The Intelligent Use of Energy: Thermodynamics Made Simple
Richard R. Vaillencourt, PE,
Canterbury Engineering Associates
Editor’s Note: This is first in series of articles on intelligent
energy use in buildings by consulting engineer Richard Vaillencourt. We
hope you’ll find them helpful as you work to optimize your building’s
There are many measures Hartford Steam customers can take to be sure
they use their thermal energy efficiently and wisely. But they can start
by embracing one simple rule of thermodynamics: Energy always moves from
hot to cold.
The neat thing is that this rule cannot be broken. It cannot be
negotiated. It cannot be bent. But once you understand it, using energy
intelligently becomes relatively easy.
You make something hot by putting something hotter next to it. The
energy will move from the warm object to the cool object, making the
warmer object colder and the colder object warmer.
You make something cold by putting something even colder next to it.
That’s the same principle: One object is warmer than the other; the
colder object sucks the energy from the warmer object, making the warmer
object colder and the colder object warmer.
For example, the coldest parts of your refrigerator are the inside
walls. They suck the heat out of the air in the refrigerator. The air is
next to the bottle of milk that you put in the refrigerator, and it
sucks the heat out of the milk. The inside walls don’t get warmer
because the energy that is pulled into them is constantly being sucked
away into the compressor and pushed out by the condenser into your
Notice that heat behaves like water contained in two connected tanks: It
tries to reach a common level between the two objects. Also notice that
the heat from the warm objects placed in the refrigerator does not
disappear. It is simply (well, not so simply) moved from inside the
refrigerator to outside and dumped into the kitchen. If your kitchen is
air-conditioned, then the heat is picked up and transferred to the
There is also an important corollary to the first rule: The greater the
temperature difference between the hot and cold sides of the transfer,
the greater and faster the energy moves from the hot to the cold.
Applying these simple thermodynamic principles can help you lower your
building’s energy bill. How? The first and easiest thing to do is to try
to keep the indoor temperature as close to the outdoor temperature as
you can get away with. (If you actually kept your inside temperature
equal to the outside temperature you would reduce your energy need to
zero – but you would probably also need a new job.) This is where night
setback controls can help you save energy. They reset thermostats closer
to the outside temperature when no one is in the building to complain.
On the other hand, if you let the space temperature on the inside become
significantly warmer in the winter – or colder in the summer – than the
air temperature on the outside of your building (either through
calibration errors, or unrestrained occupant control, etc.), then the
energy transfer through the walls to the rest of the world is
significantly greater. And that means you’re using – and paying for –
more energy than you need. (Something to consider as the thermometer
starts to edge toward the freezing mark!)