Materials for energy efficiency and thermal comfort in commercial buildings

Materials for energy efficiency and thermal comfort in commercial buildings

23 Materials for energy efficiency and thermal comfort in commercial buildings D. H. C. Chow, University of Nottingham Ningbo, China Abstract: Comm...

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Materials for energy efficiency and thermal comfort in commercial buildings

D. H. C. Chow, University of Nottingham Ningbo, China

Abstract: Commercial buildings contribute to a significant portion of the total energy usage and subsequent carbon emissions. Due to their nature, they can use much more energy than they are designed to use, and could be labelled as ‘energy wasters’. What this also means is that there is a large potential for improving their performance. In this chapter, the nature of office buildings, retail spaces and warehouses will be examined and issues affecting their energy use discussed in detail. Ways in which to reduce their energy consumption will also be considered. These include changes in building design and materials used in construction, changes in user behaviour, the increase of control and monitoring and the advancement in building technology and mandatory regulation. Key words: commercial buildings, energy efficiency, passive systems, climate change, control, monitoring.

23.1

Introduction

In Part L of the Building Regulations for England and Wales, Conservation of Fuel and Power, commercial buildings are classed as non-domestic buildings together with public buildings. The reason is that in terms of total energy usage and usage pattern, non-domestic buildings are very different from domestic buildings. Non-domestic buildings account for about one-sixth of the total UK CO2 emissions and approximately one-third of building-related ones (Bordass 2001). The basic nature of buildings in the non-domestic sector is very different from that in the domestic sector. Often these buildings use much more energy than they should and could. Before thinking about the carbon content of the delivered energy, building designers need to look at the current trends in usage and how these can be lowered. Many non-domestic buildings use far more energy than they need to, and can be termed ‘major energy-wasters’. Even many new buildings are using much more energy than their designers anticipated. There are many reasons for this, including designers underestimating the energy requirement, or the occupants not understanding how the building should operate. In this chapter, the types of commercial buildings we will be looking at in detail are offices, retail spaces and warehouses. The energy requirement 562 © Woodhead Publishing Limited, 2010

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specific for these types of building, the possible differences between the design usage and actual usage, the ways which this gap could be reduced, and also the trends in energy usage due to climate change in the UK will be discussed.

23.2

Energy efficiency and thermal comfort in offices

The office building is an important building type to consider, as many people spend most of their day inside one. As a result, its energy usage and CO2 emissions are comparable to that for dwellings. It has its unique characteristic technologies such as raised floor and suspended ceiling, which affects its performance and also consequential environmental impacts.

23.2.1 Main differences from dwellings Compared to dwellings, office buildings differ in many ways. The way which offices use energy may be less diverse than for dwellings, so the range of CO2 emissions may be smaller. Offices also tend to contain more high-embodied energy equipment (such as specialist luminaires) than dwellings. Based on data from the Movement for Innovation (M4i) (2001), Fig. 23.1 shows that in terms of emission per area, the average office emits less operational CO2 than the average dwelling. However, the range of emission is much greater. For embodied energy, this trend is reversed, whereby on average, the office emits much CO2, but the range is smaller than that for dwellings.

23.2.2 Situation in offices There are a number of factors that determine the energy consumption load for office buildings. Generally, these factors induce extra thermal gains in offices, usually from occupants, equipment and solar gains, so the requirement of cooling in summer is usually much higher than in dwellings. Dress code The average office worker wears business suit or dress, which has a clo value of around 1.0 in the CIBSE Guide A (2006). In some offices, this dress code is strict, and restricts the possibility of removing items when it is too hot and putting on extra items when it is too cold. As a result of this lack of clothing adaptability, the band of occupant comfort is narrow, and extra mechanical cooling and heating may be required.

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Operational CO2, kg(CO2) m2 pa

300 250 200 150 100 50 0

Dwellings

Offices

Dwellings

Offices

Embodied CO2, kg (CO2) m2

1200 1000 800 600 400 200 0

23.1 Range and 50th percentile for operational and embodied CO2 for dwellings and offices.

Office equipment The majority of equipment used in offices emit vast amounts of heat. These include computers, printers, photocopiers, etc. This adds to the cooling load of offices, especially in summer. Lighting should also be included here, as it is a major source of internal gain in offices, as well as specialised equipment. The amount of heat generated by office equipment and machines can be found from manufacturers’ data; otherwise general values are available from CIBSE Guide A. Although the efficiency of most office equipment is improving constantly, resulting in a reduction in the amount of waste heat generated, there is also a growing trend in the amount of equipment in offices, which puts the internal heat gains at approximately the same level.

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External design of office buildings Modern offices tend to prefer glass façades, which can result in excess solar heat gain. Developments in glass technology have resulted in glass that lets in light, but keeps out most of the solar heat gains, but excessive glazing on the façade still lets in a large amount of solar gain into the building. The use of photovoltaic cells on glazed façades will serve to reduce the amount of solar gains as well as generating electricity for the building, without changing much of the architecture and appearance of the building. Internal design of offices Office buildings can be cellular or open-planned. Open-planned offices may create a better working environment, but if the design is deep-planned, it may not be possible to use natural ventilation to serve the central locations. It is also difficult for natural daylight to penetrate into the core areas at sufficient levels. False ceilings and carpeted floors will also reduce a building’s ability to absorb heat, limiting the building’s ability to use thermal mass and thus passive cooling strategies such as night-cooling, where the heat stored inside the building fabric is released to the cooler air at night time, to restore its thermal storage capacity. Productivity in office buildings Surveys of office workers reveal that the physical environment of the office is a main factor that affects productivity. It was found that thermal problems, poor air quality (stuffiness), sick building syndrome factors and crowded work places are amongst the most frequent complaints (Clements-Croome 2003), and by improving office environmental conditions, improvements of 4–10% in productivity is suggested. All these factors contribute to a far greater need for cooling in office type buildings than in domestic buildings. In recent years, office buildings in the UK are acquiring more and more air conditioning or other forms of mechanical cooling. With the effects of climate change, this is becoming even more common. A recent study by Chow (2005) shows that in the UK, in order to preserve occupant comfort and maintain productivity, all office buildings in the south of England will require mechanical cooling by the 2020s, those in the north of England by the 2050s, and those in Scotland by the 2080s. Sick building syndrome Sick building syndrome is connected to the use of full air conditioning systems in offices. Symptoms in sufferers mostly disappear when natural © Woodhead Publishing Limited, 2010

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ventilation is introduced. This is a problem that needs to be tackled as the need for mechanical cooling increases with climate change. Where possible, natural ventilation should be encouraged in office buildings, and when this is not capable of achieving the cooling demand, mechanical cooling or air conditioning can be used. This is known as mixed-mode ventilation (see Chapter 3), and is an effective strategy in reducing energy usage and cases of sick building syndrome as well as maintaining occupant comfort and productivity.

