Integrating Electrochromic Glazing Technology into Conservation-Focused Lighting Design for Museums

Degree Project in Architectural Lighting Design

Second Cycle, 15 credits

Integrating

Electrochromic Glazing Technology into ConservationFocused Lighting Design for Museum Collections

Integrating Electrochromic Glazing Technology into Conservation-Focused Lighting Design for Museum Collections

Adrian Stapleton

Tutor: Andreas Schulz

AF270X VT22-1 Degree Project in Architecture

Second Cycle, 15 Credits

Stockholm, Sweden, 2022

KTH Royal Institute of Technology

School of Architecture and the Built Environment

KTH Architectural Lighting Design Master, 60 ECTS

... the Sanctuary of Art is the Treasury of the Shadows

Louis Kahn, Light is the Theme, 1975

Abstract

Museums, art galleries, and historical sites house items of important cultural value. They must provide sufficient lighting to allow for the public viewing of these items, but are also responsible for conservation of them, which requires strict control of the light levels on delicate materials. Windows provide many benefits to building occupants, but for light control, museums restrict the use of daylight. Electrochromic (EC) glazing changes opacity based on electrical charge, so it is possible to vary the amount of daylight admitted through windows. EC glazing can be integrated with museum lighting through a building management system, which can modulate light levels based on a variety of inputs. The Renwick Gallery is used as a case study for the potential application of EC glazing in a museum space. Because of other requirements for the management of environmental conditions, the use of EC glazing will not show a significant reduction in energy consumption. However, the benefits of access to windows, daylight, and views justify its use. EC technology is advancing rapidly. Due to its current limitations and the logistics of application into a historic structure, the Renwick Gallery may best be served by future advancements.

Keywords Dynamic Glazing, Cultural Preservation, Energy Conservation, Historical Conservancy, Smart Windows

All photographs and illustrations are by the author unless otherwise stated.

01.1.1

01.1.2 Electrochromic

01.3 Methodology

01.4 Limitations

02.1 Information and

Museum lighting.

02.2

03.4

03.5

04.3

Acknowledgements

Introduction

Can modern technologies be harnessed to help conserve the most delicate objects of the world’s cultural heritage? Museums, art galleries, and historical sites which house delicate artefacts have the responsibility for protecting them from damage. Light has been demonstrated to have significant damaging effects on many materials, which has resulted in the exclusion of natural light from many of these spaces. This paper examines the potential uses of electrochromic (EC) glazing as an integral part of lighting design to open up exhibition spaces to the controlled use of daylight.

Background and motivation

Worldwide, a great number of important cultural works are housed in buildings which were constructed before much was known about the damaging effects of light on materials. Until the end of the 19th century, museum lighting was accomplished through daylighting via windows and skylights, so historic museum spaces had large expanses of glazing to provide as much light as possible on the artworks (figure 01.01). But with the increasing availability of electric light, daylight was used less and less (Ulas, 2021). Subsequently, many of these spaces have closed or covered any daylight openings in an effort to maintain control of the light levels impacting their works, and conservation is often cited as a primary reason for this (Cannon-Brookes, 2000; figure 01.02). But these buildings are part of our cultural heritage, and so it is our duty to preserve their functionality and design as much as possible. According to Marina Chistyakova (2022), chief curator at the State Historical Museum in Moscow, the rooms are also historical monuments, and the interiors inform the exhibition.

Museum lighting

Museums, art galleries, and historical sites face unique challenges in designing lighting for their interior spaces. In preserving the world’s cultural heritage, the curators of these sites must provide public access to items of cultural importance and provide sufficient lighting to allow for the public viewing of these items. But it is also their responsibility to conserve the items for the future, which means strict control of the light levels on delicate materials.

figure 01.01: The Uffizi Gallery in Florence, Italy.

The gallery was designed with large amounts of glazing to maximize light. Tapestries originally hung on the left wall, which have since been removed for conservation. Modern screening is also visible on the windows at right.

(Petar Milošević, licensed under Creative Commons, https://creativecommons.org/licenses/by-sa/4.0/ deed.en.)

figure 01.02: Textile exhibit at the Aachen Cathedral Treasury. These historic garments are very susceptible to light damage. The lighting design for this UNESCO World Heritage site specifically excluded daylight in order to protect delicate objects such as these (Zumtobel, 2015).

(Torsten Maue, licensed under Creative Commons, https://creativecommons.org/licenses/by-sa/4.0/ deed.en.)

Museum lighting falls into two categories: exhibit lighting to illuminate and focus attention on the museum collection, and ambient light to allow people to move about, orient themselves, and find their way. The items on display must be lit in a way which allows for appreciation and understanding, and each type of display has its own unique requirements.1

Ambient lighting is not directed at the items on exhibit, but is intended for the visitors.2 Lighting aimed at featuring architectural elements becomes a source of ambient light, so this must be part of a unified design intent. Ambient lighting may be partially or completely accomplished with daylight, but must almost always be supplemented with electric light. Even such iconic uses of daylight as Louis Kahn’s Kimbell Art Museum (figure 01.03) supplement natural light with artificial in order to remain open in the

figure 01.03: Louis Kahn’s 1972 Kimbell Art Museum in Fort Worth, Texas. Ambient daylight is supplemented with artificial lighting on the artworks.

(Andreas Praefcke, public domain.)

1 For paintings with varnish and items under glass, the focus light must be angled to come from a direction which does not create a reflective glare to disturb the viewer. In some cases, such as when a painting is on a wall opposite an unshaded window, the angle of the mounting needs to be changed.

2 The overall level of ambient light need not be constant through the museum, but can be much dimmer in rooms housing the most delicate artefacts. There must be a progression from the initial entrance level to the dimmest space to time for allow for eye adaptation along the way.

evening, and to focus attention on the paintings, although this is not done without criticism (Pierce, 1998).

Before the advent of artificial lighting, museums were designed with daylight as the primary source of light. However, this limited the museums to being open only during the day and in bright weather. This limitation was cited as a primary reason for the adoption of artificial lighting as it became more readily available.

