Transcript Energy

Developments
• Preindustrial Era: prior 1800s where the
building envelop was the principal means of
controlling thermal environment and
illumination within the building
• Industrial Era: Architecture has changed due
to changes in materials, technology even
knowledge
Developments
Pre Industrial Era
Industrial Era
Thick external
Thin minimum skin
Tight thermal envelop
Short depth for light
Short depth for ventilation
High Ceiling
Low rise buildings
Materials was restricted to available resources
Mechanical HVAC
Greater depth for light due to artificial lighting
Big depth for ventilations due to forced convection
Low ceiling
High rise buildings
All Materials are available due to transport
Energy
• What is Energy: is an indirectly observed
quantity which comes in many forms
• Energy Forms:
1. Kinetic Energy Which depends on
motion
2. Potential Energy which depends on
position
3. Radiant Energy is the energy of
electromagnetic waves
Energy
• Units:
• The most important energy units are:
1. Joule (J)= NM (work) =Force*Displacement
1kJ=1000J
1MJ=1000000J
2. kWh = 3600 kJ
3. Calorie =4.1868 J
4. British Thermal Unit (BTU)=1.055056 kJ
Energy
Examples:
• Convert 10 J into Calorie
Answer is 10/ 4.1868= 2.388459
• Convers 10kWh into Calorie
Answer: 10kWh? In kJ
kJ=3600*10=36 MJ
Calorie=36000000/4.1868=8598452.27859=8.6MCalorie
Principle of Conservation of Energy
• It states that the total amount of energy in an
isolated system remains constant over time
• Energy can not be created or destroyed. It can
be changed from one form to another.
• This law means energy is localized and can
change its location within the system, and it
can change form within the system, for
example, mechanical energy can become
electric energy
Heat Transfer
• Heat is energy transferred from one body to
another by thermal interactions (energy
transit or moving energy)
• Heat transfer is a discipline of thermal
engineering that concerns the generation,
use, conversion, and exchange of thermal
energy and heat between physical systems.
Heat Transfer
• Heat transfer Mechanism:
1. Thermal Conduction (Solid materials have
better conductivity than liquids and gases)
2. Thermal Convection(dominant form of heat
transfer in liquids and gases)
3. Thermal Radiation
Example of mechanism
Thermal Conduction
• Conduction heat transfer: Heat conduction
occurs as hot, rapidly moving or vibrating
atoms and molecules interact with
neighbouring atoms and molecules,
transferring some of their energy (heat) to
these neighbouring particles
Thermal Conduction
• If one end of a metal rod is at a higher
temperature, then energy will be transferred
down the rod toward the colder end.
Thermal Conduction
• The rate of conduction heat transfer or loss is:
kAThot T cold 
Q

t
d
•
•
•
•
•
Where Q is heat transfer in time t
k is the thermal conductivity of the barrier (next)
A is the surface area
T is temperature
d is barrier thickness
Thermal Conductivity (k)
Material
Thermal conductivity
(W/m K)*
Material
Thermal conductivity
(W/m K)*
Diamond
1000
Fiberglass
0.04
Silver
406.0
Brick, insulating
0.15
Copper
385.0
Brick, red
0.6
Cork board
0.04
Gold
314
Brass
109.0
Wool felt
0.04
Aluminium
205.0
Rock wool
0.04
Iron
79.5
Polystyrene (Styrofoam)
0.033
Steel
50.2
Polyurethane
0.02
Lead
34.7
Wood
Mercury
8.3
Air at 0° C
0.024
Ice
1.6
Helium (20°C)
0.138
Glass, ordinary
0.8
Hydrogen(20°C)
0.172
Concrete
0.8
Nitrogen(20°C)
0.0234
Water at 20° C
0.6
Oxygen(20°C)
0.0238
Asbestos
0.08
Silica aerogel
0.003
0.12-0.04
Thermal Conduction
Example: what is the rate of heat loss for a steel
door of 2.5 m^2 area with 6 cm thickness if the
hot temperature interred this door at 318.15 K
at exited at 300 K?
• Answer
kAThot T cold 
Q
t

d
Q
=(50.2*2.5(318.15-300))/6
t
=379.6375
Thermal Convection
• Thermal Convection heat transfer is heat
transfer by mass motion of a fluid such as air
or water when the heated fluid is caused to
move away from the source of heat, carrying
energy with it.
• Convection above a hot surface occurs
because hot air or fluid expands, becomes less
dense, and rises
Thermal Convection
• Natural Thermal Convection heat transfer occurs
when bulk fluid motions (steams and currents)
are caused by buoyancy forces that result from
density variations due to variations of
temperature in the fluid.
• Forced Thermal Convection heat transfer is a
term used when the streams and currents in the
fluid are induced by external means—such as
fans, stirrers, and pumps—creating an artificially
induced convection current
Natural Thermal Convection
Forced Thermal Convection
Radiant heat transfer
• Radiation heat transfer happens when
electromagnetic field travel through space.