23.2.3 Good practice/typical practice: ECON19 or ECG019 From the early 1990s, the Energy Consumption Guide 19 (Carbon Trust 2000) summarised a comprehensive energy survey for office buildings. This publication is regularly updated and is otherwise known as ECON 19 or ECG019. Based on results from 200 offices across the UK, four categories of office types were distinguished for ECG019. These are: 1. 2. 3. 4.

Naturally ventilated, cellular Naturally ventilated, open-plan Air-conditioned, standard Air-conditioned, prestige

CO2 emissions in kg (CO2).m–2 pa

It was found that the biggest difference in terms of energy usage between the categories was the requirement for air conditioning and electrical equipment. The increases needed for heating, hot water and lighting were negligible in comparison (Fig. 23.2). As well as dividing office buildings into four categories, ECG019 gives benchmarks for ‘Typical’ energy consumption 60 50 40 30 20 10 0

Type 1

Type 2

Other electrical equipment

Type 3 Air-Con

Lighting

Type 4 Heating & hot water

23.2 Carbon dioxide emissions from ECG019’s office types (‘Typical’ offices).

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and ‘Good practice’ energy consumption, depending on how energy is used in the building. These are defined as follows: ∑



‘Typical’ energy consumption patterns, which are consistent with median values of data collected in the mid-1990s for the Department of the Environment, Transport and the Regions (DETR) from a broad range of occupied office buildings. ‘Good practice’ examples in which significantly lower energy consumption has been achieved using widely available and well-proven energy-efficient features and management practices. These examples fall within the lower quartile of the data collected.

Different office types have different energy usage and CO2 emission. It was also found that the difference between ‘Typical practice’ and ‘Good practice’ also has a large effect. A similar breakdown of CO2 emissions for ‘Good practice’ office types is shown in Fig. 23.3. ECG019 suggested that offices built from the 1990s should be ‘Good practice’. Although this is being implemented, the existing stock of older office buildings is still a major cause of concern. From the 2002 edition of the Building Regulations Part L2, Carbon Performance Rating (CPR) is included. This is specifically aimed at Type 3 and 4 offices, as they use air conditioning and mechanical ventilation.

23.2.4 Journey to work

CO2 emissions in kg (CO2).m–2 pa

The actual CO2 emissions directly accounted for by the construction and operational energy use of buildings is around 50% of the total emissions in the UK, whereas transport between buildings accounts for around 22% 60 50 40 30 20 10 0

Type 1

Type 2

Other electrical equipment

Type 3 Air-Con

Lighting

Type 4 Heating & hot water

23.3 Carbon dioxide emissions from ECG019’s office types (‘Good Practice’ offices).

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(McEnvoy and Dye 2008, p. 150). This is a substantial amount, and could be attributed to office buildings as most office workers commute to work on average five days a week, more frequent than journeys to other buildings from their home. As a result, BREEAM (Building Research Establishment Environmental Assessment Method) includes transportation as part of its assessment criteria, and the provision of cycle racks to encourage workers commuting by bicycle would earn extra credits on the BREEAM Rating (Baldwin et al. 1998).

23.2.5 Lighting and artificial lighting Glazing in offices needs to be carefully designed to make optimum use of daylight. A balance between heat loss, daylight and solar gain needs to be considered. Ideally, the internal finishes should be light in colour. Artificial lighting contributes to a significant proportion of the operational energy used in office buildings. Its use is unavoidable as sufficient daylight is not always available (this is particularly true for deep open plan offices), and offices are also often used well into the night when daylight is no longer available. Since artificial lighting is indispensable in office buildings, it should be designed to provide ambient conditions similar to that provided by natural lighting. Energy efficient lighting is therefore necessary to minimise the amount of energy used. This means not only energy efficient lamps, but also for luminaires and the whole lighting strategy and system. Occupancy sensors for switching lights on and off, as well as external sensors for dimming lights according to the amount of daylight available are some of a large array of strategies that could be used. PSALI (Permanent Supplementary Artificial Lighting of Interiors) is another popular system of combined daylighting and artificial lighting where parts of the interior are lit for the whole time by artificial light, which is designed to balance and blend with the daylight (Fig. 23.4). The advance and development of low energy LED lighting has also reduced the lighting energy in many office buildings and it is envisaged that their use will become more commonplace in the near future. As well as providing energy efficient artificial lighting, office buildings can also reduce the required amount of artificial lighting by introducing more daylight into the building, especially in areas far away from the building perimeter. Sun-pipes, light-wells and light-shelves are examples of such methods.

23.2.6 Air conditioning and natural ventilation High internal gains and the general reluctance to use passive methods for summer cooling due to security concerns have led to an increase in the use

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Materials for energy efficiency and thermal comfort Psali light on

Total illumination Window Illumination due to PSALI fitting

Illumination due to daylight

Illuminance level

Night light off

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23.4 Schematic of the theory behind the PSALI system.

