January 5, 2018 dga.energy Admin

The truth about glazing

In providing Rational Design energy assessment services we have modelled and assessed every classification of property type, in every climate zone in the country, and are yet to see any single building that couldn’t be shown to be fully regulatory compliant with single-glazed clear glass when alternative more cost-effective design solutions could be brought into play to ensure that the energy efficiency targets of the regulations were achieved.

When one looks at the payback period of installing any design solution it becomes impossible to substantiate the use of high-performance glazing systems when one could achieve a similar, or frequently better, level of energy efficiency through enhancing the hot water system, introducing air-conditioning to control thermal comfort, minimising electrical consumption with LED lights, etc, on any building at a fraction of the capital cost.

Competent energy modelling would look at the true energy loads incurred through the prescriptive glazing and would seek to identify alternative more cost-effective ways of substituting that energy requirement.

Energy modelling is not however just about making single-glazing magically seem possible without validation; it is about being able to competently demonstrate that the heat loads therein have been assessed and that alternative solutions can be clearly validated in trading back the resultant energy consumption caused by reducing the glazing specification.

On heavily glazed properties, particularly in KwaZulu Natal where solar heat gain is the major challenge, the energy loads incurred by the windows can be substantial and single-glazed tinted glass can frequently prove to be the ‘right’ solution when insufficient alternative energy savings measures prove to be available and the impact of solar heat gain is competently assessed. Good architectural design always wins and in any hot climate area the provision of adequate shading against peak summer solar ingress is paramount to a truly energy efficient building.

Tinted or low-e glass can frequently be shown, and validated with calculated data, to reduce internal heat loads in some buildings helping enhance thermal comfort and reducing the kW loads on HVAC equipment saving clients money in the long term. This can be true on highly-glazed residential properties and certainly on office buildings were radiant heat may be problematic for people sitting and working near to windows.

Single-glazed fenestration systems can almost always be shown to be compliant but do not assume that clear glass is always the right answer…!

In this instance below, spending R150,000 excess on high-performance glass, even though it appeared to be the better performing product, was futile given a paltry R1,112 per annum saving on theoretical heating and cooling costs…? Single-glazed clear glass was thus the optimised design solution given the acceptable compromise on cost and performance.


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