Integrating Weather Data with Internet Connected Thermostats to Manage Residential HVAC Load Shifts

One of the largest demands on the electrical grid in the summer is due to residential air conditioning loads. The total power that a residential HVAC unit consumes depends not only on the set point schedule of the thermostat, but on the weather and in particular, the outside temperature and total solar insolence. New connected thermostat technologies allow for unprecedented modeling and analysis of residential HVAC loads. In early 2010, Earth Networks began efforts to apply thermodynamic grey box modeling to residential homes to gain better insight into home energy use and to determine the efficacy of shifting electrical grid power from peak use times to non-peak times in order to even out overall grid demand. This modeling accounts for heat diffusion through the walls, convection on the inner and outer walls, solar irradiance, infiltration, thermal mass, and HVAC system performance. Transient temperatures within the wall are accounted for by solving for the temperatures at nodes within a uniform property wall using an explicit tridiagonal matrix algorithm. Inputs to the model include outdoor temperature, solar insolation, and wind speed data from local WeatherBug (Earth Networks) weather stations, indoor air temperature, and HVAC status data from internet connected thermostats, and electricity data from smart meters. In this study, Earth Networks will present results of a summer demonstration project with Centerpoint Energy to shift residential HVAC loads. Results will also be presented on the ability of the model to present actionable information to a homeowner on steps they can take to reduce their overall HVAC power load.