Development of an Evidence-Based Calibration Methodology Dedicated to Energy Audit of Office Buildings. Part 1: Methodology and Modeling.

1 Introduction
To promote improvements in the HVAC installations of existing buildings, the article 9 of the EPBD directive establishes mandatory audits and inspections of air-conditioning systems. The development of auditing tools and procedures and the training of future auditors are the main objectives of the HARMONAC project launched in 2007.
Four audit stages are generally distinguished: benchmarking, inspection, detailed audit and investment grade audit. Answering the questions encountered along the audit process requires some diagnosis, which has to be established on the basis of the very scarce information currently available: technical data contained in as-built files actually available and, generally, very global recordings of energy consumptions.
A dynamic hourly building energy simulation (BES) model is being developed in the frame of the HARMONAC project to help the auditor in establishing his diagnosis despite of the lack of data. Two simulation tools dedicated to assist the auditor are developed on the basis of this equation-based BES model:
- The first tool is dedicated to a preliminary benchmarking of the installation.
- The second tool is used from inspection stage to evaluation of selected energy conservation measures (ECMs).

2 Simulation-based audit methodology
The first step of the audit methodology consists in gathering the as-built and utility data, applying a first treatment and analysis method to this data and using the BES model to perform benchmarking. For this benchmarking targeted work, the actual building is coupled to a typical HVAC system whose performances are defined according to EPBD standards. If the benchmarking indicates that potential energy savings should be studied in the building, the calibration-based audit procedure is launched.

In the second step, the BES model is integrated in an iterative evidence-based calibration method adapted to audit purposes. The calibration starts directly at the beginning of the inspection, before realizing any additional measurement. This calibration process includes sensitivity and measurement issues, in order to help the auditor identifying critical points and understanding the building operation. Graphical and statistical methods are used in order to quantify and evaluate if the calibrated baseline model satisfies the predefined tolerances.

Finally, the calibrated baseline model can be used to evaluate ECMs and savings uncertainty.

The development and the implementation of the BES model are presented in this paper. The mains issues of the proposed calibration-based audit methodology are discussed. An example of application of the whole methodology (from benchmarking to evaluation of ECMs) is presented in a companion paper.