PDF Document

Smart Surfaces and Functional Coatings in the
Modern Built Environment
May 2008
Author: Kevin Tinkham, SMART.mat
MBE Contributors: Flavie Moulinier and John Morlidge
Authorised by: Alan Partridge, SMART.mat and Colin Seabrook,
Chairman, SMART.mat
Key Contacts for SMART.mat
Project Director
Email contact
Jackie Butterfield
[email protected]
Project Manager - Structures
Email contact
Chris Laurence
[email protected]
Project Manager - Surfaces
Email contact
Helen Stork
[email protected]
Copyright of this document remains the property of NAMTEC and SMART.mat.
Requests for permission for wider use or dissemination should be sought from Helen Stork.
2
Contents
Executive Summary
4
1
Introduction
5
2
Energy Efficiency
2.1
Photovoltaic electricity generation
2.2
Solar heating
2.3
Electrochromic windows
2.4
Electroluminescent displays
6
6
8
10
10
3
Health and Safety
3.1
Health
3.1.1 Antimicrobial and hygienic surfaces
3.2
Fire Safety
3.2.1 Intumescent coatings
3.2.2 Pyroelectric sensors
3.2.3 Shape memory alloys
3.3
Displays and Signage
3.3.1 Photoluminescent displays and signs
3.3.2 Chemochromic gas monitoring
3.7
Thermochromic displays
11
11
11
14
14
16
17
18
18
19
19
4
Enhanced Durability
4.1
Easy clean coatings
4.2
Self-cleaning photocatalytic coatings
4.3
Anti-graffiti materials
4.4
Self-repair coatings
20
20
22
23
25
5
Occupier Comfort
5.1
Phase change materials
5.2
Photochromic windows
5.3
Anti-static coatings
5.4
Reflective coatings
26
26
29
29
30
6
Summary of Smart Material Availability and Development in the
Modern Built Environment
32
7
Conclusions
34
8
Acknowledgements
36
9
References
36
3
Executive Summary
The use of coatings in the built environment is not new. Paints, for example, have been used
for a very long time to provide substrate protection and to enhance the look and feel of
construction materials and continued development work has undoubtedly resulted in
significant performance improvements. These improvements to established coating products
combined with cost pressures, a general industry conservatism and, perhaps most
significantly, a lack of awareness means that the emergence in recent years of a new,
diverse class of materials has gone largely unnoticed. Nevertheless, these so-called smart
and functional materials have the potential to transform construction materials coating
technology and, thus, to change the way in which buildings are designed, fabricated and
utilised.
The emergence of new coatings with added functionalities is particularly timely as there is
increasing pressure on the construction sector to deliver new buildings that are carbon
neutral, exhibit enhanced durability and sustainability, provide greater flexibility and which
also meet higher levels of occupier health, safety and comfort. Against this background, the
current report seeks to create a greater awareness of smart and functional coatings by
providing information about their key characteristics, availability and current or potential
applications within the built environment.
Some smart and functional materials are already widely used in our buildings. Intumescent
coatings, electro- and photoluminescent signs and displays, anti-graffiti products and antistatic floors are all familiar and well-established materials. Less well known, though, are
more recently commercialised products such as self-cleaning coatings on glass,
electrochromic windows, antimicrobials and phase change materials, while the potential for
thermochromic displays or self-repair coatings is clear, but implementation is still subject to
further development work.
Many issues influence material choice but by discussing the use of smart materials within the
context of four main themes it is hoped that potential opportunities can be appreciated more
easily. These themes are Energy Efficiency, Health and Safety, Enhanced Durability and
Occupier Comfort.
Whatever the drivers for their introduction, the report demonstrates that smart and functional
materials offer a myriad of new properties that could make a major contribution to the
enhancement of the modern built environment. Forward thinking businesses now have the
opportunity to add functionality and value to their products and buildings through the
introduction of this exciting class of materials.
Colin Seabrook
Chairman – SMART.mat
May 2008
4
Smart Surfaces and Functional Coatings in the
Modern Built Environment
1.
Introduction
The modern built environment (MBE) can be described broadly as the manmade
surroundings that provide the setting for human activity. These surroundings range from
large scale civic projects to small personal spaces and also include road, rail, water and air
infrastructure assets. Smart surfaces can be defined generically as coatings and materials
that can sense some stimulus from their environment and react to it in a useful, reliable,
reproducible and, often, reversible manner. Such materials are now finding applications
within the MBE and these applications are presented in this report, however, as there is still
so much unexploited potential for these types of materials, an indication of some possible
future applications has also been included. Functional coatings, which are materials that
exhibit their functionality at all times, can also play a significant part in enhancing the built
environment and their uses are presented in the report.
The activities of the Modern Built Environment Knowledge Transfer Network (MBE KTN),
with whom SMART.mat are collaborating on this report, are focused on three primary
sectors, which are healthcare, offices and infrastructure. In healthcare the objectives are to
identify and facilitate implementation of innovative built environment solutions to provide
flexible, sustainable and energy efficient healthcare solutions for the 21st century. For the
offices sector the manner in which offices are constructed and reconfigured is an important
factor in determining their use, occupier requirements and future re-use and a modern,
responsive infrastructure is a vital element in supporting the UK’s economic prosperity.
Smart materials and functional coatings impact on all three major MBE KTN sectors but
smart systems, such as sensors in structural monitoring, tend to be more important than
smart surfaces in the infrastructure sector and, consequently, infrastructure applications will
not feature in this report. However, smart and functional coatings are an important class of
materials in the offices and healthcare sectors and they also occur in the housing, public
building, retail, factory, sport and leisure sectors, and applications in all these areas have
been illustrated within this report.
Rather than listing by material property, MBE applications of smart surfaces and functional
coatings have been incorporated in four major themes. These themes are Energy Efficiency,
Health and Safety, Enhanced Durability and Occupier Comfort. By highlighting the general
benefits of current and emerging applications in this way it is hoped that potential
opportunities can be appreciated more readily, to the benefit of both suppliers and end users.
Smart surfaces and coatings can add very practical functionalities to our domestic and public
buildings but they also provide exciting opportunities for designers and architects to work
with an emerging class of new materials. Hence, this review aims to showcase the diversity
and importance of smart coatings and gives a glimpse into the future of a ‘smarter’ modern
built environment.
5
2.
Energy Efficiency
Energy efficient buildings help to reduce occupier running costs but, despite their obvious
appeal and the progressive tightening of the Building Regulations for energy efficiency since
the 1970s, the level of heating, lighting and appliance usage in most domestic, public, office
and retail buildings has far outweighed any improvements in insulation standards. Housing
stock in the UK is amongst the least efficient in Europe(1) and it accounts for around 30% of
all energy use in the country(2). Public buildings, offices, hospitals and much of the retail
sector share many of the same energy use characteristics as the domestic sector and the
increased use of air-conditioning units in all these areas has further increased energy needs.
Compared with 1990 levels, energy use by UK industry in 2004 had fallen by over 5%(3)
(achieved due to improved efficiencies but also the loss of a proportion of the manufacturing
and engineering base) but, in a similar period (1990-2005), overall energy consumption by
UK companies and the public sector has risen by 10.6%(4).
