Deviation analysis of the design intent and implemented controls of HVAC systems using sensor data: A case study

Sustainable building system design techniques aim to find an optimal balance between occupant comfort and the energy performance of HVAC systems. Design and implementation of effective heating ventilating and air conditioning (HVAC) controls is the key to achieve these optimal design conditions. Any anomalies in the functioning of a system component or a control system would result in occupant discomfort and/or energy wastage. While occupant discomfort can be directly sensed by occupants, measurement of waste in energy use would require additional sensing and analysis infrastructure. One way of identifying such a waste is to compare as-designed system requirements with the actual performance of the systems. This paper presents an analysis of an air handling unit (AHU) in a five story office building and provides the comparison results of design requirements against the sensor data corresponding to the AHU parameters. One year sensor data for the AHU parameters was analyzed to assess the correctness of the implementation of the design intent. The design intent was interpreted from the sequence of operations (SOOs) and confirmed with a commissioning engineer, who worked on the project. The design intent was then graphically represented as a pattern that the sensor data corresponding to the controls is expected to follow if it follows the design intent. Any deviation in the sensor data as compared to the expected operation pattern of the design intent indicated incorrect operation of the system with incorrectly implemented controls. The findings in this paper substantiate the need to formally define the sequence of operations and also point to the need to verify the implemented controls in a given project to detect any deviations from the actual design intent.