CHAPTER 7 ENERGY CONSERVATION

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CHAPTER 7ENERGY CONSERVATION
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Introduction

• Energy conservation means reducing the amount of
  energy we lose after it has been converted to a
  desirable form e.g.
• Reduce flow of heat energy out of a building
• Reduce flow of cold air into a building
• Moderate heating/air condition temperature
  settings
• Increase light output for same electrical power
  input
• Reduce consumption of fossil fuels per mile in
  transportation systems
• It does not refer to the physics law of
  conservation of energy, but the law still holds.
• Energy conservation also relates to efficiency of
  engines and motors
• Remember heat engines have a maximum theoretical
  efficiency
• But electric motors are candidates for increased
  efficiency
• Re-use and recycling are important contributors
  to energy conservation
• The bottom line is that energy conservation is
  equivalent to discovering more energy in terms of
  the coming energy shortage

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Conservation Works

• In the late 1970s the predicted energy usage in
  the USA for the year 2000 was 160 Qbtu
• In 1999 the energy usage was 96.6 Qbtu
• This is attributed to energy conservation in a
  variety of ways
• The conservation was probably triggered by the
  energy crises of the 1970s
• Sharp increase in energy costs
• Realization that the sources of energy we were
  able to convert were not limitless.
• The distribution of energy use in three main
  categories is
• Commercial and residential 35
• Industrial 38
• Transportation 27
• We will focus on Commercial and Industrial in
  this section, dealing with transportation
  separately in the next section.
• Space heating/cooling
• Appliances
• Reuse, repair and recycling

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Building Heat Losses

• One of the important advances in energy
  conservation in recent years has been the
  extensive use of insulation in buildings.
• Primarily reducing the heat loss by conduction
  through all outside surfaces of the building
• Also the loss of heat and cooling by cracks in
  the building at doors and windows

Heat losses reduced by Insulation Caulking Modera
tion of temperature
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Thermal Insulation (1)

• The flow of heat energy through a solid depends
  on the area (A) and thickness (l) of the solid
  the temperature difference across the thickness
  (Ti-To) and also another parameter characteristic
  of a particular material called its thermal
  conductivity (k).
• The heat energy can be expressed in Joules,
  Calories, but we will use the heat engineers unit
  of Btu.
• The rate of heat flow is then given by

If k is in units (Btu.in)/(hr.ft2.F) Then the
heat flow is in Btu/hr if A is measured in square
feet , l in inches and the temperature
difference in F
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Thermal Insulation (2)

• In practice another measure of the degree of
  insulation is widely used
• The R-value which includes thermal conductivity
  and thickness
• R is used because it represents resistance to
  heat flow

The heating engineer units of R are
The big advantage of using R rather than k is
that for composite walls etc. with layers of
different R-values
Rtotal R1 R2 R3 ...
(Large R-value Good Insulation)
Then the total heat lost for a time t is
(A in ft2, t in hrs, R in units above, T in F)
See table 7.3 for R-values of common building
materials
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Degree Days

• In order to utilize the previous equation to
  calculate the total heat loss over a season (and
  hence the heater capacity needed) for a building
  the concept of degree days is used.
• Degree days for 1 day 1 x (65 - Tout)
• Where Tout is the average temperature for a
  given day
• For a season of say 150 days with an average
  outside temperature of T(av)out
• Degree days 150 x (65- T(av)out )
• We can use this number in the heat loss formula
  to show that the total heat loss for a season is

(The factor of 24 converts days to hours) A
area exposed to outside
Heating season degree days for various cities are
tabulated in table 7.2
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Air Infiltration

• Buildings often have gaps around doors, windows
  etc.
• Recall 38 of heat loss is by this mechanism in
  the average house
• Outside air can enter through these gaps and mix
  with the warmer air in the building and cool it
  thereby placing greater demands for energy output
  from the heating system.
• This effect is often called a draught
• It is possible to reduce this infiltration to a
  very low level by sealants, careful construction
  etc.
• Would produce significant reduction in heat power
  output of heating systems
• But can reduce oxygen to dangerously low levels.
• Can increase carbon dioxide to dangerously high
  levels
• Poisonous gas concentrations can increase up in
  the building
• All building designs require air exchange in the
  building of 2 air exchanges per hour.

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Energy Conservation in Buildings

• Both the buildings themselves and their
  infrastructure are amenable to energy
  conservation practices.
• Space Heating
• Water Heating
• Lighting
• Home/Business appliances
• The most energy is saved by moderating the
  thermostat setting
• 65 - 68F for heating
• 73 - 75F for cooling

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Space Heating

• Furnaces
• In office and domestic environments this is the
  term given to systems that use the chemical
  energy in fossil fuels to heat air.
• The heat energy in the air is distributed around
  the building by forced convection using a fan.

Modern furnaces Are 50-90 efficient
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Space Heating (Electric Heaters)

• Convert electrical energy to heat energy in wires
• Heat energy transferred two ways
• By conduction to air
• Hot air transported by natural or forced
  convection
• By radiation of infrared emission from heated
  wires
• Heat energy of target increased by absorption
• 100 efficient
• Even so the high cost of electricity makes them
  more expensive furnaces

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Space Heating (Wood Stoves)

• Only 40 - 65 efficient
• Heating is localized to room containing stove
• Not the most effective way of using biomass
• Significant pollution source
• Production of carbon monoxide is a potential
  health hazard
• Production of tar can lead to chimney fires.

