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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 energy use.

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 kitchen.

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 outside world.

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!) More Articles/Resources


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