Overview

The energy balance is the fundamental process by which temperatures, pressures, relative humidity, indoor air quality, and other measurable quantities are related to heat transfer and power. The energy balance provides the means to determine the amount of energy that is contained within a specific mass. This mass can be anything such as room air, the glass in a window, a wall structure, or a cup of coffee. Energy content is not measured directly. Instead, temperatures, pressures, and the chemical compositions are measured, which are then related to the energy content.

In the case of a built environment, heating and cooling systems add energy by electrical resistance heating, burning of hydrocarbons, or through the use of refrigeration cycles. Using the energy balance allows us to predict the local temperatures within the built environment. For example, as a cup of hot coffee sets on a desk, heat transfers from the hot coffee to the room air. Since heat (energy) is removed from the coffee, the temperature of the coffee decreases. A second example of this same concept is the air in a room. If the room air temperature is 70 F (21.4 C) and the outdoor air temperature is 0 F ( ?17.4 C), then a certain amount of power (e.g., 1000 W) is transferred through the room walls, ceiling, and floor...