Pressure builds for action on focused solar reflection.
December 16, 2014 By Vincente Montes Amoros
Solar reflectivity has generated attention in the design world due to
the appearance of “fryscrappers” or “death ray buildings,” as they have
been referred to in public media.
Solar reflectivity has generated attention in the design world due to the appearance of “fryscrappers” or “death ray buildings,” as they have been referred to in public media. These creative nicknames come from accounts of the Siege of Syracuse in 214-212 B.C., when Archimedes supposedly used an array of mirrors to set an adversary’s warships on fire. Ancient scribes named these “death rays.” The principle is to concentrate reflected light on a small surface to increase its temperature, which should be familiar to anyone who played with a magnifying glass on a summer’s day.
|Reflections from building facades can blind neighbours, ruin energy models and even damage buildings, cars and vegetation. Time for an industry response?
The so-called death ray buildings (officially two have been registered to date) have several things in common. They both exhibit concave south-facing walls, which happen to be all glazed. The reflectance of the glass used is excess of 40 per cent. The focused reflections melted plastic and raised temperatures nearby. One of these buildings is located in Las Vegas, and it raised temperatures by 10 C, causing plastic bags and cups to melt. The second one is located in London, England’s Financial District and it raised ambient temperatures from 29 to 72 C. Surface temperatures of some materials nearby were recorded at 110 C. This building caused plastic components of a car parked nearby to melt. Other building materials such as TPO roofs and metal panels can produce a reflectivity effect similar to what happened in Los Angeles when the Walt Disney concert hall facade clad in stainless steel panels blasted condos across the street with blinding glare and heat.
Cases of melting gaskets in glazing systems, blistered paint, warping car consoles and tarps melted off buildings have all been reported in public media. However, not all cases make the news and not all cases get the coverage and exposure a very few have gotten. Solar reflectivity can indeed be a nuisance and also produce severe and hazardous conditions that can jeopardize public safety. If this issue has already been recognized and recorded, why is the industry still silent about the topic? Why are there no limits or a widely accepted performance criteria?
When trying to find the right measure or limit to effectively address solar reflectivity, several factors need to be considered. The first is discomfort to drivers. Drivers can be blasted by reflected light and get distracted with potentially dangerous consequences. Cities located 40 degrees or more from the equator represent a particular challenge because the sun’s natural position during the winter months is relatively low. At angles of less than 20 degrees, direct sunlight and reflections caused by sunlight can be within motorists’ cone of vision and produce glare.
Nuisance to neighbours is another problem. A case in the Dallas Arts District was reported in 2012 where a residential high-rise building with highly reflective glass (in excess of 40 per cent reflectance co-efficient) casted reflections into a nearby museum. Reflections from the residential tower entered the museum’s galleries through a unique skylight design that was intended to allow only indirect sunlight from the north. The reflected light’s intensity increased not only the temperature on the museum’s garden but exceeded the acceptable light levels to safely display some works of art. At extreme thermal loads, the temperature increase can produce discomfort to pedestrians and at gathering places nearby.
Energy models can be invalidated by focused solar reflection. Depending on the project’s context and the intensity and duration of the reflected light, a building’s adjacent properties could see an additional thermal load that was not considered in their energy modelling.
Solar reflectivity will intrinsically produce and increase heat in the surrounding environment. The intensity will depend on the material producing the reflection. Vegetation is adapted to a range of natural heal levels and it is possible that with a sudden increase in heat, it can start to decay and eventually die.
Light is comprised of different components: ultraviolet (UV), visible light and infrared. Human eyes can only see the visible light portion from the solar spectrum. To get the most benefit from natural daylighting without unnecessary heat gain, some glass coatings prevent the infrared portion from getting into the building. Whatever is not transmitted through the glass to the interior of the building is reflected and sent back to the environment, and that is not the visible light portion only. Reflected infrared light is essentially radiated heat that will raise the temperature of anything it hits. Reflected UV causes cell damage to living things and can break down certain materials, especially plastics.
To date, only Singapore and Sydney, Australia, have limits on the effects of solar reflectivity. The building code in both cities states that reflectance of construction materials is limited to 20 per cent and that a solar reflectivity assessment must be submitted for approval. The City of Dallas recently tried to modify its building code to address this phenomenon due to recent events in their Arts District. However, the proposal did not survive the public comment phase and the idea was abandoned.
