How through small yet effective changes to window system design, we can see tangible increases in the energy efficiency of these systems
Since 2006, regulation surrounding energy efficient building design led by the Building Code of Australia The tools that are available to designers to measure thermal performance of the glazing systems Provide a quick overview of commercial curtain wall facades and their thermal properties I have conducted 3 Case Studies 1. Prior to the energy efficiency regulation being introduced in 2006 2. What has happened to our methods of measuring performance afterward 3. Cost-efficient measures taken to improve upon the glazing systems, which see positive gains in the overall performance of the façade FINALLY different areas of investigation and the role of other regulation in this industry
Australian Building Codes Board (ABCB) RESULT of a task force set up in the 1980s to standardise building construction methods BCA is a performance-based standard – i.e. Provides different methodology to achieve different targets Currently updated annually on the 1 st of May Click for set and sub-set terminology: Physical layout: Sections – alphabetical Parts – alphanumerical
Energy consumption in commercial buildings accounts for…. ABCB were aware of the need to reduce building design Section J is underpinned by an objective to reduce greenhouse gas emissions What does this mean for designers? Prior to inception of Section J – thermal performance was measured only on the glass a very low conducting material. Since this statement has been introduced into the BCA, we now have to account for the glass plus the frame. In commercial buildings, the frame is often aluminium, a highly conductive material. Building industry overestimated the energy efficiency of these systems.
DTS calculators readily available via the ABCB website Simple spreadsheet – pull information from different sections of the BCA: building type, climate Project-specific information Click for tips to appear... AFRC – Australian Fenestration Rating Council is the Australian arm of the NFRC. As they adopt procedures and standards directly from the NFRC which is a well-established body, ..... take information directly from the NFRC, bypassing the Australian Fenestration Rating Council
1979 Energy Crisis – in the wake of the Iranian Revolution, lower volumes of oil exports out of the country pushed the US prices up to crisis levels Body set up for on a different premise – outright economic as opposed to ‘energy efficiency’ DoE – Department of Energy (US) demanded that a body be set up to guide and improve developments in industry If not, it threatened to regulate over the top of the industry NFRC procedure documents incorporate: material properties, temperature conditions, boundary conditions
1 st Law of thermodynamics – transfer of heat is from the hot object to the cold object Range: 0.0 to 1.0 – 1.0 denotes maximum solar gain through the glass Centre of Glass U-Values: 5.0 to 5.5 W/m 2 .K for single clear glazing; < 2.0 for double-glazed systems with high performance coatings These values are typically provided by the glass manufacturer . As the glass manufacturer has no input in the construction of the entire unit, they have limited understanding of the impact of the frame upon the performance values, in particular the U-Value as the aluminium has a very high thermal transmittance (around double the glass-only) which brings the overall U-Value UP = WORSE
I’m looking at commercial unitised curtain walls Curtain wall facades typically made up of a vision area and spandrel area The façade panels are constructed from vertical and horizontal aluminium frame components and are hung from the building base structure – like curtains!! 3.6m x 1.5m modules They are common in commercial construction as unitised systems can be pre-fabricated off-site to a high construction standard. Then transported to site where they can be swiftly assembled.
DOUBLE GLAZING: two sheets of glass separated by a gas infill Low emissivity is a high performance metallic coating applied to the surface of the glass, radiate Low-emissivity or “low-e” coatings are commonly used in commercial curtain wall design coupled with insulating glass units (IGUs). IN Australia used primarily to reduce solar heat gain through the glass. VNE 19-63 Viracon - Australian Glass manufacturer IGUs and low-e is considered common building practice in the façade industry The gas infill has been modelled here with air and argon alternatively. Argon is a relatively inexpensive gas in Australia – it acts to improve the thermal efficiency of the glass without compromising light transmission or aesthetics.
