The University of Texas at Austin
College of Engineering



Welcome to Building Mass and Energy Balances

Engineers model the physical world by describing real-world phenomena with scientific principles and mathematics. Two of the basic principles used extensively in many engineering disciplines are the conservation of mass and energy. These two laws of conservation can be used to write and solve mass and energy balance equations that describe many different commonly encountered scenarios. For example, architectural and indoor environmental engineers apply mass and energy balances to determine various properties of buildings, such as concentrations of pollutants in the indoor air or a building's heating or cooling load. This software application is intended as an educational tool, allowing students to explore various components of mass and energy balances as related to indoor environments.


This section provides pre-defined scenarios as well as steady-state and transient mass balance calculators. In Scenarios, there are four real-world examples that will show you how varying certain key parameters of a building influence the concentrations of several common indoor air pollutants. With the Steady-state and Transient calculators, you have freedom to vary the parameters of the building to calculate the resulting indoor air concentrations of pollutants for specific cases.



This section provides one large scenario that allows you to change different parameters on a typical house in either Austin or Chicago and to determine the resulting heating and cooling loads. Parameters that can be changed are (1) type of wall assembly, (2) window type, (3) thickness of attic insulation, (4) air exchange rate, or (5) types of internal energy gains.