This paper describes the study of thermal performance of glazed buildings. The research is based on data from the United Kingdom and other areas and countries were referenced. This is due to the data available and the sources found and used to complete the study. The investigation will question the frequency of use in the commercial industry of glazing. The aim of this investigation is to determine the most suited type of glazing for the commercial industry. The type of glazing which would offer benefits over other alternatives would also have to be the most economical, in terms of maintenance, lifespan and external elements. The external elements in question are the mechanical operations that help control the thermal environment. These systems vary depending on the type and the performance of the glazing used. Solar gains will have to be coincided as an external factor. The outdoor environment being part of the solar gains subject will be dependent on the climate and geographic of the area of the data. The thermal properties of the different types of glazing have been analysed Retail buildings were chosen for the second guide because of the impact of their energy use in the commercial building sector. According to the Energy Information Administration's (EIA) Commercial Building Energy Consumption Survey (CBECS) in 2003, retail buildings account for 319 trillion Btu of energy use, or approximately 5.5% of the energy use of all commercial buildings (CBECS 2003). (Pacific Northwest National Laboratory, 2006, p. 12) to be done at end.
1.1 Rationale for the research
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"Householders are looking for far more contemporary designs in their buildings which often include larger areas of glazing or even fully glazed structures, but obtaining Building Regulations approval for extensions with a high degree of glazing has proven difficult for some architects and builders. This is because Approved Document L1B of the Building Regulations limits the amount of glazing to a total of 25% of the floor area plus any window/door openings that would be covered over by the extension.
However, there are other ways to demonstrate compliance with the glazing requirements. One method that can be used requires an energy calculation involving the averaging out of all of the 'area weighted 'U' values' of the extension and comparing them to the average U value of a notional extension of the same size where the minimum standards of L1B have been met including glazed areas. If the proposed 'area weighted average U value' is lower than that of the notional extension then the proposed extension is compliant."
(Elmhurst Energy Systems Ltd)
This problem has many influencing factors including the type and scale of the glazing involved in the property and the external factors. In having to choose which glazing fits the purpose of generating the correct u-value and is still in keeping with the design, the task requires a strategy in managing the fluctuations in the environment and accounting for seasonal change. Installing external systems to help the internal environment to adapt to the changing climate would be an option. This could be air conditioning units and space heaters. These systems incur additional costs and maintenances.
There are advancements in glazing that should reduce such additional costs and maintenances. However, these can only be installed if the increased price for such advancements can be justified through payback time.
"Architects are increasingly using glass in modern designs - such as for the planned "Shard of Glass" London Bridge Tower, potentially the highest skyscraper in Europe - as it creates light places for people to live and work...
...But many windows also let in great quantities of heat, especially in hot climates. This drives demand for air-conditioning."
(BBC News, 2004)
This issue which BBC News has identified is the increased demand for air- conditioning. This demonstrates how there must be further research undertaken into glazing to reduce the thermal gains or to control the thermal gains in a more energy efficient way.
"In some cities, such as Tokyo, all the air-conditioning equipment creates a haze across the skyline in summer.
Air-conditioning in summer frequently uses more energy than heating a building in winter." (BBC News, 2004)
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To prevent similar events and conditions appearing in other places, actions to minimise the energy used to cool and heat buildings have to be taken. The range of solar shading and new glazing on the market should stop this situation. This dissertation will research into the glazing available and come to the conclusion as to which type of glazing will best suit a commercial retail unit.
"The Government also wants to introduce improved energy efficiency standards for new non-domestic buildings, and in its 2008 Budget announced an ambition for all new non-domestic development to be net zero carbon from 2019. We are therefore proposing a similar phased improvement beginning with 25 per cent in 2010 and plan to consult on the further trajectory towards zero carbon new non-domestic buildings later this year."
(Department for Communities and Local Government, 2009)
The Government have the target for all new non-domestic buildings to be zero carbon from 2012 and twenty five percent of all new non-domestic buildings in 2010 to be zero carbon. Reviews are to be estimated later this year.Â This shows the importance of lowering the carbon emissions in the building and construction industry. It also shows how not only the industry but the Government are making changes to lower overall carbon emissions. New buildings are incorporating more glazing into their design which involves the structure and the cost to manufacture, install and maintain the glazing which has to be in keeping with the government initiative and budget.
"Glazings and fenestration have always been a prominent element of architectural form and expression. Significant changes have already occurred in glazing and facade design over the last 25 years... New trends in building design and operation, the changing utility marketplace, and new global environmental concerns are likely to continue to create interest and opportunities for further advances in glazing systems... These glazing and façade systems will become essential elements of virtually all "green buildings," the best of which will reduce energy use by 70% compared to buildings today..." (Stephen E. Selkowitz, Building Technologies Department, January 1999)
While Architects and designers still use glazing as elements for building there will always be a need for development in new methods and styles of glazing.