When electromagnetic waves come into
contact with an object, the waves transfer the
heat to the object
• Examples
Microwave oven
Light pulp
Radiant heat transfer
Solar Radiations
Solar Radiations
• The figure shows the solar radiation spectrum for
direct light at both the top of the Earth's
atmosphere and at sea level
• The sun produces light with a distribution similar
to what would be expected from a 5525 K (5250
°C) blackbody, which is approximately the sun's
surface temperature
• As light passes through the atmosphere, some is
absorbed by gases with specific absorption bands
Radiant heat
• When the heat radiation is projected onto the
object surface, usually three phenomena
occur:
1. Absorption
2. Reflection
3. Transmission
Absorption
• Absorption: is the fraction of irradiation
absorbed by a surface.
• Absorption of electromagnetic radiation is the
way in which the energy of a photon is taken
up by matter, typically the electrons of an
atom. Thus, the electromagnetic energy is
transformed into internal energy of the
absorber, for example solar panels
Reflection
• Reflectivity: is the fraction reflected by the
surface.
• It is generally refer to the fraction of incident
electromagnetic power that is reflected at an
interface
Transmission
• Transitivity is the fraction of electromagnetic
radiation at a specified wavelength that
transmitted by the surface
Distribution of Sun’s energy
Solar energy on Architecture and
urban planning
• Sunlight has influenced building design since
the beginning of architectural history: Solar
effect on urban planning were first employed
by the Greeks and Chinese, who oriented their
buildings toward the south to provide light
and warmth
• Agriculture: Agriculture and horticulture seek to
optimize the capture of solar energy in order to
optimize the productivity of plants
Solar energy on Architecture and
urban planning
• Agriculture
• Greenhouses: in greenhouses solar light is converted into
heat enabling year-round production and the growth (in
enclosed environments) of specialty crops and other plants
not naturally suited to the local climate.
– The first modern greenhouses were built in Europe in the 16th
century to keep exotic plants brought back from explorations
abroad
Solar energy on Architecture and
urban planning
• Solar thermal: Solar thermal technologies can
be used for water heating, space heating,
space cooling and process heat generation
• Solar electric: where sun light converted to
produce electricity
Microclimate
• Microclimate is a local atmospheric zone where
the climate differs from the surrounding area.
Example this room climate is different from the
whole building, The building climate is different
from the whole university climate, etc. It may
refer to areas as small as a few square meters or
as large as many square meters
• It is important to architect to understand
microclimate to design houses that more energy
efficient.
Microclimate
Microclimate
Microclimate
Microclimate
Factors affecting Microclimate
1.
2.
3.
4.
Temperature
Humidity
Wind
Solar radiation
Factors affecting Microclimate
1. Temperature: temperature affected by:
1. Altitude: Air temperature drops 1°C for 100 m rise in
altitude during summer and 130 m in winter
2. Proximity to water: Sea and lakes drops surrounding
temperatures
3. Ground Cover: Natural vegetation tends to moderate
extreme temperature (Green roof houses)
4. Urban development: it raises air temperature
because it blocks winds.
Factors affecting Microclimate
2. Humidity: the amount of water vapour in the air
Humidity affected by:
1. Altitude: Humidity decreases with higher altitude
2. Proximity to water: Sea and lakes increases Humidity
3. Ground Cover: Natural vegetation tends to increase
humidity(Green roof houses)
4. Urban development: decreases humidity near the
ground
Factors affecting Microclimate
3. wind affected by two factors which
determine wind speed. The pressure gradient is
the first. The second is friction
1. Altitude: wind speed increases at higher altitude
2. Urban development: decreases wind speed
Factors affecting Microclimate
4. Solar radiation affecting microclimate as
south facing slope receive greater solar
radiations than north slopes resulting higher
ground temperature.
Factors affecting Microclimate
The usage of overhangs and shades
Optimum site location
Temperature (in winter) we need to make the site
warmer by implementing:
1. Maximize solar exposure
2. Provide means to reduce outgoing
radiation at night
3.Remove shading devices during day
4. Use heat retaining structural materials i.e.
concrete
5. Locate outdoor on the south or south west
side of the buildings
Optimum site location
Temperature (in summer) we need to make the
site cooer by implementing:
1. Extensive use of trees as shade
2. Use overhangs and light colour blinds
3. Use ground covers on earth surfaces rather than
paving
4. Use areas on north and east of the building for
outdoor activities
Optimum site location
Humidity to make the site more humid we need
to implement:
1.
2.
3.
4.
Allow standing water on the site all the time
Increase overhead planting to add moisture
Use grass as ground cover
Add water fountain, pool, water features and etc.
