Presentation on theme: "Developments Preindustrial Era: prior 1800s where the building envelop was the principal means of controlling thermal environment and illumination within."— Presentation transcript:
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 EraIndustrial Era Thick externalThin minimum skin Tight thermal envelopMechanical HVAC Short depth for lightGreater depth for light due to artificial lighting Short depth for ventilationBig depth for ventilations due to forced convection High CeilingLow ceiling Low rise buildingsHigh rise buildings Materials was restricted to available resourcesAll 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=1000J1MJ= J 2.kWh = 3600 kJ 3.Calorie = J 4.British Thermal Unit (BTU)= kJ
Energy Examples: Convert 10 J into Calorie Answer is 10/ = Convers 10kWh into Calorie Answer: 10kWh? In kJkJ=3600*10=36 MJ Calorie= /4.1868= =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: 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)* Diamond1000Fiberglass0.04 Silver406.0Brick, insulating0.15 Copper385.0Brick, red0.6 Gold314Cork board0.04 Brass109.0Wool felt0.04 Aluminium205.0Rock wool0.04 Iron79.5Polystyrene (Styrofoam)0.033 Steel50.2Polyurethane0.02 Lead34.7Wood Mercury8.3Air at 0° C0.024 Ice1.6Helium (20°C)0.138 Glass, ordinary0.8Hydrogen(20°C)0.172 Concrete0.8Nitrogen(20°C) Water at 20° C0.6Oxygen(20°C) Asbestos0.08Silica aerogel0.003
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 K at exited at 300 K? Answer =(50.2*2.5( ))/6 =
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
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.
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.Allow standing water on the site all the time 2.Increase overhead planting to add moisture 3.Use grass as ground cover 4.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.Remove all obstruction (trees, structures, etc.) 2.Trim all lower branches of tall trees 3.Limit all trees grow to 3 m 4.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
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 m 3 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 .
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 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
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
– 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 19 th century Age of artificial refrigeration – From 19 th 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
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 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 air- cooled 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