18.3. Using Thermal Energy http://www.ck12.org
Heating Systems
Warming homes and other buildings is an obvious way that thermal energy can be used. Two common types of home
heating systems are hot-water and warm-air heating systems. Both types are described below. You can watch an
animation showing how a solar heating system works at this URL: http://www.montereyinstitute.org/courses/AP%
20Environmental%20Science/course%20files/multimedia/lesson67/animations/4e_solar_heating_system.html.
Hot-Water Heating System
A hot-water heating system uses thermal energy to heat water and then pumps the hot water throughout the building
in a system of pipes and radiators. You can see a diagram of this type of heating system inFigure18.12. Typically,
the water is heated in a boiler that burns natural gas or heating oil. There is usually a radiator in each room that gets
warm when the hot water flows through it. The radiator transfers thermal energy to the air around it by conduction
and radiation. The warm air then circulates throughout the room in convection currents. The hot water cools as it
flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and
the cycle repeats.
FIGURE 18.12
When water is heated in the boiler, it
expands. It might burst the pipes of the
system if it weren’t for the expansion tank.
This tank holds excess water after it ex-
pands.Warm-Air Heating System
A warm-air heating system uses thermal energy to heat air. It then forces the warm air through a system of ducts.
You can see a diagram of this type of heating system inFigure18.13. Typically, the air is heated in a furnace that
burns natural gas or heating oil. When the air is warm, a fan blows it through the ducts and out through vents that
are located in each room. Warm air blowing out of a vent moves across the room, pushing cold air out of the way.
The cold air enters an intake vent on the opposite side of the room and returns to the furnace with the help of another
fan. In the furnace, the cold air is heated, and the cycle repeats.