Optimum site location
Humidity to make the site drier we need to
implement:
1. Maximize solar radiation exposure and reduce
shadings and overhangs
2. Increase ventilation and air flow
3. Install efficient drainage system
4. Use pavement like tarmac
5. Reduce grass and plantings
6. Eliminate water fountains, pools and water features
Optimum site location
Wind to make the site less windy:
1. Use extensive wind break like trees and
structures
2. Do not trim lower branches of tall trees
Optimum site location
Wind to increase wind flow:
1.
2.
3.
4.
Remove all obstruction (trees, structures, etc.)
Trim all lower branches of tall trees
Limit all trees grow to 3 m
Built dicks or platforms on the areas most
exposed to breezes
Cooling Load
• Cooling load (heat gain): Is the amount of heat energy to be
removed from a space by the HVAC equipment to maintain
the space at a certain comfort level
Cooling Load Types
 Latent heat: Is the heat content due to the
presence of water vapour in the atmosphere
 Sensible heat: Is the heat content causing an
increase in dry bulb temperature
 Total gain: Is the sum of latent and sensible
Cooling load
Indoor environment quality groups
HVACs’ systems main task is to maintain indoor
optimal comfort standard with minimal energy
consumption and minimal negative impact on
the environment
Indoor environment quality groups
Indoor thermal comfort
• Thermal comfort can be maintained when the
generated heat by human body (metabolism)
is dissipated to the environment while keeping
thermal symmetry with surroundings
Indoor thermal comfort
• Standards
ASHRAE 55
They indicate that thermal environmental
conditions must be acceptable to 80% or more
of a building’s occupants
It is not 100% due to an expected group of
occupants’ dissatisfaction with thermal
environment during a building operation
Why Maintaining thermal comfort
standards in a building
• Thermal discomfort can lead to what is known
as sick building syndrome (SBS)
– Symptoms of sick building syndrome are eyes
irritations, nose dryness, sore throat, skin
irritations and dryness and other general health
problems
Metabolism
• What is Metabolism: The combustion of
nutrient materials and the transport of
substances between the body cells produces
heat
Human Bodies
• Human body generate heats because we are
warm blooded creatures
• Heat is produced depends on the metabolic
rate
• Metabolic rate depends on human activity
level
• Some of the energy generated by muscular
activity will be translated into work and the
excess energy will be dissipated as heat
Parameters of indoor thermal comfort
• influenced by various environmental
conditions
– indoor air temperature,
– mean radiant temperature,
– humidity
– air speed,
– and other personal like clothing
indoor air temperature
• The suitable indoor temperatures are
between 20° and 22°C in winter and 26° to
27°C in summer when the ambient
temperature is above 30°C
Mean radiant temperature
• Mean radiant temperature is known as the mean
temperature of the surfaces that environs an
inhabited space
• the difference between indoor air temperature
and mean radiant temperature should not be
greater than 2 ºC
• Therefore, a bright coloured or reflective external
window blinds can be used to minimise the affect
of mean radiant temperature
Humidity
• high humidity will prevent the evaporation of
human skin sweats and respiration system
vapours leading to discomfort
• low humidity produces dryness, itching and
annoying static electric sparks which lead to
discomfort
• humidity should be 40 to 70%.
Air speed
• During cold ambient conditions human bodies
feel uncomfortable with air velocities above
0.15 m/s
• In summer and hot days human bodies are
comfortable with higher velocities up to 0.6
m/s
Indoor air Quality IAQ
• Human beings as a condition of survival need
a continuous supply of fresh and clean air.
• The need for air is relatively constant at 10-20
m3 per a day.
Indoor air Quality IAQ
• Indoor air quality (IAQ) is defined as the
essence or the nature of a conditioned air
within a building or a structure. It is
considered as the scenery of air that affects
the building occupant’s health and their well
being
Indoor air Quality IAQ
• Or where the air is free from any known
contaminations at a harmful level.
• In addition, whether this air satisfies thermal
comfort, normal concentration of respiratory
gases (oxygen and carbon dioxide) and
acceptable limit of air pollutants.
Importance of IAQ
• Indoor air quality is a major concern for
building designers, developers, operators,
tenants and owners
• because human exposure to poor indoor air
quality may cause a high health risk; like
respiratory illness, fatigue, nausea and
allergies.
• Indoor air quality affects occupants’ comfort,
production, job satisfaction and performance.
Importance of IAQ
• Presently, humans become alert for potential
health hazards associated with poor indoor air
quality and its negative impact on human
production. This is due to gaseous or
substances contaminants as well as biological
and building particles released into indoor air
and inadequate building ventilation.
Why Poor IAQ Happens
• In addition poor indoor air quality can be
exacerbated by the implementation of
• energy conservation strategies
• the awareness of environmental issues
associated with energy usage
• sealed buildings
• the wide spread of photocopiers and printers
and
• other resources of air contaminators
Factors affecting indoor air quality
Source
• Indoor air pollution sources: Indoor air
contamination sources are internal and external.
