Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for monitoring an HVAC system. One of the methods includes receiving pressure data from one or more sensors monitoring a supply air duct of an HVAC system at a property that indicates a pressure in the HVAC system; determining, using the pressure data, that the pressure satisfies a pressure threshold for the HVAC system; and in response to determining that the pressure satisfies the pressure threshold, adjusting an actuator-controlled damper between the supply air duct and a return air duct or adjusting a fan speed of the HVAC system.

Abstract: A vortex particle separator has an impeller at a housing inlet with impeller blades spiraling around an impeller shaft and longitudinal axis of the separator to impart either clockwise or counterclockwise rotation to air flowing through the impeller when viewed looking downstream along the axis. The upstream end of each impeller blade is inclined in a direction opposite to the direction the air rotates when passing through the impeller, measured from a radial baseline through the axis and the juncture of the blade with the center shaft of the impeller. Thus, in each orthogonal plane along the axial length of the impeller the juncture of the blade with the housing is offset from the baseline in the rotational direction opposite the direction in which air flows through the impeller. An offset angle of 45° to 55° is believed suitable.

Abstract: A vortex particle separator has an impeller at a housing inlet with impeller blades spiraling around an impeller shaft and longitudinal axis of the separator to impart either clockwise or counterclockwise rotation to air flowing through the impeller when viewed looking downstream along the axis. The upstream end of each impeller blade is inclined in a direction opposite to the direction the air rotates when passing through the impeller, measured from a radial baseline through the axis and the juncture of the blade with the center shaft of the impeller. Thus, in each orthogonal plane along the axial length of the impeller the juncture of the blade with the housing is offset from the baseline in the rotational direction opposite the direction in which air flows through the impeller. An offset angle of 45° to 55° is believed suitable.