Efficiency, obscuration and condensation

Phil Brown, technical advisory service manager at Pilkington, answers some of the questions he gets asked most frequently by end users – issues that will likely be raised with glazing businesses across the supply chain.

I’d like my home to be cooler in the summer and warmer in the winter – how can I achieve this?

Glass can play a big role in passively controlling the temperature in your home with reduced need for heating and air conditioning.

During the summer, excessive heating is caused by solar gains raising the temperature inside a building. This effect can be reduced by installing glass with a solar control coating to reflect near infra-red radiation from the sun, while leaving a neutral appearance to the glass.

Heat loss during winter is caused by a combination of conduction, convection and radiation of heat. Conduction and convection can be reduced by the appropriate specification of double or triple glazing.

The low-e coating has been developed to reflect back into the room the far infra-red radiation generated by radiators, electrical equipment and even body heat.

By increasing the amount of heat reflected back into the building, Pilkington low-e glazing units can make your home more than twice as energy-efficient in comparison to standard double glazing.

I want to use glass in my bathroom – what different privacy levels are available?

The Pilkington range of decorative glass offers five different levels of privacy – also known as obscuration. That is, you can choose products that obscure whatever is behind it by varying degrees, from 1, which introduces an attractive decorative pattern but maintains a high level of visibility, to 5, where only vague colours and shapes can be seen, dependent upon lighting conditions.

For bathroom use, where the aim is to allow in natural light but prevent visibility, a high level of obscuration will be desirable, so privacy levels of 4 and 5 are recommended.

Privacy glass is available in the form of both textured glass, where the pattern has been impressed onto its surface by a roller during manufacture, and acid-etched glass, where the design is etched into the surface of the glass.

A good supplier will be able to show you samples from the range, so you can get a better idea of the options available both in terms of obscuration levels and patterns.

I have low-e glass and it gets a lot of external condensation – why is this, and is there anything I can do about it?

Condensation occurs when the temperature of a surface falls below the dew point – the temperature at which water vapour in the air condenses into droplets of liquid.

Low-e glass works by preventing windows from radiating heat out into the environment, significantly reducing levels of heat loss from buildings. A side effect of this is that the outer surface of the glazing is colder than standard double glazing would be, increasingly the likelihood of condensation forming, especially in spring and autumn.

For some people, this condensation is not a problem, and is in fact a sign that their energy efficient windows are working effectively.

However, in some cases – for example with windows where the view is a major feature of the house – excessive external condensation might be undesirable, even if it will disappear as the temperature increases during the morning.

The solution is to choose an anti-condensation glass with a coating that has been designed to retain a higher temperature on the outer surface of the window, without compromising its performance U-value.