Yet daylight, and the windows by which it enters, are desirable for several reasons. Much recent literature has demonstrated the human need for natural light and the adverse effects that lack of daylight has on us (Wolska et al., 2021). Additionally, windows link us to the world around us. Quality views are becoming more recognised as important to human psychology, and visual connection to the exterior orients us within a space and relates us to the broader context of the location (Boyce et al., 2003).

In addition to housing and displaying artefacts, conservation is a primary objective of museums, art galleries, and historical sites. The goal of conservation is to minimize damage to important and delicate resources, but unlike preservation, conservation acknowledges that these items must sustain some damage if they are to be viewed (Ajmat et al., 2011). Modern technologies may provide a way to open up these spaces to the original daylight intent without impacting the conservation of delicate works.

Electrochromic technology

EC glazing utilizes a material which changes light transmission depending on its electrical charge state. EC glazing products are designed to be automated according to the levels of incident light on the window, and the simplest control forms have an illuminance sensor on the exterior of the building which triggers window darkening when light reaches a pre-set level. The most basic installation includes a manual override switch. The system can be scaled in complexity from there, with commercial EC windows designed to integrate with Building Management System (BMS) control through existing protocols. The largest manufacturers of EC glazing for the architectural field design their glazing to integrate with BMS control. The BMS is also able to control the building lighting system, allowing the integration of lighting and EC glazing control. Although it is theoretically possible to integrate control of EC windows directly with a lighting control system, the benefits to integrating both into a general BMS system are numerous. EC windows have a larger impact on building energy than just on lighting, as they also regulate thermal gain through the reflection of infrared light. The lighting control system is also managed by the BMS, making lighting and EC windows work in parallel rather than as a single system. The larger range of systems control offered by BMS, such as HVAC systems and emergency protocols, allows a larger variety of inputs and a more complex and robust hierarchical control algorithm than is possible with an independent lighting control system.

The Renwick Gallery

The Renwick Gallery of the Smithsonian American Art Museum is one of the oldest museum spaces in the United States (figures 01.04 & 01.05). It was constructed in 1859 as the first purpose-built art museum (Robertson, 2015) and likely the first French Renaissance style building in the United States (National Register of Historic Places, 1969; figures)

Located on Pennsylvania Avenue at 17th Street NW in Washington, DC, it is near Lafayette Square and within sight of the White House (figures 01.06—01.08). This history

figure 01.04 (above): “The new gallery of art, Washington, D.C.”

James Renwick’s original drawing for William Corcoran’s art gallery was published in Architects and Mechanics Journal, 1859 (Robertson, 2015).

(Library of Congress)

figure 01.05 (left): “Corkrans’ Art Gallery, cr 17th St and Pennsylvania Avenue.”

The Renwick Gallery, Washington, DC, as it appeared in the 1860s.

(Library of Congress)

DC

figure 01.06: Map of Washington, DC, area.

Location of the Renwick Gallery (✪) and the central area.

figure 01.07: Map of central Washington, DC.

Showing location of the Renwick Gallery (✪) in respect to other landmarks.

figure 01.08: Aerial view of the White House and the Renwick Gallery. (MSGT Ken Hammond, public domain)

and location make it an important structure in the Smithsonian Institution’s collection. The three galleries along the front of the building on the second floor have large windows with a southern exposure, housing revolving collections of American crafts. The windows have expansive views across Pennsylvania Avenue of the White House and the Eisenhower Executive Office Building, but due to concern for conservation of artworks, the windows are darkened to such an extent that the views are almost imperceptible. That these galleries combine dramatic views, direct solar exposure, and the housing of important works of art make them ideally suited to the study of the application of EC glazing.

Objectives

The goal of this thesis is to examine the feasibility of using EC technology in museums, art galleries, and other structures housing delicate, historical, and culturally important objects so that daylight and views may be reintroduced without compromising the conservation of artefacts.

Methodology

The thesis will approach its objectives through an analysis of current knowledge on the subjects of museum lighting, EC technologies, and control systems to integrate the EC windows into the lighting design of these spaces. Museum lighting study will focus on issues of conservancy, techniques for lighting works of art, and the use of daylight in exhibition spaces. It will touch on historical attitudes to daylighting and the impact of artificial lighting in museum spaces, as well as issues of light degradation of delicate materials. The electrochromics section will examine the current state of EC technologies and what is commercially available at this time. The lack of need for continuous power and the low voltages required for transition of opacity (less than 5 v DC) make operating costs of EC glazing very low compared to the energy required for artificial lighting. Parallel to this study will be a case study analysis of the Renwick Gallery to determine the applicability of what is learned to a real-world example.

Limitations

Many electrochromic technologies could find application in buildings housing delicate cultural and historical artefacts, but the focus of this thesis will be on darkening technologies. Throughout this paper the term “electrochromic” will be used in the context of a material which reversibly changes from transparent to opaque states by the temporary application of electric current. EC technologies requiring constant current to maintain states, such as liquid-crystal display (LCD) and suspended particle devices (SPD) are excluded, as are materials which change from transparent to diffuse states, and passive technologies such as photochromics and thermochromics.

Methodology

The primary focus of this thesis will be a review of current knowledge and the state of technology in the fields of museum lighting and EC windows. A parallel case study of the Renwick Gallery will be used to assess the feasibility of applying EC glazing to a historic site (figure 02.01).

Information and technology

Museum lighting

To adequately light museum pieces for viewing requires a variety of light typologies and techniques. These are covered in depth in such works as Christopher Cuttle’s “Light for Art’s Sake” (2013) and the Illuminating Engineering Society’s “RP-30-20 Recommended Practice: Lighting Museums” (2020), both of which are important inspiration for this paper.

Daylighting and sidelighting for exhibits

This section will examine historical and current methods for the use of daylight within cultural spaces, and compare them with current needs.

