Residential building energy analysis : development and uncertainty assessment of a simplified model

Abstract

Effective design of energy-efficient buildings requires attention to energy issues during the preliminary stages of design. To aid in the early consideration of a building's future energy usage, a simplified building energy analysis model was developed. Using this model, a new computer program was written in C/C++ to calculate annual heat and cooling loads for residential buildings and to provide information about the relative importance of load contributions from the different building components. Estimates were made regarding the uncertainties of parameter inputs to the model, such as material properties, heat transfer coefficients and infiltration rates. The new computer program was used to determine the sensitivity of annual heat and cooling loads to model input uncertainties. From the results of these sensitivity studies, it was estimated that the overall uncertainties in the annual sensible heat and cooling load predictions amount to approximately ±30% and ±40%, respectively, for two buildings studied in Boston, Massachusetts. Further model simplification techniques were implemented that reduced annual load calculation times on a 180 MHz computer to about 8 and 12 seconds for a lightweight and massive building, respectively. The error introduced by these simplifications was approximately 4% and 10% for the annual sensible heat and cooling loads, well below the overall uncertainties in the load predictions. Comparison studies were performed with this new computer program and Energy-10. Overall, good agreement between the programs' annual load predictions was found.