Against this background of a general increase in energy use within the built environment,
with all its implications for natural resource depletion and possible global warming, the UK
Government has set challenging targets for energy reduction in the coming years. For
example, in its 2006 Pre-Budget Report(5) the Government declared its ambition that all new
homes should be zero carbon within a decade. Updated Building Regulations should ensure
that energy use in new housing should be cut by 20% compared to a similar building
constructed to the 2002 standards and the Government has also announced that all the
central government office estate is to be carbon neutral by 2012. A recent announcement by
the Prime Minister(6) concerning the UK’s commitment to the EU’s 2020 renewable energy
target could mean that the UK will need to produce up to 50% of its electricity from
renewable sources within the next 12 years.
Whether it be due to material production, construction or the heating and lighting of buildings,
it is clear that the built environment consumes vast amounts of energy each year. It is equally
clear that energy efficiency and ‘green’ issues are being taken ever more seriously at
Government level. Tighter regulation is driving the development of energy efficient
technologies and smart coatings are at the forefront of this development. The following
sections describe some of the most important ways in which smart surfaces and coatings
contribute to enhanced energy efficiency.
2.1
Photovoltaic Electricity Generation
Photovoltaic (PV) systems utilise an array of cells to convert sunlight into electricity. When
sunlight strikes a photovoltaic material photons of the absorbed sunlight dislodge electrons
from the atoms of the cell. Free electrons then flow through the cell, generating electricity.
Current PV materials and devices fall into two categories: crystalline and thin film. Over 90%
of PV cells are made from either single crystal or polycrystalline silicon wafers that are sliced
from ingots or castings. Such materials have photon-to-electricity conversion efficiencies of
between 10 and 20%. Thin film PV cells utilise a thin film, or ribbon, of PV material (usually
amorphous or microcrystalline silicon) deposited onto a low cost supporting substrate such
as glass, metal or plastic foil. Compared with crystalline materials, thin film PV manufacture
is faster and more suited to mass production but typical conversion efficiency is less than
10%.
Photovoltaic systems contain no moving parts and require minimal maintenance. Crucially,
electricity is also generated without the emission of greenhouse gases. Stand-alone systems
are available for applications where grid power supplies are not available, such as telephone
6
kiosks or street lighting, but most interest is concerned with grid connect systems. These
systems are usually integrated into buildings and are connected to the local electricity
network. During the day, therefore, the electricity generated can be used immediately, as is
often the case with offices or other commercial buildings, or sold to the electricity supply
company. In the evening, when the PV system cannot supply the required electricity, power
can be bought back from the network.
Stand alone PV systems, such as the street lighting and sign lighting modules shown below,
are now becoming quite common and are readily available(7,8,9).
PV Street Lighting (Advanced LEDs Ltd.)
PV Sign Lighting (SolarGen Solutions)
Solar panels are supplied by a range of manufacturers(10-13) and examples of their use in
office and domestic housing grid connect systems is shown below. The CIS Tower in
Manchester (left below) is 400 feet high and is covered by 7000 PV panels. A comprehensive
list of PV system designers and installers can be found on the British Photovoltaic
Association website(14).
CIS Tower, Manchester
Domestic Home Solar Panels
Recently, silicon supply has become an issue in the PV industry, with demand for solar grade
silicon now exceeding that from the semiconductor industry. The shortage of suitable silicon
feedstock has prompted an increase in the price of solar cells based upon conventional
silicon technology, which has led to a modest increase in thin film solar cell manufacture.
However, the lower efficiencies associated with these thin film silicon technologies is limiting
their commercial impact.
7
Given the issues associated with silicon-based systems, it is not surprising that much of the
current development work involves the use of other materials. In particular, thin film cadmium
telluride (CdTe) and copper indium diselenide (CIS) technology is now being incorporated
into PV modules. There is also considerable interest in new technologies that have much in
common with the photosynthesis process in plants. These dye sensitised solar cells (DSSC)
combine an electrolyte, a layer of titania (TiO2) and either a ruthenium or an organic dye
sandwiched between glass panels. Light falling onto the DSSC is absorbed by the dye and
its energy generates excited electrons that can escape into the TiO2. These electrons diffuse
through the titania to the electrode, generating a current. DSSC systems are expected to
have a significant commercial impact in the very near future(15,16).
2.2
Solar Heating
One of the simplest and most direct methods of harnessing solar energy is to convert the
incident solar radiation into heat. The heat generated in a so-called solar collector system is
used to heat water, to back-up heating systems and to heat swimming pools.
The key component in a solar collector is the absorber, which is generally made-up of
several narrow metal strips. These strips are usually coloured black as dark surfaces are
particularly effective at absorbing light. Connected to the absorber strip is a heat-carrying
tube filled with carrier fluid that transports the heat from the absorber to a water-filled tank or
pool.
Conventional solar paints, which are applied using brushes or sprays, absorb over 90% of
the incident radiation but, unfortunately, as the absorber warms to a temperature higher than
the ambient temperature they also lose a significant amount of energy due to heat emission.
Thus, instead of paint, the most efficient solar collectors have selective surface coatings on
the absorber. Selective coatings also absorb high levels of incident radiation but, crucially,
emission losses are much less than when using paint. Selective coatings are normally
applied galvanically and they include black nickel, black chrome and aluminium oxide with
nickel(17). Also available is a titanium-nitride-oxide layer that can be applied via steam in a
vacuum process(17).
Two types of solar collector are available; flat-plate and evacuated-tube. A flat-plate system
consists of an absorber, a transparent cover, a frame and insulation. The transparent cover
is chosen to transmit as much of the short-wave light spectrum as possible, whilst minimising
emission of long-wave heat rays. It also reduces heat loss through convection. Flat-plate
collectors can be mounted on the roof, in the roof itself or as unattached units.
Flat-plate Solar Collector (Solarserver)
8
In an evacuated-tube collector, the absorber strip is located in an evacuated glass tube. Heat
transfer fluid flows through the absorber directly in a U-tube and several tubes connected
together form the solar collector. A heat pipe collector contains fluid that vaporises even at
low temperature and the steam generated in each individual heat pipe collector warms the
carrier fluid in the main pipe by means of a heat exchanger. Condensed liquid then flows
back to the base of the heat pipe.
Evacuated-tube Solar Collector (Espinoza Energy)
Solar heating systems for both domestic and commercial applications are readily available(18. Compared with flat-plate systems, evacuated-tube systems are more efficient at higher
absorber temperatures and with low levels of incident radiation. They can also generate
higher temperatures for steam production or heating. Evacuated-tube collectors are,
however, approximately three times the cost of flat-plate collectors.
24)
Solar water heating can reduce both the annual hot water heating bill, by up to around 60%
(approximately £40 for a domestic system), and the level of CO2 generated (350kg). The
installation cost of a typical domestic system is between £3 200 and £4 500(25) but the BERR
low carbon buildings programme(26) provides grants to help with costs. Solar water heating
systems should last for at least thirty years.