of heating, ventilating and air conditioning (HVAC) systems in UK offices. There are also pollution and health reasons for office buildings situated close to heavy traffic not to employ simple natural ventilation. The use of HVAC is particularly difficult to avoid in prestigious conference rooms and also inner spaces in office buildings. However, there are situations where natural ventilation could be used, either totally or as part of a hybrid system. This may gain greater user acceptance if they are given more control and if it matches more closely to the varying outdoor climate (adaptive comfort). Problems of air leakage will also need to be addressed, in order to control the amount of air passing through the building. This is a particular problem with high-rise office buildings, as the velocity of wind increases with the distance above ground due to a reduction in resistance from other buildings and obstructions. Recently, atria and internal stairwells have been used as part of a natural ventilation strategy. These strategies allow fresh air to be brought into the building even when the windows are shut. For building designers, the aim is to have ‘Building tight and ventilating right’ (McEnvoy and Dye 2008, p. 158). The CIBSE Recommendation (CIBSE 2006) is that for natural ventilation alone to be feasible, the dry resultant temperature of the office should not exceed 25 °C for more than 5% of the occupied time (approximately 100 hours a year). The European Recommendation (Cohen et al. 1993) has a similar rule, with the dry resultant temperature not exceeding 28 °C for more than 1% of the occupied time (approximately 20 hours a year). If an office complies with either rule, then it is suggested that natural ventilation alone is sufficient to provide summer cooling. However, other considerations such as the outside air quality, particularly if there is heavy traffic, would need to be taken on board. At present in the UK, there are already days in the summer when the outdoor temperatures are greater than the indoor comfort temperatures. In

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these cases, using external air for cooling will not work, so windows are best kept shut, and mechanical fans are used to generate a draught for cooling. Climate change models such as HadRM3 (Chow et al. 2002) suggest that the occurrence of this situation will increase in the next 100 years in the UK, so the use of mechanical ventilation appears unavoidable. It then becomes a case of maximising the potential of natural ventilation where possible. Hybrid ventilation (or mixed mode ventilation) will become the standard means of ventilating in sustainable office buildings. Control systems and intelligent window systems could all be part of the overall strategy. Passive solar heating in winter Office buildings designed to make use of passive solar heating in winter will usually have glazing facing southwards. These will have reduced solar gains in the summer as the solar altitude would be higher, and the overhangs (some also double up as access for window cleaning) should be sufficient. However, special attention should be paid to glazing facing east or west. In summer, the altitude of the sun is still low enough for strong solar radiation to penetrate into the buildings. The problem is particularly true for west-facing or south-west-facing elevations, as the daily maximum temperature in summer usually occurs at around 14:00 to 15:00 (Chow and Levermore 2007). These elevations will be faced with a ‘double effect’ of high external temperature and also direct solar radiation entering the space. In terms of thermal storage, on hot summer afternoons, the building fabric could reach its thermal capacity making further passive cooling unavailable. So the situation for west-facing façades is particularly problematic in the summer. Adjustable shading could be used, but moving parts mean that maintenance could be an issue. Although the main source of overheating is by solar radiation entering through windows, shading the external wall can also be beneficial as it keeps the building fabric cool. There is now glass that allows light to pass through, but is also relatively successful at blocking out thermal radiation (Ohsaki and Kokubu 1999).

23.3

Energy efficiency and thermal comfort in retail spaces

Just like office buildings, retail spaces have specific needs. A successful retail space will be able to attract customers into the shops from the streets outside. Typical methods include using elaborate lighting and providing indoor conditions which are more comfortable and appealing than the outside. In hot and humid locations such as Hong Kong, indoor shopping malls, as well as restaurants and cinemas, often used to turn on their air conditioning units to provide temperatures of under 15 °C (Chow and Fung 1995), as

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the low temperatures will draw passers-by into the retail space who want to escape the heat and humidity outside. However, once the brief satisfaction is achieved, most people actually find these spaces too cold. Despite this, many retail spaces continued this practice as it promoted a healthy turnover of potential customers into the shops. In terms of public health and excessive use of energy and subsequent carbon emissions, this is not good practice, and in 2005, the government of Hong Kong recommended an air conditioning set-point of 26 °C, with the inside temperature kept between 23 and 25 °C (Yang and Zhang 2008), to limit the minimum internal temperatures in public and retail spaces. As well as a seemingly more comfortable indoor environment, retail spaces also use extravagant lighting to attract potential customers. Sometimes these dazzling lights are left on at night-time even when the retail spaces are closed for business. Again, this leads to energy wasted unnecessarily. In many places, this also applies to office buildings. To combat this, ‘lighting curfews’ are in place for cities such as Shanghai (Da Yong 2004), where lights need to be switched off or dimmed in retail or public buildings after a certain time. In Shanghai, the time for switching off lights is 23:30. However, in most countries, this is difficult for security and insurance policy reasons.

23.3.1 Shopping centres and supermarkets In the UK, retail spaces have the same environmental issues to consider. In the last 20 years, more and more large-scale shopping centres are being built in out-of-town suburban areas. These are typically low-rise developments using large areas of land, and surrounded by vast amounts of car parking. To a certain extent, the same is also true for supermarkets. Under guidance issued by the Planning Policy Statement 6: Planning for Town Centres (PPS6) (DCLG 2005), however, retail spaces should be accessible by different modes of transport, but with public transport the preferred option rather than relying exclusively on the use of cars. With this in mind, outof-city centre, peripheral sites are not ideal, whereas city centre sites would be more favourable environmentally when the transportation of shoppers is taken into account.

23.3.2 Lighting and artificial lighting Despite the fact that natural lighting has better colour rendering than artificial lighting, daylight is rarely exploited in retail buildings. The main reason is that any wall spaces available are usually taken up and used for display purposes. Another reason is that the UV in daylight may damage certain goods for sale. There is also an increasing trend for retail buildings to be used after sunset, so the use of artificial lighting is almost unavoidable. Well-designed

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display lighting will improve the appearance of goods in the shops, and is especially true for food products in supermarkets, where colour rendering is highly important. A good lighting scheme in retail spaces encourages people to enter, it allows shop windows to be used for display purposes, and is highly important for the success of the retail space. Similar to the situation with office buildings, the advance and development of LED lighting has also transformed how artificial lighting is used in retail spaces. LED lighting can mimic natural daylight very closely, and is extremely energy efficient, so more and more retailers are using LED lighting to enhance the products they are trying to sell. These are often left switched on to attract potential customers even when the shops are closed for business. As LED lighting is much more energy efficient than traditional artificial lighting, and the quality of light produced is also far superior, it is envisaged that they will be used more and more in retail spaces.

