Thermal PrinciplesA2P1065: Decades of Insight: Applying Age-Old Thermal Principles in Contemporary Construction

Introduction

The understanding of building surface temperatures and thermal principles has been a topic of intrigue and research for over six decades. As evidenced by D.G. Stephenson’s groundbreaking article from November 1963, “Extreme Temperatures at the Outer Surfaces of Buildings,” the thermal behavior of building surfaces has long been recognized as an integral component of good design and peak functionality.

In revisiting some of this topic’s foundational insights, we recognize that the interplay isn’t just about the choice of construction materials or external color schemes. It encompasses a series of thermal energy interactions, such as absorption, reflection, and thermal radiation heat transfer, influenced by diverse factors from regional climate patterns to urban planning paradigms.

Consequently, the materials used in construction must possess service temperature ranges broad enough to accommodate these varying thermal interactions. With a deep understanding of this relationship, engineers and architects can achieve higher levels of design efficiency.

Surface Temperature vs. Service Temperature

First, let’s briefly define these two similar-sounding measurements and outline their relationship.

At its core, surface temperature is the immediate, tactile temperature of a material’s exterior. Imagine walking barefoot on a concrete pathway during a sunny afternoon. The warmth you feel underfoot is a direct result of the pathway’s surface temperature, influenced by environmental factors like sunlight, wind, and ambient air temperature. This temperature can fluctuate throughout the day and across seasons, making it a variable factor in construction considerations.

On the other hand, service temperature operates on a broader spectrum. It defines the range of temperatures within which a material can maintain its structural integrity and optimal performance. For instance, a specific insulation material might be designed to perform optimally within a temperature range of -20°F to 150°F. If installed in conditions outside this same temperature range, the insulation might not function effectively, leading to issues with thermal properties like reduced thermal resistance, heat loss, condensation buildup, or even material degradation.

 

The interplay between these two temperatures is where the importance of material science in construction truly emerges. When selecting materials for a project, architects and builders must anticipate the potential surface temperatures a material might encounter and ensure they align with the material’s service temperature range. This temperature alignment is crucial for several reasons:

• Materials exposed to low or high temperatures outside their service range can degrade faster, leading to reduced lifespan and increased maintenance costs.
• Performance can be compromised. For example, an adhesive might lose its bonding capability, or an insulating material might fail to provide adequate thermal protection.
• Most importantly, there are safety implications. Materials that can’t withstand their environment can pose structural risks, endangering occupants or users.

For these reasons, selecting materials with the widest-ranging service temperatures offers architects and engineers a strategic advantage in design and construction. Such materials demonstrate versatility across diverse climatic conditions, ensuring thermal resistance and structural integrity whether in the scorching heat of the desert or the biting cold of polar regions.

By opting for these materials, professionals not only future-proof their projects against unpredictable high temperature fluctuations but also enhance the longevity and resilience of their structures. This choice, therefore, not only broadens the scope of potential applications but also embodies a commitment to sustainability and durability, hallmarks of thoughtful and forward-looking design.

The relationship between surface and service temperature is a testament to the meticulous planning and foresight required in construction and architecture. By understanding and respecting this relationship, professionals ensure the longevity, functionality, and safety of their structures, making the built environment both enduring and reliable.

Challenges of Thermal Energy and Heat Flow

With this foundational grasp of the interplay between surface and service temperatures, grounded in thermodynamics and material science, let’s delve into some of the challenges that informed architects and engineers face in practical applications of energy transfer. These considerations are essential for crafting structures that are efficient and visually appealing. As we seek to establish best practices for building envelopes, embracing these foundational basic principles of heat transfer will be pivotal in engineering sustainable and dependable built environments.

