Energy Efficient Homes
and Buildings
Introduction
EU households, heating and hot water
alone account for 79% of total
final energy use
(192.5 Mtoe Heating and cooling
account for about 48% of the energy use
in a typical U.S. home,
In the East it is the cooling load that dominates the households energy
utilization .
Heating and
cooling of buildings do not get the same attention as climate change, but these
should be paid attention as, both are carried out in a very inefficient manner.
Buildings are a long way away from efficient thermal insulation and are not
leak proof. .Much of heating and cooling is lost through leaky floors, poorly
sealed windows, improperly insulated roofs and walls.
The growing use of air conditioners in homes and
offices around the world will be one of the top drivers of global electricity
demand over the next three decades, according to new analysis by the
International Energy Agency that stresses the urgent need for policy action to
improve cooling efficiency. Using air conditioners and electric fans to stay
cool already accounts for about a fifth of the total electricity used in
buildings around the world – or 10% of all global electricity consumption
today. But as incomes and living standards improve in many developing
countries, the growth in AC demand in hotter regions is set to soar. AC use is
expected to be the second-largest source of global electricity demand growth
after the industrial sector, and the strongest driver for buildings by 2050.
Regulation
The Developed countries have issued
regulations for cooling and heating of buildings and homes, this is both an
economic waste and cause of emissions. The regulations, however, are applicable
to new construction only;, there is need to require renovation of excising structures
as well. In the developing world, there is frequently no such regulation, and
only very few people pay attention to efficient cooling and heating. It is only
high energy prices that induce some people to go for thermal insulation and
sealing of windows and doors.
Orientation
Properly insulated
and sealed houses and buildings seldom need central heating Walls are the main
source of heat loss or cooling loss in homes and buildings. Thermal insulating
sheets installed between double walls assist in reducing heat and coiling
losses, this, however, is only possible at time of construction. The roof
similarly can be insulated by placing a layer of thermal insulating sheets at
the time of construction. Insulating sheets can also be placed after
construction but this will involve the cost of removing existing materials on
the roof.
Windows are also
the means of significant heat losses or cooling losses. For starters the
placement of windows should be such that the sun should provide the heat and
lighting needs for at least a part of the time, this requires pooper placement
and directions of windows. The
first consideration for energy efficient homes should always be the location
and orientation of the building. You should attempt to maximize the use of
passive solar gain while reducing heat gain during summer months. Simple
directional and design related tweaks can make a big difference to enjoy the
summer sun without overheating the house. Good design control of passive solar
gain helps reduce heating loads during winter and cooling loads during the
summer.
Windows
The maximum losses occur due the losses from
the frame and the fittings. Double or triple glazing of windows help, in severe
climate placing inert gasses between the panes also assist in arresting heat
losses. Adopting low U-value frames and Low-E (low emissivity) glazing appropriately for
the climate and direction is another critical design consideration. For
example, higher altitude locations benefit from good UV rays all year round
except cold winters. Proposed glazing for any site should take account of
occupants' comfort level on completion.
Insulation as a solution
Reducing the heat loss from building elements such as walls and
floors is imperative for designing an energy efficient home. A good design of
these composite components minimizes the u-Value and R-Value, which provides a
passive and long lasting benefit to the buildings' lifetime costs. There are
many energy efficient systems and materials available such as ICFs (Insulated
Concrete Forms), thicker wall constructions and roof insulations. Additionally,
blown-in foam is also a well recognized, viable solution. It's easier to design a well insulated, efficiently
lit, correctly orientated and efficiently heated building than attempt to
retroactively improve it. Taking good consideration of the local climate and
geography, as well as supplementing accordingly with passive shading strategies
will pay dividends in the long run for your dream home. Energy efficient design
should always be a key consideration for any design team for any building.
Air tightness
Air tightness
assist in achieving energy efficiency Windows and doors frequently have gaps
that allow heat and cooling losses, simply closing these gaps results in a
significant improvement in arresting heat losses.