– Internal contamination sources are originated from
buildings internal envelope .
– External contamination sources are originated from
outdoor sources.
– The possible sources of contaminants and pollutants
to indoor air are: biological contaminants, building
materials and substances, tobacco and smoke,
cleaning products and maintenance, combustion
sources, HVAC systems, and outside sources [69].
Building layout
• Physical buildings’ layout: Physical building
layout including sight, climate, building materials
and furnishings, moisture, processes and
activities within the building controls air pressure
differentials and the way how indoor air moves
inside a building as well as how much fresh
outdoor air enters the building.
• Thus a sudden change of air patterns can affect
contaminant concentrations in different spaces
within a building that have a direct impact on
IAQ.
HVAC
• Buildings HVAC systems: The main function of buildings
HVAC systems is to change the indoor air property of
an occupied space of a building in order to provide
thermal comfort for occupants.
• Poorly designed or maintained ventilation systems will
cause indoor air quality problems.
• In general, economic and environmental restrictions
control buildings’ ventilation system which has a direct
impact on indoor air quality. For example in some cases
buildings’ operators reduce the amount of fresh air
through the building in order to reduce the cost of
HVAC systems operation.
Buildings’ occupants:
• Buildings’ occupants are considered as a main
source of contaminations.
• Buildings’ occupants’ contribution to
contaminants and pollutants varies from one
occupant to another as a result of different
people having different metabolism rates and
different activities such as cooking, washing,
smoking, and body odour production.
Buildings’ occupants:
In some cases there are special groups of
occupants that require different air purity
standards and special conditioned air needs
such as people with allergy, asthma, people with
respiratory disease, people whose immune
system is suppressed, people who require
radiation therapy and people with contact
lenses, etc
Types of contaminants and pollutants
• different from building to another depending on
buildings’ nature and site such as building’s
geographical position, building’s different
materials which have been used during its
construction or operation and traffic volume
around it.
• the most common indoor pollutants are Carbone
dioxide (CO2), Nitrous Oxide (N2O), Carbone
Monoxide (CO), Nitrogen Dioxide (NO2), Sulphur
Dioxide (SO2), Ozone (O3) and Radon.
indoor air problems can be eliminated
or decreased by adopting
• Source control: This strategy is considered as the
most cost effective approach in order to eliminate
or to reduce IAQ problems. Methods of source
control strategy are:
– Pollutions and contaminations sources elimination or
reduction.
– Pollutions and contaminations source cover or
concealment.
– Buildings’ environment modifications e.g. indoor
humidity and temperature control.
indoor air problems can be eliminated
or decreased by adopting
• Buildings’ ventilation modifications: This strategy
is effective when buildings are under ventilated
and when the source of contaminations or
pollutions are unknown. Methods of ventilation
modifications are:
– Diluting contaminations and pollutions with outdoor
fresh air.
– Air pressure control to isolate pollutions or
contaminations.
– Increasing the flow of outdoor air.
indoor air problems can be eliminated
or decreased by adopting
• Air cleaning process: This strategy is the most
effective way to mitigate IAQ problems specially
when combined it with either source control or
ventilation. Moreover it is the only strategy can
be used when the contamination sources are
external. Methods of air cleaning processes are:
–
–
–
–
Particulate filtration.
Electrostatic precipitation.
Negative ion generation.
Gas sorption.
indoor air problems can be eliminated
or decreased by adopting
• Exposure control: This strategy is a set of
administrative tactics can be used by
buildings’ managerial team and operators to
tackle IAQ problems by controlling occupants’
behaviours and activities. Examples of
exposure control strategies are:
– Scheduling contaminant-producing activities.
– Relocating susceptible individuals.
– Education and communication.
Energy conservation strategies
• Buildings energy consumption depends on
building envelop, efficiency of HVAC and
lighting systems, amount of required fresh air,
internal and external heat gain and the
building operation hours and maintenance.
Energy Reduction
• Buildings’ energy demand can be reduced by
implementing certain strategies:
– Operational management: This process is based
on rescheduling after hours activities and
implementing of building management system
(BMS) which enable building operators to control
full or partial shutdown of building as well as
control and regulate temperature in each space or
zone to comply with ASHRAE comfort standards.
Energy Reduction
• Reduction of cooling loads (heat gain): This
can be achieved throughout a set of
procedures including solar radiation control
which leads to a reduction of heat gain
throughout the building envelop. Solar
radiations control can be done using plants,
vegetation and using light coloured exteriors
walls.
Energy Reduction
• Buildings envelop modifications: The most
common techniques used in building envelop
modifications are installation of internal and
external shading devices, double glazing and
walls and roofs insulations.
Energy Reduction
• Equipment modifications: Examples of this
strategy are installing heat recovery wheels,
ventilation and radiant terminals.
