Deflect Unwanted Heat

Deflect Unwanted Heat
The biggest way that the building deflects unwanted heat is by the solid shade provided by the roof. We have greatly enhanced this deflection of heat by painting the roof with heat reflective paint, and by replacing the old skylights that were effectively a hole in the roof, with the roof windows that have solid canopies and appropriate eaves.
Heat Reflective Paint
Applying heat reflective paint was the single biggest and most cost effective impact we have had on the operation of this building. For approx $14 000 excl. GST, the 1600sq metres of roof over both buildings has been painted. The paint we used, Astec Energy Star white, is said to reflect 89% of heat, and is also very good at releasing heat to the night sky – 89% emissivity. 
Kevin Jacka applying heat reflective paint to the roof of the Meeting Room. It is bright up there!

Afternoon on the roof of the Community Complex. The sun is behind the camera, so the light and heat is being reflected away. This roof is mostly flat or low angle, so the glare mainly only effects people walking on the roof, or passing helicopters. For a steeper roof a darker colour of heat reflective paint could be used, to produce less glare. Note also reflective tinting on high windows of Hall, visible to left of picture. It is 3pm on 23rd February, and the sun is just about to start shining onto (before tinting, into) these high windows.

After applying this paint we received many comments from the regular users of the building that it is now appreciably cooler in summer. The cost to supply and apply this paint worked out to about $9.50 /sq metre, including GST. It is expensive as a paint, but can be relatively cheap as a cooling strategy for difficult to insulate roofs.

Most of my direct experience with this paint is with this building, with its very poorly insulated ceiling. However Kevin Jacka, the painter, then went home and painted the metal roof of his own weatherboard house with this paint. His ceiling had about R2.5 insulation. On the summer's day that he put just the primer/undercoat on, his wife came home and said “The house is cooler.” Kevin put the top coat on, and is pleased with the effect. The paint may well be worthwhile applying on roofs where the ceiling is insulated.

However it is a plastic paint and I would like to know more about how it degrades in sunlight before using it on roofs that supply drinking water. I have asked the supplier for more information about this, which they have not as yet provided.

Heat reflective paint is also available for tile roofs, and for walls. Tony Nicholas has used it to very good effect on a west facing wall of his brick house in Hurt St Violet Town. [At Tony's initiative the EcoLiving Project is also encouraging VicTrack to put this paint on the metal shelters on railway platforms.... we'll see how we go with that. I am sure it would be very worthwhile, if they decide to do it.]

Replace skylights with roof windows
see also
Use Energy from the Sun  The old skylights leaked air, occasionally water until patched up, and definitely leaked heat and cold.

This old skylight above the kitchen needed to be replaced, and was a hole in the roof letting in heat, cold, and the sun's rays in summer.

Andrew Otto installing the supper room roof window at midday on December 21, summer solstice. Note the shadow line from the eave extends right to the front of the flashing, well away from allowing sun to enter the room below.

Install apropriate eaves on north windows
There were a number of north facing windows around these buildings that, while being valuable in winter, needed an eave to keep out summer sun.
New canopy/eave installed over north facing window in library courtyard. Shown in May 2010, with warm light entering the library.

Window tinting
Window tinting film can be applied to the inside of existing windows to deflect unwanted heat. This is a compromise solution, because with the deflection of heat comes reduced light passing into the building. A basic purpose of windows is to let in light. However some windows in these buildings, particularly in this case west and south west facing windows, were problematic for letting in summer sun, and we accepted the compromise of reduced light.

Paul Natalizio applying film to a west facing window in the Supper Room. Reduced light from these windows is now more than compensated for by light from the new roof windows. In summer the blinds were kept drawn anyway, because of the sun's heat, so the windows are now more functional than they were.

We used Optitune 15% film, which lets 15% of light in, and rejects 84% of heat. Paul of GV Window Tinting gives a lifetime guarantee on his application of this film for private homes, and a 10 year guarantee for commercial installations. Why the difference? Because the tinted windows must only be cleaned with mild cleaners, and he has found that cleaners of commercial buildings tend to use stronger cleaning products that reduce the life of the film. Sheryl Taylor, the VT Hall Committee, and Strathbogie Shire have all taken note of this. Sheryl only uses mild cleaners at the Hall, anyway.

Mike Larkin preparing wiring for the big fan in the Hall. Note reduced light coming in from the tinted SSW facing windows to right of picture, compared with the NNE facing windows at left. Before the windows at right were tinted, the sun would start shining right into the Hall in the late afternoon, heating it up just before a summer's evening event.

Heat Reflective Blind
Unlike permanently applied tint film, a heat reflective blind can be raised and lowered, giving control over when the effect. It can be raised to allow more indirect light into the room when the sun is not shining in, or to allow winter sunshine in to warm the room. It is more expensive than tinting, but preserves more of the use value of the window.

Sean, Indigo and Steven demonstrate the open-able heat reflective blind installed on a west facing window at Violet Town Community House. This does require someone to think about how the blind works, and actually open it when appropriate – in winter for example to allow the afternoon sun to shine in.

Landscaping for shade
Of course buildings, or badly sited windows, can be also be shaded with vegetation, which is a less energy expensive, and financially cheaper, strategy than high tech window tinting. This works well if well managed. Best if a gardener lives in the building, thinks about how it works, and manages that vegetation to best effect. For this public building we mostly had to accept that the landscape plantings will remain pretty much as they are.

Cutting back the tops of the existing photinia bushes to let winter sun into the Main Hall is one exception. See Use Energy from the Sun. Creating shade for the entry courtyard is another exception. If we can create a leafy shaded space over that courtyard we will deflect heat, create active cooling through transpiration of moisture through the leaves, and create a cool air space from which air can be drawn into the building.

Pergola frame over south facing courtyard garden is to carry four grape vines, which will be guided up the chains hanging from each corner. Shade from the vines will further cool this space. Pergola constructed by Comspread Engineering. Courtyard garden about to be re-landscaped by Graham Jones and Yuta.

Constructing this pergola to carry grape vines and shade this courtyard in summer is an excellent cooling / energy efficiency strategy, but the decision to construct the pergola out of steel is very questionable. I took advice that it should be constructed  with galvanised steel for a longer life than timber. On reflection I would prefer to have used very dense Australian hardwood such as Sugar Gum, Ironbark or local Box eucalypt, which in my own and others experience is very durable for outdoor construction.

For any sustainable / energy efficiency project, the embodied energy in the material needs to be taken into account. For the steel, think about the energy cost of digging up the iron ore in Western Australia, digging up the coal in NSW or Queensland, freighting both to port, shipping them to China, freighting these to the steel mill, burning lots of coal to make the steel, then freighting / shipping / freighting the steel back to Violet Town! Compare this with the small energy cost of cutting up a log from within 100 kms, possibly much less, to get durable hardwood timber.

David Arnold


Irwin Floto said...

We all want to feel comfortable when we are staying at home, and keeping the heat out is one way to ensure this. Heat reflective paints are a wonderful invention. Commercial uses of this include shipping vessels. The choices are there, it's only up to us to decide if we want to use it or not.

Irwin Floto

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