Ventilation
Air tight and
sealed home, the recommended solution is to use heat exchangers as simple fans
would defeat the purpose of sealing, will, however, need ventilation, as sealing
will starve the home of fresh air. Heat exchangers use heat transfer from the
leaving air to the entering air so that either heat of cooling is transferred
from the outgoing to incoming air. Heat recovery
should be another integral part of the building design for all energy efficient
homes. there are excessive amounts of technologies
for ventilation systems. Although the fact that they can now further tweak your
home's energy efficiency is a relatively new technology for the domestic
market. Technologies such as Flue Gas Heat Recovery (FGHRS) or Waste Water Heat Recovery systems can
provide additional cost savings.
Air
tightness or leakage has an enormous impact on the energy efficiency of any
building. Energy efficient homes should have proper sealing of joints, sills,
ducts, doors and vents. This will significantly reduce heating costs for the
final building. "Build tight, ventilate right" is a good adage to
follow. Clearly, some areas need mechanical ventilation e.g. wet rooms,
kitchens, etc.Ventilation systems have become very sophisticated and often include heat recovery
technology.
Trees
Engineering the landscape around the building can also play a
major role in energy efficiency. Planting deciduous trees on the west and south
sides (depending on your geographical location of course) can help provide
shade for the building during summer months. On the other hand, in autumn the
trees lose their canopies and allow winter sun to heat your home passively.
Heating design
Heating costs tend to comprise at least 50 percent of a home's
energy bills. Choosing the most efficient heating system is an essential design
consideration and will affect the lifetime running costs of the building.
Another consideration should be the addition of controls such as thermostats,
weather compensators, etc. to provide an autonomous control of the heating
plant. More sophisticated control systems, Building Management Systems, can
actively manage the building heating schedules.
Lighting Issues
Lighting design is another key factor for improving your home's
energy efficiency. Although fluorescent lighting is great, LED's are taking
over . The technology has come a long way over the last decade and will save
you hundreds of dollars (or any currency) over 10-20 years before needing
replacement. LED's are one of the quickest returns on investment and can fit
most of the existing light fittings.
Quantify losses
Traditionally, hot water used to be either generated or stored
in a cylinder or a tank. Hot water accounts for around 15-20 percent of most
domestic energy bills. When designing your domestic hot water system you should
seriously consider tank-less water technology systems such as combination
boilers. Clearly, the size of the house, number of occupants and hot water
capacity requirements of the final home will ultimately dictate the design. A
series of combination boilers instead of a large storage tank should provide
the volume and supply rate needed for most situations. Additional venting and
installation costs would be incurred but, this method of providing instant hot
water eliminates storage or standing heat losses in the long run. Solar heating
is at apr with gas heating of water , it is suggested that use of solar water
heaters be mandated .
Utilize by the sun
Being able to generate
your own electricity or supplement heating/hot water generation systems using
PV or solar thermal systems is a good design consideration. In most cases, you
can sell your excess electricity to the grid. However, future technology
systems are also expected to enable you to store your self-generated power.
It’s not easy to calculate the return of investment as the
market shifts, but it’s a fact that energy costs increase. Correspondingly, so
does the cost of solar installations and your cost-savings. The applicability
of this technology is of course latitude-dependent and the system size, design
and orientation may not be flexible. Solar water heating should be mandated as
this is at par with gas water heating. There is no economic sense in not using
solar for eater heating
Efficient building Materials
Every homeowner
should take advantage of the new eco-friendly technological advances in home
building, because they're affordable, more efficient and greener these include: Scrap . steel It could take as many
as 40 - 50 trees to build an average house. If recycled steel is used it will
take just 6 scrap cars to serve the same purpose. Steel beams can be used as a
replacement for wooden ones and can be ordered to fit a specific design. Steel
is a very durable material and particularly useful in areas where there are
earthquakes and high winds; Concrete is poured between two insulating layers
and left in place. It can be used for free-standing walls and building blocks; Plant-based
Polyurethane Foam. Plant-based polyurethane foam is usually made from
natural materials such as bamboo, hemp and kelp. Used as insulation it offers
high resistance to moisture and heat and protects against mold and pests. It
insulates better than fiber glass or polystyrene. It's not really a surprise
that nature once again has provided us with a better solution to our insulation
problems than artificial science; Straw Bales, this material actually
is. It's been used for centuries for various purposes (beds, roofing) but
nowadays it can help us with its excellent insulation properties. If kept dry
they can last for hundreds of years and they bond well to plaster and external
render; Cool Roof, Cool roofing technology will
improve the heat dissipation and will lower temperatures in your home during summer
A lot. It's also safe for the environment because it lowers heat in the atmosphere.
