MBCx at San Diego State University Arts and Letters Building
According to research conducted by the Lawrence Berkeley National Lab, monitoring-based commissioning (MBCx) in UC and CSU buildings yields energy savings with a median simple payback of 2.5 years, making a compelling case for investment in such projects. A recent example of a successful commissioning effort may be seen at the Arts and Letters Building at San Diego State University, where campus and utility incentives led to a simple payback of approximately two years. The project was implemented with engineering consultants from P2S Engineering and installation provided by campus facilities staff and the controls contractor.
Continuous monitoring and improvements are required even in relatively new buildings to maintain optimal energy and comfort performance.
The building’s age, occupancy and and systems did not immediately make it an obvious choice for an MBCx candidate. Constructed in 2006, the building houses offices, lecture halls and conference rooms — uses that do not typically lead to high energy use seen in other campus building types such as laboratories and food service kitchens. Also, the building’s systems were originally designed to provide relatively good energy performance, equipped with direct digital controls (DDC) and mostly variable volume control. However due to past control system changes, the building was no longer being operated in an optimal manner. For example, the building was operating with a narrow temperature deadband of only 1.5°F, operating schedules had been extended beyond occupied hours, and the supply air temperature reset was causing every supply fan to operate at maximum speed.
Chart showing total electricity savings before (light green bars) and after (dark green) the MBCx process.
Chart showing gas savings before (light red bars) and after (dark red) the MBCx process.
The commissioning process identified and implemented a series of recommendations, most of which could be done through control system changes, with only a few physical changes to the building needed. First, the building had two control panels that served different parts of the building and were not integrated. The building management system (BMS) also did not provide remote access, and did not have the capabilities needed to implement some of the MBCx recommendations. For these reasons the control system was replaced with a Tridium BMS that provides the required capabilities, and is expected to allow building operators to better manage the building in the future through remote access.
Numerous operational changes were implemented with the new control system. The air handling schedules were reduced by 30 to 40 percent, and were programmed to adjust based on the predicted weather for the following day. The supply air temperature reset was lowered from a range of 50-90°F down to 52-65°F, greatly reducing the average speed of the supply air fans, which were previously operating at maximum speed much of the time. Similarly, temperature settings in data closets were raised from 74°F to 85°F, saving energy in 12 fan coil units that ran almost continuously before commissioning. These changes provided additional savings through reducing the obvious inefficiencies that result from simultaneous heating and cooling.
A number of changes were implemented to improve the economizer system operation. Failed outside and return air dampers were repaired, the system was reprogrammed, and outside airflow monitoring was added to each air-handling unit in order to verify correct and optimal operation.
Combined, a total of eight energy conservation measures implemented in this MBCx project reduced the building energy use intensity from 106 to approximately 67 kBtu/ft2/yr, a reduction of 36 percent, with estimated annual utility savings of $39,000. Tom Abram, the Assistant Director of Facilities Services who is responsible for Campus Sustainability at SDSU, notes that an important lesson learned from the project is that even buildings equipped with variable volume and DDC systems may still provide significant energy savings through the MBCx process.
Building photo by Nehrams2020.