23.3.3 Environmental design As discussed earlier, lighting is usually the largest proportion of energy usage in retail spaces, as retailers try to attract consumers. In larger shopping centres, electricity used for air conditioning and possibly for lifts is also dominant. The energy used for heating usually contributes a smaller proportion as most retail spaces are well-insulated, and during winter, most shoppers retain their outdoor winter clothing in shops. Due to the basic forms of enclosure, some supermarkets have slightly different energy usage characteristics from other retail spaces. A large proportion of energy use goes to lighting, and because most tend to have high ceilings and so a large volume to heat, space heating and domestic hot water also accounts for a fair proportion of the energy usage. Many supermarkets also include in-store bakery, delicatessen and restaurants. Figure 23.5 shows that in this case, food refrigeration is responsible for approximately half the total energy cost, air conditioning and lighting a quarter of the cost, with the bakery, space heating, domestic water and other electrical uses accounting for another quarter (DETR 1998). ele Oth Sp c u er a he c se ati e s ng

Bakery Lighting

Airconditio ning

Food refrigeration

23.5 Energy cost breakdown in a typical supermarket.

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23.3.4 Freezer cabinets in supermarkets One of the distinctive features of supermarkets compared to other types of retail buildings is that they have a large number of refrigeration equipment for their products, and this alone contributes to a large proportion of the overall energy usage, with most of the energy consumed by the compressors. Depending on the layout of the store, it is possible to make use of the by-product heat from the refrigeration compressors to heat up parts of the supermarket. There are also simple yet effective ways to reduce energy use in freezer cabinets in supermarkets, such as having a regular maintenance schedule and ensuring that they are effectively defrosted. It is also important to check that doors in refrigerated store rooms are not left wide open, especially during restocking. The above may seem simple and obvious, but are not carried out in many supermarkets. There are self-closing doors with safety overrides that some supermarkets use. However, these are not yet extensively used, and there are known to have been cases where workers use heavy boxes to keep the doors open, as they think it is easier and quicker for them to restock. This is another example showing the way in which occupants use the building has far more impact than how the building is designed to be used.

23.3.5 Natural ventilation and air conditioning in supermarkets Supermarkets are mostly deep plan buildings. This, together with its particular usage, means the use of air conditioning may be unavoidable. Most modern supermarkets also include circulation spaces around the building, as well as public spaces such as cafés. These are usually located at the perimeter of supermarket buildings, and the use of natural ventilation may be feasible. Measures such as having roof-lights facing away from the sun and minimising the area of roof-lights will reduce the amount of solar gain entering the store, thus reducing the amount of mechanical cooling required. Solar shading on south-facing glazing using overhangs and louvres is also beneficial. In supermarkets with high volumes, the need for air conditioning is reduced, as the heat will rise and stratify above head height.

23.3.6 Typical construction Compared to office buildings, retail construction has a much wider variety of typologies, with inner city department store, suburban DIY depot, multi-storey shopping mall and suburban supermarket being probably the most common (McEnvoy and Dye 2008, p. 242). Insulation is particularly important in the UK to ensure energy efficiency. Newly built retail buildings complying

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with the latest building regulations are environmentally efficient. For older existing retail buildings, improvements can be made to the building’s envelope when it is being refurbished. Shopping centres are very frequently refurbished, usually around every 8–10 years and as frequently as 6–7 years for popular locations. So, over the years, this input of materials and energy in refurbishment will be substantial over the life of the building. Improvements in older buildings when they are refurbished include upgrading wall and roof insulation, replacing or upgrading windows to double/multiple glazing, low-emissive coating, and introducing revolving doors to reduce heat losses and draught. For retail buildings, it is important to maintain a contemporary appearance, in order to retain market position for rents and mix of tenants (Prior 1999, Male et al. 2003). An example of this is the refurbishment of the Arndale Shopping Centre in Manchester, after it was damaged by bombings in 1996. The refurbishment programme took a total of five years to complete, at a cost of around £15 million. All work was undertaken whilst the centre remained in full public use, and the enhanced new malls have attracted major new retail operators.

23.4

Energy efficiency and thermal comfort in factories and warehouses

For the last 30 to 40 years, the trend in UK industry has been a reduction in heavy industry and a shift towards light engineering and services, which have significantly different requirements, so buildings for factories and warehouses are very different from those built before the 1970s (Jones 1990). In fact, closer control and construction standards means new factory and warehouse buildings may have similar performance to new office buildings, and it is existing older factories and warehouses, which have more air leakage and lower levels of thermal resistance, that pose a much bigger problem. Doors are a particular problem for factories and warehouses. If loading doors face away from the prevailing wind, the amount of heat loss through them will be minimised. They also need to be easily operable, so they would not be kept open when not required. Shelter belts of trees around the site could also reduce wind speed around the site, thus minimising heat loss. Reducing the slope of the roof would also reduce heat loss as this will create a smaller volume of space. It is estimated that much of the energy savings in UK factories and warehouses could be saved by changing a relatively small number of factors, notably the building’s insulation and air leakage, inadequacies in the heating system, loss in distributing heat around the building, lack of controls, lack of maintenance and inefficient lighting installations (Energy Efficiency Best Practice Programme 2004). It has been shown that most industrial buildings could be refurbished to a standard similar to new buildings (McEnvoy and

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Dye 2008, p. 257). This suggests that the potential for energy savings and improved energy performances in the industrial sector is very high.

