High Performing Buildings - Spring 2008 - (Page 55) Electric Room The electric room includes the building’s main and distribution panels, two 100 kW ac 277/480V threephase solar inverters, and a transfer switch for a future 200 kW gas-fired emergency generator. Although solar panels generate electricity in dc (direct current) power, most building systems use ac (alternating current) power. Inverters connected to the rooftop solar panels convert the dc (kW dc) power from the solar panels to ac (kW ac) power. The inverters have a capacity of 223.3 kW dc and allow LAN-based communications. Custom software monitors, in real time, the energy use and flow in and out of the building. periods, additional meters are needed to determine building load and the amount of surplus electric energy sent to the grid. Utility Metering The utility company’s gas and electric meters have pulse output signals monitored by the building’s DDC system, providing a visualization tool and important feedback. For the electric meter, as the building’s photovoltaic array output approaches the building load, the pulse meter slows and then stops. During these Solar Thermal Hot Water In addition to the solar photovoltaic system that provides electricity for the building, a solar thermal system provides hot water for domestic use (showers, kitchen and bathrooms). Two 80 gallon preheat tanks serve an 80 gallon backup electric hot water heater via a double wall heat exchanger in the closed loop solar system. The solar The 42,000 ft2 commercial facility produced more electricity than it used in one year. Spring 2008 HIGH PERFORMING BUILDINGS 55
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