ASHRAE Journal - October 2019 - 68

COLUMN ENGINEER'S NOTEBOOK

conversion of the source energy to heat, the subsequent
conversion to electricity will be inefficient.
* Most renewable energy sources, with the exception
of low-grade solar thermal, are converted first to electricity after harvesting.
* Because of the multiplicity of non-GHG-generating
sources that convert initially to electricity, reduction
of societal GHG production is more easily approached
through "greening" of grid power sources than it is
through "greening" of a gas pipeline system. The feasibility of large scale removal of CO2 from the atmosphere
after it has been emitted has not yet been proven nor
have the actual costs been identified.
* Many energy conversion processes involve the
production of significant amounts of waste heat that
is usually wasted into the atmosphere or into surface
water resources. Co-location of electric generation
sources with low-grade heat consumers enables cost
effective energy conservation through heat recovery.
District heating systems fed by waste heat from power
plants are common in many European cities, and
micro-turbine cogeneration of domestic hot water has
been successful in New York City high-rise apartment
buildings.
Application of these principles tends to invert scale
and location preconceptions that have limited our efficient utilization of our energy resources. The current
trend for energy conversion location puts our renewable conversion devices (wind turbines and photovoltaic
cells) on our buildings diminishing their performance,
while remotely locating our heat engine electric generation, precluding utilization of recovered waste heat.
Wind turbines belong on the Great Plains, mountain
ridges or the continental shelf. Photovoltaics should be
deployed in low-latitude deserts, with a south-facing
slant. Heat engine electric generation belongs in our
buildings in cities where the waste heat can be harvested
to heat our bathwater.
Some widely heralded innovations come up short
when exposed to the analysis described above.
Hydrogen, for example, while it has a high energy density by mass, has less than 20% the energy density of
gasoline by volume, doesn't store or transport easily, and
has a round trip efficiency (reversible fuel cells) that is
worse than lead-acid batteries (50%). It isn't a source,
because it is produced by applying electricity to water, or
by conversion of natural gas, and has sourcing efficiency
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issues. The popularity of hydrogen as a potential remedy
for our energy woes is based upon a simplistic analysis
focusing on only one aspect of its entire supply chain:
direct conversion of hydrogen to electricity produces
only water and no carbon dioxide. Positing it as a potential cure ignores its deficiencies for conversion efficiency, sourcing overhead, transport and storage.
Application of this framework also gives significant
insight into the nature of our energy "crisis." Some of the
immediate conclusions are:
* Single technology "revolutions" are unlikely to
significantly impact the global energy and greenhouse
gas equation unless they address conversion efficiency,
sourcing overhead, transport and storage.
* Exergy analysis of conversion processes uncovers
simplistic efficiency fallacies and reveals hidden opportunities for savings.
* A revolution in electrical storage energy density
would bring electric conversion efficiency, and sourcing
overhead advantages to both mobile and stationary end
uses, resulting in significant reduction of greenhouse
gas generation.
* Optimal siting of renewable and conventional
electric generation assets can reduce greenhouse gas
production by optimizing efficiency and enabling waste
heat recovery.
While recent technical advances for fossil fuel production have likely delayed the dreaded onset of "peak oil,"
the issues with greenhouse gas production and climate
change have been exacerbated. Emerging economies
have little interest in energy conservation that precludes
"first world" lifestyles. Reconciliation of world needs
with the legitimate individual desires requires consideration of global energy problems in a systemic context.
Potential improvements to our energy problems should
be evaluated for their effectiveness, not as isolated processes, but as components of a global supply and consumption chain.3

References
1. Fraunhofer-Gesellschaft. December 19, 2010. "Which methods
of heating are most efficient?" ScienceDaily Retrieved December 20,
2010. https://www.sciencedaily.com/releases/2010/12/101213121706.
htm.
2. Lajunen, A., P. Sainio, L. Laurila, J. Pippuri-Makalainen. 2018.
"Overview of powertrain electrification and future scenarios for
non-road mobile machinery." Energies (5).
3. Nall, D. 2013. "A new approach to evaluating societal energy
solutions." ASHRAE High Performing Buildings Newsletter (Summer).

https://www.sciencedaily.com/releases/2010/12/101213121706.htm https://www.sciencedaily.com/releases/2010/12/101213121706.htm https://www.ashrae.org

ASHRAE Journal - October 2019

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