In what situation are flow hoods particularly useful?

Flow hoods are particularly useful when the Ak factors (airflow coefficients) of outlets are unknown. These factors play a crucial role in determining how much air is being delivered or extracted from a particular outlet or device in a ventilation system. When Ak factors are not determined or readily available, employing a flow hood allows for direct measurement of airflow at the outlet. This measurement is essential for ensuring that ventilation systems operate effectively and meet the required air changes for safety, comfort, and efficiency.

In situations where Ak factors are unknown, flow hoods provide a convenient means to obtain accurate data without needing extensive calculations or assumptions. This information can then be used to adjust fan speeds, register performance, or diagnose issues within the system, ultimately enhancing the understanding of system functionality and efficacy.

The other options, while they may pertain to scenarios involving airflow, do not directly highlight the primary utility of flow hoods. For instance, during new building construction, while flow hoods may be used, they are not as critical as in cases where specific outlet data is missing. Similarly, areas with high humidity may necessitate different strategies for managing airflow and moisture, and system maintenance and repair could involve various other tools and techniques to ensure efficiency and effectiveness.