, it’s their reflectiveness which gives
them the name. They reflect the sunlight and thus reducing the heat in your
home; Structural Insulated Panels, Manufactured from a layer of foam
insulation which is sandwiched between plywood or cement panels. It is fire
resistant and suitable for floors, basements, foundations as well as load
bearing walls. You can choose from a variety of materials but the principle
remains the same. This material will help you reduce your energy bill greatly.
You can consult a handyman services company if you want to know more about
this; Plastic Composite Lumber, Often manufactured from waste plastic
and wood fiber it is more durable and less toxic than conventionally treated
wood. It is resistant to mold and rot and more rigid in the cold and pliable in
the heat than purely plastic building materials. Also the one in the picture is
the anti-slip variety which is suitable for bathrooms and outside decks; Low-E
Windows, Low-E windows or also known as "high performance"
windows are another great substitute for normal glass which will help you
reduce heat during summer and block infrared radiation. They have a clear coating
of metal oxide. It also helps keep the heat in during the winter. They can
reduce heat flow by up to 50%; Vacuum Insulation Panels, Vacuum
insulation panels or VIP (even the name sounds important) are a quick glimpse
in the future of home building. Currently only used for commercial
refrigeration units they could become available for general home building in
the future. They comprise of a textured silver rectangle that encloses a core
panel in an airtight envelope. All of this means heat loss will be reduced to a
minimum and we'll have much greener homes; Earth, Earth walls. Have
many advantages over other building materials. Mainly, earth is practically
everywhere around us, meaning it's pretty cheap. Walls made from earth provide
an excellent thermal mass and it is up there with other renewable sources of
building materials.
Cooling Efficiencies in Pakistan
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The energy, consumed in a building, can be reduced by adopting simple methods through the use of suitable building design and energy efficient strategies, such as, passive cooling strategies. Passive cooling eliminates the use of mechanical equipment and provides cooling through the use of passive processes. To improve the efficiency of the building envelope, passive cooling strategy reduces heat gains from the external sources and helps heat loss to the natural sources of cooling, such as, cool air, earth coupling and evaporation. Passive cooling is based on the principle of preventing heat from getting into a building during a hot day and bringing in external cool air into the building when the external temperature falls.
There
are various parameters that affect the thermal behavior of buildings, such as
the climatological ones, which are environmental variables and which are not
subject to human control. The other type of parameters is the design
variables, which are under control at the design stage. Inadequate attention
to the aspect of a building’s thermal behavior at the initial stages of its
design can lead to an unwelcoming internal environment. During summer,
buildings located in hotter regions often face overheating conditions due to
exposure to intense amount of solar radiation and high temperature. When
these overheating conditions inside the buildings surpass the threshold of thermal
comfort; cooling them becomes extremely significant.
Energy
consumption of buildings both in the developed countries as well as in the
developing countries for cooling the building has increased tremendously over
the past few decades . The reason for
this is the extensive use of mechanical air conditioning for cooling the
buildings. One reason for heavy reliance on mechanical cooling is due to
affordable cost and easy availability of electricity as well as cooling
equipment.
