Energy and Human Ambitions on a Finite Planet, 2021a

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6 Putting Thermal <strong>Energy</strong> to Work
We have already encountered thermal energy in two contexts. The
first was infrared radiation (Eq. 1.8; p. 10), <strong>and</strong> the second was in the
definition of the kilocalorie (Sec. 5.5; p. 73). Otherwise, heat has often
been treated as a form of “waste” in a chain of energy conversion:
friction, air resistance, etc. The insinuation was that heat is an unwanted
byproduct of no value.
Yet 94% of the energy we use today is thermal in nature [34]:weburn
a lot of stuff for energy! 1 Sometimes heat is what we’re after, but how
can we use it to fly airplanes, propel cars, <strong>and</strong> light up our screens?
This chapter aims to clarify how heat is used, <strong>and</strong> explore limits to the
efficiency at which heat can perform non-thermal work.
Like the previous chapter, this topic represents a slight detour from
the book’s overall trajectory, which otherwise aims to build a steady
narrative of what we can’t expect to continue doing, what options we
might use to change course, <strong>and</strong> finally how to bring about such change.
Nonetheless, the way we utilize thermal energy is a key piece of the
story, <strong>and</strong> relates to both current <strong>and</strong> future pathways to satisfying our
energy dem<strong>and</strong>s.
6.1 Generating Heat ........ 84
6.2 Heat Capacity .......... 85
6.3 Home Heating/Cooling .... 86
6.4 Heat Engines .......... 88
Entropy <strong>and</strong> Efficiency Limits 90
6.5 Heat Pumps ........... 95
Consumer Metrics ....... 97
6.6 Upshot on Thermal <strong>Energy</strong> . 99
6.7 Problems ............. 99
[34]: U.S. <strong>Energy</strong> Inform. Administration
(2011), Annual <strong>Energy</strong> Review
1: The exceptions are wind, hydroelectricity,
<strong>and</strong> solar.
6.1 Generating Heat
Before diving in to thermal issues, let’s do a quick run-down of the
various ways we can generate heat.
Example 6.1.1 Ways to Generate Heat: Roughly arranged according
to degree of sophistication:
A locomotive engine as an example heat engine. Photo credit: South Australian Government
Photographer.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.