Window Selection Parametric Study
Natural Ventilation (Fall, 2016) | Prof. Alejandra Menchaca Harvard Graduate School of Design (GSD), Cambridge, MA
To investigate an adequate window type for our building, we conducted parametric studies with different types of windows based on equivalent areas. The assumption for this calculation is ignoring solar chimney effect and only considering buoyancy ventilation effect with 25W/m2 heat gain of interior space. Therefore, the baseline calculation for value of delta T is relatively small at around 2C. However, we can expect that the increased value for overheating due to the solar chimney, while maintaining higher air velocity and ACH rate. After the calculation with the different window types, casement window type was selected due to the largest max equivalent areas, which increase ACH as well as varied range of air velocity.
With a selected casement window, we run several parametric studies based on the opening areas, which result in average delta T between 1.67 to 2.3 with ACH 5.4 to 1.99 respectively. This can be used for the window scheduling in different seasons and daytime to achieve reasonable indoor temperature through natural ventilation.
The upper two story of the office building can be heated from the solar radiant heat, thus average 100 to 300 W/m2 heat gain will be achieved from the internal solar chimney. We extracted the solar heat gain data per m2 from the LadyBug sunpath analysis tools, and averaged them to generate schedule for the each month.
21st day of January, March, July and October was selected for the scheduling of openings. The design of opening size is based on optimized overheating (deltaT) for each seasons meeting up the indoor comfort temperature. While changing values for deltaT, we tried to ensure reasonable air velocity and increased ACH for indoor comfort.
Based on the finalized geometry from the result of coolvent simulations, we adjusted degree of opening and the size of the roof operable areas. With 5 degrees opening and 10m2 roof operable areas, the average delta T for January can be increased upto 6.5 shifting four hours to the occupants’ comfort range during daytime. In March, an average delta T at 5C was achieved maintaining air velocity under 1m/s and relatively higher ACH than January.
Due to the relatively higher outdoor temperature of July and October, we tried to decrease delta T for those seasons ensuring reasonable air velocity and ACH for the indoor spaces. Thus average delta T at 3.83 and 2.58 for July and October are suggested for the final proposal. To achieve those values, we maximized roof operable areas at 45m2 with fully open window areas. With this practice, comfortable wind velocity and ACH for indoor spaces can be expected with relevant temperature increase.
As you can see the figure above, most of the time we presented is achieving indoor temperature level on the comfort range (green box) except January morning and July afternoon. The results show that the solar chimney generally works throughout the year by increasing delta T with higher ACH. When the outdoor temperature below 12 degree C in winter season, it can be suggested that the window will be closed for the purpose of heating. When the outdoor temperature higher than 25 degrees C, it can be suggested that the window will be closed for the purpose of cooling. Besides those conditions, windows and the roof operable areas will be controlled based on the proposed schedule maintaining indoor occupants’ comfort.
Ellie Jungmin Han
Harvard Graduate School of Design
48 Quincy Street Cambridge, MA 02318