Now,
the world realizes that eventually there would be running out of fossil fuel;
the main source of energy in buildings at present thereby creating problems
in fulfilling the energy demands. Extensive use of fossil fuel is also
causing an irreparable damage to the environment. One of the solutions to
address the above issues is to build energy efficient buildings using passive
heating and cooling strategies. Passive cooling techniques not only offer
energy and environmental benefits but they are also very economical.
Materials and Methods Methods of passive cooling Passive cooling can utilize several heat sinks and a variety of climatic influences to create thermal comfort in warm regions, unlike the passive heating, which is driven by sun only. Traditionally, passive cooling has been in use in indigenous buildings
The
first step towards achieving thermal comfort conditions is to take preventive
measures against the radiation from the sun, by shading and reflective
barriers and also by heat transfer through the envelope (by insulation and
infiltration and infiltration sealing).
Minimizing
the need for mechanical cooling and extending the range of passive cooling is
dependent on good control over thermal gains. The thermal gains can be due to
multiple sources such as infiltration of outside warm air, heat conduction
through building structure, solar heat gains through windows, heat gains from
the occupants and equipment inside the building Evidently, the more these gains are, the
higher will be the cooling load to achieve a desired thermal condition in the
building. It is, therefore, important to control these gains in summer months
in order to reduce the energy requirements for cooling.
Besides
the preventive measures to attain passive cooling other methods include the
evacuation of heat from the building to the heat sinks. The natural heat
sinks of the planet are the atmosphere, the sky and the earth. The main
techniques of natural cooling according to the mode of heat transfer and
fluid flow can be classified as follows:
Some of
the techniques provide a direct instantaneous cooling effect, in others the
coolness is collected during night time and is released the next day, thus smoothing
the effect to the accumulated heat inside the building.
Natural
ventilation is the movement of outside air into a space without mechanical
support. One of the oldest cooling methods in buildings is ventilation.
Purpose made openings in buildings, such as, doors, windows and non-powered
ventilators can be used to control natural ventilation, that provide a
certain degree of ventilation besides infiltration.
Other
methods may include, wind towers, solar chimneys and atrium (Khan et
al., 2008). In each case, the system is designed to take
advantage of prevailing driving forces. An air movement is also important
aspect of ventilation cooling since it offsets increase in temperature while
maintaining comfort ventilation cooling.
When
heat transfers from a hotter surface to a colder surface or external space,
it is known as radiative cooling and the basic principle for radiative
cooling is that a hot body emits heat energy in the form of electromagnetic
radiations to the cold body that faces it. Similarly, the envelope of the
building absorbs heat during the day and becomes warm. During the night when
the temperature drops, the building emits this heat to the atmosphere due to
which the building gets cooled down. The radiative potential of a
roof/horizontal surface is greater than a vertical surface. The radiative
potential of a building is reduced during hot summer nights because the hot
air adds heat to the building by convection.
When
the sensible heat in air exchanges with latent heat of water droplets on
moistened surface, it is called evaporation. In evaporation, the state
changes into vapour from liquid. This is accompanied by release of huge
quantities of heat (sensible) from the air that comes in contact with the wet
surface where evaporation takes place. When comparatively dry air is passed
over a moistened surface then direct evaporative cooling occurs. For example,
when a draft or wind blows through a fountain or over a pool of irrigated
field, it is cooled by direct evaporation. These landscape features have
aesthetic benefits in addition to a relatively automatic control of the
process.
Passive
cooling strategies: The bioclimatic chart tells us that conditions
are comfortable in the shade and in still air; if the plotted point lies
within the comfort zone. If the points lie outside the comfort zone, we need
to take corrective measures to get the conditions into the comfort area. A
brief description of different passive strategies shown on the chart for
bringing conditions into comfort zone is elaborated in the subsequent
paragraphs.
Natural
ventilation is the movement of fresh air into a space without mechanical
assistance. Deliberate openings in buildings, such as, doors, windows, etc.,
can be used to control natural ventilation. In natural ventilation the
movement of outdoor air across the building is caused by pressure difference.
