ENERGYPHYX 1020USU 1360 CHAPTER 7 ENERGY CONSERVATION 2002 1 CHAPTER 7 ENERGY CONSERVATION Window Insulation Wall Insulation Draught Exclusion Fluorescent

1

ENERGYPHYX 1020 USU 1360C

HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

CHAPTER 7ENERGY CONSERVATION

Window Insulation

Wall Insulation

Draught Exclusion

Fluorescent Lights High Mileage Cars

2


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

3


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

Conservation Works• In the late 1970’s 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 1970’s– 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

4


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

Moderation of temperature17%

1% 20%

5%

38%

3%

16%

5


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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:Qt

=kA(Ti −To)

l

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

6


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

R=lk

The heating engineer units of R are hr•°F • ft2

BtuThe big advantage of using R rather than k is that for composite walls etc. with layers of different R-valuesRtotal = R1 + R2 + R3 + ...

Then the total heat lost for a time t is: Q=ARtotal

(ΔT)(t)(A in ft2, t in hrs, R in units above, T in °F)

See table 7.3 for R-values of common building materials

(Large R-value = Good Insulation)

7


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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:

€

Q=24•ARtotal

•(#degreedays)(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

8


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

9


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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 - 68°F for heating– 73 - 75°F for cooling

10


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

Blower fan usesElectrical energy Fuel oil or

natural gas

Combustion airFrom outside

Some heatexchange fromchimney

Modern furnacesAre 50-90%efficient

11


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

12


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

13


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

14


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

Recommended Heating Requirements

15


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

16


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

17


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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)

Light KWhUsed

$ InitialCost

Repl.#

$ Total$

Fluor. 150 10.50 15.00 0 0 25.50Incand. 750 52.50 0.75 8 6.00 59.25

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.

18


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

19


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

Potential House Energy SavingsNote 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.

20


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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:

21


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

22


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

23


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

24


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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.

25


HA

PT

ER

7 E

NE

RG

Y C

ON

SE

RV

AT

ION

2002

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

Documents

ENERGYPHYX 1020USU 1360 CHAPTER 7 ENERGY CONSERVATION 2002 1 CHAPTER 7 ENERGY CONSERVATION Window Insulation Wall Insulation Draught Exclusion Fluorescent