1. A method of manufacturing an HVAC data processing and communication network, comprising: forming an HVAC network by causing a plurality of HVAC system devices to be coupled to a data bus, at least one of said HVAC system devices constituting an HVAC demand unit having an integral network controller; configuring a first HVAC system device to receive an initial value of a specified first parameter that is dependent upon a value of a second parameter of either said first HVAC system device or of a second HVAC system device; configuring said integral network controller to: determine that a value of said second parameter has changed after said first HVAC system device receives said initial value; and send said first HVAC system device a message modifying said first parameter in view of said second parameter change.