High-latitude Challenges: Designing for daylight

by Katie Daniel | March 7, 2018 3:36 pm

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By Andy McNeil
Daylight and view consistently rank high on a list of desirable attributes in homes, schools, and workplaces. Delivering them, however, can be challenging, as there are often competing interests. In an urban context, for example, site constraints often affect building shape, which might force façade orientations problematic for harnessing daylight. For example, downtown Vancouver’s street grid is 45 degrees north, the least desirable orientation for daylight. Another consideration is the developer’s desire for maximum leasable floor area, which can increase the depth of floor plates, another factor impeding daylight. Buildings designed to maximize daylight and views are also negated by blinds and shades that are pulled down to block glare and often remain in that position.

Daylighting rules of thumb providing basic advice for shading elements on various façades focus on the middle latitudes, leaving out advice for equatorial and for higher latitudes. Daylight design for higher latitudes must be tweaked in order to optimize effective daylight and account for many factors, including:

• low sun angles;
• summertime sun reaching further north;
• high occurrence of overcast conditions; and
• cooler climates.

For example, a common rule of thumb is to provide fixed horizontal shading elements such as overhangs and light shelves on south-facing façades. However, this rule fails in northern locations as fixed horizontal shading elements perform poorly against year-round, low-angle sun. Automated fabric shades or venetian blinds are more suitable in the north. In equatorial locations where the sun is only low at sunrise or sunset, vertical shading is a better option on a south façade for the purpose of blocking the rising or setting winter sun.

Latitudes and sun angles
Major Canadian cities range from latitudes of 43 degrees north (Toronto) to 53 degrees north (Edmonton). These latitudes are comparable to European cities, but Canada does not experience the warming effect of the North Atlantic Ocean currents. For example, Edmonton and Hamburg, Germany, share the same latitude, while Vancouver’s is similar to Munich. Despite the climate differences, one can draw daylighting design inspiration from central European cities, particularly from the methods employed for shading low-angle sun.

The term ‘solar altitude’ refers to the angle between the sun and the horizon. The lower the solar altitude, the deeper the sunlight penetrates a building. Low-angle sun is a major cause of glare in office buildings because of the depth of penetration. Cities at all latitudes experience low-angle sun on east and west façades during sunrise and sunset. West-facing façades, in particular, suffer from direct glare because the low-angle sun coincides with the time a building is occupied. For this reason, designers from around the world have put more effort into identifying shading solutions for the west façades. In Germany, designs commonly employ motorized venetian blind systems on the exterior of a building—they can tilt, raise, and lower as needed to block the sun, as well as retract to admit diffused light into a building.

Higher-latitude cities experience low-angle sun on the south and north façades as well. In the winter, the sun stays very low throughout the day at high latitudes and shines mainly on the south façade. On December 21—the shortest day of the year—the solar altitude never exceeds 24 degrees in Toronto and 14 in Edmonton. During the winter, office buildings in Canadian cities require shading solutions on south-facing façades to mitigate glare from direct sun. In the summer months, the setting sun is situated to the northwest, shining deep into the north façade of a building. Glare from the setting sun is an issue for employees working into the evening.

Canadian cities also experience frequent cloud cover. Overcast conditions mean diffuse daylight providing excellent levels of glare-free illumination, if shades are raised and blinds are left open. Field studies, however, have shown manually operated shades are unlikely to be raised on overcast days. Occupants often lower shades to mitigate glare on a sunny day and leave them down indefinitely. One of the biggest obstacles to daylight is allowing shades to remain lowered when not needed.

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Solar heat gain
Designing for daylight is often a balance of admitting light while blocking solar heat. In warmer climates, building design is dominated by a year-round need for cooling. While cooling is still relevant for commercial buildings in cooler climates, heating begins to play a bigger role.

It is particularly important in the mornings, when the building is cooled from the previous night and occupants are just arriving. The fraction of incident solar energy a window transmits into a building is called the solar heat gain co-efficient (SHGC), which is commonly a static property of the glazing system. Building designers have to balance the opportunity for passive solar heating against the risk of increased summer cooling when selecting the glazing assembly. For warmer climates, where cooling is used nearly all year, the decision is a simple one. However, for cooler climates, designers and engineers must put much more effort into optimizing glazing properties and also account for building shape, orientation, functional use, and climate, if one wants to minimize energy used for HVAC.