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Space Heating (Open Fireplaces)

• Ineffective form of heating
• Remove more heat from the building than they
  supply
• Heating is mainly by radiation and is localized
  near and in line of sight of the fire
• Room air drawn up chimney
• Cold air infiltrates readily because of reduced
  pressure
• Can be improved by piping in outside air
• Significant pollution source

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Recommended Heating Requirements
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Water Heating

• 10 - 20 of home consumed energy goes into water
  heating.
• There is a steady loss of heat energy from the
  heater whether in use or not
• Electrical heaters eliminate the flue losses
  found on gas powered systems.
• But costs may be higher due to high cost of
  electrical energy
• The energy usage can be minimized by
• Reducing the temperature of the water
• All heat losses are temperature dependent
• Improve insulation of tank
• Turn temperature down to a low value for extended
  absences.

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Lighting

• The energy converted to provide lighting is about
  20 of electrical energy or 5 of the total
  energy consumed in the US
• Although lighting requirements in public
  buildings have increased in the last 50 years,
  the widespread use of more efficient fluorescent
  lighting has alleviated the energy demands.
• Lighting sources have a wide range of
  efficiencies
• Incandescent 17 lm/watt
• Fluorescent 80 lm/watt
• High pressure discharge 100 lm/watt
• (lm is lumen, a unit of light intensity)
• The long life and low power consumption of
  fluorescent lamps result in large savings over a
  long period despite their higher initial cost.
• Switching off lights when not required is good
  practice
• It will not make much difference to individual
  costs
• But if large numbers of people complied then the
  energy saving would be significant.

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Example of result of increased Light Bulb
Efficiency
Comparison of run-out costs of fluorescent and
incandescent bulbs for 10,000 hours of
illumination. 75W incandescent bulb, 15 W
fluorescent bulb, both provide about the same
light intensity. Assume electrical costs stay at
0.07 per unit (KWh)
Over the short run savings are small for an
individual, but if large numbers of people
converted the total electrical energy saving
would be significant.
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Home Appliances

• Apart from air conditioners and water heaters,
  the refrigerator and clothes washer/dryer are the
  largest electrical energy consumers in the
  average house with dishwasher and range not far
  behind.(Table 7.5, p 229)
• Steps have been taken to reduce the consumption
  of energy for these appliances
• Better insulation in refrigerators, dishwashers
  and ranges (at the expense of internal volume)
• Front loader washers use less water and hence
  less energy to heat it
• Note that other appliances and home entertainment
  are not large consumers of energy
• It is becoming more common that appliances do not
  stop using energy when they are switched off.
• It is estimated that in the typical house 50W are
  driving keep alive circuitry for instant
  gratification.
• Across the country this has been estimated to
  amount to energy costs of about 3B per year

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Potential House Energy Savings
Note a factor of three saving in annual energy
use is possible with sufficient investment
The figure is only a guide because how much is
saved depends on the way energy is used (e.g)
cooling or not.
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Recycling (1)

• When goods are manufactured energy must be used
  to perform the various processes between the raw
  materials from the earth and the finished
  product.
• For many products re-cycling results in a
  significant saving in energy over complete
  re-manufacturing.
• Some examples can be seen from the table from the
  book

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Recycling (2)

• In addition to saving energy re-cycling has other
  favorable features
• The use of land for landfills is slowed down
• Re-cycled products from biomass (e.g. paper) slow
  down the use of biomass (e.g. wood)
• Slows down the depletion of natural sources of
  the raw materials
• Reduces pollution from the initial extraction
  from the ores which can be bad for the
  environment.

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Re-use

• Even more energy saving is to repair, refurbish
  and re-use manufactured objects.
• This is unpopular with manufacturers who counter
  tendencies to do this by the concept of FASHION
• There is a tendency to follow this policy with
  major domestic appliances.
• The existence of a secondhand car market is an
  example of re-use
• But it is driven by cost rather than
  considerations of energy conservation.
• Also the refurbishment is rather minor, when
  major work is needed the vehicle is usually
  abandoned and may eventually find its way to a
  steel re-cycling plant.

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Learning Objectives (1)

• Understand the difference in our meaning between
  Energy Conservation and Conservation of
  Energy
• Be aware that over the last 20 years our total
  annual energy usage is less than was predicted by
  a substantial amount.
• Know the distribution of energy use between the
  three primary sectors of Commercial/Residential,
  Industrial and Transport.
• Be aware that large advances have occurred in the
  last 20-30 years in the thermal insulation of
  commercial and residential buildings.
• Be familiar with the parameters which affect the
  rate of flow of heat energy through material by
  conduction.
• Know what is meant by the R-value of an insulator
  and why it is associated with a particular
  insulator and not just the material itself.

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Learning Objectives (2)

• Understand that R-values simplifies the
  computation of the equivalent R-value of
  composite materials.
• Know what is meant by degree-days.
• Understand how this can be used to estimate the
  total heat source requirement of a building.
• Understand the need to reduce air-infiltration
  into heated buildings.
• Be aware of the dangers of too complete sealing
  of buildings
• Know the four items in buildings for which energy
  saving techniques can be employed.
• Be aware that thermostat settings are very
  important in energy conservation.
• Be familiar with the parts of a gas-fired furnace
  for building heating needs.
• Be familiar with other forms of space heating and
  their disadvantages.

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Learning Objectives (3)

• Be aware that water heating is a significant part
  of the energy used in buildings.
• Understand the techniques available for water
  heating
• Be aware of energy conservation techniques
  available.
• Know that 5 of all energy consumed in the
  country is used in lighting.
• Be aware of the development of more efficient
  light sources, particularly fluorescent lights
  for buildings.
• Know that the home appliances which are the
  largest consumers of energy are the refrigerator
  and the Washer/Dryer.
• Be aware of the increasing used of household
  electrical appliances with standby power
  consumption.
• Be familiar with energy savings by re-cycling
  manufactured material
• Be aware of the other advantages of re-cycling.
• Understand that repair and re-use can be an
  effective form of energy conservation