1.1.1 Research aims and Objectives
The aim of this research is to identify the ideal type of glazing for retail commercial units while still meeting the building regulations. Also, to investigate the thermal elements of a building to see if they benefit or hinder the carbon footprint of a retail unit and to see if the thermal gains can be controlled without the use of external systems.
- To establish the rationale behind the decision for using glazing in retail units
- To establish the thermal benefits of using glazing in retail units
- To establish the problems involved in using glazing
- To review the current methods of tackling thermal (solar) gains.
- To identify any relationship between glazing and carbon emissions.
- To understand the impact of glazing within the retail market.
1.1.4 Key Questions
1. How does the use of glazing in retail influence the general public into approaching the retail unit in terms of style and design?
2.Â How does the thermal environment inside a retail unit affect the overall space?
3. Would energy saving glazing reduce energy costs in retail buildings?
4.Â Which type of glazing would best suit a retail unit?
1.1.5 Outline research Methodology
In accordance with the objectives outlined it will be essential to implement an approach to the research that will take bearing from existing information available combined with the experience and knowledge of individuals involved in the specific area of glazing and retail glazing. Existing buildings shall be examined to identify their benefits and problems with thermal gains.
The information gathered shall be divided into several stages to get a balanced and complete understanding of the nature of the problems and current solutions.
Stage 1.Â Literature Review
The initial stage will involve a review of all relevant literature available on the subject of glazing, retail environments and thermal gains. This literature will include research papers, books, journals, newspapers archives, industry magazines, government reports and relevant web sites. The literature review shall give me a full detailed understanding of the subject matter of glazing and provide direction, from the conclusions drawn, on how the research will be carried forward.
Stage 2.Â Exploratory interviews
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This stage will involve investigating the opinions and views of the key personnel of retail outlets in Nottingham. This will help by understanding the decision making and issues surrounding the use of glazing in retail units. The outcome of these interviews shall shape and give guidance to the next stage of data collection.
Stage 3. Questionnaire
In order to fully understand the impact of this topic it is necessary to gather the views and opinions of all parties affected by this subject area. This stage shall involve the development of a questionnaire to be sent. The questionnaire will also be issued to manufacturers and suppliers.
Stage 4.Â Data Analysis & Case studies
The fourth stage will involve the analysis of the data gathered in relation to the key questions outlined in the research aims and goals. Conclusions will be drawn from the data gathered and the analysis of this data. Three case studies shall be reviewed to test the findings of the conclusions. These will be assessed in relation the overall objectives to find if the all the targets have been fully met.
2.0Â Literature Review
Glass is a key element of buildings and is essential architecturally, socially, psychologically as well as environmentally.
"Today more attention is being given to the performance of windows and they are being designed to do exactly what is required of them." (T.Muneer, 2000, p. 1)
This extract tells us that glazing advancements are heading in the right direction and are being developed for a purpose. This review will examine the current market for the types of glazing which would fit the retail sector; especially glazing which would give the best thermal performance.
"Recently, high levels of insulation, lower infiltration rates and larger areas of glazing aperture have been required in the design of buildings. In the view of this increasing demand, the conventional window has become the weakest thermal fabric in a building." (T.Muneer, 2000, p. 1)
This is true in most cases where the glazing used is not to the current standard (e.g. double glazing) in terms of the new technology currently being developed and implemented.
"Studies show that 6% of the United Kingdom's energy consumption is due to heat losses from domestic glazing alone.Â In addition to their poor thermal performance, conventional windows can create comfort problems and damaging accumulations of condensation." (T.Muneer, 2000, p. 1)
These studies show that these disadvantages have pushed the need and demand for windows with a higher thermal performance. Double glazing is the most common method of providing an average level of thermal resistance in order to resolve this issue. Within double glazing, technologies have been introduced to enhance the performance. (T.Muneer, 2000, p. 1)Â
"Examples of new advancements include spectrally selective low-emissivity coatings on glass and on thin plastic films, solar control coatings, infrared transparent glazing, anti reflective surface treatments, low-conductivity infill gases, honeycombs, silica areogels, multi-layer film suspension systems, holographic coatings, optically switchable glazing, polarised glazing and evacuated enclosures." (T.Muneer, 2000, p. 1)
Most double glazing windows produced normally have two panes of glass separated from each other by an edge seal. This edge seal separates the two panes creating a cavity and in turn making it suitable for non-durable coatings and infill gases, but the edge seal also creates a thermal bridge where the internal and external environments can meet. This affects the energy, which will be lost at the perimeter of the window or glazing unit. This is known as cold bridging and can also causes condensation build up inside the panes. (T.Muneer, 2000, p. 1) (Stephen E. Selkowitz, Building Technologies Department, January 1999, p. 1)
"Windows provide humans with a variety of functions which include the supply of interior spaces of buildings with light, solar energy, air and view according to the desires of the occupants and the shield them from dust, noise, rain and excessive heat or cold. (T.Muneer, 2000, p. 2)
This shows how important glazing is to a building no despites its purpose as not only does it benefit a building from the internal aspect but also from the outside. It can provide others with attractive views from the outside inwards.
