-
changer. In the case, the heating capacity of the system may be reduced because of the time spent by the
system in removing the frost build-up.
The defrosting correction factor takes this time into account and applies the heating capacity correction.
To calculate the correction factor, please see section
different values of f
D
temperature of -4 ºC DB does not appear on the table, an interpolation will be needed.
Finally, the resulting defrosting correction factor is 0.885.
- Calculation of f :
LH
Both the length of the refrigerant piping used and the height difference between the outdoor unit and the
indoor unit, directly affect the performance of the unit. This concept is quantified by means of the piping
length correction factor.
To determine this value, it is necessary refer to section
be seen that for the characteristics of our example (equivalent piping length of 20 meters and the indoor
unit located 15 meters lower than outdoor unit), the resulting piping length correction factor is 0.992.
- Calculation of Q :
H
Once the correction factors to be applied have been determined, the formula for actual heating capacity of
the RAS-4HVRNME-AF + RWM-4.0FSN3E system can be applied:
Q = 11.2 kW x 0.885 x 0.992 = 9.83 kW
H
As can be seen, the actual heating capacity of the RAS-4HVRNME-AF + RWM-4.0FSN3E system (9.83 kW) is greater than
the heating load required by the installation (9.0 kW). Therefore, the pre-selection will be considered valid.
N O T E
If the actual heating capacity calculated is lower than the required regular heating load, the calculation must be
done again with the unit immediately above. If there is no unit higher than the pre-selected one, some other sys-
tem (combination with boiler for example), or the regular use of the electric heater, should be considered.
71
TCGB0070 rev.3 - 04/2012
tables, (for example, -3 ºC), an interpolation will be needed, using the values
Q = Q
H
) of the RAS-4HVRNME-AF + RWM-4.0FSN3E system is 11.2 kW.
MH
depending on the ambient temperature (ºC DB). If the correction factor at an ambient
x f x f
MH D LH
Defrost correction factor
Heating piping length correction
which shows a table with
factor, where it can
4