This paper describes a method to improve the accuracy of predicted space-heating energy usage in existing buildings simulated using eQuest, an energy modeling program. The method is an adjustment of actual energy usage data using heatingdegreedays( HDD)encoded in the inputted TMY weatherfile and short-term weather data collected on site. TMY weather files, in many cases, do not give an accurate representation of actual site temperatures around a building. An energy model that accurately reproduces energy use for an existing building under pre-retrofit conditions allows greater confidence in the predicted impacts and effects of any proposed changes. This is particularly valuable to stakeholders in the building industry, including contractors, consultants, owners, and managers. The method presented is simpler and less time intensive than obtaining (if available) multiple years of hourly weather data or collecting those data onsite and then creating a custom TMY weather file. Rather, this method normalizes the model output using a shorter period of on-site weather data. Results of this method in the example used improved the modeled energy usage to within -0.14% (95% CI: -0.98%, +0.68%) of metered energy usage.

This approach to adjusting actual energy consumption data to the weather file offers a high level of confidence in the model's accuracy,which is vital to designandeconomicdecision-making.