Integrating Electrochromic Glazing Technology into Preservation-Focused Lighting Design for Museum Collections

Synthesis and Summary Discussion Information and Technology

Control & Monitoring Systems

Electrochromic Technologies Conservation Requirements Daylighting and Sidelighting for Exhibits Glazing Systems

Renwick Gallery Recommendations

Conclusions Limitations

Logistics of Application of EC Technology

Daylight and Photometrics Historical Structure Requirements Energy Savings and Benefits Analysis

Case Study: The Renwick Gallery Site Analysis Existing Windows: Locations and Glazing

Conservation requirements

Conservation is the fundamental requirement for any museum, art gallery, or historical space. Museums must maintain strict control over a variety of environmental factors in order to minimize the damage to artefacts.

Glazing systems

Quality dynamic glazing promotes sustainability goals in multiple ways. Daylight harvesting reduces the energy required for interior lighting, access to daylight and enjoyable views has been shown to improve human health, and control of IR ingress reduces HVAC reliance. The use of EC glazing in a museum may contribute toward these goals.

EC glazing

EC glazing falls within a broader category of dynamic glazing, or “smart window” technology, but refers specifically to materials which change light transmission state when an electric current passes through them.

Control systems

A control system is required to integrate EC technology into the lighting design of a museum. BMS controls are able to monitor device function, and may receive inputs from a variety of in-gallery sensors. The failure state of the EC system can be addressed by the BMS in conjunction with other emergency systems.

EC use limitations

Limitations of EC materials include concerns of durability, specific spectral transmission, “irising,” and response to moisture, so these will be examined.

Case study of the Renwick Gallery; site analysis

Historical structure requirements and logistics of applying EC technology

The site analysis (figure 02.02) will look at the requirements and logistics of integrating EC technologies into historical spaces. Weight, size, and shape limitations of EC glazing may be a factor in the feasibility of applying EC glazing. The supply of power and control data to the EC windows is also a factor in their use.

Current daylight and photometrics; energy savings and benefits analysis

An examination will be made of the impact of the sun on these galleries and the current response to daylight. This will be paired with a look at the potential energy savings which EC glazing may provide.

Existing Windows

The typologies of the existing windows and the daylight and views they provide, as well as other benefits to them, will be looked at. A comparison of the current treatment of the windows will be made in order to determine other benefits EC glazing may produce.

Synthesis and site application

The results section will attempt to synthesize and summarize the information found, and apply it to the case study.

Results Museum daylighting

Historical usage and perspective changes

The Victoria and Albert Museum in London was the first museum to adopt artificial lighting. In 1859 it began the changeover from natural light to gas light, and by 1864 it was installing curtains to block natural light (Smith, 2013). In 1890 the British Museum adopted electric lights, believing “that the beauties of the sculpture were brought out by them more effectually than by such daylight as is at times rendered possible by our northern climate” (The Electric Light at the British Museum, 1890). Seventy-five years ago, it was predicted that “the future may see such structures designed for electrical illumination only” (Illuminating Engineering Society, 1947). By the mid-20th century, “many art galleries started excluding natural light in an attempt to create a more controlled environment” (Buro Happold, 2021; figure 03.01). And as recently as 2019, Van Gogh Museum in Amsterdam covered over internal skylights. According to Domenico Casillo (2022), lighting designer for the museum,

due to the fragility of Van Gogh’s paintings we have decided to drastically reduce the amount of light up to 50 LUX. To make this change possi-

figure 03.01: The Octagon Room of the Renwick Gallery, c. 1975. Heavy curtains obscure most of the window, leaving only a narrow slit of very bright daylight. (Library of Congress)

ble it was necessary to transform the museum from a museum that used natural daylight to a museum that uses only artificial lights.”

Benefits of windows in museums

Gertrude Stein once said, “I have always enjoyed going to museums, because the view from museum windows is usually very pleasant” (Kaplan, 2007). It is true that view to the outside is an important function of windows, and that access to views is important psychologically (Boyce et al., 2003). They provide orientation, connection with the larger world, and distant points on which to focus to reduce eyestrain (Reinhart, 2018). The changing aspects of daylight create visual interest, a dynamic space, and help prevent “museum fatigue” (Iordanidou, 2017). Positive links have been demonstrated between the use of daylight in museums and visitors’ satisfaction, although the control of the daylight is as important a factor as its presence (Kaya & Afacan, 2017).

Conservation

The most damaging environmental conditions are air temperature, humidity, pollution, and light (Ajmat et al., 2011). The first three are controlled through the HVAC system. In addition to heating and cooling the air in the museum, the HVAC system provides filtration, and may include humidification and/or dehumidification systems. The Renwick Gallery, for instance, uses a refrigerant dehumidifier to cool the air and then reheat it. Cooling the air causes moisture in the air to condense, after which the air is reheated to the correct temperature (National Park Service, 2016). Unfortunately, this means that the use of windows to bring a potential thermal benefit provides minimal, if any, reduction of HVAC system usage (IES Museum and Art Gallery Lighting Committee, 2020).

Effects of light on materials

Although visible light is damaging, much material damage is caused by electromagnetic radiation in non-visible areas of the spectrum. It is recommended for museum light sources to “remove wavelengths of light to which the human eye is insensitive” (Macchia et al., 2013). Short-wavelength ultraviolet (UV) light has enough energy to break molecular bonds in the surface of materials, and in especially delicate materials even visible light will have this effect.1 UV and visible light can also break down the molecular structure of dyes and pigments, causing colour loss (Cuttle, 2007). Since daylight is the strongest source of UV radiation, glazing should be filtered to remove it as much as possible (Boyce & Raynham, 2009).

Longer-wavelength near-infrared (NIR) and thermal infrared (TIR) light heats the surface of the material, causing damage from thermal expansion and contraction and by triggering chemical reactions. Unfortunately, daylight carries great quantities of radiant energy in the non-visible, but damaging, realm. “About 40 per cent of the solar radiation received at the earth’s surface on clear days is visible radiation,” while 51 per cent is infrared (Bhatia et al., 2014).

