#understandingenergyefficientwindows

[solar-city-eco-homes]

GLAZING FOR ENERGY EFFICIENCY

Helping you understand window  components and ratings

What type of glazing does my home need, to be energy efficient you might ask.  Do I need double glazed windows, argon filled windows and what is the U-Value and SHGC measurement that is listed on my home plans?  Let’s take a look at some of these factors to help you understand what they mean and how they will work to make your home more comfortable.

U-Value

It’s commonly known that insulation is measured in terms of an R-Value and the higher the R value the better your home is insulated, so to help explain a U-value, it is actually the inverse of an R-Value. Ideally, you want your window to have a low U-Value rating. Ratings are typically specified between 2 – 10, so a U-value in the lower spectrum is ideal to ensure warmth stays inside the home.

 U-Values measure how well a product prevents heat from escaping.   A U-Value measures the rate of non solar heat transfer via conduction and convection. It is also important to note that the calculation of a U-Value considers the whole of the window, which includes the frame, glass, seals and spacers. 

 SHGC

Solar Heat Gain Co-efficient (SHGC) measures how much heat can be blocked from the sun via the window.  SHGC is measured between 0 – 1 so if your window has a .58 measurement, this means that 58% of the heat from the sun will be penetrating through the window.  Since homes in the Shepparton region are looking to gain heat through their North facing windows, they will be looking for a window with a high SHGC.  This will allow the winter sun to penetrate into the home, warming it up.  It will be important though to ensure this window has good shading in the Summer months to ensure unwanted heat gain. For other windows in the home, which might endure some Summer sunlight, a low SHGC would ensure less heat penetrating the home.

VT

Visible transmittance (VT) is referring to how much light transfers through a window as a percentage.  A measurement of .61 means that 61% of light will come through this window.  Measurement of VT ranges between 0 – 1 so the higher the number, the more light that will be transmitted.

Air Infiltration

Looking to achieve optimum energy efficiency in your home?  Air infiltration is a key factor.  Windows, if not made or installed correctly can contribute to a large amount of heat loss or gain through cracks in the assembly.  A home can be tested for air infiltration and is measured as L/s m2. (leakage per second per square metre). The lower the air infiltration figure, the more you will improve your energy rating.

Double glazing

New homes are commonly installing double or even triple glazed windows to help improve energy efficiency. These windows combine multiple glass panes into a single window system.  Each layer of glass is separated by a spacer and a still layer of air or gas. The glass panes are assembled into a window frame.  The space between panes generally ranges between 6mm to 20mm however 12mm and above is recommended for optimum thermal performance.  The space between the panes of glass acts as an insulator, therefore reducing any unwanted transfer of extreme heat or cool into your home.  Argon gas is commonly used to fill between the glass panes as it has low conductivity properties.  The added benefit of multiple glazed windows is that it also reduces noise from outside.

Size

Glazing will play a pivotal role in enabling thermal mass to work during the winter months.  A good rule of thumb is for your North facing windows to be at least 15% of your floor area to ensure adequate heating is achieved.  Our local area would benefit from 20% ratio.

Further Help

Glazing is rated by the Window Energy Rating Scheme (WERS). To understand more about how windows affect the comfort of your home you can visit the WERS frequently asked questions page via the following link: https://www.wers.net/werscontent/faqs

If you need help selecting the right windows for your climate zone, you can download a guide from the following link: https://www.wers.net/werscontent/how-to-select-windows

Alternatively, compare the savings and benefits of different window types with the “Window Tool” via the following link: http://www.efficientglazing.net/userguide.aspx (The Window Comparison Tool allows comparison of different WERS Certified window products against a base window. It is important to understand that the results displayed by this tool are generic. They are based on generic house types with specified insulation levels, specified design and the same window installed in every opening in the house).