Symphony Tower Office Building
This demonstration of the Whole-Building Diagnostician (WBD) documents the results of the single-building-operator on-line demonstration. The on-line test was designed to evaluate the Outdoor-Air Economizer (OAE) diagnostic module’s capabilities to automatically and continually diagnose operational problems with air handling units (AHUs).
The single-building operator demonstration took place at the Symphony Towers building in San Diego, California. Crowned the “International Building of the Year” by the Building Owners and Managers Association, (BOMA) in 1994, Symphony Towers is a 34-story 601,000 sq. ft., “Class-A”, mixed-use development located at the hub of downtown San Diego’s financial corridor. Its net rentable floor space is 528,869 ft2, mostly leased to tenants who are legal and accounting firms.
Symphony Towers was selected for the demonstration because of its visibility and energy conscious management. In San Diego, Symphony Towers is a superior property, affiliated with numerous associations including the BOMA, The International Facility Managers Association (IFMA), The Association of Energy Engineers (AEE), and the San Diego Building Engineers Association (SDBEA). The building owner is SPP Investment Management, which has a growing portfolio of 37 buildings in the U.S. In the U.S. Region, Symphony Towers is the “King Pin” project for the owner. The building’s HVAC (heating, ventilating and air-conditioning) system consists of two three-stage centrifugal chillers of 550 tons each, and two natural gas hydronic boilers of 3,000 MBtu/hr each. The occupied space is served by four variable-air-volume air handlers, equipped with enthalpy-controlled economizers and variable speed drives (see table below). The air handlers only supply cooling; no heating coil is present. The control system is manufactured by Johnson Controls Metasys, and provides convenient on-demand access to data by the WBD via a DDE (dynamic data exchange) server.
Symphony Towers Air Handlers in the Demonstration| Air-Handler | Rated Flow (ft3/min) |
|
| AHU-1 | 80,000 | |
| AHU-2 | 144,000 | |
| AHU-3 | 144,000 | |
| AHU-4 | 126,000 |
As part of this demonstration, all four AHUs at Symphony Towers were monitored. The measured data that were collected on a continuous basis included: 1) outdoor air temperature, 2) return-air temperature, 3) mixed-air temperature, 4) supply-air temperature, 5) chilled-water valve position, 6) supply-fan status, 7) outdoor-air relative humidity, and 8) return air relative humidity. The relative humidities of the air streams were needed because the AHUs at Symphony Towers used enthalpy-based economizer control. Because the building was heated using hot water that was supplied directly to the terminal units, hot-water valve position was not monitored at this site. The air-handler control strategy for outdoor-air ventilation and economizing, and the schedule (times of day and days of week) for which the minimum outdoor air must be supplied for the occupants were entered into the WBD’s configuration for each air handler. This information was largely obtained from Symphony Towers’ staff; some items were ascertained by observation of the raw data delivered, as is typical in most WBD installations. Symphony Towers was found to not have a fixed schedule for outdoor-air supply. For on-line tests, data from the AHUs were automatically collected and logged into the diagnostician’s database using a data acquisition module, which is part of the WBD. Although data requests can be made at any frequency, at Symphony Towers, the data were requested at 5-minute intervals and integrated over the hour before being processed by the OAE diagnostic module. The on-line data collection process started in April of 2000 for all four AHUs. The data collection process worked well when all parts of the software were properly running. There were several occasions where the data acquisition module on the operator’s workstation was manually terminated and this went undetected for several weeks. Although several weeks of data were lost as a result of this problem, all four AHUs have more than a year of data.
All four AHUs at Symphony Towers had unresolved problems. The predominant problem for each of the four AHUs are: 1) AHU-1 had the minimum damper position set too high, 2) AHU-2 had a temperature sensor problem (most likely the mixed-air temperature sensor), 3) AHU-3 had a temperature sensor problem (either outdoor- or mixed-air sensor) and 4) AHU-4 also had a temperature sensor problem (the outdoor-air sensor).
When an AHU has a faulty temperature sensor, cost impacts cannot be calculated directly. More detailed analysis using estimation procedures is required to estimate the energy impacts from faulty temperature sensors. As a result, energy impacts were not estimated for the three AHUs with faulty temperature sensors. Energy impacts for AHU-1 were estimated using a simplified method implemented in a spreadsheet. The annual cooling energy impact for this problem for typical San Diego weather is about 81,000 kWh, and the corresponding annual cost impact is about $12,000.
Although the problems identified by the OAE diagnostician were known to the building operators, only one problem (which was found during the off-line test and corrected immediately after it) was corrected during the demonstration. Energy manager for Symphony Towers indicated that the WBD tool set was useful and added that he would like more diagnostic tools such as WBD for other heating ventilation and air-conditioning (HVAC) systems. The operator also indicated that the user interface for both the WBD and the OAE diagnostician were easy to use. Although the problems identified by the OAE diagnostician were know to the building manager and operators, only one problem was corrected (immediately after the off-line test). In addition, the building operators were trained on how to view OAE results and interpret the information it provides; none of them actually reviewed the results during the demonstration. This may be a critical missing link in the process of using such tools that needs further investigation in future applications.
The OAE diagnostician successfully identified problems with all four AHUs at Symphony Towers. These findings are consistent with the other field demonstrations of the WBD where the OAE found similar problems that should have been detected during commissioning. The demonstration showed that diagnostic technology can provide useful information on equipment status but its value isn’t realized unless building staff implement fixes to the problems. It is insufficient to merely identify problems and their impacts; building staff must correct them. If users are not proficient in using their control systems to correct problems, are too busy with other duties, or lack resources to obtain help from contractors, diagnostic technologies alone will not provide system-efficiency improvements. The staff at Symphony Towers were occupied with renovation and upgrading activities during this demonstration and did not find time to correct the problems detected by the OAE. If timing had been different, staff might have corrected these problems. In general, however, improvements can only be realized in buildings where identified problems are corrected. Future demonstrations or broad deployment of the WBD must include a mechanism for ensuring that identified problems get fixed. This could be done by building staff or outside service providers, but it is necessary if diagnostics are to do more than simply identify problems and actually proceed to deliver energy savings.
Click here for the "Enhancing Building Operations through Automated Diagnostics: Field Test Results" paper. (PDF 508KB)