UNIT 2�CONSTRUCTION TECHNOLOGY

Dr Adewale Abimbola, FHEA, GMICE.

www.edulibrary.co.uk

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Learning Outcomes and Assessment Criteria

D1 – Compare the construction terminology used in different types of construction project.

Aim:

Thermal transmittance

Objectives:

At the end of the lesson, the students should be able to:

• Discuss the different processes heat is lost from a building.
• Produce heat-loss calculations from various construction elements.
• Differentiate between active and passive design strategies.

Heat Losses from Building Surfaces

• When the surrounding air temperature is lower than that of the building, the surfaces of the building can lose heat by the following processes:
• Conduction:
• This is the process by which heat travels through a material or between different materials that are in direct contact.
• For example, heat conducts through walls, floors, and roofs when there is a temperature difference on either side of the building envelope.
• Materials with high thermal conductivity, such as metals, conduct heat more easily than insulating materials like wood or fiberglass.
• Water has a higher thermal conductivity compared to most building materials, such as bricks, concrete, or plaster. Therefore, damp walls can increase heat loss through conduction.
• Effective insulation, like adding layers of thermal-resistant materials, can reduce heat conduction through building components.

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Heat Losses from Building Surfaces

Radiation:

• This is the transfer of heat energy in the form of electromagnetic waves, without the need for a medium (such as air or solids).
• For example, the sun radiates heat, and this radiant energy can enter a building through windows or be absorbed by exterior surfaces.
• Reflective surfaces, such as light-coloured roofs or window films, can reflect or absorb radiant heat, affecting the overall heat gain.
• Radiant barriers, often installed in attics, reflect radiant heat away from the building, reducing heat transfer.

Convection:

• Heat convection involves the transfer of heat through the movement of fluids (liquids or gases) caused by temperature differences.
• Warm air rising and cold air sinking, creating air currents, contribute to convective heat transfer. This occurs, for instance, near windows or poorly sealed doors.
• Adequate ventilation helps control indoor temperatures by reducing stagnant air and promoting the movement of conditioned air.
• Unintentional gaps, draughts, and leaks in a building's envelope can lead to convective heat loss.

Heat Losses from Building Surfaces

Evaporation:

• This involves the phase change of a substance (usually water) from a liquid to a vapor, absorbing heat in the process.
• Moisture on surfaces (e.g., wet walls, damp floors) can evaporate, absorbing heat energy from the surroundings.
• Proper humidity control is crucial to managing evaporation-related heat loss. Excessive moisture can lead to increased heat absorption during evaporation.
• Adequate ventilation, vapour barriers, and moisture-resistant materials help manage evaporation-related heat loss.

Thermal Conduction

• Heat flows through solid materials only by thermal conduction.
• Thermal conductivity is a measure of how good the material is at conducting heat.
• Higher values denote that the material is a good thermal conductor. Low values denote good thermal insulator.

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Table 1. Thermal conductivity of various materials (Millward et al., 2000).

Thermal Conduction

Thermal Conduction – Worked Example 1

Thermal Conduction – Self-assessment Task

Thermal Resistivity and Resistance

Thermal Resistivity and Resistance – Worked Example 2

Insulation Materials

• Insulation materials are designed primarily to prevent heat loss from buildings through walls, lofts and other unheated spaces. Many also provide sound insulation.

Insulation Materials

Thermal Resistance – Self-assessment �Task

U-values: Thermal Transmittance Coefficient

Active and Passive Design Strategies for Heating and Cooling Buildings

• Passive strategies emerge when a building is designed to function autonomously. The arrangement of the plan, sections, material choices, and site placement collectively foster a harmonious energy flow within the structure, contributing to energy conservation.
• Passive design strategy endeavours to regulate comfort, managing both heating and cooling, all while avoiding the reliance on conventional fuel consumption.

• Active strategies rely on acquired energy sources, encompassing electricity and natural gas, to maintain optimal comfort levels within buildings. These encompass mechanical system elements like air-conditioning, heat pumps, radiant heating, heat recovery ventilators, and electric lighting.

Figure 1. Passive solar design (Megan, 2015)

Solar Geometry

The study of solar geometry is essential to understanding how to both obtain free heat (passive heating) and reduce the amount of cooling through heat avoidance (passive cooling) on a building project.