"Views into buildings that can be used effectively on the design of commercial premises."(T.Muneer, 2000, p. 2)
Throughout history buildings have played a key role in enhancing the human experience. This includes the rudimentary shelters that were built to protect against the dangers and discomforts of the external environment as well as the advantages of modern buildings.
"Humans in seeking shelter need to be able to remain in touch with the outside world that is the shelter must have some form of visual contact." (T.Muneer, 2000, p. 2)
The method of allowing natural light to enter the building or structure is the oldest way of bringing light into a shelter or building. This method can also include openings which would allow fresh air to circulate. The climate, the materials and the external environment control the amount of light that can enter a building. Regulation of the internal space is also important; this could be to control the dust, noise or weather etc. It is crucial to know what is required to remain inside but what also needs to be left outside. It is the advancements in modern technologies which have overcome these issues. Windows have allowed humans to look out onto the external or internal spaces. (T.Muneer, 2000, p. 2)
"People must have windows in their buildings" (T.Muneer, 2000, p. 2)
This shows the importance of this review to find the glazing or windows which would fit ideally into the retail sector. Without glazing or windows all buildings would have a different purpose and feel which would in turn change the function of the building as well as the people's experience inside it. The quote below show how important buildings and internal spaces are.
"NHAPS respondents reported spending an average of 87% of their time in enclosed buildings" (Neil E. Klepeis, 2001)
2.2 History Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
The history of glazing identifies the earliest origins of glass as starting in the form of natural glass. This was formed through nature by the likes of volcanoes and lighting as a result of the intense heat and the melting of sand. It is said man's first used natural glass as tips for their spears. (Britsh Glass)
4000 BC marks the date for the earliest evidence of man-made glass found in the form of glazes used for coating beads. It was not until 1500 BC that the first hollow glass container was made by covering a sand core with a layer of molten glass. (Britsh Glass) (Addis, 2000) (Pilkilngton plc)
In the first century BC glass blowing became the most common way to produce glass containers. During this time glass made was normally highly coloured due to the impurities of the raw materials. In the first century AD glass was produced uncoloured. To colour the glass additional colouring materials were applied. (Britsh Glass) (Glass online, 2010) (Addis, 2000) (Pilkilngton plc)
The art of glass making came to Britain with the Romans. The skills and technology required to produce glass was closely guarded by the Romans and it was not until the Roman Empire crumbled that these skills and technologies for glass manufacture spread throughout Europe and the Middle East. The Venetians in particular gained a reputation for their technical skill and artistic ability in the making of glass bottles. Many of the Venetians craftsmen within the city left to go to Italy to set up glassworks. (Britsh Glass) (Addis, 2000) (Pilkilngton plc)
In Britain the glass industry round Jarrow and Wearmouth date back to 680 AD, while from the 13th century there is evidence of glass and glass industry in the weald and the afforested area of Surrey and Sussex around Chiddingford. (Glass online, 2010) (Britsh Glass) (Pilkilngton plc)
The key milestone in the history of glass occurred with the invention of lead crystal glass by George Ravenscroft. His target was to counter the effect of clouding that sometimes occurred in blown glass by introducing lead to the raw materials used in the process. The new glass he created was softer and easier to decorate and had a higher refractive index, adding to its brilliance and beauty, and it proved invaluable to the optical industry. It is thanks to Ravenscroft's invention that optical lenses, astronomical telescopes, microscopes became possible. (Britsh Glass) (Pilkilngton plc)
The modern glass industry only really started to develop in Britain after the repeal of the Excise Act in 1845 which relieved the heavy taxation that had been enforced. Before that time duties were placed on the amount of glass melted in a glasshouse and tolled continuously from 1745 to 1845. (Pilkilngton plc)
The Great Exhibition of 1851 of Joseph Paxton's Crystal Palace marked the beginning of the discovery of glass as a building material. The ground-breaking new building encouraged the use of glass in public, domestic and horticultural architecture. Glass manufacturing techniques also improved with the advancements of science and better technology. (Britsh Glass) (Glass online, 2010) (Pilkilngton plc)
The semi-automatic process was developed and took over more traditional methods of blowing glass.Â In 1887 Ashley introduced a machine capable of producing two hundred bottles per hour in Castleford, Yorkshire. This was more than three times faster than the previous production methods. (Britsh Glass) (Glass online, 2010) (Pilkilngton plc)
In 1907, the first fully automatic machine was developed in America by Michael Owns from a major glass manufacturer, Owens of Illinois, and was used at its factory in Manchester, Illinois making 2500 bottles per hour. (Britsh Glass) (Pilkilngton plc)
