Cooling Design tab on Model Options dialog.
The Cooling Design margin is a 'safety factor' used to multiply calculated cooling loads in each zone to give a recommended maximum cooling equipment capacity. It accounts for the additional cooling which might be required to cool the building down in a reasonably short pre-cool period and allows you to be confident that comfort conditions will be maintained in all but the most extreme summer conditions. The risk depends on the Summer Design Weather Data options selected at site level.
The default design margin is 1.15 which means that the cooling system will be oversized by 15%. This is value comes from ASHRAE recommendations.
Sizing methods available are:
When calculating the design airflow rate from the cooling load DesignBuilder can use one of 2 methods:
Design flow rate = SizingFactor . DesignCoolingLoad / (Tzoneairdb - Tsupplyair) . CPair . Densityair
where:
CPair is the specific heat capacity of air
Tzoneairdb is the zone dry bulb temperature
Tsupplyair is the supply air dry-bulb temperature
Design flow rate = SizingFactor . DesignCoolingLoad / (Ezoneair - Esupplyair) . Densityair
where:
Ezoneair is the zone air enthalpy
Esupplyair is the supply air enthalpy