About cooling load calculation with CDD and CDP
Explains the concept of cooling load calculation with the Cooling Design Day and Cooling Design Period.
The Cooling Design Day (CDD) is the hottest day of the selected calculation period. From the geographical position and the depletions of the atmosphere, the diffuse and direct radiation acting on each enveloping surface of the building is calculated for each hour of the design day (= the warmest day of the selected determination period). During the design day, the influence of radiation and internal loads is 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. This stabilized state forms the basis for calculating the room cooling load according to ASHRAE.
14-day preparatory phase: This phase is used to calculate reproducible starting conditions. This is based on a average monthly overcast day.
4-day start-up phase: During the 4-day start-up phase, the outside temperature is adjusted linearly to the design day (CDD). The solar radiation during these four days is equivalent to that of the CDD.
CDD (one day): This is based on a average monthly clear day.
Since all building masses in the room participate with their heat capacity in the radiative radiation exchange and in the thermodynamic process, all room components should be recorded or entered as completely as possible.
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 numerical U-value is not sufficient for most components and layered components have to be created in the master tables. This applies for 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.