Glazing systems: Considerations for the mechanical engineer

Window glazing and shading or louvers have a direct impact on the HVAC load of a building. Mechanical engineers often are tasked with specifying window and shading systems. Know about building envelope, and how it can be managed/altered by window system selection.

06/19/2014


Learning objectives

  1. Understand how glazing systems can affect a building’s heating and cooling loads.
  2. Learn how to design the building envelope to match the designer’s intent.
  3. Understand the items that can compromise an envelope model.

This article has been peer-reviewed.The abundance of sunlight in buildings is a mixed blessing. In the world of green design, natural light has been found to have enormous positive effects on building occupants. At the same time, the glazing systems that provide this natural light consume a significant amount of the energy required to condition these buildings. With this in mind, effective—and integrated—design and construction of these glazing systems is critical in managing both heating and cooling loads and, perhaps at least as important, infiltration loads in our buildings.

The increasing use of daylighting (the use of natural light in lieu of electric lighting) is an important element of sustainable design in architecture. In addition to the benefits of natural light on the building occupants, managing the operating cost of building lighting systems can have significant positive effects on a building’s energy profile. With building lighting systems alone representing one-third of the average building’s annual energy consumption at the end of the 20th century, reduction in lighting system operating hours can significantly reduce its contribution to building cooling costs.

Finally, creative solutions to managing solar radiation incident on the glazing systems through sun screens leverage the solar heating effect to reduce both heating costs in the winter and cooling costs in the summer.

Given the obvious benefits to each of these strategies, the first challenge engineers often face with the building envelope is accurately modeling its performance. The second and perhaps greater challenge is constructing the envelope elements to match the designer’s intent.

Figure 1: The Anthony J. Celebrezze Federal Office Building, a 32-story structure completed in 1966, was constructed with a glass and stainless steel façade. Forty years after initial occupancy, the façade deterioration had advanced to the point of compromising the integrity of the exterior enclosure, and resulting reductions in energy efficiency and interior environmental controls. After reviewing alternatives including both overclad and double-wall systems, the design team developed a “double-skin” facade design, which is being created by the installation of a glazed curtainwall over the original exterior walls. The Celebrezze project’s use of a double-wall facade replacement system is believed to be the single largest such application in the United States to date. The installation of the new curtainwall, separated from the original façade by a space of approximately 24 in., is allowing work to be completed while the building remains occupied. The new double-skin façade system is intended to reduce energy consumption with three types of design elements: an insulating layer of air between the new and old walls, a high-performance glazed curtainwall that eliminates uncontrolled air movement through the exterior wall assembly, and the use of coated glass and shading devices in the interstitial space between the original and new façades. All graphics courtesy: SebestaProblems and challenges

Radiant heat gain: A building’s exterior enclosure absorbs short-wave radiation from sunlight, converting that solar energy to heat in the envelope assembly. Short-wave radiant energy passes through the glazing into the space, warming the objects inside. Longer-wave radiation in the sunlight is absorbed by the glass itself, heating the glass surfaces and re-radiating that heat into the building. This phenomenon—the “greenhouse effect”—produces solar heat gain in buildings.

We can employ a number of strategies to effectively manage solar heat gain in design. One of the most popular of these strategies is to apply a coating to the glass to reduce solar gains and/or glare. An uncoated glass surface has a thermal emissivity of 0.84 to 0.91, meaning that it absorbs and re-radiates up to 91% of the radiant thermal energy to which it is exposed. By selectively reducing the emissivity of the glass surfaces, by reducing the amount of energy that is both absorbed and transmitted through the glass, we reduce the amount of solar heat gain through the glazing by as much as 75%. 

Solar glare: The glass that brings natural light into the building can also create a problem with solar glare, when the glazing is oriented toward the sun. Sunlight that reaches work surfaces where visual tasks are performed (both direct and reflected sunlight) can reflect off those working surfaces and into the eyes of the occupant, interfering with the ability to see the task. The most effective way to control solar glare problems within the building is by blocking direct sunlight before it reaches the exterior face of the glazing. Architects have increasingly employed sun shading devices that are designed to block direct sunlight from entering glazing systems in a variety of solar orientations. The design of solar glare controls can affect the engineering of both air conditioning and lighting systems.

Conductive heat loss: Glazing itself adds to building loads and comfort challenges by increasing conductive heat gains and losses. And, while these heat gains are significant, the heat gain/loss through thermal bridging (interruptions or penetrations of the insulation barrier by structural elements of the building envelope) is one significant controllable element of the envelope system and the structures in which glazing is mounted. 

For example, gaps in the exterior wall construction for insulation are specifically called for in many new school buildings constructed in the mid-Atlantic region. Where glazing is to be installed, concrete masonry walls are thickened to allow window framing to be secured to backup walls. Insulation is often omitted at these window openings, creating gaps in the thermal insulation barrier. Glazing systems often are deeply recessed into wall openings or are installed so that the glass is flush with the surrounding exterior wall material. Either design decision can create a condition in which the thermal plane of the glazing (the insulated glass) is not contiguous with the thermal barrier in the surrounding wall system. Laboratory testing has shown a decrease in thermal performance of up to 5% can result from gaps in the insulation coverage equal to 1% of the wall area.

Many solar shading devices are supported on the structural framework at the outer walls. Whether integral to or independent of a curtainwall system, such shading devices typically require structural support members to penetrate the exterior wall systems to enable direct attachment to building structural members. These connections create conductive heat losses via “thermal bridges” that pass through the insulation barrier. These thermal bridges are often seen in infrared images of interior and exterior envelopes.


<< First < Previous 1 2 3 4 Next > Last >>

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Improving flowmeter calibration; Selecting flowmeters for natural gas; Case study: Streamlining assembly systems using PC-based control; CLPM: Improving process efficiency, throughput
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me