23.4.1 Environmental design in warehouses In the 1990s, a government-funded research programme classified factory buildings into four types (Energy Efficiency Best Practice Programme 2004): ∑ buildings for storage and distributions ∑ factories for light manufacturing ∑ factory/office buildings ∑ general manufacturing buildings. Warehouses are buildings mainly for storage and distribution, and can be seen as factory buildings with no production, so with far fewer problems, such as pollution and the energy intensity in the production process. They belong to the first of the four categories above. They typically have a clear height of around 7.5 m, and could be naturally ventilated and heated to around 16 °C. Natural ventilation is suitable for warehouses as they do not have excessive heat gains, and occupancy levels are usually low. The biggest problem for warehouse buildings in terms of energy efficiency is heat loss through air leakage. This applies to warehouses both new and old, and potentially this could double the amount of heating required. Air leakage is related to external wind speed, so for buildings in exposed sites, the problem is more severe. For reducing the amount of air leakage, doors should be well-sealed. However, the use of roller shutters could allow uncontrolled air infiltration as they have a gap at the top (as the diameter of the roller increases when the shutters are closed). The level of air leakage in warehouses is 15.0 m3 per hour for each m2 of envelope area at 50 Pa reference pressure difference, for good practice factories and warehouses, and 3.5 m3 per hour for each m2 of envelope area at 50 Pa reference pressure difference for best practice ones (Webb and Barton 2002). Some warehouses are refrigerated due to the nature of the goods stored. These have far greater energy consumption and the refrigeration accounts for the majority of the energy used in these buildings. Lighting and daylight control Lighting in warehouses is usually high pressure sodium lamps, achieving 150 lux (McEnvoy and Dye 2008, p. 267). Higher lighting levels are only required in dispatch and office spaces. Depending on the nature of the goods stored, the amount of solar gains should also be kept to a minimum to keep the goods fresh. In order to reduce the amount of solar gain, yet providing

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enough natural light into warehouses, north-light roof designs and light-pipes are now often incorporated into the overall design of warehouses. Heating requirement and systems In older buildings, insulation levels are lower, and air leakages are high. A high proportion of convective heat will be lost through fabric, so radiant heaters would be more effective. However, these often lead to overheating. Radiant heaters are also energy intensive and result in very high fuel bills. With warm air systems, warm air tends to be collected beneath the roof, where it is not needed (see Fig. 23.6). There are now also warehouses that use transpired solar cladding for low temperature heating. Also known as Solarwall, this usually involves a dark perforated cladding that absorbs most of the solar energy; outside air is drawn through small holes in the cladding and is heated as it travels through the cavity behind the cladding and into the building. An example of this is the Sainsbury Distribution Centre in Pineham, UK, built by ProLogis. This type of heating system is particularly suitable for buildings with high ceilings and large indoor spaces, and could be used to offset the heating load of an existing warm air system. Solar thermal arrays are also being used in some of these state-of-the-art warehouses, to maximise the use of the solar energy reaching the building.

23.4.2 Typical construction A typical form of building for factories and warehouses is the mediumspan shed, and the use of steel and pre-cast concrete frame and lightweight cladding remains the norm. For lower cost installations, the use of three-layer

Warm-air system

Radiant heating system

23.6 The collection of heat for a warm-air system and a radiant heating system.

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construction: inner liner panel, insulation (in quilt form or higher density batts) being loose laid between it and the outer plastic coated profiled sheet, is the vernacular solution (Architects’ Journal 1990). Summertime condensation is a particular problem for a three-layer cladding system. On hot humid days, the night-time air temperature will drop considerably, especially when the skies are clear. The outer surface could drop significantly and the moisture-laden air trapped within the corrugated outer sheet may condense at the back of the cold outer cladding. This can soak the insulation, making it less effective. A solution to this could be placing a breather membrane to the outside of the insulation, to allow moisture from within the building to escape (see Fig. 23.7).

23.5

Embodied energy

Apart from the operational energy that commercial buildings use, the embodied energy in their construction and maintenance is also becoming a more significant issue. Traditionally, the construction industry has not given much consideration to the embodied energy of a building, because this is relatively insignificant compared to the operating energy for the building over its lifetime. As a result, most effort has been put into reducing operating energy by improving the energy efficiency of the building envelope and educating occupants to switch off lighting and appliances when they are

Three-layer insulated profiled sheet outer panels and internal liner panels

Breather membrane

Cold formed steel purlin

23.7 The vernacular construction for warehouses: the three-layer construction with breather membrane to prevent condensation.

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not in use. However, research in Australia (Tucker et al. 1993) has shown that as the operational energy reduces steadily, the proportion of embodied energy (including energy required for maintenance) becomes more significant. It could take many years before the cumulated operational energy reaches the same level as the cumulative embodied energy (including energy for maintenance). This is particularly true if the building is efficient and has low operation energy. Figure 23.8 shows an example from an office building in Australia, where it could take 50 years of low level operation to reach the same total amount of cumulative energy as the embodied energy.

23.5.1 Embodied pollution As well as embodied energy, building designers should also consider embodied pollution, which is caused during the manufacture of building components, and also its transportation to site. This is a controversial area, and where the pollution is a major issue, emissions are controlled by legislation and by bodies like the Environmental Agency and HMIP. In general, the use of the precautionary principle is recommended, in that materials should be selected to perform the task set while minimising all impacts including pollution.

23.6

Material choice

Modern commercial buildings in the UK typically have steel or concrete structures, with curtain walling using glass or panel a popular form for the

30

Cumulative life cycle energy of example office building

Cumulative energy (GJ)

25 20 Low operation energy

15

Normal operation energy High operation energy

10

Embodied energy

5 0

0

10

20 30 40 Years since completion

50

23.8 Comparison of cumulative life cycle energy for an office building.

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façade. Environmentally, there are ongoing discussions to the benefits of steel or concrete over the other.

23.6.1 Advantages and limitations: steel versus concrete Steel and concrete frame buildings constitute the majority of office buildings in the UK (British Steel 1995, Clarke and Somerville 1992, Edwards and Hyett 2002, Stevenson and Spooner 1992). Compared to concrete, steel has up to 20 times more embodied energy as a result of its highly intensive production process. This also leads to very high embodied pollution, about 60 times more CO2 than the process for concrete. However, steel is relatively stronger than concrete, and the mass of steel used in steel structures is very much less than the mass of concrete used in concrete structures, so the actual difference between the amounts of embodied energy is not as great; also steel structures are easily demountable, and so are easily recycled or re-used. In construction, the recyclability and reusability of steel is extremely high, where between 95% and 98% of the steel used is re-used or recycled. The steel industry often argues that the initial embodied energy of the structure actually represents a very small proportion of the building’s total energy consumption in its lifetime. In comparison, the largest amounts wasted from buildings are concrete, aggregates, blocks and bricks, while the process of recycling concrete is still in the early stages of development. Concrete structures require steel reinforcements, but these are usually made entirely from recycled steel. Thermal mass Apart from the comparison of embodied energy, embodied pollution and recyclability, there is another important criterion to compare the performance of steel and concrete structures: the disposition of thermal mass. For passive or hybrid ventilation strategies, the ability of the building fabric to store thermal energy is essential in controlling and stabilising the indoor temperature. Buildings that are particularly susceptible to summer overheating, such as office buildings, would benefit greatly from this strategy; and the use of a heavyweight material like concrete, which has a large thermal capacity, would delay the time when the heat is transferred into the building by up to 6 hours, resulting in a reduction of peak internal temperatures by 3–4 °C. Although steel also has a high density, it is not used in as much quantity as concrete, and also its thermal capacity is about half that of concrete. For thermal storage to perform effectively, the materials with high thermal mass should be visible to a large area within the room. This usually means the soffit of the concrete slab. To increase the surface area of the soffit, corrugated forms of concrete construction are sometimes used. The troughs