It was not until the First World War when Britain was cut off from essential glass suppliers that glass became part of the scientific sector. Up until then glass was seen as a craft rather than a precise science. Other developments followed rapidly. (Britsh Glass) (Pilkilngton plc)
Today glass production is a modern, hi- tech industry operating in a fiercely competitive global market where quality, design and service levels are critical to maintaining market share. Modern glass plants are capable of making millions of glass containers a day in many different colours, but green, brown and clear remain the most popular. (Britsh Glass) (Glass online, 2010) (Pilkilngton plc)
There are various types of glass which are used in the building industry. These include: Float and window glass, Cast and ornamental glass, Polished wired glass, profiled glass and glass blocks. (Kaltenbach, 2004,p. 10) (Pilkilngton plc)
There are certain surface finishes and structures that were developed for diffusing daylight in a room in particular. The maximum dimensions and thicknessess differ in accordance to the design and the manufacturer. (Kaltenbach, 2004, p. 11) (Pilkilngton plc)
These types of glass have been defined in Translucent Materials as follows:
2.3.1Â Float and window glass
"Float glass is the most commonly used type of flat glass. The maximum strip dimensions are 321 x 600 cm with a thickness of 2 to 19 mm. Greater lengths are possible, but significantly more expensive. Thin glass (only 0.6 to 1.8 mm), windows glass (1.8 to 3.8 mm) and thick glass (over 19 mm thick) are often made by the drawing process. All the glass mentioned will be clear and distort free." (Kaltenbach, 2004, p. 10)
2.3.2 Cast and ornamental glass
"Cast and ornamental glass is also produced as a continuous band. The glass melt is calibrated with rollers and stamped with a surface structure on one or two sides. A spot-welded wire mesh can be set in the soft glass during manufacture. Cast and ornamental glass is translucent, because the light is diffused by the more or less strongly marked surface texture." (Compagno, 2004, p. 10) (Pilkilngton plc)
2.3.3Â Polished wired glass
"Polishing the surfaces produces a transparent wired glass with plane-parallel surfaces. Wired glass panes are used for optical reasons, but are not classed as safety glass. The maximum dimensions of wired glass are 1.98 cm wide, 1.65 to 3.82 cm long and 6 to 10 mm thick." (Compagno, 2004, p. 11)
2.3.4Â Profiled glass
"Cast glass strips can be supplied as louvered elements with textured surfaces. The webs reinforce the glass elements. The surface can be textured in various ways and provided with sun - or heat-protective coatings. These elements are available in standard widths of 22, 25, 32 and 50 cm, and 6 meters long. They are also made with wire inlays to make them more shatterproof."Â (Compagno, 2004, p. 11)
2.3.5Â Glass blocks
"Glass blocks, formally called glass bricks, consist of two shell-shaped glass sections that are reheated until they fuse at the points of contact to form a hollow glass body. They can be coloured in the body, and their surfaces can be smooth or textured. Glass block walls meet the requirements of fire prevention classes G60 and G120. The standard dimensions are 15 x 15 cm to 30 x 30 cm, with a depth of 8 - 10 cm. Extra large glass bricks of 43 x 43 cm were developed and manufactured specially for a Tokyo department store." (Compagno, 2004, p. 11)
2.4 Qualities of glass
Glass as a structure is dependent upon its physical properties and the intended use. The properties of glass fall under: optical properties, thermal properties, physical properties, bending strength, tempered glass. (Compagno, 2004, p. 12)
2.4.1 Optical properties
It is the "Molecules [which] solidify without forming crystals" (Compagno, 2004, p. 12) which cause the transparency because light is able to penetrate through the glass without being diffused. The wavelength of solar radiation which can pass through glass is between 315 and 2,500 nm. Translucent Materials defines the technical details as follows:
"Glass allows the transmission of solar radiation with a wavelength between 315 and 2,500 nm, i.e. from the ultraviolet range of 315 to 380 nm via the visible range of 380 to 780 nm to the near IR range of 780 to 2,500 nm. The UV range under 315 nm and the long wave IR range above 2,500 nm are completely absorbed. This impermeability to long wave radiation explains glazing's greenhouse effect: solar radiation is transformed into heat in the interior, but cannot then escape as long wave heat radiation." (Compagno, 2004, p. 12)Â
2.4.2Â Physical characteristics
The physical characteristics of glass can be determined by the reflection, absorption and permeability of the material. They are given as a percentage of the total incident radiation. The light transmission value measures the percentage of direct light admitted. The total solar energy transmission value is the total of the directly transmitted vertical radiation and the secondary inward heat dissipation by the glazing as a result of the heat radiation, conductivity and convection. The thermal coefficient (u value) is the rate of heat loss through an element per hour with a temperature difference of one Kelvin between the air outside and inside over an area of one square metre. (Compagno, 2004, p. 12) (Stephen E. Selkowitz, Building Technologies Department, January 1999) For further details and illustrations see page 12 of the Translucent Materials book published by Detail Praxis.
