Tuesday, September 15th, 2009
September 15, 2009 was a cooler summer day. Temperatures ranged from the mid-sixties to low eighties, and electric prices remained fairly constant (fig 1). Because of the lower overnight temps, the Optimizer chose to pre-cool the building for only two hours (fig 2). In spite of the mild temperatures and low electric prices that day, the Optimizer still achieved 16% cost savings and a 12% reduction in HVAC electricity consumption (fig 3).
Outside Temperatures & Market Prices – Figure 1 CUE uses forecasts of outside temperature, humidity, and solar radiation to anticipate building cooling loads. Forecasts of volatile hourly electric market prices create a CUE arbitrage opportunity – we shift cooling loads to low-priced hours using use building thermal mass. We execute this shift by sending OPT temperature setpoints to the building automation system from our central servers. |  |
 | Zone Temperature Setpoint Control – Figure 2 NSU (Night Set-Up) defines the normal temperature setpoints (or thermostat settings) that are programmed into the building automation system. Typically the setpoints are set up at the end of occupancy – thus shutting down HVAC operation – and set down in the early morning – to restart HVAC operation in advance of building occupancy. OPT (OPTimal) defines the setpoints recommended by CUE to reduce a building’s HVAC expense. |
HVAC Electricity Consumption – Figure 3 Using CUE’s set-point strategy, this building reduced its HVAC expense for the day by 16% and its total kilowatt-hour usage by 12%. |  |