Sunlight can damage paintings by degrading and yellowing the varnish and breaking down the pigments (AIC, nd). UV light will weaken, yellow, and bleach paper documents (Northeast Document Conservation Center, 2022). Light damage occurs at the surface of a material where light falls on it, so it follows that historic silk textiles, containing some 1 Near UV (UV-A) light is categorized as wavelengths between 315 to 400 nm, although visible light is defined as wavelengths down to 380 nm, meaning there is a 20 nm overlap between UV-A and visible light. Light in this range is still considered very harmful to high responsivity materials (Cuttle, 2013), but EC materials tend to block these frequencies very well.

of the finest fibres, are very susceptible to light damage (Koussoulou, 1999). To simplify categorization of materials, the International Commission on Illumination (CIE) has created four categories of responsivity for museum objects, and recommendations for maximum light exposure for them (2004; figure 03.02).1 These are partially developed from the International Standards Organization (ISO, 1995) “Blue Wool Standards” scale for testing material lightfastness (figure 03.03).

Sustainability standards for museums

Due to prioritizing the requirements of their collections, museums and historic sites have not necessarily focused on sustainability, but this is beginning to change. The United Nations Sustainable Development Goals provide a focus for sustainable development. As of 2018, European standards recognise the importance of view quality in building design (Swedish Standards Institute, 2018). The International WELL Building Institute stresses the importance of daylight in interior spaces, and of access to quality views (Unnikrishnan, 2021), and the US Green Building Council (2013) offers credits towards LEED certification based on daylight harvesting, quality of views, and, importantly, renovation of historic buildings to improve these. And the Climate Heritage Network is organizing institutions in the arts and heritage sector to address climate change goals. Appendix A contains further information on sustainability goals within the cultural sector.

Category of Responsivity (Material Classification)Description

1. Irresponsive

2. Low Responsivity

3. Medium Responsivity

The object is composed entirely of materials that are permanent, in that they have no light responsivity.

The object includes durable materials that are slightly light responsive. 7-8+200600 000

The object includes fugitive materials that are moderately light responsive. 4-650150 000

03.1.4

4. High Responsivity

Materials

Most metals, stone, most glass, genuine ceramic, enamel, most minerals.

Oil and tempera painting, fresco, undyed leather and wood, horn, bone, ivory, lacquer, some plastics.

Costumes, watercolours, pastels, tapestries, prints and drawings, manuscripts, miniatures, paintings in distemper media, wallpaper, gouache, dyed leather and most natural history objects, including botanical specimens, fur and feathers.

The object includes highly light responsive materials. 1-35015 000 Silk, colourants known to be highly fugitive, newspaper.

figure 03.02 Table of CIE light responsivity categories for museum objects. (With modifications from International Commission on Illumination, 2004)

1 It is important to note that these recommendations for light exposure do not prevent damage to the objects, but only extend the time over which the damage takes place. “In reality the commonly accepted measures of maximum light level are based on the exposure before which a detectable change would be observed over a ten year period on display” (Ajmat et al., 2011). It is also relevant that the 50 lux recommendation on artworks is based on studies of the minimum acceptable light levels for viewing. These levels are determined by studies of the illuminance levels required for adequate colour discrimination (Hunt et al., 2003; Knoblauch et al., 1987). In general, older viewers require higher illuminance levels for good colour discrimination, but “visitors of all ages will experience objects as less colorful at 50 lux than at more optimum illuminances (200 to 400 lux)” (IES Museum and Art Gallery Lighting Committee, 2020).

I. Excellent lightfastness

II. Very good lightfastness

III. Fair lightfastness (impermanent)

IV. Poor lightfastness (Fugitive)

V. Very poor lightfastness (Very fugitive)

The pigment will remain unchanged for more than 100 years of light exposure with proper mounting and display.

The pigment will remain unchanged for 50 to 100 years of light exposure with proper mounting and display.

The pigment will remain unchanged for 15 to 50 years with proper mounting and display.

The pigment begins to fade in 2 to 15 years, even with proper mounting and display.

The pigment begins to fade in 2 years or less of light exposure, even with proper mounting and display.

figure 03.03: Sun damage to pigments on an ISO Blue Wool Standards card. The left side was protected from light, while the right received approximately 40 hours of direct sun exposure. The ISO has developed this standardised card of pigments with known responsivity to light, which may be placed at the location of an object as a way of measuring the amount of damaging light the location receives, or the responsivity of a material. Each level is approximately three times as resistant to fading as the preceding one. A small sample of material is exposed to light concurrently with the Blue Wool Standards to determine the responsivity of the material. When the material shows a just-noticeable level of fading, it is compared to the Blue Wool level which shows the same amount of fading to determine its responsivity (James Heal, 2021).

(table data adapted and quoted from Materials Technology Limited, nd)

EC window technologies

The concept of EC glazing was first introduced in 1984 (Lampert, 1984; Svensson & Granqvist, 1984), but has been commercially viable for less than 20 years (Kelly Waskett et al., 2013).

Technology overview

EC materials transmit 60-80 per cent of incident light in the transparent state, and 1-5 per cent in the opaque (Snow et al., 2018). This means that even in the opaque state, a view of a bright exterior is still visible. The minimal light transmission allows the window to retain its appearance and function, which is important in historic architecture (Rosenfeld, 2022).

The most common EC materials use metal oxides such as tungsten oxide and nickel oxide as the electrochromic component. The EC material is paired against an ion solution, so that when an electrical current is applied, the ions bond to or detach from it, changing its level of transparency (figure 03.04). This process takes time—between tens of seconds to ten minutes for a complete transition—meaning that intermediate dimmed states are possible (Gordon et al., 2021), although in practice commercially available EC

Polyester

Polyester

figure 03.04: Layers of a commercially produced electrochromic film. This design of an electrochromic foil may be used as the lamination layer between glass panes. Arrows indicate direction of ion movement when a voltage is applied for darkening the film.