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and coffers provide greater surface area. The use of thick carpets and false ceilings should be avoided for effective use of thermal storage. The steel industry suggests that the thickness of thermal mass is not as important as previously thought (McEnvoy and Dye 2008). A concrete slab, exposed on one side, need only be 75–100 mm to be effective, and slabs of greater depth may reduce its performance as it becomes more difficult for the heat stored deep inside to be extracted for night cooling. The argument is that light steelwork constructions can still have efficient thermal mass, as the whole construction would still consist of a sufficient amount of concrete.

23.7

Modelling and monitoring thermal performance and comfort

When commercial buildings are in their design stage, it is necessary for designers to know how the geometry of the design and the materials chosen will affect the final thermal and energy performance of the building. Previously designers used tools for manual calculations such as the LT Method (Baker and Steemers 1996) and the CIBSE Building Energy Codes (CIBSE 1999a, 1999b) for estimating the performance of their design, and also to improve upon earlier designs. With the advance in computer software programs, it is now relatively simple to run building simulations using packages such as IES Virtual Environment, TAS, Energy Plus and ECOTECT to do the same task with more ease and greater accuracy. The Building Regulations also require non-domestic buildings to meet carbon targets, similar to the Code for Sustainable Homes (DCLG 2008) for domestic buildings, and SBEM (Simplified Building Energy Model) is the Building Research Establishment (BRE) approved default program.

23.7.1 SBEM Under the amendments to the UK Building Regulations, Approved Document L2A in 2006 (DCLG 2006), new non-dwellings have to meet carbon targets based on a whole building energy calculation. This allows designers more flexibility in their design, but at the same time, they also need to meet, wherever practicable, the worst acceptable standards or ‘limiting values’ for the following: ∑ envelope insulation ∑ air permeability ∑ efficiency of building services. Designers will also be required to confirm the absence of summer overheating, demonstrate the quality of construction and commissioning, and confirm the provision of information to the owner/occupier.

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As for the whole building calculations, carbon emissions, based on 2002 standards for various elements, are first calculated for a notional building. A notional building is one that has the same size and shape as the actual building, and each space contains the same activity, so the activity schedules and parameters are equivalent to the actual space in the design. Then, placed in the same orientation and using the same weather data as for the design building, it goes through SBEM (Simplified Building Energy Model), the BRE approved default method for calculation, to calculate the Target Emission Rate (TER). The same process is then applied to the actual design, and a Building Emission Rate (BER) is produced. BER must be equal to or less than TER for the design to be approved. The use of SBEM automatically generates the ‘notional building’ from the data for the ‘actual building’. It calculates the appropriate improvement factor and shows whether or not a building meets the Building Regulations carbon target compliance test. It can show the effect on the compliance of different design decisions. However, it should be noted that it is not a design tool and does not prove that a design will work in practice. SBEM is required for both compliance with the Building Regulations and also Energy Performance Certificates (EPCs), but according to the EU Energy Performance of Buildings Directives (EPBD) Article 10, SBEM must be used in an independent manner, and by qualified and/or accredited experts. Therefore, there is a need to train people in the expertise to use SBEM.

23.7.2 Fingerprinting Although there is plenty of guidance when it comes to designing buildings and building services, the ultimate test that a building needs to pass is one of satisfaction by its end-users. Occupant feedback is usually obtained by conducting a questionnaire survey. Levermore has devised a double-Likert scale for occupants to rate 22 to 24 factors relating to the interior environment and the organisation (Levermore 1998). A seven-point scale is used for each factor, and as well as how much the occupant likes the factor in the working environment, they are also asked to rank how important this factor is to them (see Fig. 23.9). The importance score is then transformed by adding 4 to all values, and the product of the two scores is then normalised. The average scores for the factor for all the respondents then form the fingerprint for the building. Figures 23.10 and 23.11 show examples of fingerprints for real buildings including their overall average score. Each building will have its own unique fingerprint and also an overall score. The overall score could be positive or negative. A successful building, with its occupants mostly satisfied should achieve a high positive score, whereas a negative score usually denotes the occupants are dissatisfied with

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Materials for energy efficiency and thermal comfort in buildings How important is this in the design of your ideal office? Unimportant Important

Do you like the… Dislike

Like

–3 –2 –1 0 1

1. noise level

2

3

–3 –2 –1 0

1

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23.9 An example of the double-Likert scale for a building performance criterion. Deep plan office with atrium and underfloor ac. Fingerprint of ranked scores (overall score = –17%)

60 50 40

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Appearance

General

Colleagues

Space

Daylight

Management

Health

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23.10 Building fingerprint for a deep-plan office with atrium and underfloor air conditioning.

many aspects of the building. The fingerprint also gives information about which aspects of the building are working well, and which need improving. Although currently not used in conjunction with TER and BER in the latest Building Regulations, fingerprinting allows users and designers to know precisely the positive and negative aspects of a building.

