About calculation according to ASHRAE

Explains the concept of cooling load calculation according to ASHRAE.

The hottest day of the calculation period (year, month) is determined from the climate data as the design day. From the geographical position and the atmospheric clouding factors, the diffused and direct radiation for each hour of the design day acting on each individual enveloping surface of the building (according to its alignment) is calculated. Over the course of the design day, the influence of radiation and internal loads are simulated for each room. The design day simulation is repeated until there is no longer any change to room temperatures and the temperatures have stabilized. (Worst case: The hottest temperatures in the year persist for several days or weeks). This stabilized state forms the basis for calculating the room cooling load.

As all structures in the room take part with their heating capacity in radiation exchange and in the thermodynamic process, all components of the room should as far as possible be recorded or entered.

In addition to geometry, thermal conductivity, density, the thermo-optical properties of a substance and the specific heat capacity are used to calculate the cooling load. This means that entering a numeric U-value for most components is insufficient and layered components must be created in the master tables. This applies to walls, ceilings, floors and roofs. Entering a numeric U-value suffices for doors and windows. The mass and thermal capacity of these components is so low that the heat storage effect is negligible.

The layer structure of the walls is considered from the inside to the outside. In addition, the influence of air temperature, solar radiation, internal heat exchange and corrective processes are calculated.