(With modifications after Granqvist et al , 2018)

windows are limited to four tint states (Dutta, 2018). When electric current is not present, the material is stable in its transparency state (Granqvist et al., 2018). An advantage of an oxide-based EC material is that in the opaque state, the majority of the incident light is reflected, rather than absorbed, preventing significant heat gain at the window surface. The EC material reflects infrared light at a much higher rate than visible light in both states.

Manufacturing can now be done by a roll-to-roll process to produce a continuous material. This has reduced manufacturing costs dramatically, and also ensures greater consistency in colour and opacity transitions. The film produced is laminated onto an interior surface of an Insulated Glass Unit (IGU; figure 03.05). “EC IGUs are nearly identical in form factor to a standard IGU, except that they have a wire exiting the IGU for electrical interconnections” (Sbar, 2012). Any historic building which can be retrofitted with modern insulated glazing can make use of EC windows, as long as there is a way to provide power.

Limitations

For EC materials installed in glazing, durability is crucial. Both lifetime and the ability to achieve a high number of switching cycles without optical degradation are key. EC devices on the market are tested for at least 50,000 switching cycles (Wheeler et al., 2017). However, regardless of how the EC windows are supposed to function, they can and do fail. The St. Johnsbury Athenæum in Vermont installed EC glazing in its 2011 skylight restoration. Within three years, panes began to fail, requiring costly and logistically difficult repairs. The director of the Athenæum advises:

03.2.2

2.2

VisibleLight SolarHeat

figure 03.05: Light transmission through an IGU with integrated EC layer.

The layers of the IGU reflect and absorb visible light and infrared light (solar heat) in both the transparent and opaque states.

(With modifications after Sanders, 2015)

When considering such an installation it is imperative to understand what will be involved in replacing glazings: cost, time involved during which the building is unavailable to visitors, overall difficulty, and potential damage to artworks unless all are removed from the work area… Any institution considering such an installation needs to understand what will be involved to replace failed glazings. (Joly, 2022)

EC materials attenuate light at different levels across the spectrum, so the light entering through them will not have a perfectly neutral colour, and most show a significant colour shift between the transparent and opaque states. Combinations of EC materials are used to even out the spectral transmission in commercial products (figure 03.06). Colour rendition of tested EC window systems are very good in the transparent state, but much reduced in the darkened state. New advancements are working toward much more colour neutral EC materials (Arvizu et al., 2017).

EC materials require protection from moisture, as slight changes to the concentration of the ion solution will impact their function. To create even colour, opacity, and transition over the whole pane, the EC window must maintain even voltage across the transparent electrode surfaces, which necessitates very specific shapes and sizes. Due to the requirement for a consistent voltage across the electrodes, curved edges are not manufactured, which has a direct impact on the Renwick Gallery study. More detail on EC technologies and the solutions to their limitations is provided in Appendix B.

figure 03.06 Spectral transmission of two common EC oxides. Light transmission of nickel oxide and tungsten oxide EC films, and when combined. Shown at transparent, semi-transparent, and opaque states.

(With modifications after Granqvist et al , 2018)

Tungsten oxide-based

Nickel oxide-based

Combined

Transparent state

Semi-transparent state

Opaque state

Control of EC coatings

Control of EC windows is designed to work with a BMS through existing protocols, such as BACnet and LonWorks.1 Using a BMS to integrate lighting control and the tinting of the EC window allows for dimming the lighting to different levels based on the level of light entering through the window. Such dynamic reactive dimming maximizes the energy savings from daylight harvesting (Ander, 2003). However it should be noted that controlling the window too precisely defeats the purpose. “There is little point in controlling daylight so closely that it cannot be distinguished from electric lighting” (Boyce & Raynham, 2009). BMS-controlled lighting systems can use wireless mesh or Bluetooth communication between the controller and the components, including luminaires. This allows monitoring of the components, over-the-air firmware updating, and better energy and usage analytics.

Monitoring requirements for museum light

In addition to controlling the maximum visible light exposure to objects, temperature control is important in conservation. Therefore, the control of the EC windows requires input from temperature sensors, thermostatic systems, and light sensors, which are part of the BMS. Although protection from UV light is an important factor, permanent filtering of UV can be accomplished with passive filtering materials as part of the glazing. That EC materials also block UV frequencies well even in their transparent states is an added benefit.

1 The two largest manufacturers of EC glazing for the architectural field are Sage Glass, a division of the French conglomerate Saint-Gobain, and California-based View, Inc., a division of Corning (Market Research Reports, Inc., 2019). Both manufacturers’ entire line of products are compatible with BMS control. Sage Glass can be configured with BACnet, LonWorks, Ethernet, or their proprietary SageBus protocols (Sage Electrochromics, Inc., 2020). View, Inc. devices use BACnet, CANopen®, and Ethernet (10/100 Mbps) protocols to communicate with BMS systems (View, Inc., nd).

The Renwick Gallery

Details

of the southern second floor galleries

The area of study focuses on three small galleries connected along an east-west axis (figures 03.07 & 03.08). The Southwest Gallery and the Southeast Gallery flank the central Octagon Room. The Octagon Room contains a single window, while the two other galleries each contain two windows on the south façade and one on the side (figure 03.09).

Since these galleries face directly south, they receive the full impact of the sun most of the year. Due to the latitude of Washington, DC (38.9° N), the sun has much less impact on the galleries in summer than in winter (figure 03.10). At the summer solstice, the noon sun altitude is over 75°, and the stone window alcoves are deep enough to prevent it directly entering the rooms through the southern façade. However the winter sun is low enough and is not blocked by any structures to the south, so it would shine through the whole depth of the galleries if they were not protected (figure 03.11).

figure 03.07: North-south centre-line section of the Renwick Gallery.

(With modifications from plans provided by the Smithsonian Institution)

Galleries Under Study Other Areas

figure 03.08 Plan of the second floor of the Renwick Gallery.

The case study focuses on the Southeast Gallery, the Octagon Room, and the Southwest Gallery.