2.4.3Â Bending strength
The bending strength of glass depends on the amount of silicon dioxide content, which in controlling the hardness and bending strength produces the characteristic undesirable brittleness. This brittleness means that beyond the limits of the elastic distortion the glass would break. This principle is true of many materials which after surpassing their elastic limit are unable to transform back due to Hooks Law. (Stephen E. Selkowitz, Building Technologies Department, January 1999) (Compagno, 2004, p. 12)
"The theoretical tensile strength of glass is 104 N/mm2 but practically it achieves a maximum of 30 to 60 N/mm2 because of flaws and barely perceptible surface cracks." (Compagno, 2004, p. 12)
2.4.4Â Tempered glass
Tempering glass by using chemicals can increase the low tensile strength. This is achieved through building up compressive stress in the surface and creating excess pressure in the cracks and flaws. This means the load has to relive the compressive pre-stress until it matches the tensile strength of the glass. This is illustrated on page 12 of the Translucent Materials book.Â For thermal tempering the glass is heated to approx 680 degrees Celsius and has cold air blown at it so the glass surface hardens immediately, while the inside core cools slowly whilst contracting. This method gives the core area more tensile strength as well as increasing the surface area's compressive forces. A pane of glass which has been thermally tempered is more likely to shatter into many small pieces without sharp edges. This minimizes the risk of injury which is why Tempered glass is known as Tempered Safety glass. (T.Muneer, 2000)
2.4.5Â Thermal Properties
The most important factor of thermal loss through glass is the thermal conductivity. The thickness of the glass only has a marginal affect on the thermal properties. The amount of radiation can be controlled by coatings and convection can be controlled by the construction. (Compagno, 2004, p. 12) This show how the different types of glass have varying expansion differences.Â Â
"Thermal expansion depends on the chemical composition of the glass. Alkaline calcium silicon glass has a thermal expansion of 8 and borosilicate glass 3-6." (Compagno, 2004, p. 12)
2.5Â Surfaces treatments and finishes
Another way to change the properties of glazing is to change the surface finish which could also be a treatment. These could be subtractive or an additive. Subtractive treatments work on the surface of the glass like grinding, polishing whereas an additive works differently. The surface is coated thinly or thickly or a film is applied. (Compagno, 2004, p. 15)
2.5.1Â Grinding and polishing
Ground and polished glass also known as "mirror glass" was most commonly used for shop windows because of its finish. Being ground and polished on both sides through casting and rolling it was mostly used because of its distortion and resistance to blemishes up and until the 1960s. (Compagno, 2004, p. 15)
2.5.2Â Matt surfaces
A matt or roughened surface can disperse daylight which reduces its transparency. It can be achieved either chemically or mechanically and as not all the glass has to be treated patterns and other designs can be created.Â A type of treatment is an acid application which is etched into the glass finish. Sandblasting is a mechanical process which gives a similar finish matt finish. (Compagno, 2004, p. 15)
2.5.3Â Thin coatings
Thin layers could include layers of precious metals or metal oxides or a combination of both. They can be applied to a variety of different types of glass. They can be applied "online" which means as soon as the glass is made. In this case "offline" means after the glass is made. (Compagno, 2004, p. 15)
2.5.4Â Heat insulation and sun screening
To reduce the emissive quality of the glass Low-E coatings are normally applied. This layer reduces the amount of radiant heat loss. Conductive metals like gold, silver and copper are layered and used in this coating. Silver based coatings are the most common because they offer maximum colour neutrality with the greatest possible light transmission. (Compagno, 2004, p. 15)
Sun screening uses reflective metals like silver, gold and metal oxides, which are based on nickel-chrome, stainless steel and other alloys. These layers increase the reflectivity and thus reduce the transmission and radiation generally. They can be applied to clear or tinted glass. (Compagno, 2004, p. 15) (Johnson, 1991, pp. 1,4)
2.5.5Â Special coatings
Special coatings can be applied to enhance the optical properties; for example, in special uses in medical and lighting industry. These coating include cold mirror coatings which work in the opposite way to low-e coatings. They are used in projectors and Dichroic lamps. Other special coatings include anti-reflective layers, Dichroic coatings, electro-conductive coatings and dirt resistant layers. (Compagno, 2004, p. 17)
2.5.6Â Thick coatings
Thick layers are always produced "offline" and normally comprise of enamel coatings or laminated plastic films.Â Protective layers in the thick coating are produced by adding a lacquer to the thin layer of silver on a mirror. It is manufactured using the technique of fogging. This involves the mirror being drawn through a fog created by a slit nozzle. (Compagno, 2004, p. 17)
Enamel coated glass has a ceramic coating which is resistant to wear, tear and weathering. The enamel is created by applying a frit of finely ground glass with various colours and additives and then firing it. A dosing roller controls the thickness of the layer. (Compagno, 2004, p. 17)
2.5.7 Plastic films
Plastic films are used to bond the splinters together; they can also be applied to glass as a safety feature to minimize the danger of injury when a pane of glass breaks.Â There are also films on the market which offer thermal insulation and sun screening. These films have yet to be approved in Europe and certified. The films are applied to the glass from a roll in the manufacturing process. (Compagno, 2004, p. 17)
