Double duct changeover HVAC system

Claim 1

An HVAC system for providing heating and cooling in a building with multiple exterior exposures and heating and cooling zones, which comprises: a first conditioned air source, for providing cold air with a selected temperature to said HVAC system; a second conditioned air source, for providing conditioned air to said HVAC system, in which said second conditioned air source has the capability of supplying hot or cold air; a first main duct system which includes a plurality of first main ducts, with at least one first main duct for each exterior exposure, with each first main duct connected to said first conditioned air source and terminated at a distal end; a second main duct system which includes a plurality of second main ducts, with at least one second main duct for each exterior exposure, with each second main duct connected to said second conditioned air source and terminated at a distal end; a plurality of exposure dampers installed in said distal ends of said first and second main ducts of said first and said second main duct systems, which variably open or close upon command, to allow a selected flow of conditioned air to pass through said exposure dampers; a distribution duct system which is attached to said distal ends of said ducts of said first and said second main duct system, and which extend as a single duct to a plurality of zone dampers with zone diffusers; a plurality of temperature sensors positioned in said heating and cooling zones, with at least one temperature sensor positioned in each heating and cooling zone, for sensing a measured temperature of air in said heating and cooling zones; a plurality of air flow sensors positioned adjacent to said zone dampers in said heating and cooling zones, with at least one air flow sensor positioned in each heating and cooling zone, for sensing a measured airflow through a zone damper and into a heating and cooling zone; a plurality of temperature set point selectors, with at least one temperature set point selector positioned in each heating and cooling zone, which are settable by a user to a desired temperature in a heating and cooling zone; a plurality of airflow set point selectors, with at least one airflow set point selector positioned in each heating and cooling zone, which are settable by a user to a desired airflow in a heating and cooling zone; return air intakes and return air ducts, for returning air from said heating and cooling zones to said first and said second conditioned air sources; and a computer which for each heating and cooling zone, compares said desired temperature with said measured temperature, and determines by vote of said heating and cooling zones in a particular exterior exposure a temperature of air to be sent to each of said exterior exposures, and which for each heating and cooling zone, compares said desired air flow with said measured airflow, and determines an airflow for each heating and cooling zone, and adjusts said exposure dampers and said zone dampers to deliver heated or cooled air to said zone to achieve said desired temperature and said desired airflow in each said heating and cooling zone.