05 | Ventilation Simulation: Phoenics 5.1 Natural Ventilation To reduce energy demand for ventilation, natural ventilation is desirable. In spring and autumn, when the weather conditions are favorable, natural ventilation is used in the office to provide fresh air. The following model and starting points are taken for the calculation: office floor 28mx41m blockage as core of 15mx15m walls with a surface temperature of 23 °C ceiling with a surface temperature of 25 °C adiabatic floor people and computers with 18 W/m2 heat flux 3 degrees tilted operable windows openings with -0,25 Pa and 0,5 Pa pressure outdoor air temperature of 18 °C To determine whether the input gives results which
are comfortable for users, temperature, draught and air change rate are checked. Windows on the positive pressure side are located at the South-West, the negative pressure on the North-East. The grey area represents the core. The temperature is logically lower at the air inlet sides and higher at the outlet. the average temperature is 23 °C, well within the comfort range. Locally, at the side of the outlets, the temperatures are slightly higher. (Figure 56) One office level with an occupancy of 50 people needs 25-50 m3/h of fresh air per person. This is equal to a flow rate of 1250-2500m3/h. The volume of the space is 923 m2 * 2.7 = 2492 m3. Hence the air change rate needed equals to 1250-2500/2492 = 0.5-1.0. With a minimum air change rate of 2, the entire office has sufficient fresh air. (Figure 57)
Figure56: Temperature spread across the office floor.
Figure57: Air change rate. Climate Design | MEGA 2020
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