2.6Â Insulated glass
Insulating glass is made up of two or more panes of glass connected by one or more spacers, this is because they can create a shear and gas tight seal. This acts like a heat buffer because of the dry air filled space. Currently all glass types can be used for insulating glass. (Compagno, 2004, p. 22)
Heat loss occurs in four ways with insulated glass: radiation between the panes of glass, convection within the space between or cavity, heat conduction via the filling or via the peripheral connection. There are some measures which can prevent heat loss or reduce the amount of heat loss. A thermal insulation coating can be applied to prevent radiation exchange between opposite glass panes. (Compagno, 2004, p. 22)
"An untreated glass surface has an emissivity of about 96%, but a surface with a thermal insulation coating has an emissivity of 3-12%" (Compagno, 2004, p. 22)
This also means that the U-value of the glass has been reduced.Â This U-value would be low but could be even lower by filling the glass cavity with gases like argon or krypton. Inert gases also reduce convection. (Compagno, 2004, p. 22)
"With argon filling the U-value is 1.1 W/m2k, with krypton filling 0.8 W/m2k" the U-value without the fillings and just the coatings are "3 W/m2k to under 2 W/m2k" (Compagno, 2004, p. 22)
In aluminium frames heat can be conducted through the spacers. This can be changed to a stainless steel plastic with a metal inlay or thermoplastic material for the connection system. The U-value can be further reduced by fitting a third pane of glass into the gap or cavity. With a membrane or additional vacuum in this gap the U value will be greatly reduced. (Compagno, 2004, p. 22)
"Triple glazing with two low-E coatings and an argon filling achieves a U-value of 0.7 W/m2k, and with krypton filling a U-value of 0.5 W/m2k" (Compagno, 2004, p. 23)
The fitting of a low-emission coated membrane removes the disadvantages in terms of the weight and thickness of a third glass pane.Â Creating a vacuum inside the gap of the panes can reduce the heat conduction through preventing it from occurring. This method also creates a problem of seal tightness and thermal separation. (Compagno, 2004, p. 23)
"Early vacuum glazing prototypes achieve a U-value of 0.6 W/m2k, but it will still take some time before full industrial production is possible." (Compagno, 2004, p. 23)
2.7Â Glazing in Retail & shop front
When measuring up for a shop front it is necessary to use considerable accuracy, especially where double mitred edges appear. At corners the glass panes have to be mitred to half the angle between the faces. In some cases the glass will have to be drilled for a clip(s) to be fitted. Outside beads make the shop front glazing simple because glazing can then be undertaken from the pavement. However, in Great Britain inside beads are frequently used in order to minimise the effects of weather. In such cases the beads should be bedded to the glass and frame to prevent the entry of water. With glass to glass joints adhesives are used to give the best finish. (Thompson, 1983, p. 11 - 12)
With increasing consumer concern for the environment, glass has again come to the forefront proving to be an ideal material for recycling. Glass recycling is good news for the environment. It saves used glass containers being sent to landfill and less energy is needed to melt recycled glass than to melt down raw materials, thus saving energy. Recycling also reduces the need for raw materials to be quarried which therefore saves precious resources. (Britsh Glass)
The government have announced a plan to gradually improve the energy efficiency of buildings. In 2010 there are expected changes for windows, the announcement of which should take place in April 2010 and be implemented in October 2010. There are plans for further changes in 2013. All new buildings are to achieve 25% reduction in carbon dioxide emissions compared to the 2006 target levels. Window energy ratings (WER) will be the new route for compliance for windows, which will replace U-values. In new non- domestic buildings the overall emissions and efficiency will be judged by SBEM calculation, which will include the choice of glass and its rating. The U-value, however, will remain at 2.2 W/m2K. There are no constraints presently set for display windows, cars or similar glazing. For existing non domestic buildings the limit of the window U-value will be 1.5 W/m2K for replacement windows. There will also be emphasis on solar control in these types of buildings and glazed doors will have a maximum U-value of 1.8 W/m2K (Pilkington plc, 2010, pp. 4, 5,10, 11) (Goverment Document, 2006)
"Glass as a material in its own right will always exist." (Britsh Glass)
Looking at current architecture it is clear that there is a great variety of innovative glass products available for exterior and interior use. The most recent progress in glass in terms of building physics has meant that the use of insulating glass can achieve very low heat loss, and sometimes passive energy gains can even lead to heat gains. The aims for many glazing companies is for their coatings to adapt to the changing weather and seasons in the relevant climates. Early products exist as prototypes, but currently the product is not entirely finished with technical as well as economic aspects needing more progress. (Compagno, 2004, p. 25) (Britsh Glass)
"Development potential in the field of glass technology is far from being exhausted... as a building material it will continue to impress." (Compagno, 2004, p. 25)
2.11Â Concluding Remarks
This section of the literature review was to evaluate studies into the properties and effects of glazing thermally in a retail environment.
