Patent ID: 6169850
Filing Date: 2001-01-02
Classification: F24H

Abstract:
An electric air heating device especially suited for low pressure air and used for heating air flowing within a duct of an air temperature control network for a house or a building, said device comprising an enclosure with air inlet and outlet through which variable low pressure air flow is circulated, an electric heating element mounted within said enclosure inbetween said inlet and outlet and to be exposed to and to heat the air circulated therethrough, said heating element emitting radiant heat inversely to the air flow circulating through said enclosure, a power line connected to an alternating current source and to said element, an electronic switching means series connected in said power line, a first thermistor located in said enclosure adjacent and along said heating element and exposed to the radiant heat emitted by said heating element, and a first thermistor dependent control circuit means for controlling said electronic switching means to cause the latter to change between a conducting and a non-conducting state in accordance with the radiant heat emitted by said element, said radiant heat being decreased with respect to the increasing velocity of the air flowing through said enclosure and with decreasing temperature of the air entering said enclosure, said first control circuit means includes a calibrating means to adjust a minimum and a maximum temperatures of said first thermistor between which said electronic switching means gradually changes from a conducting to a non-conducting state, resulting to a permanent heating condition of said heating element and a permanent non-heating condition respectively, said first control circuit means also includes a first pulse generating means and a first pulse duration modulating means to send a first signal to modulate the number of state changes and duration of the conducting state of said electronic switching means during each cycle of said alternating current source, between both said permanent heating and non-heating conditions; thereby providing a gradual heating of said heating element controlled by said first thermistor that acts as an air flow sensor to allow for maximal heating capability of said heating element depending on said air flow circulating through said enclosure.