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Transactional Network

Cloud-based Smart Monitoring and Diagnostic System (SMDS) for Packaged Roof Top Units (RTUs)

Challenge

Roof top units (RTUs) frequently run at degraded efficiency and capacity resulting from the presence of physical and operational faults.

Objective

Detect RTU refrigerant-side performance degradation and several operation faults using only three measured variables, outdoor-air temperature, total RTU power consumption, and the fan speed control signal for units with variable-speed supply fans. No configuration setting is required by the user.

Implementation

The SMDS provides fault detection and diagnostics for RTUs. Measured data are collected continuously at 1-minute intervals from sensors on the RTUs by an agent in the platform. The SMDS periodically receives data from the Data Historian and stores it in the SMDS application data based in the Cloud. It then processes the data once per day to produce new results, which are sent to the user interface for display for each RTU.

Smart Monitoring and Diagnostic System application in the Cloud

The SMDS application resides in the Cloud. Measured data are collected at 1-minute intervals for outdoor-air temperature, RTU total power consumption, and supply-fan speed signal (for RTUs with variable-speed supply fans only) by the Transaction Network platform for each RTU connected to the network. 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.

AFDD Diagram

Inputs - The measured inputs for the SMDS are:

  1. outdoor-air temperature
  2. total RTU power use
  3. supply-fan speed signal as a percentage of full speed, all measured at 1-minute time intervals

Outputs - The outputs from the SMDS include:

  1. indicators that a performance change has occurred
  2. the increase or decrease in energy use resulting from the performance change
  3. indications that each of the operation faults has occurred or not occurred
  4. supplemental information regarding the nature of each operation faults and the significance of its impacts

Configuration Parameters

No configuration or set-up data entry by the user is required. All information on the nature of each RTU is measured or inferred.

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