Browse Forums Eco Living Re: Roof space heat - eave vents and whirlybirds ... 13Oct 14, 2009 10:36 am dymonite69 All studies that have looked at this as a proper before and after or side-by-side comparsion have not shown roof ventilators, ridge vents or soffit vents makes much of a difference. If it worked reasonably well, I would have expected at least one study that showed it made a difference. The Your Home technical manual now also says that whirlys don't work (after saying for years that it did) Did that study included Eco-vents - the thingys that open up when the under roof temp hits 35 degs ? Chris My father rode a camel, I drive a car, my son flies in a jetliner, his son will ride a camel.Saudi saying Re: Roof space heat - eave vents and whirlybirds ... 14Oct 14, 2009 10:30 pm In the absence of a radiant barrier, ventilating a roof space with a whirly is insignificant. Here is the rationale: The roof space air temperature contributes a small heat load into the living space because: - Functionally the roof space and living space are separate systems - Natural convection in the roof space results in a much cool boundary layer at the top surface of the ceiling (lower than the mean air temperature) - The volumetric heat capacity of air is low i.e. it doesn't contain a lot of heating energy - The thermal conductance of air is low - Trivial amounts of heat energy is actually conducted to the ceiling material and hence to the living area In contrast a significant contribution to the heat load is radiant heat from the roof which is generally an order of magnitude higher. Yet the convective thermal flows removed with passive fan vents are small compared to the radiant heat. To purely negate the radiant heat load by ventilation would actually require about 1 air change per minute. as recommended by the US Dept of Energy. The largest impact would be to duct a roof ventilation system directly into the conditioned area to draw hot air away from the occupants - not the roof. Re: Roof space heat - eave vents and whirlybirds ... 15Oct 18, 2009 8:08 pm I've been thinking about the question of colour... and then it struck me. My work colleague and i have the same model car. Same year, same manufacturer, same model. Hers is black, mine is white. When parked out in the sun, my interior gets pretty hot, but hers is like an oven!! I can't comment on other colours, but ours are at opposite ends of the spectrum and the difference in temperature is subjectively substantial (we've never put thermometers in our cars to quantify this though). Re: Roof space heat - eave vents and whirlybirds ... 16Oct 20, 2009 10:15 am bigdenis Hers is black, mine is white. When parked out in the sun, my interior gets pretty hot, but hers is like an oven!! That's the classic difference between heat reflection and heat radiation. Re: Roof space heat - eave vents and whirlybirds ... 17Oct 26, 2009 8:47 pm Jillamint - roof vents will make a bit of a difference - but IMO Adelaide heat is not as intense as WA heat and the benefits may not be as much as you require from the sounds of your posts. As for the grey roof versus white roof - certainly makes a difference, http://www.colorbond.com/index.cfm?objectid=8B47C5CE-A52F-FE7E-1932836BE38355FB but I suspect that the heat is getting in via other means. ie exposed windows, non insulated walls, walls that are heating up during the day, or more likely non insulated areas of your ceiling where the insulation it is not is installed properly. Re: Roof space heat - eave vents and whirlybirds ... 18Oct 26, 2009 10:10 pm We have chosen an Ironstone roof (dark grey) and while it looks terrific it will obviously get hot, we have opted for a couple of whirly birds and the whole house is insulated but we now wish we spent the extra (about $3500) and got the sarking, I was up in the roof last week with our Air Con friend and it was only mid 20's and it was VERY hot up there, admittedly the Whirly Birds are in yet but a high 30's + it will be an oven up there! We might go through a season and after that see if it's worth getting sarking, does anyone know if it's MORE expensive getting it done post building ? Re: Roof space heat - eave vents and whirlybirds ... 19Oct 27, 2009 8:09 am From The Your Home Technical Manual - Common Myths (click on link) "Myth: Roof ventilators will keep your house significantly cooler. Fact: Roof ventilators do not make an appreciable difference to house temperatures if the roof is insulated, particularly if reflective insulation is installed. If your ceiling is uninsulated a ventilator might make a small difference, but insulation is a better investment. There may, however, be other valid reasons for installing roof ventilators such as moisture removal." Re: Roof space heat - eave vents and whirlybirds ... 20Oct 28, 2009 7:24 pm dymonite69 In the absence of a radiant barrier, ventilating a roof space with a whirly is insignificant. - Natural convection in the roof space results in a much cool boundary layer at the top surface of the ceiling (lower than the mean air temperature) And guess what will happen to that boundary layer if you introduce enough ventilation to stir up the air space without actually allowing enough air out to take much heat away! I believe an experiment could well find that only having a couple of eave vents or a single small whirlybird could be worse than having none at all. "Now, supposing a house to have a southern aspect, sunshine during winter will steal in under the verandah, but in summer, when the sun traverses a path right over our heads, the roof will afford an agreeable shade, will it not?" -- Socrates, ca. 400 BC Shade the brick with large eves. Since going to minimum of 600mm eaves on my build, I've noticed much improved cooling off the house after hot summer days. Can see the… 1 2959 Old Home Restoration / Renovation Cheers mate! This is exactly what I was thinking but wasn't sure if it was something I'd find on the shelf. I agree with you, fixing the brackets to the board will look… 2 4042 retail its around double the price of a similar sized actron/dakin system from memory, They are excellent systems though. But with how builder gouge on AC/heating, you… 4 16437 |