Buoyancy effect or the wind can be used to create pressure difference, which
is created by humidity difference or difference in temperature. Ventilation
based on the buoyancy effect utilises stacks, which are tall spaces inside
the buildings. The cooler outside air moves into the building from openings
near the ground, whereas the hot air leaves the building through openings
close to the top of the stack. In ventilation, in order to allow to airflow
through buildings, we need to keep the building open during the day.
Ventilation
in buildings is needed not only to provide cooling in summer but also
provides fresh air for occupants to dilute and exhaust pollutants. A good
ventilation design not only caters the residents comfort by making the spaces
inside the building ‘airy’ (not draughty) and ‘fresh’ (not stuffy) but also
ensures good air quality that has low levels of pollutants. We need to have
optimum ventilation, because excessive and unnecessary ventilation during the
heating season incurs an energy penalty while too small ventilation can
adversely affect the health and comfort of the residents.
Ground
cooling, evaporating cooling, radiative cooling and convective cooling
utilises the heat dissipation techniques for cooling the buildings.
Dissipation of the additional heat mainly relies on two conditions: presence
of a suitable environmental heat sink; and creation of a suitable thermal
coupling between the sink and the building, besides adequate temperature
difference required for the heat transfer.
For the
above referred techniques the following heat sinks are used:
Materials,
like, brick and concrete, have high thermal mass because of their capacity to
store both cold and heat. Materials having high specific heat capacities and
high densities are ideal for thermal mass.. Any matter that has mass whether
solid, liquid or gas will have some thermal mass. Not only soil, earth or
concrete has thermal mass but the air has a thermal mass as well, though it
is substantially low. Various materials are used for thermal mass, but the
most common ones are mud brick or adobe brick, mud, earth, natural rocks and
stone concrete, clay bricks, water, etc.
In
these commonly used materials, the volumetric heat capacity of water is the
highest. Normally, large containers are used for keeping water. The heat
capacity of other materials, such as, earth, dirt and mud, depends on a
number of factors, such as, its density, particle shape, moisture content,
composition and temperature.
The
type of thermal mass in buildings varies from climate to climate. The
prevalent climatic conditions in a region decide the right use and
application of thermal mass. The internal temperature peaks inside a building
can be reduced by the use of the correct thermal mass which, in turn, minimizes
the requirements for mechanical ventilation. The use of thermal mass to
decrease temperature peaks during daytime normally needs ventilation cooling
during night time to decrease the mass temperature. High thermal mass
together with ventilation at night, depends on the daily heat storage of
thermal mass along with night time ventilation which lowers down the
temperature of the mass. During the daytime the buildings need to be closed,
whereas during night time they need to be opened to remove the heat.
Advantages
of passive cooling: Passive cooling decreases the need for
conditioned cooling by minimizing or eliminating the periods in which cooling
is required.
The
energy requirement for heating and cooling of buildings is around 6.7% of the
total world energy consumption Out of this, we may save around 2.35% of the
world energy output, just by making appropriate environmental design. The
cooling energy requirements are normally two to three times higher than the
heating energy requirements on an annual basis in hot climates. Utilisation
of the basic principles of heat transfer coupled with the local climate and
exploitation of the physical properties of the construction materials could
make possible the control of the comfort conditions in the interior of buildings.
A
proper building design may be used to achieve thermal comfort inside the
buildings, even in regions, that have average maximum ambient temperature
around 31.7 °C and helps to eliminate the use of air conditioning in
buildings. For example, suitable orientation with respect to the sun and the
use of adequate insulation material in the construction of dwellings will not
only reduce the summer and winter discomforts but also decrease the noise
complaints. Passive cooling helps in protecting the environment because air
conditioning is associated with various environmental problems, such as,
ozone depletion etc.
Studies
carried out for various cities in Queensland, Australia, show that the passive cooling strategies are
very suitable for these hot and humid subtropical climatic conditions
Results and Discussions
Climate: The climate has clear effects on human thermal environment. A strong understanding of the environmental features that affects a building site is extremely important for designing an energy conscious building. While designing an energy efficient building, we must incorporate the useful factors that the environment and the climate have to offer and guard against those that are unfavorable to comfort.