Evacuated-tube Solar Collectors (Riomay)
9
2.3
Electrochromic Windows
Smart windows are a new series of products that are
sometimes referred to as switchable glazing. These windows
change their properties, such as shading coefficient or visible
light transmittance, in response to an electric charge or
changes in ambient temperature or light. Of the technologies
being developed, only electrochromic windows can currently
be considered as commercial products. Others, such as
thermochromic and photochromic windows (section 5.2), are
not yet available. Electrochromic windows change from fully
clear to fully darkened or any degree of intermediate tint at
the flick of a switch, allowing solar transmission to be
optimised for occupier comfort and privacy and for reducing
heating and air conditioning requirements
In a typical electrochromic device, the electrochromic film (often tungsten oxide) is in contact
with an ion conductor and an ion storage film, all of which are sandwiched between two
layers of transparent conductor. These five films are further sandwiched between two layers
of glass. When a low voltage (1-3V) is applied across the conductors ions move from the
counter-electrode to the electrochromic layer, causing a change in colour. A range of colours,
including blue, red, yellow, orange and black, can be obtained and the glass can be
programmed to absorb only part of the light spectrum, such as solar infrared.
Electrochromic windows currently cost 2 to 3 times as much as conventional windows but
savings in both heating and air-conditioning can be significant(27). Units can be purchased for
both commercial and domestic applications(28-30).
2.4
Electroluminescent Displays
Electroluminescent materials emit light when an electrical current or voltage
is applied to them. They take the form of thin films of either inorganic
phosphors (e.g. doped zinc sulphide) or organic semi-conductors known as
organic light emitting diodes (OLEDs).
Electroluminescent Displays and Products (E-Lite Technologies)
At present only monochrome electroluminescent display panels, strips, sheets and rolls are
readily available(31). Applications within the built environment have so far been limited to
backlighting for displays, safety signs and decorative lighting. Colour OLED displays are
used in mobile phones, where their limited lifespan is not generally an issue, and Sony
recently demonstrated their future potential for television and computer displays.
10
3.
Health and Safety
There can surely be no greater priority in the modern built environment than health and
safety and intelligent building design helps to ensure occupier safety and aids in the
maintenance of good health.
Legislation has driven many of the health and safety improvements in the built environment
but more subtle occupier requirements and expectations are also playing an increasingly
important role. For example, sick building syndrome(32) (a range of ailments that is associated
with the workplace and which can cause high levels of employee sickness and lower
productivity) has been attributed to a range of factors including poor heating or ventilation,
poor or inappropriate lighting, high noise levels or bad acoustics, poorly designed
furnishings, furniture and equipment and microbial contamination of heating, ventilation and
air conditioning systems. It has also been found that improved design and better use of
materials can help to reduce infection levels and speed up recovery times in hospitals(33). As
the following applications demonstrate, some smart materials and functional coatings are
already well established in the built environment but, equally, there is still a lot of scope for
extended use.
3.1
Health
3.1.1
Antimicrobial and Hygienic Surfaces
The importance of high standards of hygiene and cleanliness has long been recognised
across a broad spectrum of industries and in a wide variety of public and domestic situations.
Avoiding infection from surface contact is particularly important in environments such as
hospitals, schools, kitchens, catering establishments, food production, storage and retail
facilities, dairies, breweries and heating, ventilation and air conditioning systems. This is a
long, and by no means exhaustive, list but poor attention to hygiene is costly. For example,
Hospital Acquired Infections (HAIs) affect around 9% of patients in NHS Trust hospitals.
They lead to serious illness and, in some cases, death but they also cost the NHS about
£1billion per year(34) due to increased periods of hospitalisation, additional drug charges and
requirements for repeat surgery. Of course, many HAIs are associated with biomedical
devices, rather than handles, bedrails, work surfaces etc., but it is clear that a general
reduction in bacteria levels on hospital wards could have a major impact in reducing HAI
incidents. Similarly, greater control of bacteria throughout the food processing, packaging
and distribution system could help to cut the microbial spoilage that can destroy 25 to 80% of
fresh produce before it reaches the consumer(35).
It should be stressed that good cleaning practice is paramount to maintaining safe and
healthy surfaces(36,37). However, a range of antimicrobial and hygienic coatings is available
that can aid the process.
Antimicrobial Materials
Organic Biocides
Traditionally, microbial attack by bacteria, fungi and algae has been prevented through the
use of organic biocides, which are often present as additives in paints and polymers. Many
organic biocides, which are often known by their trade name, are available and they are
applied most frequently as anti-fouling treatments in the marine environment. However, they
have also been used as additives in a range of construction materials and products(38-41).
11
Organic biocides have been in use for well over 100 years but the migratory, volatile and
toxic nature of many of them has, in more recent times, raised significant concerns about
their long term impact on health, safety and the environment. Consequently, many have
already been banned and new legislation will prevent the use of others. Of course, safer
organic products continue to be introduced by manufacturers but alternatives to organic
biocides are being developed and a number are already on the market.
Silver and Copper Technology
Perhaps the most established ionic inhibitors are those based upon silver(42-44) and copper(45).
In both cases, ions are released slowly from an inorganic matrix via an ion exchange
mechanism. These ions are then able to combine with hydrogen ions on the microbial thiol
(SH) groups of the enzymes in the membrane of the bacterium, which disrupts the
metabolism, inhibits respiratory capacity and prevents multiplication.
Most applications of antimicrobial copper and silver technology within the built environment
are associated with touch surfaces such as door handles, push plates, bed rails and work
surfaces. To date, most copper products have been fabricated directly from copper-based
alloys but silver antimicrobial products generally have silver particles incorporated into
polymers and powder coatings. Copper and silver are highly effective in killing a range of
bacteria, including MRSA, E-coli, salmonella and listeria. Both metals are creating significant
interest for healthcare applications. Trials in two out-patient wards at Heartlands Hospital,
Heart of England NHS Foundation Trust concluded recently(46). Compared with the
conventional ward, the ward containing silver-treated furniture and equipment was found to
contain 95.8% less bacteria in the environment. Similar copper efficacy trials at Selly Oak
Hospital, University Hospital Birmingham NHS Trust are on-going(47).
Hospital Copper Touch Surfaces (CDA)
Antimicrobial Silver in Polymers and Powder Coatings (BioCote Ltd)
12
Titanium Dioxide
In the presence of sunlight and moisture, the anatase form of titanium dioxide (titania) is able
to generate free radicals. These highly oxidising species have the ability to break down
organic bonds and, hence, under the appropriate conditions, titania can act as an
antimicrobial agent.
Outdoors, where UV levels are high, titania nanoparticles are usually incorporated into
coatings where they kill bacteria and mould, essentially using this property to maintain
surface appearance (see section 4.2). Indoor applications generally require the presence of
an additional source of UV light but titanium dioxide has found use in air-conditioning and air
purifier units(48), sanitary ware surfaces and on ceramic tiles in hospitals and food processing
areas(49,50).
Air Purifier (Rokenergie)
Antimicrobial Tiles
Hygienic Surfaces
All the agents described above can be considered to be truly antimicrobial. They act by killing
bacteria. However, an alternative approach is to generate a hygienic surface. Such surfaces
do not kill bacteria; rather they provide hostile conditions that hinder colonisation and growth.
One method is to cover a surface with a non-stick coating. Bacteria find it very difficult to
adhere to such coatings, hence colonisation is slow and removal is quite easy even with very
mild cleaning solutions. Non-stick coatings are generally based on fluorine or silicon
chemistry. Examples include PTFE (polytetrafluoroethylene), cross-linked silicones and
siloxane polymers.