Solutions to maximize daylight
Daylighting requires natural light, and the amount of natural light available to any given structure depends on location, particularly the latitude of the building site. Latitude determines the availability of sunshine and the sun’s angle—important considerations when designing for daylight. However, the best daylighting strategies can fail if there is not an intelligent way to manage sunlight.

Automated shading systems with smart control capabilities lower shades when there is an elevated risk of glare and raise them when the sun is not shining on the façade. Given manual shades tend to stay down, the biggest benefit of smart shading control systems is they remove impediments to daylight when shading is not necessary. In Canadian cities, where shades are needed on nearly all sides of a building, smart control systems substantially increase daylight infiltration.

Windows featuring smart-tinting glass show the most promise in maximizing daylight and views in buildings, as they can offer both a high SHGC when clear and a low SHGC in the dark state. In winter, smart-tinting properties can keep the windows clear on the east façade to help heat the building before employees arrive. In the summer months, the east windows can be tinted in the morning to keep the building cool. Smart-tinting windows enable full automation of when to clear/tint and by how much. Since they can be programmed to clear groups or individual windows when there is diffused light and to tint to mitigate glare, natural light is maximized at all times while controlling solar heat gain.

Successful daylighting design for high-latitude projects incorporates shading with sufficient opacity to prevent glare from the direct sun on all façades, as well as smart controls that retract shading or untint windows, while also selectively admitting or rejecting solar heat gain.

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Views and health
The desirability of natural light in buildings and homes is rooted in an intrinsic physiological human need. Daylight affects one’s endocrine, nervous system, and circadian rhythms. Exposure to daylight affects biological clocks, signalling when to sleep or wake during a 24-hour period. When people get enough daylight, they feel and sleep better, focus more easily, and are less anxious or stressed. Inadequate daylight can cause productivity and health issues.

Windows and views have often been status symbols in the workplace. Corner offices with windows on two sides conveyed the hierarchical importance of their occupants. While these spaces are slowly becoming obsolete in favour of more open, equitable, and collaborative workplaces, the demand for natural light for all occupants has grown. This is, perhaps, in response to the numerous studies suggesting the significant health benefits of daylight exposure in offices.

In 2013, researchers in the neuroscience program at Northwestern University (Evanston, Ill.) concluded workers in offices with windows sleep an average of 46 minutes more per night compared to those in windowless areas. A year later, researchers at Cornell University (Ithaca, N.Y.) published a study[5] that said nurses who had access to natural light were healthier and happier, and did a better job of serving patients. Other studies have shown faster recovery time for patients in rooms with a view, and reduced need for pain medication for patients in sunnier spaces. Studies looking to correlate performance, wellness, and productivity are continuing around the world, and the findings seem to suggest a positive correlation between natural light and improved health.

Humans have evolved to become mostly indoor-dwelling. Per research[6] by the U.S. Environmental Protection Agency (EPA), people spend 90 per cent of their time indoors. Prior to the advent of electric lighting, a primary objective of architecture was to provide access to natural light in every space of a building. When electric lighting became inexpensive, buildings shifted to maximize usable floor space and away from incorporating daylight as a primary source of illumination. In the last two decades, the industry has begun to understand the effect buildings without natural light have on the health of occupants and changed the approach to design. The architecture of the future can provide every occupant with the ability to look outside, biologically sense the time of day by looking at the sun’s fluctuating brightness, and reconnect with nature.

Technologies allowing us to incorporate ample natural light while minimizing the impact on solar gains are now available. Smart-tinting glass, for example, can dynamically respond to changing light conditions, blocking up to 99.9 per cent of visible light to reduce glare and block solar heat. Automated shades are another option for minimizing glare; some can also be programmed. Implementing the best of these options can have a profound effect on the quality of the indoor environment.

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Andy McNeil is an engineer at Kinestral Technologies, working on the company’s next-generation smart-tinting technologies. He has extensive experience in daylighting and fenestration technologies to reduce the amount of energy consumed for lighting and HVAC in buildings. McNeil holds degrees from Penn State University, as well as an MBA from the University of California, Berkeley. He can be reached via e-mail at amcneil@kinestral.com[8].

Source URL: https://www.constructioncanada.net/high-latitude-challenges-designing-daylight/

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