23.7.3 Sensors The use of post-occupancy sensors will also monitor how the building is performing thermally when it is in use. Ideally designers should be on-hand to monitor how the building is run for a few years after its completion, to ensure that it is being run the way it was intended. Too often, due a lack of understanding by the occupants of the environmental strategies and/or

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Deep plan, modern, naturally ventilated building. Fingerprint of ranked liking scores (overall score = –15%) 40 30 20

–40

Space

Appearance

Daylight

Colleagues

Management

Smell

General

Window dist

Colour

Attractiveness

Noise

Health

Lighting

Freshness

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Ventilation

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–30

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–20

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23.11 Building fingerprint for a deep-plan, modern, naturallyventilated building.

controls of the HVAC systems, commercial buildings use far more energy than was intended by the designers. For larger buildings, the installation of a Building Energy Management System (BEMS) is highly recommended. In BEMS, sensors are also required to monitor the conditions of the building, and appliances are switched accordingly. Movement sensors in warehouses are also common, so lighting is only switched on when there are people about. Delivery doors may also be electrically operated, so they are not left open when not being used. Under the EU Energy Performance of Buildings Directives (EPBD), since October 2008, public buildings in the UK have to put up Display Energy Certificates (DECs) (Davidson 2007) for users to see. These show the energy potential of the buildings and compare this to how much the buildings actually use. DECs are a good way for the occupiers and users of public buildings to know how much energy their building is using, and what can be done to achieve its full potential. Perhaps this scheme should extend to other nondomestic buildings, especially offices, and not just public buildings.

23.8

Future trends in design and refurbishment

Due to their nature, commercial buildings often use more energy than they require, but there are existing technologies that can be implemented to reduce this energy usage significantly (Levermore 2008). An important aspect often overlooked is the quality of workmanship. If buildings are not

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actually built to the standard specified by the designers, for example, if they are too leaky, then the thermal performance will suffer. One way to improve this would be to increase the amount of factory-made building components. The increase of pre-fabricated components will minimise the amount of time spent on site and thus reduce the possibility of low-quality workmanship when components are put together. This implies designers spending more time at the drawing table, like in Japan, where the time spent on designing is three times as much as the UK, but the time spent building on site is only a third of the time in the UK (Xiao and Proverbs 2003). Controlling and monitoring the amount of energy used is another vitally important aspect that all commercial buildings should employ. With the advancements in wireless technology, it should be much simpler to set up Building Energy Management Systems (BEMS) so buildings are controlled and run properly and efficiently. The ability to use thermal mass to store up heat should also be explored more. As well as exposing concrete elements, and reducing the use of false ceilings and carpets where possible, future buildings can also make use of phase-changing materials (PCM). These could be micro-encapsulated paraffin with a melting temperature of between 25 °C and 28 °C, and can be mixed into gypsum plaster which can then be plastered onto walls as conventional plaster. The simple use makes the material especially suitable for the renovation of existing buildings. The melting temperature coincides with the temperature when a building gets too hot. As the paraffin melts at this temperature, it absorbs latent heat from the room, thus reducing the air temperature of the room. At night time, when the temperature falls below its solidifying temperature, latent heat from the paraffin in its liquid state is released as it solidifies, warming the air in the room where it is located. As well as paraffin, some salt hydrates with a melting temperature between 25 °C and 32 °C can also be used. These dispose of a significantly greater amount of latent heat than paraffin. As the micro-encapsulation of salt hydrates poses a problem due to the increase in volume during the melting process, it is more suitable to put them in macro-elements such as flat containers or tubes rather than mixed in with plaster. Such macro-elements filled with salt hydrate can be put in suspended ceilings, which allows their application in the refurbishment of older buildings. Figure 23.12 and 23.13 show the effects of using PCM in a control room in plaster form and as a salt hydrate, respectively. This is from an experiment conducted by Hoffmann et al. in Germany. The maximum room temperatures are reduced by 2–3 °C, and the minimum room temperatures increased by approximately the same amount in the plaster form; with a salt hydrate as PCM, the reduction in maximum room temperatures are even greater, at around 5–6 °C. As well as trends in the design and refurbishment of commercial buildings for the future, there are also trends and predictions to how building materials

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45 40

Temperature (°C)

35 30 25 20 15 10 29/5/04

30/5/04 Date of experiment

31/5/04

23.12 Measured room temperatures with PCM-plaster (dashed line) and without PCM-plaster (black line). 40

Temperature (°C)

35 30

25 20 15 10 3/10/04

4/10/04 Date of experiment

5/10/04

23.13 Measured room temperatures with additional salt hydrate (grey line) and without PCM (black line).

will advance and changes to how commercial buildings will be used. Already there have been significant improvements in glass technology to produce glazing that allows in light, but prevents a large amount of heat and solar radiation entering a building. Commercial buildings generally uses a lot of glazing and the continued advances in glass technology will help reduce the

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growing need for mechanical summer cooling as a result of climate change. The growth of wireless technology and advances in the energy efficiency of office equipment and lighting will also reduce the amount of internal gains. There is also a growing trend towards a more relaxed dress code for office workers, which increases the level of adaptability by workers to change their level of clothing. More people being allowed to work from home also means less energy wasted on journeys to work, and again less internal gains with fewer occupants inside the building. For retail spaces, there is also a growing trend for online shopping, which may result in fewer shopping centres. The number of warehouses may also be reducing, as better planning and management of manufacturing process mean products could be made and delivered more efficiently, cutting down the number of goods and the time they spend in warehouses.

23.9

Sources of further information and advice

Carbon Trust (2000) Energy Consumption Guide 19 – Energy Use in Offices, Action Energy/The Carbon Trust. CIBSE (2000) CIBSE: Guide H: Building Control Systems, Chartered Institution of Building Services Engineers, London. CIBSE (2004) CIBSE: Guide F: Energy Efficiency in Buildings, Chartered Institution of Building Services Engineers, London. CIBSE (2006) CIBSE: Guide A: Environmental Design, Chartered Institution of Building Services Engineers, London. Energy Efficiency Best Practice Programme (1994) Introduction to Energy Efficiency in Shops and Stores, Department of the Environment, UK. Energy Efficiency Best Practice Programme (2004) Guide 18 Energy Efficiency in Industrial Buildings and Sites, HMSO, May. IPCC (2007) ‘Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4)’, WMO, UNEP. McEnvoy, M. and Dye, A. (2008) Environmental Construction Handbook, London, RIBA Enterprises. Prior, J. (1999) Sustainable Retail Premises: An Environmental Guide to Design, Refurbishment and Management of Retail Premises, BRE, Watford.