(With modifications from plans provided by the Smithsonian Institution)

Galleries Under Study Other Galleries Service Areas

Circulation Areas

South Façade East West

figure 03.09 Locations of the windows of the galleries under study.

The window designs shown here were manufactured by St. Cloud Window (https://stcloudwindow.com/gallery/renwick-gallery-smithsonian/). The semicircular top panes of the windows are problematic for EC manufacturing.

figure 03.10: Sun path angles for the Renwick Gallery.

top row: top view: summer solstice (left), equinox (centre), winter solstice (right).

middle row: view from west: summer solstice (left), equinox (centre), winter solstice (right).

bottom row: view southwest with surrounding buildings: summer solstice (left), equinox (centre), winter solstice (right).

(Data source: Marsh, 2014)

figure 03.11: Angle of the sun entering the Octagon Room at midday.

This diagram indicates the potential solar intrusion into the gallery through the window openings. Reflection off the varnished wood flooring is also indicated. Shown are solar noon sun angles on the summer solstice (left), equinox (centre), and winter solstice (right). The maximum solar elevation is 74.54°, 51.04°, and 27.70°, respectively.

Current solutions for daylight openings

Because of artwork conservation concerns, the Renwick Gallery windows are currently shaded so that the maximum amount of light allowed through does not exceed the maximum allowable lux levels for high responsivity materials. During the 2015 renovation, the Renwick Gallery windows were replaced with blast-resistant double-pane IGUs which later had layers of neutral darkening films applied, and a mesh screen was also installed (figure 03.12). The overall effect of these layers is to reduce incoming light to approximately 0.18 per cent of the incident light on the window. The difference in light levels between an unprotected IGU and the current solution is evident in false-colour renderings where it is also clear how much daylight could be made use of if it were controllable (figures 03.13 & 03.14). When the sun does not have a direct impact on the window, more daylight, and more view, would be accessible.

Current daylight impact on lighting design

The drastic diminution of daylight entering the galleries means that daylight is not part of the integrated gallery lighting design. Gallery ambient and artwork focus lighting are provided by track-mounted spotlights. Lighting levels are controlled via DMX protocols by a Medialon system, with input from occupancy sensors and the BMS. Each room has defined pre-set scenes for operating hours, after hours, cleaning and setup, and special events, which are scheduled to run based on time, occupancy, and manual overrides (Westlake Reed Leskosky, 2013).

Summary

Sites which house and exhibit cultural artefacts are subject to very specific lighting design requirements, which in turn are part of many environmental factors requiring

Exterior

Interior

figure 03.12: Glazing solutions at the Renwick Gallery.

A diagrammatic cross-section of the window, showing the layers involved in reducing daylight transmission (tx), and each layer’s transmission of visible light. Total visible light transmission is 0.18% of incident light. (data sources: “085123 - aluminum windows,” 2013; 3M, 2021; Crown Shade Company, 2021; Drumming, 2015; “PO 393802,” 2018; Rosco Laboratories, Inc, 2001)

Crown Shade SW2390 5% scrim, 5% tx

Roscolux #98 Medium Grey filter, 25% tx 3M Night Vision NV25 film, 22% tx

Blast-resistant Insulated Glass Unit (IGU), 67% tx composed of:

3 mm annealed glass

2.3 mm SGP interlayer

3 mm annealed glass

13 mm argon gas filled space

Pyrolitic Low-E 272 coating 6 mm tempered glass

management for the conservation of delicate objects. EC glazing can be controlled to the degree that windows can be integrated into that lighting design without compromising conservation. The control systems which manage both the lighting system and the EC windows are programmable such that very stringent light level requirements may be maintained, while overrides and emergency protocols can be in place to protect the collections. However, concerns of durability and limitations on shape manufacturing impact the effectiveness of current EC technology for the Renwick Gallery and other historic sites.

figure 03.13: False-colour Dialux renderings through the course of the day. Renderings made in two-hour increments on the equinox. The false-colour image highlights the changes in angle and intensity of natural light which the galleries could receive during the course of the day. The dynamic nature of daylight creates a more interesting environment and helps reduce “museum fatigue” (section 04.1.2.2). These renderings are based on .unshaded 60% transmission IGUs. See figure 04.15 to compare with the current shading solutions, and for colour code explanation.

figure 03.14: False colour Dialux renderings showing the darkening effect of the window treatments.

The top row of each series shows the effect of untinted 60% transmission IGUs. The bottom row shows the impact of the layers of darkening film and the screen. Due to the depth of the window apertures and the high angle of the sun in summer, the winter solstice sees much more daylight inside than the summer solstice.

Note on the colour coding:

Black-Grey: below 1 lux; very dark

Blue-Cyan: 1-25 lux; too low for viewing

Green: 26-50 lux; levels for very high responsivity objects

Yellow: 50-80 lux; range for medium responsivity objects

Orange: 81-200 lux; range for low responsivity objects

Magenta: 250-1000 lux; bright

White: over

Discussion

EC glazing has potential for use in facilities housing delicate cultural artefacts. The ability to attenuate the light levels entering through a window while still allowing access to views and the dynamic nature of daylight could benefit the museum environment.

Specific recommendations for the Renwick Gallery

EC glazing could provide access to the excellent views provided by the Renwick Gallery windows. The various tint states of the glazing could introduce controlled amounts of dynamic daylight into the galleries without compromising the protection of its collections (figure 04.01).

The second floor gallery windows at the Renwick Gallery have semicircular top panes to match the arched opening. These curves are not possible with the current state of EC manufacturing, so a different solution must be found for the top pane. This could be extra layers of tinting film, making that pane darker than the ones with an EC application, or applying a partial shade covering. The fact that the top pane would be different from the rest of the window with either solution is a design consideration.

The location of conduit runs in historic structures requires careful review, since much of it would be surface mounted and visible. The plenum spaces above the southern gallery rooms are temperature controlled, so could be ideal for locating control devices.

Research into EC windows with integrated photovoltaics and battery storage is underway (Appendix C). Although this technology is still some years away from commercialization, the current results are promising. The Renwick Gallery may be best served by such self-powering technology, rendering physical conduit runs unnecessary.

