AdelAide City CounCil Green BuildinG FACt SheetS Energy Efficient glazing INTRODUCTION Selecting Efficient Glazing Glazing is used to allow natural daylight to enter buildings, this improves occupant well being and productivity and reduces the energy used for artificial lighting. It is important that the glazing system enables daylight to enter without the associated heat and glare that accompanies direct sunlight. There are many ways that this can be achieved. When properly selected and orientated, energy efficient glazing can help provide year round comfort and reduce air- conditioning energy consumption. The main factors are the size and orientation of the windows, the amount of shading and the type of glass that is used in the windows. Shading can be applied either internally or externally. Windows and other glazed external surfaces have a significant impact on the energy efficiency of a building. A distinct improvement in comfort levels can be achieved by selecting a beyond-compliance solution to glazing for a new or retrofitted residential, commercial or institutional development. This Green Building Fact Sheet seeks to assist developers and property owners in selecting glass types that meet requirements and achieve high levels of occupant comfort. ADelAIDe (CITY) DevelOpmeNT plAN pRINCIpleS The Objectives and principles of the Adelaide (City) Development plan require new development to provide a sustainable balance between comfort levels for occupants and neighbours with minimized energy use for heating, cooling and lighting, as follows: • energy efficiency, (Objective 31; principles 104 to 113), and • microclimate and Sunlight (Objectives 34 and 35; principles 117 to 124) The Building Code of Australia has introduced new external glazing requirements for commercial buildings (Classes 5 to 9). A glazing calculator is provided at www.abcb.gov.au. BeNeFITS energy efficient glazing systems can reduce carbon emissions, provide insulation and enable cost savings for new and retro-fit developments in the following ways: • Reduce demand for cooling and heating • Reduce size and cost of HvAC plant • Reduce artificial lighting requirements • provide acoustic insulation. An energy efficient glazing system can also assist a building to CASE STUDY 1 comply with: • Australian Building Greenhouse Rating scheme (ABGR), 40 Albert Road, South Melbourne Green Building Council Australia (Green Star), National Australian Built environment Rating System (NABeRS) The building at 40 Albert Road, South • South Australian Government tenancy sustainability melbourne has a NlA of 1200m2 and is requirements owned and occupied by Szencorp. In • Australian Building Code requirements refurbishing the building the company had (part J2 – external Glazing) the vision of setting the benchmark for green Glazing Types buildings in Australia. There are many glazing types on the market, for the purposes Among a host of environmentally sustainable of this fact sheet the following four types are explored: design features, the company installed floor to ceiling high performance double glazing to • Single Clear Glazing maximise daylight penetration into the narrow • low e Single Glazing east/west oriented building. • Double Clear Glazing While allowing daylight deep into the building, the glazing qualities prevent excessive • low e Double Glazing heat transfer, the windows can also be Single Clear Glazing. Relative to all other glazing options, opened allowing natural ventilation. These single-glazed with clear glass allows the highest conductive features reduce the need for lighting and air transfer (i.e. heat loss or heat gain) while permitting the highest conditioning. solar heat gain and daylight transmission. Full length shading screens to the eastern Low-E Single Glazing. low emissivity (low-e) glass has façade along with operable internal blinds a coating that minimises re-radiated heat. It has a clear reduce glare and assist in reducing heat appearance and good thermal properties and can be used entering the building. as single glazing or double glazing. low-e glazing sometimes The ‘green’ qualities of the property have called spectrally selective low-e glass helps to reduce the been widely recognized with the Green invisible, near infrared solar radiation that contributes to Building Council of Australia awarding it the unwanted heat gain while permitting daylight transmission. first 6 star rating for a commercial office Double Clear Glazing. This offers some thermal insulation. It refurbishment, the highest standard available, is made of two clear glass panes separated by an air gap. The meriting world leadership status. air gap acts as an insulating barrier between the window panes Along with other energy saving features, the and is an effective way of reduce conductive heat transfer. glazing contributes to an overall energy saving Compared to single glazing, it can cut heat loss in half due to of 48% compared to typical office energy use the insulating air space between the glass layers. In addition to per square metre. reducing the heat flow, a double-glazed unit with clear glass will allow the transmission of high visible light and high solar www.ourgreenoffice.com heat gain. Low E Double