Example - for a 3-bedroom, 2,000-sq.ft. home, with an exhaust-only ventilation strategy, and a target ventilation rate of 50 CFM you would need to install a 50 CFM fan with an adjustable-speed DC motor for continuous operation.
Quick Answer. Trenches were built during World War I to protect stalemated troops on both sides from artillery and rifle fire. Although the war began with rapid movement of the German army, when the Allied forces stopped the Germans, both sides dug trenches to help avoid losing territory they had gained.
Trenches have been dug in warfare from the Trojan War onward, but trench warfare was a result of new weapons and old tactics. Def â¦ ense became stronger than offense. The warplane was not sufficiently advanced to break this stalemate, and the tank was not properly used.