General recommendations

The most important factor in the use of EC glazing in these environments is control. The EC glazing should be integrated with the lighting system through a BMS which can

figure 04.01: Simulation of a Renwick Gallery view with EC tint states. The left image simulates an IGU without EC or tint coating; the remaining simulate an EC IGU with a 3M NV-25 coating in different EC tint states. Label indicates approximate visible light transmission (tx) at each state. From left to right: Untinted IGU; EC IGU at transparent state; EC IGU at first intermediate tint level; EC IGU at second intermediate tint level; EC IGU at maximum opacity.

control how much of both natural and artificial light the objects receive. For application in historical buildings, logistical considerations include how the windows receive power and control data, and how the BMS senses and responds to light levels. Minimizing the installation of electrical conduit, and locating control and network systems in support areas out of sight, reduces the potential for damage and visible alteration to historical architecture.

In an emergency situation, or a loss of power to the building, the window must revert to its most opaque state. Leaving the windows transparent while light conditions outside continue to change could subject the exhibition materials to unacceptable levels of light exposure. Since the EC window requires electricity to change states, some form of battery backup is required. This system should function in the same way as the emergency lighting and exit sign system, where the voltage is applied to darken the window automatically on loss of power or signal. Much like the operation of emergency lighting, the battery should be housed locally at the window. It would make sense to include darkening of the EC windows in the BMS emergency lighting programme.

Given the relatively low requirements for light levels of sites housing light responsive materials, and that EC glazing allows some light through at the opaque state, pairing the EC glazing with a passive window tinting film is recommended. Additionally, the filters could help to block all UV and reflect much of the IR light incident on the windows. This would benefit conservation, as these invisible frequencies contribute nothing to the museum environment. The low colour rendering ability of light entering from the EC IGU in the darkened state should be considered if the light will illuminate art objects.

It is important to consider the factors involved in repair or replacement of failed EC glazing, especially in historic buildings housing delicate artefacts, where the objects must be removed before glazing repairs may commence.1

Bearing on sustainable development goals

Due to the low light levels required for a conservation environment, and other energy demands required for temperature and humidity control, EC glazing would have a minimal impact on energy use. However, access to windows, dynamic daylight, and quality views have proven benefits to human health and well-being.

Conclusions

The use of EC glazing in museums can be justified for the impact it has on the museum environment if logistics and access allow. The ability exists to control the addition of daylight and allow access to views, without impacting the conservation of delicate materials. The retrofit of glazing in historical sites to energy efficient IGUs with integrated EC coatings would allow historical architecture to maintain its original function and design, while focusing on the important objects being housed. Linking the lighting system to the EC glazing through a BMS with light and occupancy sensors and emergency protocols could create a more dynamic environment.

1 It should be noted that regardless of any warrantee on the glazing, the removal of the display objects would be the responsibility of the curatorial staff. It is unlikely that any institution would wish to leave this work to glazing contractors. 04.3 04.4

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List of Figures

01.03 Louis Kahn’s 1972 Kimbell Art Museum in Fort Worth, Texas

01.04

01.05 “Corkrans’ Art Gallery, cr 17th St and Pennsylvania Avenue”

03.03

03.08

03.12 Glazing solutions at the Renwick Gallery.

03.13

03.14 False colour Dialux renderings showing the darkening effect of the window treatments

Appendix A: Sustainability in the museum environment

The United Nations has identified 17 goals for sustainable development, among these being Good Health and Well-being (goal 3), Affordable and Clean Energy (goal 7) and Sustainable Cities and Communities (goal 11). Goal 3 generally is to “ensure healthy lives and promote well-being for all at all ages,” which access to daylight and view promotes. Daylight harvesting aims toward goal 7 in reducing energy consumption, and the use of the dynamic light blocking ability of electrochromic materials may help to protect cultural heritage, contributing to goal 11. Daylight and windows have an impact on these goals.

Green building certifications worldwide “recognize that a sustainable design is not just about energy efficiency” (Sok, 2017), but that the health and well-being of the building occupants is an important factor. Much recent literature has demonstrated the human need for natural light and the adverse effects that lack of daylight has on us (Wolska et al., 2021). Additionally, windows link us to the world around us. Quality views are becoming more recognised as important to human psychology, and visual connection to the exterior orients us within a space and relates us to the broader context of the location (Boyce et al., 2003).

Buildings, and the related construction industry, are responsible for an estimated 38 per cent of global CO2 emissions (Balaras, 2022). In most countries worldwide, buildings use more than 40 per cent of the energy produced, but the International Energy Agency believes that policy changes could reduce consumption by 30-80 per cent, “while simultaneously increasing energy security and improving the health and welfare of building occupants” (International Energy Agency, 2017). And to promote the use of energy-saving technologies in the United States, several bills have been introduced into Congress to allow for a tax credit for EC glazing installation, although none of these have been enacted.

The Climate Heritage Network (CHN) is an organization “committed to mobilising arts, culture and heritage to address climate change” which is attempting to motivate sustainability and climate action goals within the cultural sector (Thompson, 2022). CHN is working to increase the involvement of cultural and heritage institutions in sustainability. The American Association of Museums, among others, has signed the CHN Memorandum of Understanding pledging commitment to addressing climate change (Lott, 2020).

The United States Green Building Council (2022) administers LEED certification, which “provides a framework for healthy, efficient, carbon and cost-saving green buildings.” The International WELL Building Institute (nd) also provides building certification, focusing on design decisions impacting the health of the occupants . These are all tools with which museums and historic sites may address sustainability concerns within the framework of conservation.

The most common justification for the use of EC glazing is the energy savings they can bring about from reducing artificial lighting levels and improving thermal control. However, it has been pointed out that the low levels of light required for conservation, and the reliance on HVAC systems to cool and reheat air for humidity control, this impact is minimal in a museum situation. “There are many reasons to value daylight in the museum environment, but the overall energy savings from daylight harvesting is not a compelling argument” (IES Museum and Art Gallery Lighting Committee, 2020). Therefore, it is the psychological benefit of access to the dynamics of daylight and to quality views which must be the focus of sustainable design.

