Page 55 - Zero Net Energy Case Study Buildings-Volume 1

STEVENS LIBRARY AT SACRED HEART SCHOOLS
CASE STUDY NO. 2
Post Occupancy: Observations and Conclusions
Post-Occupancy: Controls and Monitoring
When the second set of power meters were installed, a discrepancy was noted between its read- ings and the data being recorded by the BMS. The difference was determined to be caused by the current transformers (CTs) of the first set of meters, a common error in low energy buiding monitoring. When these meters were replaced, the result was then a consistency of measure- ment with the two sets of meters.
There have been two initial outright failures of the monitoring and data communication systems. The first was with the recording and communication of data from the solar photovoltaic system, and the second was communication of data from the four campus buildings to the flat screen display of the energy dashboard, which is located in the library building.
The solar photovoltaic panel system initially produced the expected amount of energy but the data was not being sent from the inverter. The problem was compounded when the inverter manufacturer went out of business. A third-party interface and monitoring module had to be de- veloped ultimately to resolve the problem.
The failure of the communication from the BMS systems of the four buildings to the flat screen display located in the library caused some initial consternation with the client since the display of the energy dashboard for these buildings was planned to be part of the curriculum for the middle school students. The communication problem between the BACnet protocols and the dashboard took some time to resolve.
Post-Occupancy: HVAC
Initial occupancy occurred during the late fall of 2012 and winter of 2013, which included some below normal cold days. During times of strong heat demand, the heat pump was found to turn off. Examination of the problem revealed that the internal controller was defective and had to be replaced.
In addition, there were complaints about the building being too cold in the morning. The issue was that the heat pump was taking too long to heat the space from the setback temperature of 55°F, not atypical of this type of equipment compared to a gas-fired boiler. It was determined that the simplest immediate solution was to put the setback temperature at 65°F, with the system startup beginning at the same time. The change in setback temperature resulted in an increase in heating energy consumption as measured, compared to that in the design modeling.
Post-Occupancy: Lighting
One of the remarkable results of the first year’s performance data is that the lighting energy use is so much lower than expected by the energy modeling: less than 1 kBtu/sf annually compared to the modeling total of 10 kBtu/sf. The size of the difference illustrates the general observation that lighting energy use in buildings with good daylighting is often overestimated in the modeling. This seems to be the result of the complexity of the interactions among the lighting system, the available daylight, and the daylight and occupancy controls: sophisticated lighting design soft- ware in the hands of a skilled modeler can yield excellent results, but energy modeling software does not include this level of sophistication.
Post-Occupancy: General
The expectation of owners and users should be that post-occupancy commissioning should continue for at least two seasons, so that there is adequate time for a thorough “shake-out” of the operating systems, particularly the control systems and the overall building management system, allowing the accumulation of enough measured performance data to tune the building properly. This was the case with the Stevens Library, which is now well into its second season of operation and exceeding performance expectations in all aspects.
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