MAH_2019

MAH 2019 Companion Guidance Section C Understanding HVAC System Designs 6 Systems that bring outdoor air into a building for seasonal comfort are common in some regions. Evaporative (swamp) cooling systems have long been a common cooling system in dry climates. Heat recovery ventilators (HRV) and energy recovery ventilators (ERV) are becoming more popular across the country. Group 3-b: VARIABLE OUTDOOR AIR VENTILATION Variable Outdoor Air Ventilation (HVAC) systems are those that add outdoor air ventilation for seasonal comfort or energy savings. Such systems may service a whole building, multiple dwellings or a single dwelling or unit ventilator. Radon concentrations can vary widely from test to test based the volume of outdoor air supplied to a dwelling or room at any given time. (Very uncommon for single-family residences) Group 3-a: VARIABLE AIR DISTRIBUTION Variable Air Distribution systems are those where airflow from a single air handler is distributed to multiple dwellings, rooms or common use areas with independent controls within each area that open and close duct dampers. The normal operation of these systems can cause changes in distribution of radon or ventilation air and can also affect pressure relationships that can enhance or diminish radon entry. HRV or ERV