The "green" building movement has two opportunities for energy savings: one before the meter and one after. Before the meter is the utility cost. After the meter is the cost of running the HVAC system and lighting. Optimizing HVAC (about 40% of the consumption) for energy and IAQ is an important outcome for green buildings. One way to assess the performance of the HVAC system is to monitor key parameters, e.g. temperature, humidity, ventilation, particles - in the breathing zone.