Trend logging is a diagnostic tool that uses data gathered at short intervals, such as every 15 minutes, to understand how a building or one of its systems is operating. This data can help you identify potential efficiency problems. Four sources of data that would be useful for trend logging your building are:
Some utilities use interval meters for all commercial customers, while others limit interval meters to large commercial buildings. If you are on time-of-use billing, you have an interval meter. If you are not sure, check with your local utility representative.
Demand meters record data every 15 minutes or 1 hour. Data from interval demand meters is available in electronic format. Ask your utility for your data. Many utilities provide software that will let you download the interval data from their website.
You should be able to export the interval data into a spreadsheet or a trend-logging tool. Alternatively, some software suppliers may, with your permission, receive the interval data directly from your utility.
Your DDC system can be programmed to collect trend logs for any sensor or control point. Outdoor air temperature, differential pressures, and run time are all examples of what can be captured in a trend log and used to identify and diagnose problems with operation and maintenance. In fact, your DDC system has such extensive trending-logging capabilities that the greatest challenge is to determine which senor or control points are important enough to examine. Many examples of important trend logging for your DDC can be found in the Symptom-Diagnosis Tool. Contact your DDC vendor to learn more about setting up these features.
Utility-bill-tracking tools generally provide access to and updates of weather data. In addition, outside air temperature and humidity may be available from your DDC. If you need this data to analyze your trend logs, and it is not available from either the tracking tool or your DDC, you may be able to get it from one of these sources:
- The National Climatic Data Center is a prominent source of weather data in the country.
- The University of Washington and Oregon State University offer regional weather data through their web sites.
- The University of Dayton offers average daily temperatures for over 150 American cities.
Some businesses, such as those with large, multi-building campuses or with a number of large electrical uses, have submeters. Submeters measure end use or zone-specific electric use and help identify areas or processes that use excessive energy. Data from an electrical submeter can be collected through the DDC system, if it is connected to the submeter. In some cities, private meter-data service providers install and read submeters. Some businesses may have utility-installed submeters. In such instances, you may be able to obtain data from your utility, or with utility permission, install a shadow meter or data logger to monitor and extract the usage.