2. The outline of the problem
• Human activities often require energy
– Power for equipment
– Power for lighting
– Heating for thermal comfort
– Hot water for hygiene
– Cooling in hot weather
• All require external supplies of energy
• Majority of external energy comes from
non-renewable sources - fossil fuels
3. What are fossil fuels?
• All “fossil” fuels are a product of ancient
biological activity
• Living plants capture and fix carbon dioxide
(CO2) and water (H2O) as hydrocarbons
through photosynthesis
– Solar energy is converted to chemical energy,
stored in the hydrocarbons
• All life depends on this process and it also
releases oxygen (O2)
• Ancient plant and animal remains have been
preserved, in some cases, as fossilised
hydrocarbons – fossil fuels
6. What are the problems with using fossil fuels?
• They are finite resources which will
eventually run out - sustainability?
– There are vast reserves of coal but other
fossil fuels are beginning to run out already
• Burning fossil fuels (combining a
hydrocarbon with oxygen) to release the
stored chemical energy as heat
reverses the photosynthetic process:
CH4 + 2O2 >> CO2 + 2H2O
Heat energy released
Input: methane
and oxygen
Output: carbon
dioxide, water and
heat
7. Why is carbon dioxide (CO2) a problem?
• Carbon dioxide (CO2) is essential for life
and maintenance of life supporting
temperatures, but…
• An increase in atmospheric carbon
dioxide could lead to significant global
temperature rises through the
“greenhouse effect” which will disrupt
human societies
– Rising sea levels - flooding
– Changes in agricultural systems
– Changes in water supply
9. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
LWIR
CO2
10. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
LWIR
SWIR
CO2
11. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
The Earth, warmed by short
wave IR, emits long wave IR
which cannot escape through
the CO2 in the atmosphere.
There is a one way traffic in
energy input temperatures
rise
LWIR
SWIR
CO2
12. Reducing CO2 emissions aka low carbon technologies
• Use renewable, non-finite energy
sources:
– Direct solar radiation
– Geothermal energy
– Hydro electric power
– Tidal power
– Wind
– Biogas
– Nuclear energy
• Design buildings to make best use of
environmental energy
13. Reducing CO2 emissions aka low carbon technologies
• Use renewable, non-finite energy
sources:
– Direct solar radiation
– Geothermal energy
– Hydro electric power
– Tidal power
– Wind
– Biogas
– Nuclear energy
• Design buildings to make best use of
environmental energy
14. Designing to use the Sun
• Solar energy can be exploited three
ways
– Photo-voltaic electricity generation
– Water heating
– Direct solar heating of the building fabric
• The last two make direct use of the
greenhouse effect themselves
15. Photo-voltaic electricity generation
• Light photons fall on
“photo-cells”, displacing
electrons and thus
generating a current
• Efficiency low and cost
high
• Pay back periods only
economic due to
government sponsored
“feed in tariffs”
• They don’t work in the
dark
• Energy very difficult to
store
16. Solar Water heating
• Black painted water pipes under glass are
heated by direct solar radiation using the
greenhouse effect
• Pay back still very long in UK climate but
should become standard fitting on all new
houses.
17. Direct solar heating of the building fabric
• Exploit solar energy to the maximum
– Consider building orientation
– Exploit the greenhouse effect for building
heating
– Control excessive solar heating through
shading
– Store day time solar heat in mass
construction for night time use
18. Orientation: the sun is in the south…
• Position building and locate
windows to maximise solar gain.
• Build heavy masonry walls to
store the heat to re-emit during
the night
25. Geothermal energy for individual buildings
• High temperature geothermal energy
– Dependent on hot rocks close to the
surface
– Not viable in the UK but used intensively in
Iceland
• Low temperature “ground source” heat
– Exploits the temperature differences
between the atmosphere and the sub-
surface ground
– Concentrates low quality heat using “heat
pump” technologies
26. Ground source heat
• UK air temperature
varies between
-10 and +30ºC
• 1.5 metres below
ground the
temperature is
constant around
10ºC
• This temperature
difference can be
exploited for heating
or cooling.
1.5m
10ºC
constant
temp
-10ºC>+30ºC
28. Technical exploitation of ground source heat
• “Pump” the heat to
the surface
• To be effective, air-
conditioning
technology must be
exploited, in
reverse.
• “Heat pumps”
concentrate low
grade heat to get
higher temperatures
1.5m
10ºC
constant
temp
Large coiled pipe
full of refrigerant
fluid in the ground
Pump and valve
form the “heat
pump” which
concentrates the
heat
Small coiled pipe full of
refrigerant fluid in the
building
29. Wind energy
• Wind generation of
electricity is
renewable and non-
polluting (when
generating) but…
• It is intermittent
– Where do you get
power from when it is
not running?
• It is highly
dependent on high
wind speeds
30. Is there enough wind energy to be practically useful?
• The theoretical energy output is
proportional to the wind speed cubed
– If the wind speed doubles, the theoretical
energy output goes up eight times (2x2x2)
– If the wind speed halves, the theoretical
output falls to an eighth (2/2/2)
• High steady wind speeds are needed
for useful energy generation
• Domestic scale installations in lowland
areas simply cannot deliver useful
quantities of energy.
31. Biogas generated from waste
• Fermenting organic
waste generates
methane, a main
constituent of natural
gas.
• Digesting farm waste
generates gas and solid
residue is a good
fertiliser
• Food waste can be
digested in urban
locations to generate
biogas and reduce
quantity of waste
• Gas can be burned to
generate electricity or fed
directly into the gas
supply network
32. Summary
• Solar energy can be exploited for
heat/hot water, but electricity generation
is still in its infancy.
• Wind power is ineffective at domestic
scale
• Significant quantities of environmental
energy can be harvested through good
building design
• Biogas generation can potentially
provide fuel or energy, but needs to be
fairly large scale to be significant.