One possible oversight in this domain is the real-world temperature variation of building surfaces, such as walls and roofs. Contrary to the prevalent belief that these surfaces simply fluctuate within ambient air temperature ranges, the reality of surface area and temperature change is not so simple due to the following factors:

• Solar Radiation

• Every object, from the vastness of the sun to the confines of building walls, is engaged in a perpetual exchange of radiation emission and absorption. The sun, with its unparalleled heat, radiates “shortwave” radiation. In contrast, buildings, being cooler, emit “long-wave” radiation. This thermal energy emission from a building’s surface is intricately influenced by its temperature and a property known as emissivity, which also dictates its absorption rate.

• Surface Color

• Furthermore, the color of a building’s surface emerges as a primary factor determining its temperature. Darker shades, encompassing greens, browns, or blacks, can absorb a staggering 90% of thermal radiation. In stark contrast, white surfaces limit their absorption to around 40%. This differential absorption can lead to a temperature disparity of up to 60°F (15.5°C) between them.

• Adjacent Surfaces

• The environment surrounding a building, especially proximate structures, can significantly influence its temperature. Reflected radiation from neighboring buildings can induce notable high temperature variations. For instance, a roof situated close to a taller edifice might be subjected to additional sunlight and long-wave radiation, elevating its temperature.

•  Orientation and Vertical Surfaces

• The orientation of a building also plays a crucial role. Walls facing east and west typically register higher temperatures than their south-facing counterparts, primarily due to their exposure during peak ambient temperatures. Moreover, walls, by virtue of their vertical orientation, inherently attract more long-wave radiation than roofs.

•  Heat Storage Capacity

• The solid material composition of a building surface further determines its responsiveness to radiation shifts. Lightweight walls exhibit rapid adjustments, while their heavier counterparts take a more extended period. This characteristic can significantly influence the high temperature a surface might achieve during varying conditions.

With all these influences exerting themselves against a building’s surface, there is a range of outcomes and implications that should be considered.

First is the knowledge that dark roofs can climb to temperatures of 230°F (110°C) during summer heat and plummet to -50°F (45.5°C) during the winter. This makes it paramount to ensure that roofing systems are equipped to handle such extremes, ensuring longevity and structural integrity to prevent inadvertently surpassing material temperature thresholds.

Similarly, the color of a building’s surface, often chosen for aesthetic appeal or to align with design themes, has more than just visual implications. For instance, when a design leans towards a light-colored surface, the primary aim might be to mitigate excessive temperature gains. However, the effectiveness of this strategy hinges on the surface’s ability to maintain its low absorptivity over time. As the surface ages, factors like wear, dirt accumulation, or fading can alter its absorptive properties – and if the material doesn’t have an adequate service temperature range, it will potentially get pushed beyond its limits.

Furthermore, the incorporation of external shading devices, such as louvers or overhangs, adds another layer of complexity to the temperature dynamics of building exteriors. While these devices are instrumental in reducing direct solar gain, their design and color are pivotal. Ideally, these shading elements should possess a dark surface. The rationale behind this is to absorb much of the incoming radiation, thereby preventing it from reflecting onto adjacent surfaces with inadequate service temperatures.¹

Architects and designers can also consider not just the immediate environment of a building, but also the broader urban context in which it sits. As urban areas become denser, the influence of heat on adjacent surfaces will become even more pronounced. Urban heat energy islands, areas in cities that are significantly warmer than their rural surroundings due to human activities, will increase the need for thermally robust materials, able to withstand a wide range of temperatures.

Creating Energy-Efficient Facades

Each different color has an impact on the surface temperature – and therefore the service temperature – of the building. Darker hues, despite their visual appeal, are naturally inclined to absorb more solar radiation. This absorption can lead to less cooling and a pronounced increase in surface temperatures. In certain scenarios, these escalated temperatures can breach the system or structure’s stability threshold, leading to potential facade damages, such as cracking.

In response to this challenge, the architectural industry has begun using infrared-reflecting pigments, popularly known as IR-color. These pigments are designed to counterbalance the excessive heating often associated with darker shades. This heating is measured with a metric known as Total Solar Reflectance. Total Solar Reflectance (TSR) offers a comprehensive metric for evaluating solar reflectivity and coating temperature, as it encompasses the entire solar spectrum, including the near infrared radiation (NIR), ultraviolet, and visible radiation.

