Cooling system sizing

Cooling Design tab on Model Options dialog.

Design margin

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 method

Sizing methods available are:

• 1-ASHRAE - standard 'Heat Balance' method implemented in EnergyPlus.
• 2-Unitary DX - calculations are made through a detailed EnergyPlus simulation using Unitary DX equipment.
• 3-VAV - detailed EnergyPlus simulation using VAV equipment.
• 4-Fan coil - detailed EnergyPlus simulation using Fan coil equipment.

Note: you do not need to have the Compact HVAC model option set to use the detailed cooling load sizing options 2, 3 and 4 above.