Common air intake plenums sit behind a weather louvre and vermin mesh in accordance with HTM 03-01 Part B 3.22.
“This mesh provides a resistance of approximately 55 pascals at 3 m/s, and is notoriously difficult and time consuming to clean,” explained provider of external mesh protection screens, RABScreen. The company continued: “At Southmead Hospital in Bristol, the design of the air intake was a problem, requiring specialist contractors to clean because it involved working at height. External access on the roof provided a safe place to work, but the mesh could not be cleaned without removing the louvres.
“The solution was obvious,” RABScreen explained. “Protect the 27 aluminium weather louvres mounted on the outside walls of the plenum with an external weatherproof filter, which was secured to the framework using self-drilling screws. As the RABScreen can be cleaned by rainfall, vacuuming, or brushing, airflow is kept at optimum levels to support the air-handling unit equipment inside.
“Frost coil clogging is prevented, existing filter life is extended, and, with the removal of the existing vermin mesh, airflow is improved, with a resistance of only 17.0 pascals at 3.0 m/s.
“It was neither a difficult nor an expensive job, but the improvement in airflow will see a return of investment in under six months.”
