Summer casts cloud over NCM templates

A much bigger problem with the NCM templates generally, for all building types, is the ventilation allowance. The NCM levels allow for mininum ventilation throughout the year and, as such, cause massive overheating in the summer.

A well-ventilated building will generally need heating when the outside air tempeature is below 15ºC. With miniminum fresh air, it may only need heating from an outside air temperature of 10ºC.

It is common practice to size ventilation on the summer cooling rate required and have a constant airflow throughout the year, because variable-volume systems are expensive and difficult to commission.

The theory is that by comparing the energy for notional and actual under the same ventilation rate, the energy saving comes from the plant efficiency and hence you will save the same percentage on the ventilation energy, whatever the real ventilation rate.

The trouble is that the proportion of energy usage across the services within the building will be unrealistic. This gives more emphasis to saving lighting than ventilation, with the associated heat requirement and fan power.