Passive
cooling utilizes the processes fundamentally related to climate, air
temperature, relevant humidity, velocity and direction of wind Different climatic variables, such as,
atmosphere, sky and the earth, act as a heat sink when we are rejecting heat
from the building to the atmosphere. The applicability of passive cooling
strategies could be limited by insufficient information to designers and
building users on the potential of passive cooling. Hence, it is important to
have knowledge about climate and different climatic variables while designing
energy efficient buildings.
The
average daily temperature of Peshawar greatly varies in winter and summer,
for example in January the average temperature is around 4°C whereas it rises
up to 42°C in June. The majority of the rainfall happens in the months of
July to August and March to April while
it is quite low in other months of the year. Rainfall in other months of the
year is very low. The humidity level is not very high and hailstorms are
common in the spring
Suitability
of the weather of Peshawar for passive cooling strategies
The traditional architecture of Pakistan was very much environment friendly. In the hot areas of Pakistan, the buildings were of massive construction. Fountains, pools and vegetation could still be seen around some of the old buildings. They would help in passive cooling apart from giving aesthetic beauty to the surrounding area of the building. But during the past few decades, due to fast and speedy advancement in science and technology, the use of active air conditioning systems in buildings has increased tremendously. As a result, the cooling load of buildings has increased by a high percentage.
To
check which weather conditions are appropriate for a certain design strategy,
we can use bioclimatic charts for an early examination. When we mark areas on
a psychometric chart to help matching the design solutions to climatic
conditions, it is known as a Bioclimatic chart
Hence
this method is quite helpful in anticipating early low design approaches on
the basis of existing climatic conditions. This is achieved in two ways;
first by using the sun, wind and night time cooling and secondly only when
these are insufficient, by selecting appropriate mechanical equipment.
To
check which passive strategy is suitable for a specific area, G.Z. Brown in
1985 used bioclimatic chart. On the basis of temperature and relative
humidity the bioclimatic chart offers four passive cooling strategies The
bioclimatic chart is normally used for residential and light commercial
buildings that have low rates of inside heat gains from lighting, equipment
and people, etc.
Conclusions The climate of Pakistan has a lot of potential for passive cooling. There is a need for creating more awareness amongst the people for adopting passive cooling strategies. Bioclimatic chart can be used for preliminary investigation of the weather appropriateness of weather conditions for a building design strategy. Adopting passive cooling strategies for Pakistan would not only help to reduce the building cooling loads by a significant amount but also help to build a green Pakistan.
Although
the climate of Pakistan has a lot of potential for passive cooling but there
is a need to remove this misconception from the minds of the people that
passive cooling strategies cannot be adopted in modern building. More
awareness programs need to be created amongst the people for adopting passive
cooling strategies in building design.
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Efficient Air conditioners
In general, the more
efficient the equipment is, the more costly it is compared to the regular ones.
Here are some steps that you can take when choosing energy efficient air
conditioners to purchase.
1.
Cooling Capacity
Determine the cooling
capacity that is required of the room
Buying an oversize air conditioner is not a good choice as it is more
costly and does not necessarily provide better comfort level.
2.
Inverter Vs Non-Inverter
Choose an inverter model
as it will be definitely more efficient than a non-inverter unit. The inverter
compressor's rotation can be varied according to the requirements of the load
hence the power savings is there.
On the other hand, the
non-inverter compressor is only able to turn ON or OFF. It is not able to vary
its speed according to the load. The frequent turning ON and OFF will consume
more energy. Choose also a DC inverter compressor as it is more efficient
compared to the AC inverter.
Infra-Red
Sensor
Some manufacturers have built-in infra-red sensor that is able
to detect the presence or absence of the occupants in the room. If it does not
detect any movement for a certain period of time, it will adjust the set
temperature higher automatically to reduce the temperature in the room. This
will help to save your electricity bill.
