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The Value of Optimisation in Façade Engineering and Design

An Overview of the Multiple Variables of Sustainable and Environmental Design of

Building Facades

Real Estate, andArchitectural Design

Developers

Façade Specialistsand Engineers

Perspective and Approach to Sustainable Design of

Facades

and

What is a Building Façade?

A Building Envelope – is the group of components which separate the indoor spaces from the

outdoors. These components include all ‘physical’ barriers such as walls, roofs, windows, doors and

foundations.

The Façade is one of the components of the Building Envelope

Building Envelopeor / Shell

or / Enclosure

Building Structure,

Foundations, Internal Walls, Services…etc.

Exploded View of a One-story house

Source: Building Construction Illustrated - Ching

Conventionally; the Main Functions of a Building Envelope – or ‘Enclosure’– have been:

1.Structural support and load-bearing.

2.Control of inward and outward flow of energy and matter.

3.Aesthetic element of interior and exterior.

Source: J.F. Straube and E.F.P. Burnett. Building science for building enclosures. Building Science Press, 2005.

The Façade is essentially the External Wall Component of a Building Envelope…

Source: Visual Dictionary of Architecture - Ching

What are the Functions of a Building Façade?

Source: Façade Construction Manual – Birkhauser – 2004

The Architects / Developer Conventional View

What are the Sustainability Aspects of Façade Design

and Construction?


Heating, Ventilation and Air Conditioning (HVAC) Efficiency

In cold climates, such as that of the UK,Energy Consumption % for Domestic Space Heating

= 25% of total Domestic energy consumption

In other countries with hotter climates such as the UAE, specifically Abu Dhabi, buildings cooling energy consumption had risen from

1625 MW to 4750 MW of power from 1990 to 2007(= avg. increase 11.3% per year)


Heating, Ventilation and Air Conditioning (HVAC) Efficiency

…The Energy Conservation Aspects Become Obvious

Through Façade Control of Heat Transfer, HVAC Efficiency, and accordingly, Energy Consumption Efficiency can be achieved.


Façade Control Technique:Passive Solar Design

Passive solar design refers to the use of the sun’s energy for the heating and cooling of living spaces. In this approach, the building itself or some element of it takes advantage of

natural energy characteristics in materials and air created by exposure to the sun



Passivhaus Design(Example from Hassan Fathy’s Architecture)



Multiple Variables Specific to Façade/Envelope Design



Due to the complete dependence of Passive Solar Design Techniques on the Unique conditions of each building site; its success

necessitates Optimisation…

Passive Solar Design methods will usually achieve 15% reduction in HVAC energy costs; but usually does not exceed 45%, and anything

beyond would be considered a rare success.


Is the Undertaking of an optimum Sustainable Façade subject only to

Passive Design Theories?

Façade Design and Engineering Principles



1. Functional Criteria




Heat gains are the obvious functional criterion related to sustainability (thus the use of passive design)…




… but natural ventilation, and natural lighting are also a significant factors in the buildings Energy Conservation scheme…




Again… the concept of multi-variable optimisation is evoked to produce an integrated solution

INTEGRATED SOLUTION


Is Energy Conservation the only Sustainability aspect to Façade

Design?

What other Principles Guide the design process that can impact

Sustainability?


How about…

•Economy of fabrication and construction?

•Value Engineering and Conservation of Material?•Health and Wellbeing of Factory Workers, Site Labour,

or Construction Site Neighbours?

2. Constructional Criteria(i.e. Fundamental Criteria)



Integrated Solution


At some point in history, all facades were load-bearers and part of the main building structure…

A Cavity Wall Façade

The systematic separation of loadbearing structure and façade structure

a- External Cladding Leaveb- Air cavity

c- Main Loadbearing Structured- Insulation


Loadbearing vs. Non-loadbearing

Vertical Section Showing Façade Leaves

Source: Stone Cladding Engineering – Springer

This separation is an efficient load transfer mechanism that ultimately simplifies façade structure design and reduces material requirements

…an economic and material conserving design.