Bacterial growth is greatly enhanced in moist conditions(51). Thus, the application of very
hydrophobic coatings can help to limit growth(52). To date, most applications of this type have
been limited to textiles, bioscience disposables, filtration systems and microelectronics but
hydrophobic coatings can be bonded to most surfaces, providing a good deal of potential
within the built environment.
High chromium content stainless steels, which are characterised by the presence of a stable,
corrosion-resistant surface oxide film, have long been used in situations where high levels of
hygiene are required. Typical uses include food processing and catering surfaces and
hospital applications such as sinks and disposal units.
13
3.2
Fire Safety
3.2.1
Intumescent Coatings
Uncontrolled fires can have a devastating impact on human health and the economy. For
example, in the 12 month period up to 31st March 2005, almost 500 people in the UK were
killed when trapped inside burning buildings(53), while the annual direct losses from fire due to
property damage, death and injury and loss of output through work absence are in excess of
£2.5 billion(54). One of the main factors underlying these sobering statistics is that many of the
materials, such as wood, textiles and plastics, which are commonly used in clothing,
furnishings and construction are highly flammable. Ideally, such materials should be
protected using flame retardants but it is not always possible to add these directly to raw
materials. This may be because the substrate is incompatible with further additives, the
desired flammability rating may not be achievable with a single additive or the cost may be
prohibitive. In these situations, intumescent coatings may provide a reliable and highly
effective alternative. Indeed, for structural steelwork they are the fire protection system of
choice.
Under the influence of fire, intumescent coatings swell to between 2 and 100 times their
original thickness, producing an insulating char that protects the substrate from the effects of
the fire. The activation temperature of the coating depends upon the substrate that is being
protected but is in the range 130 to 300OC. Fire protection may last for up to 2 hours.
0 seconds
12 seconds
10 minutes
Swelling of Intumescent Coating when Exposed to Fire (Broadview Technologies Inc.)
Intumescent Coating Applications
Steel
Steel does not burn but it can lose its strength when exposed to temperatures in excess of
500OC. In a fire, therefore, steel structures have the potential to become unstable and there
is a danger that buildings may collapse.
Several methods for protecting structural steelwork exist and those employed most
frequently in the past were shielding using concrete or thermal insulation panels and sprayon chopped fibres. These systems have proved effective but are not generally visually
attractive. Modern architecture, particularly for shops, offices and other public buildings,
favours open designs that often incorporate areas of exposed steelwork. For such
applications, intumescent coatings, with their decorative finishes, combine an appealing
appearance with a high degree of fire protection(55-57).
14
Intumescent Coatings on Exposed Structural Steelwork
Festival Place, Basingstoke and City Point, London (Leigh's Paints)
Wood
Timber is a traditional material that is still widely used in the furniture manufacturing and
construction industries. Unfortunately, it is combustible and will burn if exposed to severe fire
conditions.
For wood composite products such as chipboard it is possible to incorporate flame retardants
into the products during manufacture. Pressure impregnation also permits solid wood,
plywood and hardboard to be treated with flame retardants after manufacture. However, fire
protection for many wood products is achieved by applying paints or surface coatings(58-60),
often after the product has been installed. Much of the paint and surface coating protection is
based on intumescent technology of the type used for structural steel protection.
Intumescent Coatings on Exposed Wood Surfaces, Dartford Abbey (Coatmaster)
Fire Seals
In many fire protection systems the main requirement is to block pathways for the spread of
flames and fumes. Key areas are door and window seals, conduits and ventilation grilles.
Modern fire seals(61-63) are now so effective that it is possible to fit continuous runs of glazing
without the need for masonry fire walls. During a fire, the intumescent seal swells, insulating
and supporting the edges of the glass. Full size panes will hold back a fire for up to 30
minutes after the softening point of the glass has been reached.
15
Intumescent Fire Seals around Glazed Panels,
Sheffield United FC and Huddersfield Town FC (Sealmaster)
3.2.2
Pyroelectric Sensors
Pyroelectric materials have the ability to generate an electrical potential when they are
heated or cooled. As a result of the temperature change, positive and negative charges
migrate to opposite ends of the material, thereby generating an electrical potential.
Pyroelectric Infrared Detectors (Fuji & Co.)
Pyroelectric infrared detectors (PIR) are able to convert changes in incoming infrared light to
electric signals and are, therefore, widely used in buildings as flame detectors(64). They are
able to operate in dust or smoke filled rooms and are also able to detect glowing embers.
By choosing the appropriate IR receiving electrodes, PIR detectors can be used for a range
of other applications(65-68). These applications include motion sensors, light controls and
automatic door switches.
PIR Flame Detector
(Talentum
(Developments Ltd)
PIR Motion Sensor
(Simply Automate)
Solar Security Floodlight with
PIR Motion Sensor
(Solar Illuminations)
16
3.2.3
Shape Memory Alloys
Shape memory alloys (SMAs) are materials that can be deformed at one temperature but are
able to return to their original shape following a heating or cooling cycle. The effect is due to
a solid state (martensitic/austenitic) phase transformation and alloys can undergo this phase
(shape) change reproducibly many (10 000 to 1 million) times.
The most common SMAs are nickel-titanium alloys, known as Nitinol(69), and copper zinc
aluminium and copper aluminium nickel alloys. Systems employing these materials have
great potential in infrastructure and building applications. For example, the concrete
infrastructure of a bridge could contain sensors designed to detect cracks or corrosion and, if
these are found, embedded SMA actuators would counteract the strain introduced by this
degradation. Most current built environment SMA applications, however, tend to be
associated with safety switches on systems and appliances.
SMA Memory Spring (MUTR)
Fire safety is an important area in which SMAs are having an impact. Fire sprinkler
systems(70) can be activated by the heat-induced shape change of an SMA in a fire and fire
safety valves incorporating an SMA actuator can be used to shut off the flow of flammable or
toxic gases in the event of a fire breaking out. SMA actuators can also be used to lock ceiling
plates in place as the temperature rises, protecting pipes, cables and the floor above from
the effects of a fire.
SMA-containing Fire Sprinkler (Viking Corporation)
17
SMA Coil in a Fire Damper System (AMTBE)
3.3
Displays and Signage
3.3.1
Photoluminescent Displays and Signs
Photoluminescence occurs when a material emits light as a result of irradiation by another
light source and the term covers both fluorescence and phosphorescence. Fluorescent
materials emit their light almost immediately after irradiation but phosphorescent materials
tend to emit light over a much longer period (several hours) after irradiation.
Photoluminescent paints can be purchased(71) but low-level walkway lighting and safety and
emergency signs(72-75) are the most common applications for photoluminescent materials in
the built environment.
Photoluminescent Fire Safety Signs (PLM Fire & Safety)
Photoluminescent Signs (Display Signs)
18
3.3.2
Chemochromic Gas Monitoring
A chemochromic material changes colour when exposed to a particular chemical. Hence,
they are commonly incorporated into warning devices in factories or chemical storage
facilities but, as hydrogen becomes more established as a fuel source, their presence in
other types of buildings is likely to become more common.