Solar angles vary in accordance with your position on the earth as well as the time of year.

https://www.suncalc.org/

- See how to use the sun’s natural path in summer vs. winter to provide FREE heat in the Winter, and to reduce required COOLING in the summer.

South-facing windows receive the most light and are the hottest.

North-facing windows receive the least light and are the weakest and coolest.

East-facing windows receive light in the morning and are weak and cool. West-facing windows receive light in the afternoon and are strong and hot

(Beans, 2023)

Figure 2. Solar geometry (Krishnamurthy, 2015)

Solar Geometry - Importance

Grasping solar geometry is crucial for several reasons:

• Implementing effective passive building design for heating and cooling purposes.
• Ensuring proper orientation of buildings to optimise solar exposure.
• Comprehending seasonal variations in both the building and its environment.
• Crafting efficient shading devices based on solar movement.
• Leveraging the sun to dynamically enhance the architectural features of our designs

The Perimeter Institute in Waterloo uses the sun to daylight and add character to the space.

Living Awnings

• Living awnings, exemplified by deciduous trees and trellises adorned with deciduous vines, serve as highly effective shading elements.
• These structures synchronise with the thermal cycles of the year, adeptly shedding leaves in response to temperature fluctuations.

Figure 3. Vegetative shading (American Institute of Architects, 2012a)

Solar Transmission Through Glass

Figure 4. Incidence angles and glazing types (American Institute of Architects, 2012b)

Types of Radiation

• The sun's energy, carrying solar power, infiltrates our building interiors via two main channels: directed and reflected.
• Reflective radiation, a valuable aspect in daylighting strategies, can be achieved through rebounding off light-toned surfaces on the ground (such as sand and light concrete) surrounding the buildings.
• Additionally, it may ricochet off bright materials on neighbouring buildings, encompassing light-coloured stuccos, precast concrete, or reflective glazing.
• Recognising the potential of reflected light is particularly advantageous when contemplating the illumination of a building through natural light sources.

Figure 5. Solar radiation (American Institute of Architects, 2012a)

Passive Solar Heating Strategies

3 MAIN STRATEGIES:

1. Direct Gain

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b. Thermal Storage Wall

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3. Sunspace

This space is using classic Direct Gain for heat.

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The sun shines through the windows. Strikes the exposed concrete floor. Heat is absorbed into the concrete as it is an excellent thermal mass.

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When the space cools off, the heat is radiated into the space making it warm.

The dominant architectural choice is Direct Gain.

Passive Strategies – Heating

• Orientation:
• Proper building orientation maximises exposure to sunlight during the winter months, leveraging solar heat gain.
• Thermal Mass:
• High thermal mass materials (e.g., concrete, stone) absorb and store heat during the day, releasing it gradually at night.
• Insulation:
• Adequate insulation minimises heat loss, maintaining a comfortable indoor temperature.
• Natural Ventilation:
• Designing for cross-ventilation and strategically placed openings allows for natural airflow, aiding in temperature regulation.

Passive Strategies – Cooling

• Shading:
• Overhangs, awnings, and vegetation provide shading to reduce solar heat gain, especially during hot periods.
• Natural Ventilation:
• Strategic placement of windows and vents facilitates the movement of cool outdoor air through the building.
• Cool Roofs:
• Reflective roofing materials help reduce the absorption of solar radiation, keeping the building cooler.
• Cooling Courtyards:
• Incorporating internal courtyards promotes natural cooling through the creation of shaded and ventilated spaces.

Active Strategies – Heating

• Central Heating Systems:
• Installation of centralized heating systems, such as boilers or heat pumps, that distribute warm air or water throughout the building.
• Underfloor Heating:
• Radiant heating systems placed beneath the floor provide even and efficient heat distribution.
• Electric Heaters:
• Electric heaters are commonly used for localized heating in specific areas or rooms.
• Heat Recovery Ventilation (HRV):
• HRV systems capture and reuse heat from exhaust air, improving energy efficiency.

Active Strategies – Cooling

• Air Conditioning:
• Traditional air conditioning systems use refrigerants to cool and dehumidify indoor air.
• Evaporative Cooling:
• Evaporative coolers use the principle of water evaporation to cool incoming air, suitable for dry climates.
• Heat Pumps:
• Heat pump systems can provide both heating and cooling by transferring heat between indoor and outdoor environments.
• Smart HVAC Systems:
• Advanced HVAC systems with smart controls and sensors optimise energy use based on real-time conditions.

