Page 37 - Zero Net Energy Case Study Buildings-Volume 2

Energy Production versus Energy Use: Zero Net Energy
The measurements recorded during this first year of operation indicate that the building is per- forming at roughly 20% better than ZNE, which is called “net positive” performance. The chart below shows the energy produced each month by the building’s PV system compared with the energy used by the building.
The chart showing Cumulative Net Energy Performance over the course of the year (next page) is another graphic indication of net positive performance. In this chart, the net production each month (amount of energy produced minus the amount of energy used) becomes the starting point of the following month’s net production amount. In this case, since the chart begins in May at the start of summer, the curve goes up at first since the net production is positive in the summer months. The curve then flattens and goes down through the winter months as the solar energy production is poor, turning up again as the sunny spring season begins.
If the building were precisely ZNE for the year, the curve would dip below the zero axis in winter and then just come up and touch the zero axis at the end of the measurement year in April. A precisely-ZNE building would therefore produce a basic S-curve. The chart for the DPR Office Building, however, remains above the zero axis, indicating net positive performance.
CASE STUDY NO. 7 DPR CONSTRUCTION OFFICE BUILDING
Solar Photovoltaic System Performance May 2014 - Apr 2015
Zero Net Energy Case Study Buildings, Volume 2 25