Many of us are familiar with portable carbon monoxide (CO) detectors that provide an
audible warning but chemochromic systems that give a visual warning of high CO levels are
also readily available.
Carbon Monoxide Detector
Gas permeable chemochromic hydrogen sensors are also being developed(76). Hydrogen
safety is one of the major concerns associated with the use of hydrogen and researchers at
the Florida Solar Energy Center are currently developing both reversible and irreversible
chemochromic sensors. These cadmium oxide (CdO) based paints have been incorporated
into an adhesive tape, giving a robust and simple system that allows hydrogen leaks to be
detected visually.
Chemochromic Hydrogen Sensing Tape (Florida Solar Energy Center)
3.3.3
Thermochromic Displays
Thermochromic materials have the characteristic of exhibiting a colour change when their
temperature changes. There are two types: liquid crystals and leuco dyes. Liquid crystals
have a limited colour range but their responses can be engineered to accurate temperatures.
In contrast, leuco dyes come in a much wider range of colours but setting accurate response
temperatures is difficult.
19
Thermochromic inks and paints are readily available(77,78) but their use in the built
environment is currently very limited. Applications are generally restricted to thermal overload
warning indicators on equipment and appliances. Recently, the potential for using thin,
flexible thermochromic composite films in display units has been demonstrated(79). Given
their ease of fabrication, thermochromic displays should be cheaper to build than
conventional display units, while their pulse heating control can reduce energy consumption.
For the moment, however, thermochromic display units have not been commercialised.
Thermochromic Display (Hong Kong University of Science and Technology)
4.
Enhanced Durability
There can be little doubt that the sustainable use of resources and materials will be a key
political and technical theme for the modern built environment over the next few years. Each
year the UK construction industry consumes over 400 million tonnes of resources, uses
around 30% of the UK’s industrial energy, generates more than 100 million tonnes of waste
and contributes to the country’s CO2 emissions through processes such as cement
manufacture(80).
Against this background of high consumption and waste generation, the UK government
published a consultation document(81) in July 2007 entitled ‘Draft Strategy for Sustainable
Construction’, which is the first stage in establishing a joint Government and industry strategy
for future sustainable construction. This document, in common with the ‘Review of
Sustainable Construction 2006’(82), makes it clear that in future there will be much greater reuse of existing built assets and construction of new, long-lasting, energy conscious and
future-proof (adaptable and flexible) buildings and structures that are easy to maintain,
operate and deconstruct. Durability and ease of maintenance are, thus, two key sustainability
issues and smart and functional coatings have the potential to make a major contribution in
these areas.
4.1
Easy Clean Coatings
The application of an easy clean coating to a building façade has a number of benefits. Time
and money are saved because cleaning is required less often and is easier to achieve, less
harsh cleaners can be used, which tends to extend coating lifetime, and the use of milder
cleaning agents on a less frequent basis also has clear environmental benefits.
There is no single easy clean coating chemistry but most systems are based upon silicon
(often silicone) and/or fluorine components in highly cross-linked polymers. In general, a
smooth hydrophobic (water repellent), and in many cases oleophobic (oil repellent), coating
20
is formed that causes liquids to bead on the surface. On vertical surfaces the liquid rolls
downwards, collecting dirt and dust particles as it does so. On horizontal surfaces liquids are
easily removed and fingerprints tend not to form. It is important to match the substrate to be
protected with the appropriate easy clean coating but systems are available that will coat
glass, ceramics, metals, masonry and wood.
Hydrophobic Coatings on Various Substrates (Tekon)
Many of the easy clean systems that are available commercially can be applied by
conventional spray, dip, roller coating or brush techniques(83-86) but sol gel technology (a wetchemical technique in which a chemical solution, the sol, is deposited onto the substrate,
forming an integrated ‘gel’ network that is subsequently dried and fired to form a non-porous
coating) is also utilised(87,88). Evaporator systems that are capable of coating threedimensional products with hydrophobic coatings can also be purchased(89,90).
Easy Clean Coatings Prevent Dirt Build-up on Building Facades (Protectosil)
Fluorosilane Easy Clean Coating for Glass and Ceramics (Clariant)
21
In 1975 it was first observed that the fine surface structure of leaves on several plants
caused them to repel water and dirt. One of the most effective plant is the Lotus and a
silicone based paint system that dries to give a surface texture which mimics the leaf’s
natural water repellent structure is now available commercially(91). Since 1999, this superhydrophobic coating has been applied successfully by roller coat to many hundreds of
thousands of buildings.
Water Droplets Running Off a Lotus Leaf (Stocorp)
Water Droplets Removing Dirt from Easy Clean Lotus Effect Paint (Stocorp)
4.2
Self-cleaning Photocatalytic Coatings
The application of a self-cleaning coating provides many of the same benefits as the
application of an easy clean coating but maintenance costs are further reduced because
there should be no requirement for the use of detergents of any kind. As self-cleaning
coatings actually cause decomposition of organic material and there is essentially no need
for cleaning solutions, maximum environmental benefit may be achieved because coating
performance and appearance can be maintained without the use of cleaning agents or by
generating contaminated run-off.
Self-cleaning coatings have a two-stage cleaning action; dirt breakdown and dirt removal.
The active component in photocatalytic coatings is the anatase form of titanium dioxide
(TiO2). In the presence of ultra-violet light (sunlight) the titanium dioxide generates so-called
free radicals. These free radicals are able to break bonds in organic materials and are thus
able to break down pollen, bird droppings and tree sap. The second stage in the cleaning
process occurs when water (rain or from a hosepipe) runs down the coating and removes the
22
decomposed organic species (and any inorganic material such as sand or dust). The
photocatalytic effect generates a permanent hydrophilic surface that causes water to sheet
on contact, thereby maximising dirt removal.
To date, applications of photocatalytic self-cleaning coatings have been limited to glass and
ceramic substrates(92-96). In addition to their self-cleaning capability, photocatalytic coatings
exhibit high chemical and abrasion resistance and good levels of transparency. In general,
photocatalytic coatings are used on external surfaces where sunlight and rain water can
drive the self-cleaning effect. If used indoors a source of UV light must be provided and mild
cleaning will be necessary.
Photocatalytic Coating on Glass (SGG)
Ordinary Ceramic Tile Surface
4.3
Ceramic Tile with Hydrophilic
Photocatalytic Coating (Toto)
Anti-graffiti Materials
Considered by some to be art, graffiti is generally viewed by most people as vandalism and
the cost of trying to remove it from building facades and other structures costs owners and
occupiers in the UK alone over £1 billion per year(97). Most common construction materials
can be defaced using paints or inks but those with a porous structure, such as stone and
concrete, are particularly susceptible to staining that may never be entirely eradicated.
Graffiti on Unprotected Surfaces (Tor Coatings)
23
Harsh, abrasive cleaning may remove unwanted graffiti but substrate appearance and
integrity may be adversely affected using this approach. It is better, therefore, to protect
buildings by applying a protective anti-graffiti coating. These coatings fall into two categories,
sacrificial and permanent.
Sacrificial coatings(98-101), which are usually acrylates, biopolymers or waxes, can still be
defaced by paints and inks but subsequent spraying using high pressure water is all that is
required to remove the graffiti. During cleaning the coating is also removed (sacrificed).