Passive and Active Strategies – General Considerations

• Integration:
• Many buildings employ a combination of passive and active strategies to optimise energy efficiency.
• Energy Efficiency Ratings:
• Both passive and active systems may benefit from energy-efficient technologies and appliances, reducing overall energy consumption.
• Climate Adaptability:
• Strategies should be adapted to the local climate conditions to ensure effectiveness.
• Building Design:
• Incorporating passive strategies early in the design phase can lead to more sustainable and cost-effective solutions.
• Maintenance:
• Regular maintenance and tuning of active systems are essential for optimal performance and energy efficiency.
• Renewable Energy Integration:
• Combining active strategies with renewable energy sources (e.g., solar panels) enhances sustainability.
• Both passive and active strategies contribute to creating energy-efficient and comfortable buildings, and the most effective solutions often involve a thoughtful combination of both approaches

Energy Requirements: Tiered Approach

Tier 1, Maximise Heat Retention.

Providing thermal mass to store the heat, and making the building air tight to prevent losses through cracks.

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Tier 2, Use solar heating to heat the building. The heat will have thermal mass to be stored in and will have insulation and a leak free envelope to prevent losses.

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Tier 3, Mechanical heating can then be reduced to top off the amount that is not able to be supplied passively.

Maximise the amount of energy required for mechanical heating that comes from renewable sources.

Figure 6. The tiered approach to reducing energy requirements for HEATING (Boake, 2009)

Energy Requirements: Tiered Approach

Tier 1 Heat Avoidance.

Use shading devices, plant trees, shrubs and vines around the building. Avoid dark coloured pavement and finishes.

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Tier 2 applies passive cooling.

Use natural ventilation to get rid of unwanted heat and humidity as well as impact the choice of materials. Some materials can make the building and its occupants feel cooler.

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Tier 3 uses Mechanical Cooling to make up the difference. Less mechanical cooling will be required if the loads are reduced through passive means.

Maximise the amount of energy required for mechanical heating that comes from renewable sources.

Figure 7. The tiered approach to reducing energy requirements for COOLING/VENTILATION (Boake, 2009)

Self-assessment Task

• Compare active and passive strategies.

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• Consider the Zero Carbon Building (ZCB) in Hong Kong designed by Arup and discuss at least any THREE passive and active design strategies that were each employed for the sustainable project.

Reference/Bibliography

American Institute of Architects (2012a) Shading. Available at: https://www.tboake.com/carbon-aia/strategies1b.html (Accessed: 15 October 2023)

American Institute of Architects (2012b) Solar geometry. Available at: https://www.tboake.com/carbon-aia/strategies1a.html (Accessed: 15 October 2023)

Beans, E. (2023) It’s all about the lighting. Available at: https://www.naplesgarden.org/its-all-about-the-lighting/#:~:text=South%2Dfacing%20windows%20receive%20the,and%20are%20strong%20and%20hot. (Accessed: 15 October 2023)

Boake, T. M. (2009) ‘What is sustainable design? part three: The basic principles of passive design’ [PowerPoint presentation]. Available at: http://www.eilateilot.org/wp-content/uploads/2017/05/The-Basic-Principles-of-Passive-Design.pdf (Accessed: 03 April 2022)

Brown, P. A. (2010) ) ‘Passive & active design’ [PowerPoint presentation]. Available at: https://docplayer.net/20896503-Passive-active-design.html (Accessed: 03 April 2022)

Krishnamurthy, R. (2015) Charting the sun’s motion in relation to your home and permaculture site. Available at: https://www.permaculturenews.org/2015/10/23/charting-the-suns-motion-in-relation-to-your-home-and-permaculture-site/ (Accessed: 15 October 2023)

Megan (2015) Alternative building options. Available at: https://gettingoffgrid.weebly.com/blog/building-envelope (Accessed: 05 October 2023)

Mehrak, M. (2015) Thermal comfort. Available at: https://mahdismehrak.weebly.com/thermal-comfort.html (Accessed: 05 October 2022)

Millward, D., Ahmet, K., Greed, C., Hassall, J., Heuvel, C., Roberts, K. and Longhorn, C. (2000) Vocational A-level construction and the built environment. 3^rd edn. London: Longman.

Sustainable (n.d) Passive design and active building strategies. Available at: https://www.sustainable.to/strategies (Accessed: 05 April 2022)

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