Triple Glazing – A Hot Debate – Exploring Effective U Values

Garry Smith, Principal Consultant, Glass Technology Services Ltd - A number of recent articles and debate around the “Triple Glazing Question” have highlighted the need for simple comparisons between the alternative glazing products and configurations possible for a site or location, which are clearly understandable to the, non-glass industry, public.    Confusion surrounding the Window Energy Rating (WER) scheme remains and we have discussed the need for important factors such as property location, aspect, heating and shading to be separately assessed in a number of articles and features in relevant trade press – this is not something a typical consumer can do, or would be aware of when looking at a WER Label.There are usually great benefits in replacing old windows with new, air-tight, well-insulated, modern frames in any material.  These benefits can mask the performance change derived from improving the glass alone.

Two properties are key when considering the thermal performance of glazing, the thermal transmittance (U value) and the solar factor (g value), which define the amount of heat loss and the amount of energy gained by solar heating respectively.

A little-used comparison tool is contained within the standard EN ISO 14438, ‘Glass in building - Determination of energy balance value - Calculation method’.  This method combines the effect of solar factor, g value and thermal transmittance (U value) and takes into account the installation region and orientation of the glazing.  The calculation allows any U and g values to be entered in order to calculate effective U values, or energy balance values, for Scotland, UK North and London, Thames Valley and the Midlands.  The orientation options are, unsurprisingly, north, south and east/west. The calculation applies to the period where heating is used in the home and for the UK this is based on the months September through to May.

As an example, we have taken north-facing glazing in Scotland and in the south of England.  If we compare a typical unit that might be used in an A rated DGU (U=1.2 , g =0.75 based on centre pane values) and a triple glazed unit (U=0.53 , g =0.47 ) we get:-

Worked Examples

Example 1 - Effective U Values calculated for a  North Orientation in Scotland

Example 2 - Effective U Values calculated for a North Orientation in London, Thames Valley and the Midlands

A negative value means that the glass is calculated to let in more heat than it loses. In this example triple glazing is the best performer - providing that you can ventilate any excess heat out of the room.

These figures are only based upon specific products variants used in this calculation, of course and different products, coatings or pane configurations will result in different results.  The method enables producers to compare the performance of their glazing products.  The energy balance value should not be used for energy use or heating capacity calculations in buildings.

Where windows do not naturally get the sun, due to aspect or shading, then products with a low U value will provide the greatest benefit and in these locations this is typically a triple glazing configuration.

The values of the calculation vary with location and orientation and you may find that a mixture of glass types in one building gives the best overall performance – therefore correct assessment and configuration of each installation is essential to provide optimal benefit and return on investment for the customer.

GTS have made a free “Effective U Value” calculator available on their recently launched website, which can help specifiers determine the optimal glass depending on location and aspect of each insulating glass unit:

www.glass-ts.com/effective-u-value-calculator

For more information about Glass Technology Services Ltd (GTS) please see www.glass-ts.com, telephone +44 (0) 114 290 1801 or email enquiries@glass-ts.com.

Image Credit - Franck Boston/shutterstock.com

600450 Triple Glazing – A Hot Debate – Exploring Effective U Values glassonweb.com
Date: 8 April 2014
Source: www.glass-ts.com

See more news about:

See more from these topics:

Others also read

The building received a new transparent skin glass façade made with Guardian Glass.
Glas Trösch glazing for spectacular views at the Buergenstock Hotel.
The unusual challenge for the glazing was that the maisonettes were not able to have windows along the sides. This required the creative use of rooflights and lightwells to provide plenty of natural light.
Performance engineering is at the heart of NanaWall. Their opening glass walls transcend the concept of large glass openings, facilitating a year-round connection to the outdoors, even in the harshest conditions.
Spectus’ flagship system is the Elite 70, which can be used in a full range of window, door and conservatory applications– including casement and tilt & turn windows, residential, French and bi-folding doors.
The glazing solution across the entire surface of seven floors supports the concept of contemporary architecture. Reflections on the façade reflect the natural environment and thus also involve the outside world.

From industry

Polígono Industrial El Bayo, parcela I, 19
24492 Cubillos del Sil León
Spain

NEWS RELATED PRODUCTS

Add new comment