Thus, sacrificial coatings must be re-applied afterwards for continued protection. They are
used most commonly on natural-looking masonry surfaces, such as stone and marble walls,
and on rougher surfaces that are difficult to clean.
Graffiti on AGS Sacrificial Coating Removed Using Water Spray (Tensid UK)
Permanent coatings(102-107) are clear, hard paints (usually polyurethanes) that do not bond
readily to paints and inks. Graffiti can, thus, be removed by using commercial solvent washes
that do not damage the underlying substrate or protective coating. Permanent anti-graffiti
coatings work best when used on smoother surfaces, and especially over other painted
surfaces, including murals.
Permanent Anti-graffiti coating (Actel)
Enviroguard (Actel) Sacrificial Anti-graffiti
Coating, Scottish Parliament Building
(Image: Rampant Scotland)
As mentioned above, the choice of anti-graffiti system is determined to some degree by the
nature of the material that is to be protected. However, both systems have their own
particular characteristics that will also influence the choice. Permanent coatings have the
virtue of providing protection for up to 15 years without maintenance but special cleaning
products are required to remove graffiti, they tend to change the appearance of the
underlying substrate (typically making it darker and shinier) and their limited permeability
means that in cold weather the surface is susceptible to freeze thaw damage. Sacrificial
coatings generally do not alter surface appearance, they tend to be more breathable and
they allow graffiti to be removed using water but, of course, the coating must be reapplied
where any graffiti has been removed.
24
4.4
Self-repair Coatings
Self-repair is hardly a new concept. After all, biological organisms have been able to repair
damaged bone and tissue for many millions of years. If self-repair mechanisms could be
introduced into materials, including those used in construction, then product lifetimes would
be extended, safety would be improved as damaged features in dangerous or difficult to
access locations would simply self-heal and costs would be lowered because maintenance
levels could be reduced and material replacement and refurbishment would be required less
often.
Some degree of coating self-repair can already be achieved. For example, Nissan, through
its subsidiary Infiniti, are due to launch a range of cars into Europe this year that have a paint
layer that is able to repair minor scratches automatically. The paint, developed by Nippon
Paint, is a transparent, high density synthetic resin that slowly flows back to fill in any
scratches. Similarly, HMG Paints have developed a clear, 2-pack isocyanate cured
polyurethane paint system called Recover(108), aimed primarily at the bus and coach market,
that is also able to flow back to repair minor scratches. Liberty Coating Company’s Pritec(109)
pipeline coating system also exhibits an element of self-healing. If the polyethylene coating
suffers minor damage then the butyl rubber adhesive that bonds the coating to the pipe is
able to flow into, and seal, any small cuts or gouges.
Scratch Shield Self-repair paint
on Infiniti EX 35 (Image: The Times)
As the examples above indicate, the self-repair
coatings that are currently available have not yet
had any impact in the built environment and they
are really probably best described as anti-scratch
coatings. However, this is a very active research
area and the construction sector is an obvious
market. Some developments that may lead to
commercial products in the near future are
discussed below.
For some applications, the gradual flow of material to cover an area of exposed substrate
may be sufficient to effect a repair but in other cases, particularly if the substrate is metallic, a
slightly more sophisticated method involving the additional release of corrosion inhibitors
might be desirable. Several research groups(110-113) are investigating the latter approach. The
specific chemistries involved will depend upon the coatings and substrates but, in general,
damage to the coating will cause the rupture of microcapsules that contain corrosion
inhibitors and ‘healing agents’. Pigment release, that either allows fully repaired areas to
blend in with the rest of the coating or which highlights partially repaired regions, can also be
incorporated into the repair system.
Clearly, the use of microcapsules means that it will not be possible for self-repair to occur
twice in the same area. However, three longer term developments may ultimately allow
repeated self-repair to take place. Researchers at the University of Illinois are working on
new materials that contain embedded three-dimensional microvascular networks that
emulate biological circulatory systems(114). The networks are filled with healing agents that
are able to flow into any cracks that appear in the coating. Work is also in progress at
25
Rensselaer Polytechnic Institute in the USA, where a fine grid of wires is built into the surface
of composite materials and covered in an epoxy matrix loaded with carbon nanotubes(115). By
sending electrical pulses down the wires it should be possible to locate cracks as the
electrical resistance of the nanotubes laden epoxy will be different in the damaged area.
Higher current pulses can then be used to melt ingredients in the epoxy, allowing the crack to
be filled automatically. Finally, Leeds NanoManufacturing Institute is part of a European
group that is seeking to develop self-healing, high strength gypsum board(116). The idea is to
incorporate polymer nanoparticles into the board. When squeezed under pressure, these
particles will turn to liquid, flow into cracks and then harden again to form a solid material.
5.
Occupier Comfort
Indoor environment quality (IEQ) is a general term that can be used to describe the physical
and perceptual attributes of indoor spaces. These attributes encompass the thermal,
acoustic and visual properties of the environment and also include indoor air quality. IEQ
impacts upon the health, well-being and comfort of the occupants and, for commercial
buildings, these factors will also influence productivity.
In the past, IEQ studies, and, in particular, the effects of a poor IEQ, focussed mainly on
commercial buildings such as offices. Workers were found to be affected by a range of
symptoms including headaches, breathing problems and lethargy and the effect was often
referred to as ‘sick building syndrome’(117). More recently, it has been recognised that there
are other indoor environments where health impacts have not been given adequate attention.
The very young, the elderly and the sick are most vulnerable to air pollution and
contaminants but these groups tend to spend the most time indoors in houses, schools,
hospitals or nursing homes. Hence, a range of studies on non-commercial buildings has also
been undertaken(118).
As the link between occupier comfort and productivity in commercial buildings becomes
clearer and as legislation involving factors such as indoor air quality is increased so the drive
to use new or enhanced materials in the built environment also increases. As the following
sections should demonstrate, smart and functional coatings have the potential to make a
significant impact in this previously underappreciated area.
5.1
Phase Change Materials
Phase change materials (PCMs) are compounds with a high heat of fusion that melt and
solidify at certain temperatures and are, therefore, able to store or release large amounts of
energy. Like conventional materials, PCMs absorb heat as the temperature rises. However,
when PCMs melt they continue to absorb large amounts of heat without a significant
increase in temperature. Similarly, when the temperature falls, PCMs solidify and release
their stored heat energy. A number are particularly effective in the 20 to 30OC range and they
store between 5 and 14 times more heat per unit volume than water, masonry or rock. Given
these characteristics, PCMs clearly offer great potential in the construction industry,
particularly in climate control applications.
The construction sector first recognised the potential of PCMs around 30 years ago and,
indeed, it was shown that enhanced building energy performance could be achieved.
However, the chemical instability issues, corrosion and durability problems and loss of phase
26
change capability that were associated with the early materials meant that commercialisation
did not occur. Since then, though, further work has been undertaken by PCM suppliers to
overcome these drawbacks and PCM-containing construction products are now beginning to
appear on the market.
Phase change materials can be classified broadly as two groups; organic and inorganic.
Organic PCMs are usually based on paraffin wax. Being water-free, they can be exposed to
air and it is also possible to microencapsulate them. However, some organic PCMs are
relatively expensive and, being flammable, there are significant fire performance issues
surrounding their use in, for example, residential buildings.
