Effectiveness of External Venetian Blinds
Many reputable studies have been conducted into the efficiency of external and internal shading systems. Most of the research has been carried out in Europe where high energy costs make effective insulation of glass areas a must – in fact some countries have tough legislation in place against energy inefficiency. Research findings by Australian Institutions and summary figures are available through CSIRO.
The objective with any shading device is of course to keep the inside temperature in a range where our bodies feel comfortable and perform at their best. It has been well established that these temperatures are ranging between 18o and 25o Celsius. To achieve and maintain this comfort zone we have to spend valuable energy into cooling and heating our homes and workplaces.
Shading & Insulation
External shading systems that also act as barriers against cold winter nights, will save money in 2 ways:
1. The upfront investment into a smaller cooling and heating unit.
2. Ongoing savings in running and maintenance costs.
In case of an environmentally friendly design, cooling or heating may not even be necessary by using external shading and insulation devices (Olympic Village Design).
External Shutters Outperform Internal Shading Devices
Benchmarks set by the “German Industry Standard VDI” show external shutters to be outperforming internal venetian or vertical blind system. External covers over glass areas with a northerly aspect stop over 85% of the heat whereas the internal systems allow nearly 5 times as much energy to pass.
To achieve and maintain the same temperature with internal shading devices, you need to invest twice as much into a larger cooling system. It will cost on average 115% more to maintain and 140% more to run the larger unit.
Another important fact: In achieving these results external louvres reduce daylight only by 20%. (this figure is higher with roller shutters)
Limits of Internal Applications
To achieve similar cooling results internally the air between the glass and the internal blind needs exchanging up to 20 times per hour. In situations where the glass area is more than 65% of the total wall area satisfactory results cannot be achieved by means of internal solar control.
These results clearly favour external solar control systems. You also have the additional bonus of Security.
Our second image shows the comparison of internal vs external and the benefits are clear.
Passage of Heat Flow Through Windows by Convection and Solar Radiation
Heat passage by convection is determined by the window surface and the heat passage coefficient ( the higher the quality of glazing, the lower the coefficient ) and is negligible in this instance.
The greatest contributor to heat flow through windows is solar radiation. Heat passage is calculated by determining the area of the windows surface exposed to the sun and its shading coefficient ( s ). The shading coefficient expresses the percentage of radiation passing through a window in comparison to one which is single glazed. The value of this coefficient is determined by the type of glazing and shading affecting the window.
For further information, please download our document on Shading Coefficients.
For more information about our products, you’ll find it on our website.
The annual air conditioning energy cost saving will be in excess of $ AUD 800.00 per year and this is only for one window!
Reduced dependance on Heating and Cooling