Week 12 Conservation of Energy Energy Cost of Agriculture - PowerPoint PPT Presentation

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Week 12 Conservation of Energy Energy Cost of Agriculture


Week 12 Conservation of Energy Energy Cost of Agriculture – PowerPoint PPT presentation

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Title: Week 12 Conservation of Energy Energy Cost of Agriculture

Week 12Conservation of EnergyEnergy Cost of
  • About 12 of conductive heat losses occur
    through the ceiling and 17 occurs through the
    walls of a house
  • The R-value is the figure used to indicate the
    effectiveness of a insulation material i.e. the
    resistance conduction
  • The R value is measured in m2K / W or m2C / W
  • The R value is given for a specific thickness.
    E.g. R value of 2.3 m2K / W for 100 mm thick
    mineral wool. Alternatively it is given as 22.3
    mK / W without giving the thickness.
  • Rate of heat transfer A x (TH TL) / R
  • A Area in m2
  • T Temperatures in C or Kelvin
  • R R value in m2K / W
  • Sometimes the U value for insulation
  • materials are supplied U 1/R

  • E.g. The outside walls of a house measures 10 x
    5 x 3 m
  • The average indoor and outdoor temperatures are
    25 C and 10 C respectively
  • The R value of the brickwork is 0.8 m2K / W
  • What is the heat loss through the walls?
  • Q A (TH TL) / R
  • 2 x (10 5) x 3 x (25 10) / 0.8
  • Q 1.69 kW
  • If insulation with a R value of 2.5 is added,
    what would be the heat loss?
  • Q A (TH TL) / R
  • 2 x (10 5) x 3 x (25 10) / (0.8 2.5)
  • Q 0.41 kW
  • R values add up (like resistors in series) when
    more than one layer with different R values are

(No Transcript)
Typical SA Insulation
Thickness Price/m2 R-Value
Think Pink Aerolite 100 mm R 15.63 2.5
50 mm R 6.25 1.25
Isotherm 100 mm R 23.94 2.2
50 mm R 11.97 1.1
ThermocousTex 50 mm R 44.99 1.35
Note that using 2 plies of Isotherm will give
you an R value of 4.4 for R 47.88. This seems to
be a much better deal than paying R44.99 for 50
mm ThermocousTex with a R value of only 1.35?
This is not always the case, there might only be
limit space for the insulation and then the 50 mm
option are more viable.
Solar Energy
  • The effect of window orientation and has a large
    influence on the indoor heat gain

Heat Pumps
  • The ground temperature 1 m below the surface is
    almost constant throughout the year.
  • In winter, this temperature could be higher than
    the ambient air temperature
  • A heat pump uses the ground as a heat source or
    stepping stone for heating the inside of a
  • This is more economic than directly converting
    electricity into heat using a conventional
    electric heater

Heat Pumps
  • One unit of electricity can give 3 units of

9.7 Commercial and Industrial Energy Conservation
  • Commercial buildings has a much higher standard
    for indoor air quality and light intensity in
    comparison to residential buildings
  • The heat load in commercial buildings are due to
    lights, people (on average 100 W or more per
    person) and electrical equipment
  • District cooling and district heating become
    viable options for commercial applications
  • District cooling is more economic due to
    economies of scale. If night time and thermal
    storage is used, the plant size and running cost
    can be significantly reduced

Cogeneration and district heating
  • Cogeneration (electricity and heat) is a viable
    option in many areas
  • District heating can also be fired by biomass
  • E.g. of a small town close to Munich in Germany.
    A new housing development uses a district heating
    system. The connection fee is E8000 vs the
    conventional E15000 installation cost for an oil
  • The heating cost is 50 of the conventional
    heating cost
  • Heating is done by burning agricultural waste in
    a central heating system. The process is CO2 zero
    and more economic than the conventional oil

Conservation in Industry
  • About half the electricity in the world is used
    to run electric motors
  • The majority of electric motors are constant
    speed motors. The rotate at 3600 rev/min
  • When a constant speed motor is used to power a
    pump, the flow rate is mostly done by valves.
    This wastes a lot of energy. Instead a
    variable-speed drive is the solution
  • New more efficient processes should replace
    existing processes e.g. by forming steel product
    to the desired shape rather than reheating it
    later again

East German Ampellman
LED Replacements
Seattle Bridge
LED traffic lights
LED Light emitting diodes
Energy use in Agriculture
  • First people were hunters
  • Later they settled down and became farmers
  • Later these farmers could support other people by
    their surplus
  • This lead to the enhanced development of cultures

24.1 Traditional Agriculture
  • E.g. of the Tsembaga people in New Guinea
  • Swidden Agriculture (Slash and burn) is practices
  • A section of forest is cut and the remainder
  • Human power is employed for the burning, erecting
    fences, planting, weeding, harvesting and
    transportation of the produce.
  • Total energy input per hectare is estimated to be
    5.8 GJ
  • Total energy output is 100 GJ/ha of which about
    62 GJ/ha is used for human consumption, the
    remainder for animal feed
  • Humans need 6 10 MJ/day (2.1 - 3.6 GJ/year)
  • One hectare of Tsembaga farming can support 17 of
    their people for a year.
  • The population of 200 Tsembaga people use about
    35 hectares of fields.
  • This is small enough to allow the forest to grow
    back and therefore allow for sustainable living!

24.2 Agriculture in North America
  • Humans worldwide use 25 40 of all biological
    material produced on Earth
  • The use of people for agriculture has decreased
    over the years
  • In the US, the 1900 style of agriculture leads to
    75 of the population involved. Today less than
    5 of the US populations is working in the
    agricultural field

Machines replace human labor
  • Energy efficiency varies for different kinds of
  • Primitive agricultural methods are much more
    energy-efficient than modern agricultural methods

Machines replace human labor
  • Figure 24.3 illustrates the decrease in human
    labor over the past few decades
  • The decreases are due to the increase utilization
    of other energy forms like machinery for
    harvesting and mechanical systems for feeding
  • Crops where a high portion of human care is
    required shows the lowest decrease in human labor
    e.g. tobacco

Machines replace human labor
  • The increased utilization of energy leads to
    increased yields

Pesticides and Fertilizers
  • The use of pesticides has lead to increased
  • Pesticides have side effects
  • Alternatives are relying on natural enemies,
    rotating of crops, applying pesticide sparingly
    at the optimal time, etc
  • In 1970 about 642 MJ (3212 kWh) per hectare was
    attributed to artificial fertilizer use.

Pesticides and Fertilizers
  • The use of fertilizer has increased over the
  • Nitrogen is the major fertilizer and in mainly
    use in the form of ammonia
  • Ammonia is produced from natural gas (methane
    CH4). This process is very energy intensive
  • Animal manure or rotating crops is a possible
    solution to get around without using fertilizers.

24.3 Energy efficiency of the agricultural system
  • In the US, farms consume 4 of the total energy
    supply. If the entire food systems is considered,
    this figure becomes 17
  • The figure shows all the energy role players in
    the food system

24.3 Energy efficiency of the agricultural system
  • The production of energy attributed to food has
    kept pace with population growth
  • Energy use in the food industry has far
    outstripped the population growth

Monoculture vs Diversity
  • The most stable natural ecosystem seem to be the
    most complex and to have the lowest apparent
    productivity (from a human perspective)
  • This is because in nature everything depends of
    feeds on everything else
  • Monocultures are simplified ecosystems and have
    high productivity
  • These ecosystems are fragile due to the lack of
  • Nature maximize stability by complexity.
    Productivity is total biomass produced
  • Humans maximize productivity by simplicity.
    Productivity is biomass that can be harvested
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