Definition of a Energy Balance:
Steps to Writing an Energy Balance:
- Define the system boundaries (the entire building in our case) with a control volume.
- Draw a sketch or schematic.
- Establish all the ways that energy can enter or exit the volume, and establish any internal sources or transformations of energy within the control volume. Usually, these mechanisms are labeled within the drawn schematic to aid this process.
- Write the appropriate energy balance equation.
An energy balance is a mathematical statement of the conservation of energy, and it is a systematic accounting of energy flows and transformations in a system. The theoretical basis for the energy balance is the first law of thermodynamics, which states that energy cannot be created or destroyed, only modified in form. Contrary to mass balances, a system can only have one energy balance that describes it, since different types of energy are considered interchangeable mathematically.
For our purposes, we use the idea of an energy balance to calculate the heating and cooling load for a particular building. Heating and cooling loads for a particular building are dependent on the design, geometry, orientation, and materials of a particular building, and they are calculated for the appropriate design climatic conditions during the winter and summer, respectively. With these heating and cooling loads, an HVAC system can be sized for a particular building that will be able to effectively condition the air for nearly any day throughout the year.
For this scenario, you can change different parameters on a typical house in either Austin, Texas or Chicago, Illinois in order to estimate the resulting heating load, sensible cooling load, latent cooling load, and total cooling load.