Energy Reduction
• Employing passive and renewable energy
cooling techniques: these techniques are free
cooling techniques despite the fact of their
high installation cost.
Solar Energy
Solar energy
• Solar energy is the energy produced by sun
radiation. It is considered to be the most
powerful, abundant, clean, environmental
friendly and inexhaustible energy resource
available to humans.
Solar energy
• In general all renewable energy resources
derive their energy from the sun except
geothermal and atomic energy. For example
wind energy is derived by temperature and
pressure variation that is created by sun’s
affect. Hydro energy is a result of solar driven
water cycle. Fossil fuels came as a result of
drying process of organic matters by the sun’s
radiation millions of years ago
Solar energy harvesting techniques
• Passive harvesting techniques: Examples of this
technique are materials selections favourable for
their thermal specifications, building designs with
respect to natural air circulation and building
oriented to the sun and sun light dispersing.
• Active harvesting techniques: Where solar
collectors including electric photovoltaic panels
and thermal collectors is used to convert solar
radiation and heat into energy
Active harvesting techniques
• Solar thermal collectors: where solar
radiations and heat is collected and used to
produce heat. In other words it is defined as
the conversion of solar radiation into thermal
energy (heat).
• Solar photovoltaic (PV) modules: where solar
radiations are converted directly into
electricity (Direct Current) using photovoltaic
cells (PV).
How much energy we can get
• The total annual energy output from a solar
system Eₒ in (KWh) can be calculated :
– where η is energy conversion efficiency, Ac is solar
panels surface area in (m²), G is the integrated
solar irradiance over a year (W/m²).
key problem confronting a wider use
of solar energy
• is the substantial variation of spatial and
temporal in solar radiation pattern
• Requirements of high quality information and a
comprehensive database
• The cost of solar energy production remains high
compared to other production options.
• Solar resources intermittency especially in rainy
days.
• Lack of support and grants
Solar collectors
• Solar thermal collectors: solar collectors are a
type of heat exchange that is designed to
absorb and convert solar radiation into usable
or storable forms of energy
Solar thermal collectors
• solar collectors classified into three types of
collectors:
– low temperature collectors,
– medium temperature collectors
– high temperature collectors
Low temperature collectors
• The outlet temperature of these types of
collectors normally ranges between 40 ºC and
90 ºC.
– The most common type of low temperature
collectors is flat plate collectors (FPC).
– Low temperature collectors are used for
processing heat e.g. to heat swimming pools and
in HVAC systems. Normally collector’s heat
medium is water and air.
Medium temperature collectors:
• outlet temperature of this type of collector is
60 ºC-250 ºC.
– An example of medium temperature collectors is
evacuated tube collectors (ETC).
– This technology is used on solar drying, solar
cooking and distillation.
– Normally this type of collector’s heat medium is
also water and air.
High temperature collectors
• The outlet temperature of this type is more
than 250 ºC.
– An example of high temperature collectors are
parabolic dish reflector (PDR).
– These types of collectors are used directly to
produce steam and then electricity.
– heat medium is liquid fluoride salts
Market available solar thermal
collectors
• Market available collectors’ fall into two
categories
– non-concentrated collectors where the collector
area is the same as solar radiations’ absorber
area.
– The second is concentrated collectors where
collectors have a concave reflecting surfaces or
mirrors to intercept, magnifying and focus the
sun’s radiation to smaller receiving areas in order
to increase radiation flux
Non-concentred collectors
• These types of collectors collect solar
irradiance without using magnifying or
concentration mediums like mirrors
• Types of this family
– flat plate collectors
– evacuated tube collectors
– compound parabolic concentrators.
Flat plate collectors
• Flat-plate collectors are the most common,
cheapest and simplest type of solar thermal
collector.
• These types of collectors were developed by
Hottel and Whillier in the 1950s
Flat plate collectors FPC
Flat plate collectors FPC
• FPC consist from the followings
– The first part is the absorber: This part of the collector
is a flat plate absorber of solar energy.
– The absorber consists of pipes network which has a
direct contact with the absorbent background which is
made from thin dark coloured metal sheet e.g.
thermal polymers, aluminium and steels.
– Absorber plates are normally painted with special
coatings, which is able to absorb and retain heat
better than normal black paint.
Flat plate collectors FPC
• FPC consist from the followings
– The Second part is the transparent cover (glazed):
The weatherproof absorbent box is covered by a
transparent cover (glass) and filled with air cavity
between the surfaces to prevent heat dissipation
and to minimise radiation losses
Flat plate collectors FPC
• FPC consist from the followings
– Third part is heat transport medium (fluid): A heat
transport fluid is used in order to remove heat
from the absorber and then transfer it to the end
user or a storage facility. Examples of these fluids
are air, antifreeze, glycol-water and water. Fourth
part is the heat insulation box: The absorber
system is fitted in a box that is insulated to
prevent heat loss to the surroundings.