Due to the lack of legislation or an industry standard, this phenomenon is generally not addressed during design and cannot be easily resolved after it happens. Because solar reflectivity can impact the visual and thermal aspect of a surrounding environment, different criteria and indices have been proposed but none is widely accepted or used. We have seen a handful of competing criteria with their own strengths and weaknesses. Four main ideas are out there.
The first criteria limits light brightness. Factors such as age, eye pigmentation and the pupil’s ability to rapidly adapt to contrast are just some of the variables that make tolerance to light brightness different for every person. Given these factors, limiting light brightness might not be the most objective criteria. Also, this limit does not address thermal load.
The second criteria found limits reflectance of construction materials. This limit is integrated to a couple of city building codes, as mentioned before, and can easily be met. However, complex building geometries can focus light which would produce solar reflectivity issues even with limits of this kind.
The third criteria limits thermal radiation. Although this limit can certainly be a more objective proposal because heat and its effects are measurable, one must be careful in selecting an appropriate threshold. Different levels of heat produce different effects. Some plastic materials have a melting point of less than 80 C and can be at jeopardy if a high threshold is selected. The surface temperature of materials like sealants or gaskets in glazing systems can rapidly increase when in contact with highly conductive metals in framing members.
The fourth criteria limits direct sunlight effect. By limiting the effect of reflectivity to no more than what direct sunlight produces could certainly result in conservative results. But plant species, materials and humans are accustomed to nominal sunlight conditions. In using this criteria we can be certain that the effects of solar reflectivity would be limited and controlled. This criteria addresses the visual and thermal aspect of the phenomenon.
The study of solar reflectivity can benefit not only potential death-ray buildings but more normally shaped buildings too. Pedestrian comfort and vegetation sustainability can benefit from this type of analysis by making sure the proposed material or glazing is adequate for its surroundings. Some environmentally concerned designers, aware of the issue, have retained facade consultants to perform analysis on their proposed designs. They wanted to make sure their projects will not alter the surrounding areas and cause impact to neighbours.
Although the solar reflectivity phenomenon has always been part of glazed projects, it was only recently that designers and building owners started to become aware of the issue, in part due to projects that have gone wrong. Technology now exists to model and predict anything we can imagine. Technology and talent have demonstrated that any problem can be resolved.
Tall buildings are certainly an alternative in areas with limited space to build, and glass is a relatively cheap material that serves many functions in an already size-reduced building skin system. But the problem is not building height or the amount of area covered with exterior glass panelling. Although both factors carry their own weight, the real problem is us. The real problem is that in our contemporary designs we give little or no consideration to our environment and neighbours who are being affected by our lack of holistic building design. Surprisingly, the study of light and reflection is ancient, and although it is a very well documented and studied topic we have not extrapolated that knowledge to our industry.
The time is ripe for an industry standard that limits the amount and intensity of reflected light. Waiting for more death ray buildings to be built before reacting as an industry would not be proactive. Buildings rendering energy modelling of adjacent properties obsolete is a problem everyone should be concerned about even if you never plan to build a reflective facade. The industry needs to step in and propose limits to this nuisance. It has been almost 10 years since the first solar reflectivity case was reported from a stainless steel panel façade, more than four years since the first death ray building and over a year since the second death ray building came to light. Demand for solar reflectivity studies has increased during the past five years, which is just one indicator highlighting the need for industry-wide acceptance criteria for solar reflectivity.
Glazing options available today do not compromise energy performance with the use of less reflective glass. Contrary to common belief, buildings can still meet energy requirements with less reflective glass, as has been proven with recent designs across the globe. Since glazing products are not the limiting factor to mitigating this issue, the industry needs to react simply because architectural designs are becoming more complex in shape and geometry, which can aggravate this situation.
About the author
Vincente Montes Amoros is a structural and facade engineer at CDC’s Virginia/Washington D.C. office. He has worked as a building envelope structural engineer and specialized in the design and engineering of natural stone, pre-cast concrete panels, composite panels and a variety of glazing systems. He has completed a Masters of Facade Engineering at the University of Bath in England. Montes Amoros started the solar reflectivity program at CDC and has continued to work on its development. He is published on a variety of building envelope topics in construction industry journals and magazines.
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