High TSR values indicate minimal surface heating, and low TSR values, such as carbon black and iron oxide black, translate to intense facade heating. Lab studies have shown that darker shades, especially those enriched with carbon black and iron oxide pigments, can often reach alarming temperatures, sometimes exceeding 176°F (80°C).

While studies show the incorporation of IR-black pigments can curtail surface temperatures by up to 10 K, such facade temperatures in real-world scenarios still often surpass the 158°F (70°C) mark. These temperatures were reached in climates similar to that of Eastern Canada. The disparity between lab results and real-world observations can be attributed to the synthetic radiation sources employed in laboratory settings, which don’t perfectly replicate the nuances of solar radiation. This means that building surfaces with IR black pigment are exposed to a combination of environmental factors that may not have been tested, including varying levels of sunlight throughout the day, other sources of radiation, changing atmospheric conditions, different temperature, and more.²

Ultimately, building envelope design must be considered carefully: an ill-considered decision could risk pushing the material beyond its temperature thresholds, potentially compromising its structural integrity or lifespan.

Simplifying Thermal Principles and Material Selection: Our Recommendation

When assessing thermal management across the vast array of global climatic conditions, it’s clear that structures, whether residential, commercial, or industrial, encounter a diverse range of temperatures. From the cold of winter to the heat of summer, the environmental demands on building envelopes are multifaceted. Given this broad spectrum of thermal management, there emerges a compelling argument for a more standardized approach to safe service temperature design.

Climatic data from various regions indicate that many structures are subjected to temperatures between -40°F (-40°C) to 180°F (82°C). By proactively designing structures with this range in mind, architects and engineers can ensure a broad, comprehensive level of thermal resilience. This broad spectrum provides a consistent and reliable standard, ensuring that buildings can accommodate a wide array of thermal challenges. It also allows for a streamlined decision-making process during the design phase streamline the decision-making process during the design phase, reducing the time and energy being spent on region-specific design and adjustments.

In summary, after accounting for regional climatic nuances, there’s significant merit in utilizing a robust, standardized temperature range for architectural design. By utilizing materials with a service temperature range of -40°F (-40°C) to 180°F (82°C), the industry can foster the creation of structures that are both durable and adaptable, ensuring they stand the test of time across a multitude of environments.

Conclusion

The balance between architectural design and thermal dynamics has been under the spotlight for over six decades, and its significance has only grown with the evolution of modern construction techniques and materials. Buildings must be built to withstand a complex interplay of heat and energy interactions and physical properties, shaped by a myriad of factors from solar radiation to urban planning paradigms. It’s imperative for architects and designers to embrace the use of thermally robust designs and products in order to accommodate real-world temperature variances.

The insights we’ve gleaned from past research and contemporary studies underscore the importance of this holistic approach to architectural design. It’s not merely about creating aesthetically pleasing structures, but about ensuring these structures are resilient in the face of varying environmental challenges. Each decision, no matter how minute, can have cascading effects on a building’s thermal performance and, by extension, its overall efficiency and longevity. In this way, architects, engineers, and designers can ensure a legacy of informed, practical, and appealing building designs.

If you are interested in more information on thermal principles, contact us today!

 

References:

¹ ‌Bishara, A., Kramberger-Kaplan, H., & Ptatschek, V. (2017). Influence of different pigments on the facade surface temperatures. Energy Procedia, 132, 447–453. https://doi.org/10.1016/j.egypro.2017.09.662

‌ ² Stephenson, D.G. (1963) Extreme Temperatures at the Outer Surfaces of Buildings. NRC-IRC. Web.mit.edu. Canadian Building Digest, CBD-47.
https://web.mit.edu/parmstr/Public/NRCan/CanBldgDigests/cbd047_e.html

 

 

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