External cooling loads are the loads which arise due to warmer outside air and solar radiation. The calculation of external loads is decisively affected by the following factors:
- Radiation through transparent exterior components
- Transmission through the wall
- Outside air
“Transparent components” are primarily understood to be windows. A key factor for the external cooling load is the “solar gains” input through the windows. The radiation values depend on the region, the season, the time of day, and atmospheric haze. Solar radiation protection mechanisms can considerably reduce the effects of the influx of radiant heat. The choice of suitable solar radiation protection mechanisms can reduce the investment in building cooling systems and consequently also energy consumption.
Heat storage has an influence on transfer through the walls, because of the dynamic changes in temperature difference between outside and inside. Heat storage is the property of building components to absorb heat and to radiate it again at lower temperatures. The absorbed heat in the building components has a delayed effect in the rooms, depending on how massive the construction is. Buildings with high storage mass ensure that temperature fluctuations in interior spaces are compensated and prevent the heating up of interior spaces above comfort temperatures in summer. Not only does this lead to higher comfort for the indoor climate, but also a reduction in peak load, and consequently also a reduction in energy costs.
Fresh air from the outside renews the air inside buildings. However, it must first be cooled to the desired room temperature. Outside air can be fed in by opening windows and doors, through infiltration, or through mechanical ventilation. The outside temperature is dependent on the location and height of the building. For cooling load, taking city climate into account, the VDI guideline 2078 divides cities in Germany into 4 cooling load zones. The mean daily outside temperature and the amplitude of fluctuation in °C is given for each cooling load zone. In addition, VDI provides for an adjustment to metropolitan centers in climate zones 3 and 4, which leads to an increase in the mean daily temperatures and a smaller amplitude. This results in a reduction in the day/night difference. Cities with populations higher than 100,000, with dense concentrations of buildings and without green spaces are counted as metropolitan centers.