Depict the impact of different materials in the thermal properties of the window system CS1 – Glass only system as considered by glass designers before the inception of BCA - Section J We expect the U-value to be better as the metal frame is not accounted for CS2 – framed window system typical of current curtain wall construction CS3 – minor thermal enhancements – through covering the exposed metal trims and legs with low cost polyamide gaskets (with a low conductivity) we can start to provide potential gains in energy efficiency of the system
Case Studies 2 + 3: SHGC decreases slightly (less glass area with frame taken into account) Case Study 1: CoG U-values lowest = better The enhanced frame system sees an improvement on the typical system by approximately 40% Most impressive is the combined effect of the Argon gas infill and the neoprene gaskets covering the trims and legs of the aluminium frame exposed to the outside.
Defining spandrel areas: Canada Mortgage and Housing Corporation Someway behind understanding the behaviour of these systems – due to the complex nature of its construction which often includes many different types of insulating materials. Method of analysis is currently hand calculation of R-Value of each material in the system. We have the algorithms and programmes to measure these areas, yet no consensus. So far the BCA has been leading the charge on energy efficiency however, in light of recent political development in the area of Carbon tax and a future Emissions trading scheme, we hope to see further positive developments in industry
Through increasingly accurate glazing modelling and simulation, we can begin to account for at least part of the thermal transfer occurring in buildings and start seeing tangible benefits to this increasing understanding through reduced energy costs…
ICWES15 - Improving the Thermal Performance of Framed Window Systems. Presented by Miss Lizette JC McNeill, AUST
Improving the Thermal Performance of Framed Window Systems 15 th Annual International Conference for Women Engineers & Scientists Presented by Lizette McNeill Graduate Façade Engineer AECOM Australia Pty Ltd Thursday July 21 st , 2011
OUTLINE 21 July 2011 15ICWES – Paper 202 Page <ul><li>The Regulation: </li></ul><ul><li>The BCA – Section J </li></ul><ul><li>The NFRC </li></ul><ul><li>Curtain wall facades & thermal properties </li></ul><ul><li>Case Studies: </li></ul><ul><li>Glass only </li></ul><ul><li>Typical Frame + Glass System </li></ul><ul><li>Improved Frame + Glass System </li></ul><ul><li>Where to from here...? </li></ul>
The Building Code of Australia (BCA) 21 July 2011 15ICWES – Paper 202 Page <ul><li>1st edition in 1996 </li></ul><ul><li>Updated May 1st </li></ul><ul><li>State/Territory choose to: </li></ul><ul><li>Set/sub-set terminology of the BCA: </li></ul><ul><ul><li>Sections — A, B, etc. </li></ul></ul><ul><ul><li>Parts — A1, A2, etc. </li></ul></ul>Adopt BCA in full Adopt certain Sections Vary requirements through relevant Appendix ABCB 2006, cover + contents page
BCA – SECTION J, PART J2 Page 21 July 2011 15ICWES – Paper 202 “ The Objective of this Section is to reduce greenhouse gas emissions by efficiently using energy” (ABCB 2006a, p354) “ By referring to glazing [the thermal performance is] to be assessed for the combined effect of the glass and frame” (ABCB 2006b, p474) Energy consumption in commercial buildings accounts for approximately 10% of Australia’s greenhouse gas emissions (COAG 2009; CIE 2007) Section J – Energy Efficiency Part J2: Glazing
Where does the designer go from here…? Page 21 July 2011 15ICWES – Paper 202 Hint 1: Deemed-to-satisfy (DTS) Glazing Calculators – Hint 2: Guide to the BCA – AFRC procedures…? As adopted/derived from NFRC procedures (ABCB 2010b, p487)