Flat plate collectors FPC
• FPC Principle of work
– Based on the law of blackbody radiation the
process starts by passing the sun light directly to
the absorber plate through the glass cover,
causing heat to the absorber. The heat is then
removed by the transport fluids through the pipes
network in the absorber box
– Flat plat collectors normally are installed at a fixed
solar collection angle.
Flat plate collectors FPC
• Applications of FPC
– This type of collector is commonly used to
generate hot water for residential buildings, space
heating and cooling and to heat swimming pools’
water. The use of FPC in commercial buildings is
limited to small businesses like a car wash,
Laundromat and restaurant.
Evacuated tube collectors
• evacuated tube collectors consist of an array
of parallel evacuated heat pipe tubes (EHPT)
which are connected to the top header pipe or
a heat exchanger manifold.
Evacuated tube collectors
Evacuated tube collectors
– Each heat tube is composed of a metal heat pipe
that is connected to a dark coloured absorber
plate. Absorber and the heat pipes are normally
made from copper, due to its superior thermal
conductivity
– Both components setup are surrounded by glass
tube to prevent convection and conduction heat
loss to surroundings, where the space between
the tube and the absorber is evacuated
Evacuated Tube Collectors ETC
• ETC Principle of work
– The heat process is achieved by transferring heat
into the header tube (heat exchanger manifold).
– The sealed metal heat pipes contain a small
amount of fluids below atmospheric pressure. The
low pressure fluids evaporate causing the hot gas
to rise up in the heat pipes by convection
– Then the condensed fluid falls down the heat pipe
by gravity, so the process starts again
Evacuated Tube Collectors ETC
• ETC Principle of work
– Due to evacuated tube collectors tubular design it
is capable of collecting sun energy from different
angles
Evacuate Tube Collectors ETC
• Applications of ETC
– This type of collectors is commonly used in
cooking, commercial buildings’ water heating,
solar cooling technologies (excludes desiccant)
and electric power generation.
– Evacuated tube collectors (ETC) are the most efficient solar
thermal collectors
Solar air collectors
• Solar air heat collectors are a type of
collectors where sun radiations are harvested
and used to heat air directly
– This technology can be classified into two
categories: glazed and unglazed collectors
Glazed air collectors
• Glazed collectors are transparent (covered)
collectors that have a top sheet and an
insulated side and back panels to minimise
heat loss to the environment
• air passes along the front or back of the
absorber plate gaining heat directly from it
Un-Glazed air collectors
Air collectors
• the most common market available collectors
that belong to this category are transpired
solar air collectors
• Solar heat air collectors can be used directly
for various applications or may be stored for
later use. The most common applications for
air glazed collectors are spaces heating and
drying and it is also widely used in agriculture
industry in crops drying.
Air collectors disadvantages
• However solar air heat collectors have two
known disadvantages: low thermal capacity
of air and low absorber to air heat transfer
coefficient
Concentrated solar collectors
• Parabolic trough collectors
• Parabolic trough collectors are a type of solar
energy collectors made from coated silver or
polished aluminium (mirrors) which is shaped
like the letter U as shown in the Figure
Concentrated solar collectors
• They constructed and installed to form long
parabolic mirrors with a flask tube (Dewar)
running on its length at a focal point.
• The trough collectors can be oriented on a
south south axis and have a sun tracking
devices to rotate it in order to harvest the
maximum possible sun irradiance
Concentrated solar collectors
• Operation: Heat process in parabolic trough
collectors is achieved by transferring heat
from the absorber to the heat transport fluid
(oil)
• Then the heated oil temperature increases to
near 400 °C which can be used to generate
steam
Selections
• The selection of suitable solar collectors
depends on the climatic conditions, load
requirements, costs, and output temperature.
HVAC
Heat ventilation and Air conditioning
Refrigeration
• Definition: The process of cooling of a bodies or
fluids to temperature lower than those available
in the surroundings at a particular time and
place.
– Note here in refrigeration cooling is involved but
refrigeration not exactly same as cooling
• Cooling can be spontaneous and the final temperature need
to be lower than surroundings
• Refrigeration is not spontaneous and the final temperature
should be lower than the surroundings.
Refrigeration
• Example of cooling process not refrigeration:
– Cooling of s hot cup of coffee
• Here the final temperature cannot be lower than
surrounding temperature
• Cooling of glass of water by adding ice here the final
temperature will be lower than surroundings
(refrigeration)
Air conditioning
• Air conditioning: is the treatment of air so to
simultaneously control its temperature,
moisture content, quality and circulation
– In order it is
• required by occupants
• a process
• product in the space.
