Miguel A. Camelo Rosas
MMESS - Fall 2014
Homework 6
1.- Go over your calculation of the global amount of Carbon emissions associated with the
consumption of solid fuels based only on world energy consumption, the proportion of said
energy supplied by petroleum, coal and natural gas, the heating value of the fuels and reasonable
assumptions about their carbon content. Express the results in kg of CO2 and kg of C and
compare your results with the best published data you can find. Compare also your results to the
other carbon flows on earth among land, the ocean and the atmosphere. (See excerpts from books
by Archer and Trenberth posted at
http://www.ewp.rpi.edu/hartford/~ernesto/F2014/MMEES/Readings/W08/ )
2.- Read through carefully the reports
“Examining the feasibility of converting New York State’s all purpose energy infrastructure to
one using wind, water, sunlight” by Jacobson et al. and
“Electricity Production from Solar and Wind in Germany 2014” by Burger archived in
http://www.ewp.rpi.edu/hartford/~ernesto/F2014/MMEES/Readings/W08/
and prepare a 500 word long summary highlighting the main findings for each report.
3.- Revisit the calculation of conversion of solar irradiance (in kW-hr/m2 day) into electric
power (in kW) and energy (in kW-hr) using a PV system we examined in class and carry out the
calculations for the specific house of a regular household where you live. Identify appropriate
values of the average solar irradiance and sunny hours to use in your calculation as well as
energy conversion efficiency of the PV system and determine what fraction of your electricity
use can potentially be replaced by solar energy.
4.- Revisit the ground coupled heat exchanger problem we examined in class. Consider a simple
system consisting of a water-based ground cooled heat exchanger like the one described in the
paper by Naili et al. posted at
http://www.ewp.rpi.edu/hartford/~ernesto/F2014/MMEES/Readings/W08/ .
A simple lumped parameter model of the heat transfer from the ground into water flowing inside
the buried pipe can be developed from an energy balance on a differential segment of pipe of
length dx and yields the following first order differential equation:
Mw Cw dTw/dx = U Pp (Tg – Tw)
That must be subject to the inlet condition
Tw = Ts
where
Mw = mas flow rate of water ( kg/s)
Cw = specific heat of water (J/g oC)
Tw = temperature of the flowing water at distance x from the inlet (oC)
U = overall heat transfer coefficient from the buried pipe into the flowing water (W/m2 oC)
Pp = perimer of the buried pipe (m)
Tg = temperature of the ground around the buried pipe (oC)
Assume appropriate values of water temperature at the surface and at a selected depth into the
ground and use values from the above mentioned paper for all the other parameters. To make
things simpler assume U is constant and select an appropriate value. Then solve the equation
either analytically or numerically to find the length of pipe required to deliver water at the exit
with temperature within 1 oC of the temperature of the ground at depth.