National Fenestration Rating Council (NFRC) Page 21 July 2011 15ICWES – Paper 202 THERM5.2 OPTICS5 “ [In 1989,] heat loss through buildings accounted for 25% of all heating dollars spent in the US” (DoE in NFRC 2003, p5) Late 1970s Energy Crisis NFRC established in 1991 develops maintains regulates Derived from ISO15099 Lawrence Berkeley National Laboratory (LBNL) developed NFRC-approved 2D thermal modelling software: WINDOW5.2
THERMAL PROPERTIES OF GLAZING Page 21 July 2011 15ICWES – Paper 202 <ul><ul><li>Air movement around the system </li></ul></ul>Measure of conductance The LOWER, the BETTER Ratio that measures the amount of radiant heat passing through the glass/frame <ul><ul><li>Δ T across the glazing system </li></ul></ul><ul><ul><li>Resistivity (R) of materials </li></ul></ul>U-Value (W/m 2 .K) Solar Heat Gain Coefficient (SHGC)
COMMERCIAL CURTAIN WALLS Page 21 July 2011 15ICWES – Paper 202
BASE CASE MODEL Page 21 July 2011 15ICWES – Paper 202 6mm = glass DOUBLE GLAZED SYSTEM with LOW-E COATING 12mm = gas infill 1. AIR 2. ARGON “ 6/12/6”
CASE STUDIES Page 21 July 2011 15ICWES – Paper 202 Whole of System (WoS ) Centre of Glass (CoG) Case Study 3. Thermally enhanced curtain wall system Case Study 1. Glass only - window Case Study 2. ‘Typical’ curtain wall system ‘ Typical’ aluminium frame section ‘ Enhanced’ aluminium frame section Case Study 2. Case Study 3.
METHOD OF ANALYSIS – LBNL Software Page 21 July 2011 15ICWES – Paper 202 Step 1. Create glazing - WINDOW5.2 Step 3. Re-create framed window system – WINDOW5.2 Step 2. Create frames, insert glazing - THERM5.2
RESULTS Page 21 July 2011 15ICWES – Paper 202 Case Study Type of System (Thermal Properties) Glass Type & Arrangement Infill Thermal Properties SHGC U-Value W/m²K 1 Glass-only system (CoG) VNE19-63 6/12/6 Air 0.24 1.7 Argon 0.23 1.4 2 Typical framed window system (WoS) VNE19-63 6/12/6 Air 0.23 2.9 Argon 0.23 2.7 3 Thermally enhanced framed window system (WoS) VNE19-63 6/12/6 Air 0.23 2.1 Argon 0.22 1.9
WHERE TO FROM HERE…? Page 21 July 2011 15ICWES – Paper 202 “ panel of wall located between vision areas of windows which conceal structural columns, floors and shear walls ” (CMHC 2004, pA-12) Spandrel areas currently covered under Part J1 – Building Fabric, J1.5 Walls.
FINAL WORDS Page 21 July 2011 15ICWES – Paper 202 the obstacles to reducing greenhouse gas emissions through energy efficient building design are great and many… (IPCC 2007, p390) Through modest changes to glazing design, we can start to see the ease with which energy efficient measures can be implemented...
REFERENCES Page 21 July 2011 15ICWES – Paper 202 ABCB 2006, BCA 2006 –Volume One , Australian Building Codes Board, CanPrint Communications Pty Ltd, Canberra ABCB 2006, BCA 2006 –Guide to the BCA 2006 , Australian Building Codes Board, CanPrint Communications Pty Ltd, Canberra ABCB 2011 , Energy Efficiency Glazing Calculators , Australian Government, State and Territory Governments of Australia, viewed 07 Feb 2011, <www.abcb.gov.au/index.cfm?objectid=73874810-28B9-11DE-835E001B2FB900AA> CIE 2007, Capitalising on the building sector’s potential to lessen the costs of broad based GHG emissions cut , Centre for International Economics, Canberra, Australia CMHC 2004, Glass and Metal Curtain Walls – Best Practice Guide Building Technology , Canada Mortgage and Housing Corporation, Canada, available online via <www.cmhc.ca> COAG 2009, National Strategy on Energy Efficiency , Council of Australian Governments, Commonwealth of Australia IPCC 2007, Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Intergovernmental Panel on Climate Change , Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA [pp 387-446] NFRC 2003, Behind the Glass – A history of NFRC as told by the people who lived it, National Fenestration Rating Council , National Fenestration Rating Council, Silver Spring, Maryland, USA