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Building Systems

Smart Monitoring and Diagnostic System (SMDS)

Pacific Northwest National Laboratory (PNNL) developed a very low cost smart monitoring and diagnostic system (SMDS) for retrofit on existing commercial rooftop air-conditioning systems (RTUs) and heat pumps (for cooling mode). The original SMDS is a standalone hardware package with embedded software. It detects when the performance of the refrigerant-side of the air-conditioning cycle changes (from degradation or from improvement resulting from servicing) and then quantifies the change in terms of energy and energy-cost impacts. The SMDS also detects a small number of specific system-level operational faults, such as RTUs operating continuously during times when the space served is unoccupied, not ventilating adequately when the space is occupied, etc.

The existing SMDS system capabilities were converted to a Cloud-based application and integrated with the transactional network (TN) platform. The Cloud version of the SMDS provides all of the fault detection and diagnostic capabilities embedded in the standalone system and also adds additional capability to detect faults with RTUs that have multi-speed supply fans.

Measured data are collected by the TN platform for each RTU connected to the network at 1-minute intervals for outdoor-air temperature and total RTU power consumption, with the supply-fan speed signal added for RTUs with multiple speed supply fans. The data are then stored in the network’s data historian from which the data are periodically retrieved by an agent in the platform and sent to the application in the Cloud, where the data are stored in a local application data base. The data are processed once per day to provide updated results. The SMDS detects when changes occur in the performance of the refrigerant side of RTUs. These changes can be degradations in performance from faults or improvements in performance associated with servicing. When a change in performance is detected, the SMDS estimates the energy and cost impacts of the change, enabling users to prioritize it based on the importance and value of the change. In the case of improved performance, the SMDS can be used to determine the impacts of servicing on energy use and costs. For degradations in performance, the SMDS provides information that supports the building owner, manager or operator in deciding when to schedule servicing based on the impacts of the performance degradation that occurred. The SMDS also detects the following operational faults that usually can be corrected with simple changes in control parameters:

  • Supply fan always on (24 hours per day)
  • Compressor always on (24 hours per day)
  • RTU always off
  • Supply fan cycles with the compressor only

When any of these faults is detected, the SMDS provides an alert to users through the user interface. SMDS is currently running on two demonstration sites in western Washington and northern California. Learn about the current results.

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