Further to the definition in Appendix A this will typically be the geometric open area provided by an open window (fully open windows typically having a coefficient of discharge (Cd) of 0.62).
Ymhellach i'r diffiniad yn Atodiad A fel arfer hwn fydd yr ardal agored geometrig a ddarperir gan ffenestr agored (ffenestri cwbl agored fel arfer â cyfernod rhyddhau (Cd) o 0.62).