# Downdraft Assessment of Glass Curtain Wall Buildings with a Radiant Floor Heating System
## 2 Background on Downdraft Assessment
### Preliminary Study of Downdraft Assessment  
The downdraft assessment study is mostly performed by analyzing a descending flow of cold air including the velocity of the airflow and the temperature distribution, by performing an experiment or simulation. [PERSON] [19] calculated the maximum velocity of an airflow for downdraft assessment and presented a range of allowable maximum airflow velocities by deriving a formula combining the height of the window and its \(U\)-value in a space. However, because he did not consider the temperature of the air, the cold airflow was not reflected. [PERSON] [15] evaluated the degree of downdraft occurrence by analyzing the maximum airflow velocity distribution of the descending airflow formed, depending on the surface temperature of the window via experiments under adiabatic conditions, i.e., an outdoor space and indoor space are implemented on both sides across a window. In addition, he determined the boundary layer flow in a cold airflow via flow visualization. [PERSON] [20] carried out a downdraft assessment in the case where there were internal heat gains, based on [PERSON]'s study [15]. [PERSON] derived the result that while warm airflow generated from internal heat gains ascends, rides the ceiling side, moves toward the window side, and descends, the velocity of the airflow increases. In this study, to reflect this result, a weighing factor of 1.5 was applied to [PERSON]'s formula. Meanwhile, [PERSON] [21] performed an experiment on air temperature, velocity of airflow, and Draft Rate (hereinafter DR) distribution, according to the distance from the wall, to analyze the occurrence of a downdraft in the case where a ventilation system was placed in the corner of the room far away from the windows. [PERSON] [17] analyzed the descending airflow formed because of the thermal performance of the window and width of the windowsill in the experimental room where the window was located on the upper side of a wall. [PERSON] [22] performed the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Class** & **Draft Rate** & **Description** \\ \hline A & \textless{}10 & It is desired to adhere to higher than typical comfort standards \\ B & \textless{}20 & Typical applications and should be used when other information is not available \\ C & \textless{}25 & It is desired to relax the typical comfort standards \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Class level of draft rate. assessment of downdraft through experiments and CFD simulation to analyze the velocity of airflow and DR according to the height and surface temperature of the windows. [PERSON] [23] analyzed the occurrence of downdraft by presenting the Predicted Percentage of Dissatisfied (hereinafter PPD) distribution in the room through the CFD simulation. In this study, the maximum velocity of airflow according to the thermal performance of windows was evaluated by comparing the formulas of [PERSON] [15] and [PERSON] [20]. Additionally, the limiting height of the exterior envelope, so as not to result in discomfort caused by the downdraft was presented. Similarly, [PERSON] [24] analyzed the airflow velocity distribution in the room according to various heating methods to evaluate the reduction of downdraft through the heating of cooled air. In [PERSON]'s study [25], thermal conditions of an office room with a CBRP (chilled beam having an integrated radiant panel) in heating mode were analyzed. The results of this study indicate that radiant panel heating is also an applicable solution in cold climates. Favorable thermal conditions can be ensured when the temperature of the window surface is at least 14-15 \({}^{\circ}\)C. At the same time, the vertical temperature stratification is acceptable. The experimental studies evaluating downdraft did not reflect the external environmental conditions affecting the downdraft well, because most of the experiments were conducted under insulated space conditions.