Denver Airport Office Building
Pacific Northwest National Laboratory (PNNL) tested the Outdoor Air Economizer (OAE) module in the 2000. The Whole Building Diagnostician (WBD) including the OAE was installed at two building at the demonstration site. The first building that was part of this demonstration project is the three-story administration office at the base of the air traffic control tower (ATCT Base). Although the control tower has four air handlers, security restrictions did not allow for those to be monitored using the WBD because they serve critical functions of air traffic safety. The second building was the traffic control (TRACON) building, which has two large air handlers serving the conditioned space. Security concerns similarly limited that installation to the two air handlers that serve general office space. A summary of general building information and the three air handlers is described in the table below. All air handlers involved are variable-air-volume (inlet vane control) served with chilled water from central chillers. They have heating coils, but these are not used. Heating is provided at the terminal units rather than at the air handlers.
WBD Results
Characteristics of FAA-Denver Buildings and Air Handlers as Initially Reported by FAA-Denver
| Building Name | Building Floor Area (ft2) | Heating/Cooling System | No. Air Handlers Total (Demo) | Demo Air Handler Flow Rate (ft3/min) | Economizer Type | Control System |
| ATCT Base | 26,000 | 60-ton reciprocating chillers chilled-water distribution VAV system with terminal gas heat from natural gas | 4 (1) | 18,000 | Differential temperature | Johnson MetaSys |
| TRACON | 67,000 | 200-ton centrifugal chillers chilled-water distribution VAV system with terminal heat from natural gas | 5 (2) | 18,800 18,600 |
Differential temperature | Johnson MetaSys |
The control strategy for each air handler based on the system design blueprints is shown in the table below. The design strategy provided for an unoccupied mode, with a zone thermostat setback and the fan cycling on and off to maintain it, but the buildings were operated in fully occupied mode all the time. The outside-air dampers were to close as necessary to keep the mixed air above 45oF, and the discharge air was to be reset between 54oF and 62oF based on demand from the zone thermostats.
| Control Parameter | ATCT AHU-1 |
TRACON AHU-1 |
TRACON AHU-2 |
| Type of economizer | none | none | none |
| Outside-air temperature control | mixed air | mixed air | mixed air |
| Mixed-air set point | 45oF | 45oF | 45oF |
| Discharge-air set point | 54oF - 62oF | 54oF - 62oF | 54oF - 62oF |
| Minimum outside-air damper position (occupied) | 11% | 13% | 10% |
| Closed outside-air damper position (unoccupied) | 0% | 0% | 0% |
| Floor area served (ft2) | 12,300 | 16,875 | 13,875 |
| Air flow rate (ft3/min) | 18,000 | 18,800 | 18,600 |
| Occupied schedule (hours/day, days/week) | 24/7 | 24/7 | 24/7 |
Summary of Results
Inefficient operation and improvement opportunities were identified with all air handling units (AHUs) monitored, either through the process of installing WBD, detected by the WBD itself (proving system functionality and effectiveness), and/or during the process of analyzing savings. However, one very important item to note is that few problems were corrected by the building operators. The air handlers had multiple problems and faulty air temperature sensors, which cast some doubt as to whether they were the cause of a number of the problems detected. Even if the AHUs have multiple problems, the software is designed to detect only the first (most significant) problem it encounters. Therefore, because few problems were actually fixed, we could only speculate as to the number of additional problems that would have been identified by the WBD had the problems been fixed.
In addition, although the OAE module estimates the energy and cost impacts of the problem identified, they are meaningless when a temperature sensor problem exists, which was the most prevalent problem initially identified. Therefore, the potential energy savings from correcting the problems identified with the air handlers was estimated (rather than generated by the WBD).
The overall annual savings for the air handlers, as calculated by our estimates, varied from $750 to $1750. The estimate for the three air handlers analyzed is roughly $3750 per year. At this rate of savings, the payback for use of WBD is estimated to be 2 to 3 years, if no capital costs are associated with the corrections.
The savings are also estimated on the basis of per ft2 of floor area served and per ft3/min of total air handler flow rate. These savings were about $0.065/cfm/yr and $0.095/ft2/yr-floor, respectively. Because savings are generally proportional to flow rate (assuming the outside-air fraction is proportionate), and since floor area is generally proportionate to flow rate, these figures will scale to other projects. Selecting sites with larger air handlers (larger air flow rates) will likely increase savings relative to costs. Involving all air handlers at a site, when their operating control strategies are similar and underlying control system is of the same type should also increase savings relative to costs.
Air side economizers can provide large savings of cooling energy in a climate such as Denver’s, and excess outside air can cause large amounts of extra heating and cooling to be required. The process of installing and utilizing the OAE diagnostic module identified these and many other problems with the air handlers.
The WBD and the OAE module were shown to successfully identify a number of major problems with the air handlers. Although the demonstration site was not an ideal site, these finding are consistent with the other field demonstrations of the WBD where OAE found similar problems that should have been detected at the time of commissioning. The demonstration showed that diagnostic technology is only as good as the fixes to the problems it identifies. That is, it is insufficient to merely identify problems and their impacts and expect operators will fix them as a result. 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 result in system efficiency improvements. Improvements can only be realized in the buildings where identified problems are corrected. Future demonstrations or broad deployment of the WBD must include a mechanism for ensuring identified problems get fixed. This could come from within an agency or be provided as part of the deployment, but appears 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)