Appendix B: Electrochromic technology

Some electrochromic materials, such as polymer dispersed liquid crystal (PDLC) or suspended particle devices (SPD), rely on a current passing through the material to align crystals or rod-like nanoparticles, allowing light to pass through. However, with these materials, the electrical current must be maintained, and the material becomes opaque in its absence. This makes these technologies much less practical for large-scale uses such as in windows, but they have found widespread application in the automotive and fashion industries.

The EC material itself is paired with an ion solution, either hydrogen or lithium, in layers (figure 04.05). These layers are sandwiched between transparent electrode surfaces. The molecular structure of the oxide forms an octahedral ring structure which allows large enough space for photons to pass through, making the material transparent. When a current passes between the electrodes in one direction, ions in the solution move to bond with the oxide molecules, shifting the crystalline structure to where light is no longer able to pass through the gaps, rendering the material opaque. As long as the voltage is applied, ions continue to move and bond to the oxides, increasing the opacity, until the electrochromic material is saturated. If current is passed through the materials in the other direction, the ions release from the oxide molecules and return to the solution.

The process is remarkably similar to the functioning of a rechargeable battery, in the application of electrical current in one direction increases the stored potential energy of the system, and electrical flow in the other direction reduces it (Granqvist et al., 2018). Another observed similarity to battery technology is the tendency for the function to diminish over time and repeated operational cycles, but like a battery, this diminution may be reversed by the application of larger voltages, allowing a rejuvenation of the system (Granqvist et al., 2019).

Electrochromic technologies are advancing rapidly, and new research may provide even more benefits. Many of the limitations discussed under section 04.2.2 are in the process of being addressed, and potential solutions are promising.

Commercial EC devices are tested for at least 50,000 switching cycles, but in the laboratory devices have tested for 100,000 reversible cycles “without significant change in the colored and bleached spectra” (Balakrishnan & Patathil, 2019).

No compound attenuates light evenly across all visible wavelengths. Commercial EC windows partially solve this by combining two different oxide-based films in the same device. For instance, a tungsten oxide-based film colours light primarily in the long-wavelength part of the spectrum, while a nickel oxide-based film primarily affects shorter wavelengths. The combination of the two films yields a device with a very neutral impact on visible light (figure 04.07). Research is currently underway on a number of ternary compositions which “shows that approximate color neutrality is achievable” (Granqvist et al., 2019). Arvizu et al. (2017) have developed “three-component mixed electrochromic oxides with [colour neutrality] properties that are superior to those of commonly used single metal or two-component metal oxides.”

In particular, the ion solution of the electrochromic device can be sensitive to moisture. Changes in humidity can change the solution density, impacting how well the device functions. In commercial products this limitation is solved by the application of the electrochromic film to an inner layer of an insulated glass unit (IGU) which has had air removed or replaced by an inert gas in the space between the panes (figure 04.05). The

use of multiple-pane IGUs is already being promoted for the energy savings they provide in reducing heat transference, so they are ideal for EC applications.

Over a large pane, EC materials are prone to an irising effect, where the outer part of the window changes opacity at a different rate than the interior due to subtle differences in voltage across the electrode surface. This can cause a gradient of darkness and/ or colour around the edges of the pane. Manufacturers are very aware of this issue, and their products adhere to strict size and shape restrictions to minimize this. To minimize irising, and to maintain an even charge across the electrodes, curves and tight angles cannot be manufactured (Sage Electrochromics, Inc., nd; View, Inc., 2021). This aspect of EC glazing significantly impacts its use in architectural applications, especially in historic building retrofits.

Appendix C: Looking forward; the future of EC technology

New technologies are being explored to optimize the function of EC windows. Efforts are being made to improve response, and make EC devices more self-powered and self-reliant. Wu et al. (2019) created a split-pane EC device with an embedded photometric device which dynamically dimmed the glass in real time based on the illuminance of the sky.

The integration of EC films with photovoltaics is being studied in depth.

The combination of the electrochromic solution with semi-transparent silicon thin film solar cell (Si-TFSC) placed on a glass substrate provides promising optical performance and energy benefits. The integration of electrochromic and photovoltaic devices provides better efficiency in energy saving, because photovoltaic and electrochromic devices can achieve electrochromic layer discoloration without an external power source (Hendinata et al., 2022).

Kim et al. (2022) have suggested that a transparent photo-energy harvesting unit could be the outer electrode in the EC film, making it a truly integrated device. Proposals have been made to use semi-transparent photovoltaics in a three part EC glazing system, where near-UV is used for power transmission, and multiple EC layers separately modulate visible and near-IR light for lighting and heating. “Solar cells harvesting near-ultraviolet photons could satisfy the unmet need of powering such smart windows over the same spatial footprint without competing for visible or infrared photons” (Davy et al., 2017).

Nanogenerators have also been studied as an energy source for self-powered EC devices (Yang et al., 2012). The low power requirements of EC devices allow them to be potentially powered by electricity generated by wind and rain at the surface of the device.

The use of the electrochromic system’s battery-like structure for the purpose of storing energy, thereby eliminating an external battery, is under study. “It is possible to combine energy generation, energy storage, or light-emission with electrochromics” (Balakrishnan & Patathil, 2019).

Acknowledgements

I would like to thank the following for their support and guidance:

Andreas Schulz, Licht Kunst Licht, Bonn

Scott Rosenfeld, FIES, Smithsonian American Art Museum, Washington, DC

Domenico Casillo, Van Gogh Museum, Amsterdam

Bob Joly, St. Johnsbury Athenæum, Vermont

The Smithsonian Institution, Washington, DC

ALD faculty and students at KTH Royal Institute of Technology, Stockholm

Aviva Garrett and Beth and Mara, of course.

TRITA – ABE-MBT-22218