Page 112 - Zero Net Energy Case Study Buildings-Volume 1

CASE STUDY NO. 5
SCIENCE & ENGINEERING BUILDING I
Post-Occupancy Adjustments to Lower Energy Use: HVAC Systems
The value of recording and reviewing the energy use patterns of the building systems is obvi- ously to identify locations of higher consumption than expected and opportunities to improve the overall efficiency by changing components or operations. UC Merced has been continuously en- gaged in this monitoring and evaluation activity since 2006, when the building opened, and has steadily made system changes that have resulted in improvements in the energy performance.
The charts in the previous section reflect the improved performance and the building’s EUI (site energy) has been reduced to 185 kBtu/gsf-year. The following subsections describe the principal issues and adjustments made to the building systems based on observed data over the past six years.
Correction of Basic Control System Issues
One of the largest consequences of the interruption of the commissioning process was the dis- covery after occupancy that the building’s control system was incompatible with the campus BMS. Buildings on the UC Merced campus are controlled using a central BMS so that all build- ings can be scheduled from one center. Based on the instructions from the BMS, the individual building’s control systems are supposed to operate the various system components according to those instructions. For Science & Engineering Building I, there are two local building control systems—laboratory ventilation and space lighting.
Metered data immediately revealed that schedule changes made with the BMS were not result- ing in any effect on the local building control systems. The communication “protocols” of the two systems were different: the campus BMS uses “BACnet protocols” while the local laboratory ventilation control system uses “LonTalk protocols”. A great deal of time was required for the staff at UC Merced, working with the engineers of the control system manufacturers, to recommission the controls and solve the compatibility problem. The solution ultimately was to set up a separate computer specifically to coordinate the control systems.
The importance of this problem solution was that many energy efficiency measures of the build- ing design could not be implemented nor could the building be placed into a setback mode as allowed by the building schedule.
For example, the important low-energy strategy of night purging, a method of pre-cooling the building at night with the use of low-temperature outdoor air, could not be used to reduce the peak cooling load on the following day and reduce cooling energy demand. Normally, the labo- ratory ventilation at night could be reduced to four air-changes per hour (4 a.c./hr) from the day-operating rate of 6 a.c./hr and still carry out the night purging operation. This is a significant amount of fan energy; once the communication problem was solved, the electric energy use by the fans and the peak power demand on the Central Plant were greatly reduced.
For UC Merced, this problem was the most significant one encountered because it affected the low-energy operation of the building as intended in the design and because it required so much time to solve. It was at least two years in the observation, solution and implementation to bring about the basic system operation as intended.
The principal outcome of this experience is that UC Merced has enacted the future requirement that any control system specification for new UC Merced buildings in subsequent phases must be entirely BACnet protocol to ensure compatibility with the central campus system.
Correction of Location of In-Duct Sensors
Energy meter data also revealed that an excessive amount of air was being delivered to some spaces. A study of this issue revealed that the differential pressure sensors located inside the air ducts and used to control the amount of airflow were not positioned properly. Moving the sensors to a position just before the last VAV valve ensured a proper reading of airflow and therefore the most efficient functioning of the system.
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Zero Net Energy Case Study Buildings: Volume 1