Application of refrigeration
• Food processing and preservation
• Chemical and process industries
• Comfort and industrial air conditioning
History of refrigeration
• Age of natural refrigeration
– The beginning of 19th century
• Age of artificial refrigeration
– From 19th century onwards
Refrigeration
• Natural Refrigeration methods
– It is called natural because we relay in nature to
provide Refrigeration
–
–
–
–
Use of natural ice, that is:
Transport from colder regions
Harvested in winter and stored for summer
Producing ice by nocturnal cooling
• nocturnal : The apparatus consisted of a shallow ceramic
tray with a thin layer of water, placed outdoors with a clear
exposure to the night sky
Refrigeration
• Natural Refrigeration methods
– Use of evaporative cooling
• When water is evaporate to surroundings its provide
cooling. Evaporative cooling is effective when
surroundings is dry and useless on humid regions
– Cooling by salt solution
• when we dissolve certain salts on water, the water
temperature will drop as a result of endothermic
process. The quantity of cooling is too law.
Limitation of natural methods
• Depends on local conditions
• Uncertainty due to dependence on weather
• Difficult to produce large amount of
refrigeration
• Not available to every body
Artificial refrigeration
• Classified into:
– Non Cyclic :
– Cyclic
Non Cyclic
– Non Cyclic :refrigeration is accomplished based on
total loss refrigeration principle e.g. melting ice or
sublimations of frozen carbon dioxide
– Example by melting ice, heat is transferred by
convection from the warmer air inside a
refrigerated space to the ice which absorbs heat,
making the refrigerated space cooler than
ambient.
– Non cyclic refrigeration is used on small scale
applications e.g. portable coolers, workshops and
laboratories.
Non Cyclic Refrigeration
– The principle portable coolers :
The domestic ice box used to be made of wood with
suitable insulation.
Ice used to be kept at the top of the box, and low
temperatures are produced in the box due to heat
transfer from ice by natural convection.
A drip pan is used to collect the water formed due
to the melting of ice. The box has to be replenished
with fresh ice once all the ice melts.
Cyclic refrigeration
• Cyclic refrigeration operates using
compression and expansion of refrigerant e.g.
chlorofluorocarbons (CFC) and Hydro
chlorofluorocarbons (HCFC).
• Principle : Heat is removed from a cooled
space and rejected to a higher temperature
sink by means of work and inverse work that is
carried out by a refrigerant.
Cyclic refrigeration
• Cyclic refrigeration is divided in two
classifications:
– vapour compression cycle refrigeration systems.
• Currently the dominant refrigeration and cooling
systems worldwide are electrically driven vapour
compression machines
– Gas cycle : similar to air conditioning used in air
planes
History
• General electric (GE) introduced the first
domestic refrigeration in 1911 in USA., followed
by Frigidaire in 1915 and kelvinator in 1918.
• There are a rapid growth is attributed to the
simultaneous development of:
–
–
–
–
Electric motors and compressors
Better shaft seals
Automatic control
Introducing of CFCs in 1930
Artificial refrigeration methods
• Artificial refrigeration methods classified into
three categories based on there working
principles
• vapour compression systems
• vapour absorption systems
• gas cycle systems
vapour compression systems
• The basis of modern refrigeration
– It is the most dominant in refrigeration
• The vapour-compression uses a circulating
liquid refrigerant as the medium which
absorbs and removes heat from the space to
be cooled and subsequently rejects that heat
elsewhere
vapour compression systems
• Components are :
– a compressor
– a condenser
– a thermal expansion valve (also called a throttle
valve)
– and an evaporator.
vapour compression systems
Compressor
• The cooling process starts with stage 1 by
entering (the compressor) where the
circulating refrigerant enters the compressor
as a saturated vapour and compressed to
higher pressure and higher temperature
(stage 2) to form a superheated vapour.
– Saturated vapour: contains as little thermal energy
as it can without condensing
– Superheated maximum temperature with
maximumpressure
Condenser
• The hot, compressed vapour is then in the
thermodynamic state known as a superheated
vapour and it is at a temperature and pressure at
which it can be condensed with either cooling
water or cooling air.
• That hot vapour is routed through a condenser
where it is cooled and condensed into a liquid by
flowing through a coil or tubes with cool water or
cool air flowing across the coil or tubes phase
(saturated liquid).
Condenser
– A saturated liquid contains as much thermal
energy as it can without boiling (opposite of
saturated vapour)
• This is where the circulating refrigerant rejects
heat from the system and the rejected heat is
carried away by either the water or the air
(whichever may be the case).
Expansion Valve
• Afterwards the saturated liquid from the
condenser is routed through the expansion
valve, allowing its pressure and temperature
to drop considerably.
Evaporator
• The cold mixture is then routed through the coil
or tubes in the evaporator
• A fan circulates the warm air in the enclosed
space across the coil or tubes carrying the cold
refrigerant liquid
• That warm air evaporates the liquid part of the
cold refrigerant mixture. At the same time, the
circulating air is cooled and thus lowers the
temperature of the enclosed space to the desired
temperature
Cycle
• Then the evaporative refrigerant evaporates
to the compressor to repeat the cycle
Advantages
•
•
•
•
Vapour compression cycle is characterised by
its low mass flow rate
high coefficient of performance (COP)
low cold plate temperatures and the ability to
transport heat away from its source.
