Daylighting is taking center stage in many of today’s healthcare buildings as architects look for new ways to improve energy efficiency and productivity while creating a tranquil, healing environment. To achieve these benefits, architects are looking to the latest developments in glass to deliver the right balance of solar control and light transmission. Different glass options can be used to achieve the desired aesthetics of a sun-drenched atrium, while a lower light-transmitting glass can be used to provide the privacy needed for patients’ rooms. When specifying glass, finding the right balance for a variety of building scenarios can be challenging. As architects explore more creative daylighting designs, they can be just as creative when specifying glass to achieve the optimum balance of light, glare and heat gain.

Is More Always Better?

There is a common misperception that higher light is always better light. However, the downside of increased natural light is excessive heat gain along with glare from too much sunlight. Installing blinds is one solution, but studies show that once blinds are shut to minimize temporary glare, they are rarely opened again. This, of course, defeats the purpose of daylighting designs.

Hospitals and other therapeutic settings have special requirements for darker or more-reflective glass. They tend to desire privacy and, therefore, often specify glass with lower light transmission or higher reflectivity so people cannot easily see in but patients can be exposed to as much natural light as possible. In some cases, glass that is reflective on the outside will also be reflective on the inside. This is generally not what the designer intended. However, there are newer low-E products that combine medium outside reflectivity with low indoor reflectivity, which solves this problem.

Architects designing for healthcare buildings today have many options when specifying glass that provides desirable light transmission with medium to low light reflection. For many healthcare facilities, the ideal glass is neutral in appearance and fills interior spaces with natural light while reducing solar heat gain in warm weather and preventing heat loss in cold weather. These benefits are available with today’s high-performance coated glass. Today’s low-emissivity (low-E) glass can now provide a range of visible light transmission, between 40 and 70 percent, while also offering lower reflectivity than was possible in the past. These products are available in a variety of colors with emphasis on the neutral range of light gray or green to slightly blue in reflective color.

St. Mary’s Hospital in Michigan also features SunGuard SN 68 insulated glass from Guardian and fabricator Oldcastle. The glass has a blue exterior appearance and maximizes energy efficiency while still allowing in natural light. (Photo courtesy of Guardian Industries)

Consider the Elevation

It is common for architects to specify the same type of glass for an entire building, regardless of the elevation or orientation. However, the different sides of a building can have very different energy requirements. Without the proper glass, it’s common for occupants in the western and southern exposures of a building to complain of discomfort during certain times of the year and certain times of the day. In fact, occupants will even report that the window glass is warm to the touch on the western and southern sections of the building. With today’s high-performance glass, architects can mix and match products for maximum energy savings and complementary aesthetics. For example,

an architect may specify glass that lets in more heat on the north side but blocks solar heat and glare on the south and west sides.

It Pays to Be Creative

By being more flexible and creative when specifying glass, architects can also have more impact in controlling energy efficiencies. To achieve maximum energy savings, it’s important for architects to understand that not all low-E glass is created equal. Sputter-coated glass provides high visible-light transmission and optimal transparency, and it dramatically lowers heat gain or loss. Pyrolytic low-E coatings allow more solar heat to be transferred than sputter-coated glass. Unless the correct coated glass is installed, transparent glass that allows too much solar energy to penetrate the building can result in occupant discomfort, increased energy consumption and a costly strain on cooling systems.

If a higher solar-gain low-E coating is specified, the higher heat load from solar transmission can burden the cooling system. Energy costs rise more than they should because the air-conditioning system overworks to maintain a comfortable temperature throughout all sections of the building. In addition to controlling the solar heat gain inside a building, the correct glass can affect the size and efficiency of the HVAC equipment as well as daylighting systems. Minimizing solar heat gain through low-E coatings can actually reduce the size of an HVAC unit.

A recent study by engineering company Enermodal Engineering Inc. highlights these benefits. The study compared a new high-performance low-E coating to a standard commercial low-E coating that has been popular in recent years to see how much energy savings could be realized. A 175,000-square-foot, 10-story office building was simulated. The study found that the new glass has the potential to save $2.50 per square foot of glass by downsizing the chilled water and air distribution systems. In terms of operational cost savings, annual energy costs are lowered by as much as $1.60 per square foot of glass in a building with glare and daylighting controls.

In total, the new coating offered a 30 percent improvement in energy performance for a very small increase in glass cost. The return on investment would be realized in one to two years. The new coating offered a neutral appearance, glare control and a lower solar heat gain. But what is even more impressive is that the lower solar heat gain allowed for downsizing of the building’s HVAC system upfront in addition to ongoing energy savings.

There are more ways to creatively save energy than ever before. New glass coatings with improved energy savings and more natural light can compare favorably to older dark tints or reflective glass. If you have not looked recently for new options in glass, now is the time. With today’s choices, you are likely to find one that strikes the perfect balance for your project.