Hitachi RWM-(H)FSN3E Technical Catalogue page 72

4 Capacity and selection
data
b) Selection for the coldest days of the year (use of the auxiliary electric heater)
The previous calculation shows that the RAS-4HVRNME-AF + RWM-4.0FSN3E system provides a heating capacity of
9.83 kW (-5 ºC WB), which is greater than the regular heating load necessary of 9.0 kW, but does not reach the peak heat-
ing load of 12.0 kW (-15 ºC WB) necessary on the coldest days of the year. In this cases, the electric heater can provide
the auxiliary heating capacity to cover all the peak heating load.
The aim of this section is to check that the energy system chosen (Mono-energy) covers the temporary heating require-
ments for the coldest days of the year.
• Step 1: Initial pre-selection
As the ambient temperature has fallen to -15 ºC, the Maximum heating capacity tables has to be consulted again to deter-
minate the maximum heating capacity that the RAS-4HVRNME-AF + RWM-4.0FSN3E system will provide for these new
conditions.
The maximum heating capacity for an ambient temperature of -15 ºC WB and a water inlet/outlet temperature of 30/35 ºC
is 8.9 kW.
• Step 2: Heating capacity correction for defrost and piping length
The actual heating capacity for the system selected for the coldest days of the year is calculated by applying correction
factors for defrost and piping length, following the method used above.
Q : Actual heating capacity (kW)
H
Q : Maximum heating capacity (kW)
MH
f : Defrost correction factor
D
f : Heating piping length correction factor
LH
f
- Calculation of :
D
The tables in section
ent temperature of -14.5 ºC DB does not appear on the table.
To know the defrost correction factor for this temperature it will be necessary an interpolation, using the
values above and below the ambient temperature. The defrost correction factor obtained is 0.946.
f
- Calculation of :
LH
The same correction factor than before (0.992).
Calculation of :
-
Q
H
Once the correction factors to be applied have been determined, the formula for actual heating capacity
of the unit RAS-4HVRNME-AF + RWM-4.0FSN3E system can be applied:
Q = 8.9 kW x 0.946 x 0.992 = 8.35 kW
H
72
TCGB0070 rev.3 - 04/2012
Q = Q
H
Defrost correction factor of this chapter shows that the correction factor for an ambi-
x f x f
MH D LH