23.10 References Architects’ Journal (1990) ‘Light Industry Passive Solar Factories’, Architects’ Journal, 31 January 1990, p. 59. Baker, N. and Steemers, K. (1996) ‘LT Method 3.0 — a strategic energy-design tool for Southern Europe’, Energy and Buildings, 23(3), 251–256. Baldwin, R., Yates, A., Howard, N. and Rao, S. (1998) BREEAM 98 for Offices, Building Research Establishment, Watford.

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Bordass, W. (2001) Flying Blind: everything you wanted to know about energy in commercial buildings but were afraid to ask, EEASOX and the Association for Conservation of Energy, London. British Steel (1995) Ecobuild in Steel, Scunthorpe, Marketing Dept, Redcar. Carbon Trust (2000) Energy Consumption Guide 19 – Energy Use in Offices, Action Energy/The Carbon Trust. Chow, D.H.C. (2005) ‘The Effects of Future Climate Change and Near-Extreme Weather on Office Buildings in the UK’, PhD Thesis, University of Manchester. Chow, W.K. and Fung, W.Y. (1995) ‘Indoor Thermal Environment Survey in AirConditioned Shopping Malls in Hong Kong’, Indoor and Built Environment, 4(2), 102–112. Chow, D.H.C. and Levermore, G.J. (2007) ‘New algorithm for generating hourly temperature values using daily maximum, minimum and average values from climate models’, Building Services Engineering Research and Technology, 28(3) 237–248. Chow, D.H.C., Levermore, G.J., Jones, P., Lister, D., Laycock, P.J. and Page, J. (2002) ‘Extreme and near-extreme climate change data in relation to building and plant design’, Building Services Engineering Research and Technology, 23(4), 233–242. CIBSE (1999a) CIBSE Building Energy Code 1: Energy Demands and Targets for Heated and Ventilated Buildings, Chartered Institution of Building Services Engineers, London. CIBSE (1999b) CIBSE Building Energy Code 2: Energy Demands for Air Conditioned Buildings, Chartered Institution of Building Services Engineers, London. CIBSE (2006) CIBSE: Guide A: Environmental Design, Chartered Institution of Building Services Engineers, London. Clarke, M. and Somerville, G. (1992) ‘Concrete in the Environment’, Concrete Quarterly, Winter. Clements-Croome, D. (2003), ‘Environmental quality and the productive workplace’, paper presented at CIBSE/ASHRAE Conference. Building Sustainability, Value and Profit; Edinburgh, Scotland, 24–26 September 2003. Cohen, R.R., Munro, D.K. and Ruyssevelt, P.A. (1993) ‘Over heating criteria for non air-conditioned buildings’, CIBSE National Conference, UK. pp. 132–142. Da Yong (2004) ‘Shanghai seeks to switch off light pollution’, China Daily Newspaper, 12 April. Davidson, P. (2007) ‘The energy performance of buildings directive’, Reducing the Carbon Footprint in the Built Environment, Institution of Engineering and Technology Seminar, London. DCLG (2005) Planning Policy Statement 6: Planning for Town Centres (PPS6), Stationery Office. DCLG (2006) ‘Building Regulations – Part L Building Regulations – Conservation of Fuel and Power’, NBS/RIBA Enterprises. DCLG (2008) Code for Sustainable Homes – Summary of Changes to the Technical Guidance, April, Stationery Office. DETR (1998) The Impact of Large Foodstores on Market Towns and District Centres, HMSO, September, p. 1. Edwards, B. and Hyett, P. (2002) Rough Guide to Sustainability, RIBA, London. Energy Efficiency Best Practice Programme (2004) Guide 18 Energy Efficiency in Industrial Buildings and Sites, HSMO, May, p. 1. Jones, P. (1990) ‘Low-Energy Factories: 1 Setting Priorities’, Architects’ Journal, 16 May, p. 65.

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Levermore, G. (1998) Occupant Feedback using a questionnaire rating liking and importance of up to 24 factors. Available at: http://www.inive.org/members_area/ medias/pdf/Inive%5Cclima2000%5C1997%5CP326.pdf (accessed 28 May 2008). Levermore, G. (2008) ‘A review of the IPCC Assessment Report Four, Part 1: the IPCC process and greenhouse gas emission trends from buildings worldwide’, Building Services Engineering Research and Technology, 29(4), 349–361. Male, S., Gronqvist, M. Kelly, J. and Damodaran, L. (2003) Supply Chain Management for Refurbishment: Lessons from High Street Retailing, Thomas Telford Ltd, London. McEnvoy, M. and Dye, A. (2008) Environmental Construction Handbook, London, RIBA Enterprises. The Movement for Innovation (2001) ‘The Movement for Innovation Sustainability Working Group Report, Environmental Performance Indicators for Sustainable Construction’, p. 17. Ohsaki, H. and Kokubu, Y. (1999) ‘Global market and technology trends on coated glass for architectural, automotive and display applications’, Thin Solid Films, 351(1–2), 1–7. Prior, J. (1999) Sustainable Retail Premises: An Environmental Guide to Design, Refurbishment and Management of Retail Premises. BRE, Watford. Stevenson, J. and Spooner, D. (1992) ‘Concrete and the environment’, Concrete Quarterly, Autumn. Tucker, S.N., Salomonsson, G.D., Treloar, G.J., MacSporran, C. and Flood, J. (1993) ‘Environmental Impact of Energy Embodied in Construction’, Report prepared for the Research Institute of Innovative Technology for the Earth, CSIRO, Highett, Victoria. Webb, B.C. and Barton, R. (2002) ‘Air Tightness in Commercial and Public Buildings’. BRE Press, Office of the Deputy Prime Minister. Xiao, H. and Proverbs, D.G. (2003) ‘Contractor relationships: a comparison in Japan, the UK and the US’, Journal of Construction Procurement, 9(2), 52–64. Yang, W. and Zhang, G. (2008) ‘Thermal comfort in naturally ventilated and airconditioned buildings in humid subtropical climate zone in China’, International Journal of Biometeorology, 52(5), 385–398.

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