From this investigation it has become clear that very little research has been carried out on the retail sector in terms of thermal glazing and no glazing has been specifically made for that purpose.
Through the research and guidance of Pilkington it has become apparent that current retail glazing is generally not thermally efficient. This is due to the lack of research into this field and the lack of government legislation. If the Government was to enforce the changes to glazing for shops fronts and similar outlets, there would be a noticeable difference on the inside environment. With another upcoming review of part L of the building regulations, there is a possibility of further reducing the carbon dioxide emissions in this sector. The problem with the solar gains is that they are being controlled via mechanical ventilation units. These units use a great deal of energy, meaning the easiest way to reduce the emissions would be to remove or install smaller units and replace the glass front.
The details from Pilkington (who produce 75% of all the window glass in the country) on their energy saving glass range show that the best glass currently available in terms of its thermal properties is Pilkington energiKareâ„¢ Triple which has a U-value of 0.8 W/m2K. This glass also meets the code for sustainable homes.
Whilst the Government has committed a large focus into reducing CO2 it is clear that the results of such endeavours will only be noticeable in the long term. They do not resolve the short term issues i.e. the current thermal internal environment. The number and use of air conditioning and similar mechanical units are likely to increase of the next couple of years.
There has been very little research on the subject retail glazing in relation to thermal performance. Although there are studies into glazing and their properties as I found: (Cole, 2009) (Elmhurst Energy Systems Ltd) (Stephen E. Selkowitz, Building Technologies Department, January 1999) (T.Muneer, 2000)
The investigations showed that glazing is important to retail world. The environment within the retail outlet is important because an incorrect environment could affect the operation and overall success of the unit. It has been proved that the correct internal environment it can increase sales and figures.
3.0Â Research design and methodology
3.1Â Scope of the chapter
This chapter it will show how the research problem was investigated. This was achieved by data collection and analysis. It will discuss the choice of the information collection method, the conclusion behind the collection method and the population sample and how the analysis of the data was tailored to answer the key questions outlined in the research aim and objectives.
3.2Â Statement of the research aim
The intention of this research is to assess the thermal properties of glazing in order to find which was best suited for the retail commercial use and the impact it has on the customers and employees in a retail unit.
A number of key questions have been identified to guide the direction of the research. The key questions are:
1. How does the use of glazing in retail influence the general public into approaching the retail unit in terms of style and design?
2.Â How does the thermal environment inside a retail unit affect the overall space?
3. Would energy saving glazing reduce energy costs in retail buildings?
4.Â Which type of glazing would best suit a retail unit?
The outcomes of this research may offer suggestions on the future use of glazing in the retail sector and how the conditions affect the customers and employees within the buildings.
3.3Â Questionnaire rationale
In order to answer the key questions above it is necessary to understand the views, options and experiences of all parties involved in a retail lifestyle.
The questionnaire was divided into two sections. The first section posed questions where the answers could be analysed numerically giving statistical charts. These results were used answer some of the key questions. This section was used to determine the age of the current glazing systems in question and specific problems they might have caused.
The second section was aimed at understanding the opinions and views of the employees and customers and involved a series of statements that the subjects commented on. This qualitative data applied an attitudinal approach in order to understand how the individual's perception of retail glazing was influenced by their own experiences and knowledge.
Using BBC figures produced in 2009 identifying the number of empty shops across the UK, it has been calculated that there approximately one million shops in England.
"...retail vacancy rate of nearly 14...That translates into 135,000 empty shops across the UK..." (News A. L., 2009)
The employees working in these shops provided an invaluable source of primary data. By gaining authorisation from the store managers prior to sending out the questionnaire, it was possible to obtain a high return of data. Thirty retailers in buildings where glass frontage was used ranging in age from new building up to those which were 20 years old were approached, as data from such sources would provide the most useful information.
By analysing the answers which related to the age of the retail unit in question, it was possible test if there was any relationship between the age of a building and any negative attitudes felt towards it.
A second questionnaire was issued to customers in order to recognize their views and the experiences they had. The questionnaire adopted the same method as the employee's questionnaire by gathering both qualitative and quantitative data. It was decided that by gathering information based upon familiarity in new retail buildings and in old retail buildings, a comparison between the two could be drawn and any relationship between the responses and age of the buildings could be tested.Â The customers at the Fort Retail Park were chosen as the research centre. The Fort Retail Park is located in Birmingham just off junction 6 of the M6. The Fort has 28 stores all with glass fronts. The Fort has been established since 1993, and currently accommodates some the original shops as well as new additions and renovations.