Inorganic PCMs are generally hydrated salt based materials. To date, their use in
construction has been very limited because the materials displayed a tendency to subcooling and stratification. The latter leads to a loss of latent heat recovery time. Salt based
PCMs must be encapsulated, although they cannot yet be microencapsulated, in order to
prevent water evaporation but modern manufacturing methods have largely overcome the
sub-cooling and stratification issues and they are also natural fire retardants.
PCMs can be incorporated into a range of construction materials for use in either passive
(cooling through the direct heat exchange of indoor air with PCMs incorporated into existing
building materials) or active (passive cooling with an active component, e.g. a fan, that
accelerates heat exchange by increasing air movement across the surface of the PCMcontaining material) climate control and heat storage systems. Manufactured by BASF,
Micronal PCM SmartBoard(119) is a gypsum wallboard that contains microencapsulated
paraffin wax. DuPont Energain(120) is an aluminium-laminated panel product that contains a
copolymer and paraffin wax. Used in combination with mechanical ventilation, it is designed
for installation behind conventional plasterboard on the interior walls and ceilings of
buildings. Both products are capable of reducing temperature peaks by several degrees,
which gives greater occupier comfort and lessens the need for air conditioning. Of course, as
the temperature falls the absorbed heat in the panels is released, warming rooms and
lessening the need for heating systems.
Micronal PCM SmartBoard (BASF)
Energain PCM-containing Panels (DuPont)
Microencapsulated Micronal PCM has also been incorporated into aerated cement blocks(121)
and researchers at Oak Ridge National Laboratory, USA are currently testing a prototype
roof and attic system(122) that can reduce attic temperatures by over 10OC on a hot summer
afternoon. The Oak Ridge roof system contains an inorganic phase change material
sandwiched between sheets of aluminium foil and is installed as a dynamic thermal barrier
between the roof and the attic area.
27
Inorganic PCM in Prototype
Roof System (ORNL)
Micronal PCM in CelBloc Plus
Aerated Cement Block (H+H Celcon)
Expanded graphite is a low weight, high thermal conductivity material that, in combination
with PCMs, can be used as a lightweight material in high efficiency thermal energy storage
systems. Several buildings in Germany have been fitted with Ecophit(123) panels to provide
enhanced cooling.
PCMs need not be incorporated into wall or ceiling panels. It is also possible to seal them
inside otherwise entirely functional pieces of furniture such as writing desks, filing cabinets
and seating(124,125).
Ilkazell Insulation Technology Ltd., Germany is currently developing the Ilkatherm ceiling airconditioning system(126). This is an active capillary tube cooling system based on Micronal
PCM technology that can be thermally activated using water as the heat transfer medium.
Active Capillary Tube Cooling System (Ilkazell)
Ilkatherm Ceiling Air-conditioning System (Ilkazell)
28
5.2
Photochromic Windows
Materials that exhibit a reversible change of colour upon exposure to light are described as
being photochromic. Their most common application is for sunglasses but they are used as
sun shades in cars and can also be found in novelty toys, clothing and cosmetics. In the built
environment they offer potential as coatings on windows as they can cut down glare without
producing a loss in transparency. On hot, sunny days the shading afforded by photochromic
materials could also help to keep rooms cooler, improving occupier comfort and reducing the
need for air-conditioning.
Photochromic Window Shade (One Step Ahead)
Photochromism is displayed by both organic molecules, including diarylethenes,
azobenzenes and some quinones, and inorganic substances such as silver and zinc halides.
Of the latter, silver halide is used extensively in the manufacture of photochromic lenses.
Unfortunately, however, none of the photochromic materials studied to date have proved to
be suitable for building envelopes as they are not sufficiently stable to withstand thousands
of hours of outdoor exposure.
By combining electrochromic tungsten oxide and a dye solar cell layer, Fraunhofer ISE have
been able to develop a photochromic window system that they believe is appropriate for
glazing applications in buildings(127). When illuminated with sunlight the window colour tints
blue and visible light transmittance levels of just 4% have been recorded. Large scale
commercialisation, however, does not yet seem to have been achieved.
5.3
Anti-static Coatings
Anti-static coatings are applied to materials in order to reduce or eliminate the build-up of
static electricity. The role of the coating is to make the surface of the material slightly
conductive, either by being conductive itself or by absorbing moisture from the air. Molecules
in an anti-static agent frequently contain both hydrophobic and hydrophilic areas. The
hydrophobic side interacts with the surface of the material, while the hydrophilic side
interacts with moisture in the air and binds the water molecules.
The most common anti-static compounds are based upon long-chain aliphatic amines and
amides, quaternary ammonium salts, polyethylene glycol esters and polyols but there is
increasing interest in conductive polymers and indium tin oxide can be used as a transparent
anti-static coating for windows.
29
Anti-static Coating on
Windows (RehPol)
Anti-static Floor Covering (Scrubex)
Anti-static coatings can play a critical safety role in buildings and are used primarily in
factories and industrial units in areas where sparking is to be avoided(128-130). They are also
used extensively on electrical equipment, particularly on computer screens, to help keep
them free of dust, while coatings applied to glass perform a similar function. The application
of anti-static materials to carpets, floor tiles, curtains and fabrics can also greatly increase
occupier comfort and ensure electrical equipment integrity in healthcare, airport, hotel,
residential, retail, leisure and office environments.
Anti-static Carpet (United ESD)
5.4
Anti-static Office Chair (Industrial Seating)
Reflective Coatings
The practice of using light coloured materials or paints on the external surfaces of buildings
in hot climates is a well established means of helping to keep the interior cool and,
depending upon the level of roof insulation, it has been demonstrated(131) that reflective
coatings can reduce air-conditioning requirements by between 10 and 60%. There is
additional evidence(132) to indicate that reflective coatings in hot, sunny climates can also help
to improve the durability of the whole roofing system.
30
Acrylic Reflective Roof Coating
(Global Encasement)
Fibred Aluminium Roof Coating
(Roof Contractor)
Reflective roofing products(133-135) are generally durable, white-pigmented coatings that are
based upon a variety of long-established paint formulations. More recently, the incorporation
of aluminium flakes into paints and coatings(136-137) has provided an extra degree of
reflectivity. Paint systems that use glass flakes to achieve enhanced levels of reflectivity are
also available(138,139).
Reflective coatings can also provide benefits to the occupier when applied to interior
surfaces. For example, the Dulux ‘Light and Space’ range of paints(140) absorbs just 10% of
the available visible light, which compares with a value of 20% for their conventional matt
emulsions. Available in a range of colours, the paint improves the ambience of a room by
making it appear brighter.
31
6.
Summary of Smart Material Availability and
Development in the Modern Built Environment
Material
Photovoltaic Electricity
Generation
Current Status
Silicon-based PV panel
systems readily available.
Future Development
Payback time remains an
issue.
Cadmium telluride and
copper indium diselenide
systems becoming available.
Solar Heating
Widely available.
Electrochromic Windows
Commercial and domestic
systems are available.
Electroluminescent Displays
Readily available.
Antimicrobial and Hygienic
Surfaces
Widely available.