Glazing. This is made from coated glass panes separated by argon/crypton gas. This type of low-e glazing, sometimes called spectrally selective low-e glass, reduces heat loss in winter but also reduces heat gain in summer. Compared to most tinted and reflective glazing, this low-e glass provides a higher level of visible light transmission for a given amount of solar heat reduction. Other features of glazing that can increase the energy efficiency of glazing include: • Reflectivity, although neighbourhood amenity requires consideration, often reducing the reflectivity rate to 15 to 20 percent. • Tints and tones act like sunglasses to absorb heat. • Spectrally selective glass which maximises visible light transmission while reflecting unwanted solar radiation (Uv) and heat. This can also have low emissivity. • polymers (plastic glazing) as alternatives to glass. CASE STUDY 2 Ballarat University, Vic Some advanced glazing products not only offer reductions in heat transfer and solar radiation but can incorporate solar energy generation through Building Integrated photovoltaic (BIpv) systems. Such technology has been adopted in a number of properties, one example is the University of Ballarat’s new Building & Construction Training Centre which has recently (December 2006) incorporated a 200m2 north facing glazed façade. This project uses Schott Solar’s ASI glass product which is double glazed and blocks solar radiation. This reduces the heat transfer into the building in the summer and prevents heart loss in the winter. The glass still allow for excellent visibility as it allows light through but at the same time allowing a reduction in the capacity of the air conditioning plant of 40%. The BIpv façade generates 7.300KWh of renewable energy each year and saves 9,500 kg of CO2-e. Glazing performance – Definitions When considering the properties of different glazing options, various measurements can be used to compare the performance of products against the cost. The following definitions are the most commonly used in assessing the performance of windows. U-value (U factor) measures the rate that heat transfers through glazing and window assemblies. The lower the U value the better the window’s insulation value and its ability to resist heat flow. Solar Heat Gain Co-efficient (SHGC) The SHGC measures how well a product blocks heat from the sun. The co-efficient FIND OUT mORe is the fraction of incident solar radiation admitted through a window, both directly transmitted, and absorbed and www.abcb.gov.au subsequently re-released inward and the lower the co-efficient (A Glazing Calculator has been launched by the less solar heat it transmits. (www.wers.net) the Australian Building Codes Board (ABCB). Visible transmittance (VT) measures how much light comes www.wers.net in through a product. It is an optical property that indicates the The Window energy Rating Scheme amount of visible light transmitted. vT is expressed as a number www.greenhouse.gov.au/yourhome between 0 and 1. The higher the number, the more light is Factsheets for home design transmitted. (www.wers.net) www.gbcaus.org Spectrally selective glass maximises visible light transmission Green Building Council of Australia while reflecting unwanted solar radiation (Uv) and heat. This www.abgr.com.au/new/ can also have low emissivity. Glass properties that affect the The Australian Building Greenhouse Rating amount of sunlight penetrates a building are known as the www.pilkingtons.com shading factor (SF) and the light transmission (lT) rate. www.schott.com/solar peRFORmANCe COmpARISONS TABLE Glass Type U Value SHGC VT Glazing Cost/m2 Daily Electricity Payback Savings Period W/m2/C Single Clear Glazing 5.8 0.81 0.87 $50 - low e Single Glazing 3.7 0.7 0.82 $125 $ 0.09 / 10m2 7.8 yrs Double Clear Glazing 2.7 0.7 0.78 $130 $ 0.16 / 10m2 4.7 yrs low e Double Glazing 1.9 0.66 0.73 $180 $ 0.20 / 10m2 6.1 yrs *Cost savings based on computer simulation test results based on a hypothetical1000m2 building with glazing facing N, E, S and W and air conditioning operating 12 hours per day. Based on 15c/kWhr of electricity. CASE STUDY 3 Air Apartments, Greenhill Road, SA In designing these prominent apartments, created from the shells of two former eTSA towers, it was vital to maintain the panoramic views. The project required a high performance glazing which would enable great clarity and but offer energy savings as well. The architects selected pilkingtons Clear Solar e Glass which is designed to offer high visual transmittance and good thermal performance. Adelaide City Council is committed to promoting ecologically sustainable building practices. This project gained extra energy efficiency dividends from the use of passive design in This Green Sheet is provided for introductory reference. deep balconies which act as shading and Before proceeding with an glazing system, property owners complement the qualities of the glazing. and builders are advised to engage specialists and to comply The company claims that this combination with statutory requirements including the Adelaide (City) means that in all but the warmest weather, Development plan and Building Code of Australia. natural ventilation is sufficient for comfortable climate control.