3.4Â Interview rationale
In order to answer all the key questions it was necessary to gather the views and opinions of the head figures of these retail shops. It was agreed to hold structured interviews. The first interviewee chosen was the manager of Marks and Spencer's, Robert Cook, as well as Victoria King. Robert Cook was in charge of the food department and Victoria King was in charge of the general merchandise. Victoria King came to work at The Fort branch of Marks and Spencer after being transferred from the Princess Park store located in New Oscott. The Princess Park branch was a food only store which that here background was limited to a food store retail environment. Robert Cook, on the other hand, had worked in the Sutton Coldfield branch prior to working in the Fort. In the Sutton Coldfield branch he worked in the clothing department, which therefore provides him with a both a food and clothing retail background. In this way both interviewees were experienced enough to provide valuable insight.
The information gathered from these interviews in nature provided information central to understanding on how retail buildings used glazing and what struggles they had encountered and how they coped.
4.0Â Analysis of the results
4.1Â Scope of the chapter
The purpose of this chapter is to analyses the results gathered from the questionnaires and interviews. The first step will use the expressive method of analysis to understand the information gathered. The second step of analysis will test the results further to measure any correlation or patterns in relation to the key questions set in chapter one and reviewed in chapter three. The final step will be to examine any conclusions to draw from the analysis in relative to the key questions.
4.2 Analysis of the results (Step 1)
The following results were gathered from questionnaire done by employees who work at retail shops with glazed fronts. Section one is a series of questions designed to provide quantitative data and information on their work placement buildings.
1) How long has you retail shop been on this location?
This shows that 40% of retail shop employees who answered the questionnaire worked inÂ place 5 years old or under. This shows how these building and businesses change frequently.
2)Â Does your shop have displays?
These results show how all but 3% of shops had displays. The 3% however relates to one employee. This shows the importance of having a display window and the popularity of them within the industry.Â Â Â Â
4) Has your shop been refurbished recently?
The majority of shops have not been refurbished recently (with recently meaning within the last five years). This fits with question one were a high percentage of shops have only recently been established on the premises.
4)Â Would you say your shop is thermally unbalanced throughout the seasons?
Most people would say that there store was thermally unbalanced throughout the year. This tells us that there are such issues as expected. This demonstrates how there is a need for better control.
5)Â How effective would you say your displays are in terms of adverting you products?
This is interesting to see that no one thinks that there display are ineffective. With most employees thinking they are either good or very good.
6)Â Is the temperature inside the shop a comfortable environment?
Most employees thought their shop was a comfortable environment; this was only just true with 53% of the total.
4.3Â Test of correlation or association
- ne of the key questions which were outlined in the research aims and objectives asks how the thermal environment inside a retail unit affects the overall space. By analysing the responses from the questionnaire based on the employee's views and experiences we can find any similarities or trends.
4.4.1Â Robert Cook Interview
The following interview was carried out with Robert Cook, Foods line manager at Marks and Spencer's at the Fort Retail Park in Birmingham. The responses to the questions are what were said in the interview.Â
What role do windows and glazing have in the retail sector?
"Glass is important in retail; it lets our customers see inside our store. Without displays we would not be able to entice the customer into the store, and tempt them in to purchasing what they see in the window, the window we normally put a range of items on display, like deals and offers to excusive products."
What are the main issues with glazing?
"the glass front is pretty simple run and maintain, we have to have the cleaned from inside every week to stop dirt and dust the outside is also washed weekly, the only real problem I can think of is finger print marks on the outside and inside."
Do you have any issues with the thermal properties of your store, if so what are they?
"We actually do have a few issues, upstairs in the coffee shop it is like a sweat shop working up there in busy periods and on the general merchandise sections it is also too warm so we have to have the a/c on upstairs very high and on medium downstairs. Upstairs if you're standing close to the fans in the ceiling it's like being in a wind storm, or something. With the food hall it is always fairly cold due to the food and al the fridges which is t be expected."
What energy costs are implied with glazing?
"To be honest I'm not total sure energy cost of having that glazing are, but we do have to have a/c on all times."
Would you consider energy saving glass?
"If it were to help the environment I can't see why not, but we don't make that decision it would be head office and there building team they have."
Is it correct to assume that retail buildings are not energy efficient?
"Well in a business sense we are efficient and making money, but energy efficient currently as a business we are considering further changes. We have a "Plan A" initiative which is a scheme in stores to reduce energy waste, like turning off light switches and computers and recycling paper, cans and food. With waste food at the moment we give what we can't sell to charities and shelters in the area, which come and collect the date expired food from the back. The food is perfectly still fine on that day."
4.4.2 Victoria King Interview
Unfortunately due to unforeseen circumstances Victoria king was unable to attend the arranged meeting due to her tight schedule. A meeting could of be rearranged but due to the deadline of the research project it would not be viable.
4.5 Interview analysis
4.6Â Case study one
4.7Â Case study two
4.8Â Case studies conclusions
5.1Â Dissertation aim
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An Investigation into the Thermal Performance of Glass Front Retail Buildings