National Calculation Methodology (NCM) - Scottish Government

42. The cooling and auxiliary energy in the notional building must be taken to be
powered by grid-supplied electricity.
43. The efficiency of the HVAC systems in the notional building must be as given in
Table 4.
44. The system performance definitions follow the practice set out in EN 15243 15 :
a. Auxiliary energy is the energy used by controls, pumps and fans associated
with the HVAC systems. It is the term described as “fans, pumps, controls” in
Energy Consumption Guides such as ECG019 16 . The auxiliary energy demand
must be calculated as detailed in paragraph 0 as appropriate.
b. The Seasonal Coefficient of Performance for heating (SCoP 17 ) is the ratio of
the sum of the heating demands of all spaces served by a heating system to
the energy content of the fuels (or electricity) supplied to the boiler or other
heat generator of the system. The SCoP includes, amongst other things, the
efficiency of the heat generator, thermal losses from pipework and ductwork,
and duct leakage. It does not include the energy used by fans and pumps (but
does include the proportion of that energy that reappears as heat within the
system). For DSMs, the ventilation air supplied to the zone must be taken as at
the outdoor air temperature. For SBEM, adjusted monthly average figures
should be used. Heating energy consumption is, therefore, calculated from the
following expression:
HeatingEnergyConsumption = ∑
( ZoneHeatingLoad
) SCoP
c. The Seasonal System Energy Efficiency Ratio for cooling (SSEER) is the ratio
of the sum of the sensible cooling demands of all spaces served by a cooling
system to the energy content of the electricity (or fuel) supplied to the chiller or
other cold generator of the system. The SSEER includes, amongst other
things, the efficiency of the cold generator, heat gains to pipework and
ductwork, duct leakage, and removal of latent energy (whether intentional or
not). It does not include energy used by fans and pumps (but does include the
proportion of that energy that reappears as heat within the system). The
electricity used by heat rejection equipment associated with chillers is
accounted for in the SSEER (not as auxiliary energy). The electricity used
within room air-conditioners for fan operation is also included in the SSEER
value since it is included in the standard measurement procedure for their
Energy Efficiency Ratio (EER). For DSMs, the temperature of the ventilation air
supplied to the zone must be taken as that of the outdoor air temperature. For
SBEM, adjusted monthly average figures should be used. Cooling energy
consumption is, therefore, calculated from the following expression:
CoolingEnergyConsumption = ∑
( ZoneCoolingLoad
) SSEER
15
EN 15243, Ventilation for Buildings – Calculation of room temperatures and of load and energy for
buildings with room conditioning systems, CEN, 2007.
16
Energy use in offices, Energy Consumption Guide 19, Action Energy, 2003.
17
This is referred to as Seasonal System Efficiency (SSEff) in the iSBEM User guide.
16