Week 12 Conservation of Energy Energy Cost of Agriculture

1
Week 12Conservation of EnergyEnergy Cost of
Agriculture
2
Insulation

• 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

3
Insulation

• 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
  used

4
(No Transcript)
5
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.
6
Germany
7
Solar Energy

• The effect of window orientation and has a large
  influence on the indoor heat gain

8
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
  house.
• This is more economic than directly converting
  electricity into heat using a conventional
  electric heater

9
Heat Pumps

• One unit of electricity can give 3 units of
  heating

10
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

11
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
  burner.
• 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
  systems.

12
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

13
East German Ampellman
14
LED Replacements
Seattle Bridge
LED traffic lights
15
LED Light emitting diodes
16
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

17
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
  burned.
• 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!

18
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

19
Machines replace human labor

• Energy efficiency varies for different kinds of
  production
• Primitive agricultural methods are much more
  energy-efficient than modern agricultural methods

20
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
  animals
• Crops where a high portion of human care is
  required shows the lowest decrease in human labor
  e.g. tobacco

21
Machines replace human labor

• The increased utilization of energy leads to
  increased yields

22
Pesticides and Fertilizers

• The use of pesticides has lead to increased
  yields
• 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.

23
Pesticides and Fertilizers

• The use of fertilizer has increased over the
  years
• 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
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

25
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

26
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
  complexity
• Nature maximize stability by complexity.
  Productivity is total biomass produced
• Humans maximize productivity by simplicity.
  Productivity is biomass that can be harvested