Printable dye sensitised solar
cells being developed but
conversion efficiencies
currently lower than for
silicon systems.
Systems are relatively
simple. Recent
improvements in selective
coating processing.
Uptake currently very low.
Not many UK suppliers.
Need to reduce costs.
Only monochrome ELD
panels etc. available at
present. Colour OLED
displays being developed but
these currently have only a
limited lifespan.
Very active field.
Organic dyes in combination
with gold nanoparticles
showing great promise for
killing MRSA bacteria.
Intumescent Coatings
Thermochromic Displays
Chemochromic Displays
Pyroelectric Sensors
Photoluminescent Displays
Readily available for steel
and wood substrates and for
fire seals.
Not yet commercialised for
the MBE.
Carbon monoxide detectors
cheap and readily available.
PIR sensors are cheap and
widely used.
Readily available and widely
used.
Sol gel technology to deposit
TiO2/silver nanoparticles
coatings being developed.
Systems for coil coating
operations being
investigated.
Ease of fabrication should
bring down costs and
increase uptake.
Hydrogen sensing likely to
become more important.
32
Material
Shape Memory Alloys
Current Status
Readily available. Current
applications tend to be
associated with safety
switches.
Easy Clean Coatings
Commercial coatings for
most construction materials
available.
Systems for glass and
ceramic substrates readily
available.
Widely available.
Self-cleaning Photocatalytic
Coatings
Anti-graffiti Coatings
Self-repair Coatings
Systems beginning to appear
in other sectors.
Phase Change Materials
PCMs are readily available.
Photochromic Windows
Some PCM-containing
construction materials are
starting to appear.
Photochromic materials
readily available but not yet
used in the built environment.
Anti-static Coatings
Readily available and widely
used.
Reflective Coatings
Largely based on existing
paint technology.
Future Development
Significant potential in smart
systems where SMA
actuators could counteract
strain introduced by crack
and or corrosion degradation.
Increased uptake required.
Work required to adapt
systems for use with
polymers and paints.
More environmentally friendly
waterborne systems being
developed.
Systems for the built
environment are still at the
research stage.
Fire performance remains an
issue with organic PCMs.
Inorganic PCMs cannot yet
be microencapsulated.
Current photochromic
materials are not sufficiently
durable for prolonged
outdoor exposure.
Combined tungsten
oxide/dye solar cell system
shows promise but not yet
available commercially.
Use of conductive coatings is
likely to become more
widespread.
Inclusion of aluminium or
glass flakes gives enhanced
reflectivity.
Greater uptake likely in UK if
current trend towards warmer
weather continues.
33
7.
Conclusions
This report highlights the many ways in which smart and functional coatings can be utilised
within the modern built environment. These coatings represent a hugely diverse class of
materials but, by identifying four key MBE themes, their current uses and potential
applications have been placed into context. In all cases, a little consideration has been given
to the properties of the material in question but the main focus is on how the technology can
best be exploited.
In conjunction with colleagues from the MBE KTN, the four MBE themes identified were
Energy Efficiency, Health and Safety, Enhanced Durability and Occupier Comfort. Drivers for
introducing smart and functional coatings into these areas vary but they include legislation,
competitiveness, occupier requirements and sustainability. It can be seen that for some
applications, such as intumescent coatings, smart technology is widely used and specified in
regulations, while for others, like self-repair coatings, full commercialisation is still some way
off.
Energy efficiency and the generation of power from renewable sources are topics of interest
that are being debated at the very highest levels of government. Smart technology, in the
form of photovoltaic electricity generation, will surely play a major role in helping to meet
future generation and emission reduction targets. The use of electrochromic windows and
electroluminescent displays and signage can also contribute to improved efficiency.
Health and safety is, of course, a vital aspect of any building design and utilisation and an
array of smart and functional coatings is available to ensure that current legislation can be
met and future standards can be increased. Greater use of antimicrobial-containing products
in the healthcare sector could help to reduce the level of hospital acquired infections, shorten
treatment waiting times, aid patient recovery and generate significant financial savings.
Intumescent coatings are vital in helping to maintain the structural integrity of buildings in the
event of fire, while a variety of warning and safety devices are dependent upon smart
technologies for their operation.
Annually, the UK construction industry consumes vast amounts of energy and materials and
creates huge volumes of waste. Clearly, this situation is becoming increasingly unacceptable
and it is evident that greater re-use of existing built assets and the construction of more
adaptable and flexible buildings is required in the future. The introduction of life-extending
technologies such as easy and self-cleaning coatings, anti-graffiti paints and self-repair
coatings should all help in this drive towards greater sustainability.
The relationship between worker productivity and indoor environment quality (IEQ) is widely
acknowledged in the commercial sector but only in recent years has IEQ really been
considered in other buildings such as houses, schools and healthcare facilities. Occupier
comfort is, therefore, likely to become a more important factor in building design. Thus,
thermal regulation using encapsulated phase change materials may soon become more
common. Photochromic windows could help to cut down glare, and reduce air-conditioning
costs, in heavily glazed buildings. Anti-static coatings can help to improve occupier comfort
whilst also ensuring that electrical equipment integrity is maintained and reflective coatings
can aid in regulating building temperatures and improving internal brightness levels.
In a generally conservative sector, where material integrity, cost, availability and past
performance are key factors in determining the choice of construction product, it is probably
not surprising to find that smart and functional coatings do not generally figure highly in
current building specifications. However, increased legislation, the need for greater energy
34
efficiency and improved sustainability and higher occupier expectations will all mean that
future material choice will need to be more flexible and imaginative.
Given their wide range of properties, smart and functional coatings are well placed to meet
many of the future materials challenges in the modern built environment. By highlighting their
functionalities, by giving examples of their use in the industry and by providing information
about their availability, it is hoped that this review will go some way towards allowing
designers, construction companies and occupiers to fully realise the properties of smart and
functional materials.
35
8.
Acknowledgements
The author would like to thank Dr Flavie Moulinier (BRE), Dr John Morlidge (BRE), Dr Alan
Partridge (NAMTEC), Dr David Arthur (IOM3) and Mr Paul LeGood (Corus) for their advice
and suggestions during the preparation of this report.
9.
References
1
‘Household Energy Efficiency’, Parliamentary Office of Science and Technology
Postnote, October 2005, No. 249
‘UK Energy in Brief. July 2005’, www.dti.gov.uk/files/file10738.pdf
Energy Use and Conservation in the United Kingdom,
www.en.wikipedia.org/wiki/Energy_use_and_conservation_in_the_United_Kingdom
www.statistics.gov.uk/cci/nugget.asp?id=151
‘2006 Pre-budget Report’, www.hm-treasury.gov.uk/media/2/2/pbr06_chapter7.pdf
www.news.bbc.co.uk/2/hi/uk_news/politics/7101075.stm
SolarGen Solutions Ltd., www.solargen.biz
Solar Illuminations, www.solarilluminations.co.uk
Advanced LEDs Ltd., www.advanced-led.com
BP Solar, www.bp.com/modularhome
Shell Solar, www.shell.com/solar/
Konarka Technologies Inc., www.konarka.com
Sharp, www.solar.sharpusa.com/solar/
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Nitinol SMA, www.nitinol.com
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