Loadbearing vs. Non-loadbearing

Vertical Section Showing Façade Leaves

Source: Stone Cladding Engineering – Springer


Multi-leafed /Multi-layered Design

This separation also allows for multi-layered or multi-leafed construction; which can include:

1.Insulation layers2.Building Services3.Air cavities



Ventilated Cavity vs. Non-Ventilated


Ventilated and Non-ventilated Cavities

The Cooling Effect of Ventilated Cavity Walls will result in minimization of HVAC / Mechanical cooling costs…

Ventilated CavitySource: Guide for the design, construction and maintenance of natural stone facades - Centro Tecnológico del Granito


Ventilated and Non-ventilated Cavities

Non-ventilated facades will retain energy in internal heated spaces in cold climates (air is a natural insulator)…

… thus reducing heating costs

Non-ventilated Cavity

Façade Design and Engineering PrinciplesPrefabrication

Stick-systems vs. PanelisedSource: CMHC - Glass and Metal Curtain Walls, Best Practice Guide



In Stick systems (in the case of aluminium curtain walls) all elements are fabricated separately and assembled, installed, and sealed at the construction site…



In Stick systems (in the case of aluminium curtain walls) all elements are fabricated separately and assembled, installed, and sealed at the construction site… These systems can be more cost-effective in low-rise or

mid-rise buildings… however:1.Construction is longer, and carbon footprint can be relatively high2.Health and safety of worker, and residents of nearby buildings, are harder to control and maintain.



In Panelised / Unitised systems all elements are fabricated and assembled at factories / fabrication facilities…



In Panelised / Unitised systems all elements are fabricated and assembled at factories / fabrication facilities…

These systems can be technically demanding, however:

1.Construction is much shorter, and carbon footprint is minimized2.In the controlled environment of a factory, Health and safety of workers is easily maintained, and impact at construction site is minimized.


Non-loadbearing facades do not transfer weight of the main building,

but they have to carry their own weight, and weight of incident

loads (wind, earthquakes…)


Structural Steel, Stainless Steel and Aluminium Alloys Framing and Brackets, are almost exclusively used for the Façade's structure


3- Structural Principles



3- Structural Principles

How is the Façade Material ‘coupled’ to the main structure?

What are the structural considerations?

What are the methods of fixation?


Integrated Solution



The geometry / configuration of fixing elements:

Which is the safest and most cost-efficient, and least material consuming?

a. Over entire surfaceb. Linear, vertical framingc. Linear, horizontal framingd. Linear, Peripheral framinge. Discrete (brackets)f. Multiple Discrete



How will the façade structure react to different loads?


Stresses Induced:

A 10 mm diameter steel wire rope has a breaking load of 5 tons of force when loaded in

Pure Tension

A much larger section will be required to carry the same

forces in Compound Loading (bending, torsion…etc.)


Stresses Induced:

Optimised Solutions can reduce the section size by carefully studying and adjusting the loading mechanism…

Thus, creating design with minimal material consumption…



The Movement of Fixing Elements:


The Movement of Fixing Elements:

Facades must allow for vertical movement, to account for earthquakes, or thermal expansion…

The location of movement might seem logical in the top (Standing Façade) and the other solution (Suspended Façade) will seem counter-intuitive.


Sliding

Sliding

Fixed

Fixed


The standing façade creates what is called a column effect, which induces additional loads in compression (buckling loads) and requires bigger sections, therefore more material is consumed

The suspended façade is loaded in tension only, requires a smaller section, less material, and is more efficient…


Sliding

Sliding

Fixed

Fixed

An Example of Combined Principles / Multiple Variable

Optimisation

Visualization of Thermal Loss Computer Simulation of the Bracket

Thermal Loss Rate Differentials Graph of the Bracket

Thermal Bridging of Brackets/Supports

Sources: www.halfen.de

Structural Thermal Bridging occurs when structural elements penetrate the envelope creating discontinuities in the thermal insulation creating a path for heat loss (in case of heated internal spaces), or heat gain (in case of cooled internal spaces)

An Optimised design is made to:1.Prevent thermal bridging2.Improve structural performance3.Reduce cost and material consumption

Sustainability of Steel

How does Steel fare against other construction materials in terms of

Sustainability?


Metals / Alloys in general have high Strength-to-Weight Ratios, in comparison to other construction materials

Example:Concrete =Steel =

This means less material for the same structural performance

Steel is also one of the cheapest metals for its strength


Steel is completely Reusable or Recyclable after the end of a building's life-cycle

And almost 0% waste in fabrication, with all scrap being recyclable.


Steel is fabricated, treated, coated, welded, assembled offsite in controlled factory conditions, with minimal risk of impact in terms of Health and Safety to the workers

The Value of Optimisation


Design By Routine vs. Optimum Design

Source: Optimum Design of Steel Structures


Design By Routine vs. Optimum Design

Design without goals, objective functions

Fulfilling design constraints can only be approximate

Minimum material consumption or cost is not reached

It is impossible to develop new, innovative structural types

Source: Optimum Design of Steel Structures

Exact formulation of Design Problem and goals or constraints

Inclusion of all engineering aspects

Consideration for fabrication/cost aspects

Can achieve significant cost savings in design stage

Allowing designers to innovate, and create competitive designs

Thank you…

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