Commercial HVAC
• Commercial air conditioning may be provided
by a variety of equipment ranging from low
horsepower self-contained systems to the very
large built-up central systems of several
thousand ton capacity.
architect’s/HVAC engineer's
responsibility to guide and advise the
customers the best option
Customer/user’s ultimate objective is to acquire
and utilize an air conditioning system that will
provide the most appropriate: performance on a
whole of life basis, in terms of capital, operating,
replacement and maintenance costs..
HVAC systems are importance to
architectural design because
1. The success or failure of thermal comfort efforts is
usually directly related to the success or failure of a
building’s (HVAC) systems;
2. HVAC systems often require substantial floor space
and/or building volume for equipment and
distribution elements that must be accommodated
during the design process;
3. HVAC systems require significant capital investments;
4. The HVAC system is responsible for large portion of
building operating costs.
Selection of different HVAC system
designs and operational
• every building is unique in its design and
operation. For instance residential
apartments, shopping complex, office
complex, hospital, hotel, airport or industry;
all have different functional requirements,
occupancy pattern and usage criteria.
Selection of different HVAC system
designs and operational
• The geographical location of the building,
ambient conditions, indoor requirements,
building materials, dimensional parameters,
aesthetic requirements, noise and
environment issues need different treatment.
The selection of appropriate HVAC
1. Thermal Comfort : The internal environment
of the buildings must be a major focus point
in the HVAC system selection and this
determined by:
– The activity level
– age
– and physiology of each person affect the thermal
comfort requirements of that individual
The selection of appropriate HVAC
2. Building Architecture: The HVAC system selection
is influenced by the characteristics of the building
such as:
– Purpose of the building
– Type of building structure, orientation, geographical
location, altitude, shape, size and height
– Materials and thickness of walls, roof, ceilings, floors
and partitions and their relative positions in the
structure, types of glazing, external building finishes
and colour as they affect solar radiation, shading
devices at windows, overhangs, etc.;
The selection of appropriate HVAC
3. Available Space:
• Considerable space is needed for mechanical rooms to
house the HVAC equipment. In addition shaft spaces
are required for routing ducts/pipes and other services
e.g. electrical and plumbing work.
• Early liaison is therefore required with the project
architect to proportion the building that would be
occupied by HVAC systems, as this will have an impact
on the size and cost of the building.
The selection of appropriate HVAC
4. Building ceiling heights:
• The HVAC designer must thoroughly evaluate
the ceiling space for air distribution ducts
• Inadequate spaces to run ducts, probably
force the system designer to use decentralized
or unitary air conditioning units.
The selection of appropriate HVAC
5. Building Aesthetics
• The HVAC layout should be complementary to the
building architecture. Often the requirements are
stringent for example:
– No equipment should be visible or should suitably blend
with environment
– Size and appearance of terminal devices in ceiling shall
harmonize with lighting layout, fire sprinklers, detectors,
communication systems and ceiling design;
– Acceptability of components obtruding into the
conditioned space;
– Accessibility for installation of equipment, space for
maintenance;
The selection of appropriate HVAC
6. Efficiency/Performance and Energy Use:
• To assemble the best HVAC system, the efficiency,
performance, cost and energy use will be major
considerations when selecting components for
the system.
• The cost of the energy consumed by the
components of the HVAC system is an important
aspect of the system selection. Each component
must use as little energy as possible and still meet
the performance requirements.
The selection of appropriate HVAC
7. Availability of water:
• The places where water is Insufficient for the
demand, the only choice leans towards aircooled equipment
The selection of appropriate HVAC
7. Noise control:
• Sufficient attenuation is required to minimize
equipment and air distribution noise. It is
important to select low decibel equipment
and define its location relative to the
conditioned space.
The selection of appropriate HVAC
8. Indoor environment and its control
• Equipment and control design must respond
to close tolerances on temperature/humidity,
cleanliness, indoor air quality etc.
• Zone control or individual control is important
consideration for the anticipated usage
patterns.
The selection of appropriate HVAC
9. Delivery and Installation schedules
HVAC designer must evaluate the equipment
options that provide short delivery schedules
and are relatively easy to install.
The selection of appropriate HVAC
10. System flexibility: The HVAC designer need
to consider the likelihood of space changes and
future ezpansion.
The selection of appropriate HVAC
11. Codes & Standards
The selection of the HVAC system is often
constrained by various local codes and ASHRAE
standards.
The selection of appropriate HVAC
12. Life cycle costs:
Capital, running costs, maintenance costs, and
plant replacement costs need to be taken into
account so that the selected system
demonstrates value for money to install and
operate