8. The system according to claim 7 further comprising: an FDD engine configured to instantiate the HFM graph as a runtime system for the building HVAC control system; and an interface configured to access the building HVAC control system, wherein the FDD engine executes the HFM graph with HVAC control system process and control variable data and applies rules for detecting HVAC system faults.
8. The system according to claim 7 further comprising: an FDD engine configured to instantiate the HFM graph as a runtime system for the building HVAC control system; and an interface configured to access the building HVAC control system, wherein the FDD engine executes the HFM graph with HVAC control system process and control variable data and applies rules for detecting HVAC system faults. 17. The system according to claim 8 wherein for each HFM node, based on received measurements and flow information from upstream and downstream HFM nodes, the FDD engine is further configured to perform state estimation and propagate resulting parameter ranges to adjacent nodes.