Analysis of functional requirements for the integrated framework

The primary objective of the integrated framework is to automatically provide the requested information to the computerized approaches and process their outputs。 According to the information requirements, the following functional requirements were identified for the proposed framework:

• Self-recognizing: The ability to recognize its own components and their configurations and functions。

The static information items represent the characteristics of the building elements and HVAC components。 To be able to provide this information to the computerized approaches, the framework needs the capability to recognize the configuration of its components and their functions。 For example, to provide the material information about the windows in a building to a model-based FDD approach (Salsbury and Diamond 2001), the framework should be able identify the information about the windows in the building and the associated material types。

• Self-monitoring: The ability to monitor the conditions of the building indoor environment and the HVAC systems。

The dynamic data and corresponding information items are generated by HVAC components, such as sensors and controllers, and the computerized approaches in the framework。 To collect and process these items, the framework should be able to communicate with the components and acquire the needed information items。

• Self-configuring: The ability to re-configure the HVAC systems according to the outputs of the computerized approaches。

To mitigate the faults and apply control strategy, which results in higher energy efficiency, the configuration of HVAC systems needs to be modified。 For example, to apply the supervisory control approach (Gibson 1997), the values of set-points in the HVAC systems need to be modified。 The framework should be able to reconfigure the HVAC systems according to the outputs of the computerized approaches。

Vision of the integrated framework for self-managing HVAC systems

Based on the analysis of information requirements and functional requirements, we envisioned an integrated framework for the self-managing HVAC systems。 The three functional requirements are achieved by three modules in the framework。 There is also a controller module that controls the operation of other modules。 These modules connect  the  computerized  approaches  with  the  real-world  HVAC   systems     and

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information sources。 Figure 2 shows the envisioned framework。

Figure 2。 Proposed vision of the integrated framework

At the center of the framework is the controller module。 The information requirements of the computerized approaches are sent to self-recognizing and self-monitoring modules by the controller。 The self-recognizing module retrieves the configuration information of the building and HVAC systems from the information bases。 The self-monitoring module acquires the needed condition measures from the available sensors, controllers and actuators in the HVAC systems。 After the information is acquired, the controller invokes the computerized approaches and provides the relevant information to them。 If the computerized approaches generate any output, the controller passes it to the self-configuring module to reconfigure the HVAC systems。

Prototype development and discussion

A prototype application was developed to validate the feasibility of implementing the envisioned framework and identify challenges。 A rule-based FDD approach (Schein and House 2003), a statistics-based FDD approach (Schein et al。 2006) and a virtual sensor based self-healing approach (Fernandez et al。 2009) were implemented in the framework to test the capability of integrating different approaches。 In the self-recognition and self-monitoring modules, several ad hoc procedures were implemented to retrieve the needed information from three standards: Industry Foundation Classes (IFC), SensorML and BACnet。 These modules then deliver this information to the controller module。 An integrated information model was implemented in the controller module to enable the information exchange among the three computerized approaches。 The prototype was tested with a real-world HVAC system that serves an office building in a university。 Results showed that the integrated framework was able to support the operations of the three computerized approaches。 However, one limitation of the prototype is that it does not support other computerized approaches。