Natural & Mechanical ASHRAE 62.2-2016 2. Definitions, defines Natural Ventilation as “… ventilation occurring as a result of only natural forces, such as wind pressure or differences in air density, through intentional openings such as open windows and doors.” Natural Ventilation can be unintended as is the case with infiltration. While infiltration can supply the occupants with breathable air, it is unintentional without determined volume, unfiltered, and un- tempered. It is the intent of the Energy Code and modern building science to reduce this type of ventilation as it wastes energy and increases the utility bill. Another form of natural ventilation is the use of windows or doors. AMC 2010 B] 402.1 states, “…Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors. The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants. [B] 402.2 Ventilation area required. The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated. 402.2 requires a minimum of readily controllable openings. An example: a 10 x 10 bedroom would require 4 square feet. Since the openable portion of a window is only about 50% of their gross area, the 10 x 10 bedroom window would need to be at least 8 square feet, an unusually large window for such a small room. Another section of the code,
AMC 2010 - 4.2.3 allows for combining rooms but the openings between rooms must be unobstructed and openings shall have an area not less than 8 percent of the floor area of the interior room or space, but not less than 25 square feet. Additionally, use of windows and doors for ventilation is only permissible if , ASHRAE 4.1.1 “…the authority having jurisdiction determines that window operation is a locally permissible method of providing ventilation and provided that at least one of the following conditions is met: 1. the building has no mechanical cooling and is in zone 1 or 2 of the climate zone map (Arkansas is in zones 3 & 4.) 2. the building is thermally conditioned for human occupancy for less than 876 h per year. (All area of Arkansas exceeds this amount by more than a factor of 3.)” Since, no area of Arkansas allows the use of windows or doors as the primary method of ventilation, mechanical ventilation is required. AMC-2010, 401.2, states,” Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403. Since, no area of Arkansas allows the use of windows or doors as the primary method of ventilation, mechanical ventilation is required.