National Calculation Methodology (NCM) - Scottish Government

d. The electricity used by fossil-fuelled equipment and its ancillaries, including
fans in unit heaters and gas boosters, is included in the auxiliary energy.
e. For the purposes of heating, cooling, and auxiliary energy calculations, the
ventilation should operate on a flat profile that is on during the occupied period
only, with a flow rate determined by the product of the peak occupancy density
and fresh air rate per person (both from the NCM Activity Database). The
profile is the same for both natural and mechanical ventilation and does not
modulate with the occupancy profile.
Table 4: HVAC Seasonal system efficiencies in the notional building
Servicing strategy SCoP † Cooling
SSEER
Auxiliary energy
Heating with natural
ventilation
0.73 N/A See paragraph 45.a
Heated with mechanical
ventilation
0.78 N/A See paragraph 45.b
Fully air-conditioned 0.83 1.67 See paragraph 45.c
Changeover mixed-mode
with natural ventilation
0.73 2.25 †† See paragraph 45.a
Changeover mixed-mode
with mechanical ventilation
0.78 2.25 †† See paragraph 45.b
No heating with natural
ventilation
N/A N/A 0
†
Referred to as Seasonal System Efficiency (SSEff) in iSBEM User guide.
††
This SSEER includes an allowance for fan energy when the system operates, so no
additional auxiliary energy needs to be determined beyond what is described above.
45. The auxiliary energy per unit floor area in the notional building must be calculated
as follows:
a. For heated only and naturally ventilated spaces: the product of 0.61 W/m 2 and
the annual hours of operation of the heating system from the NCM Activity
Database.
b. For mechanically ventilated spaces: the product of the outside air rate for the
space, the annual hours of operation (both from the Activity Database) and the
appropriate specific fan power from Table 5. If the zone is heated, then the
auxiliary energy should also include the energy from paragraph 45.a.
c. For air-conditioned spaces: the product of the annual hours of operation and
the greater of either:
i. The product of the fresh air rate (from the NCM Activity Database) and the
appropriate SFP from Table 5, or
ii. 8.5 W/m 2 .
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