Ventilating the shed

[Dengue]

I am looking to install a WindWorker (http://www.windworker.com.au) on my house roof and on my shed roof after the whirlybird blew over in cyclone Yasi and left a 300mm hole in my roof. ( see photos below)

The Windworker rep says they are made in Brisbane, won Australian design awards, and have never lost one in a storm or cyclone. He said the whirlybird cannot cool the space below (by the laws of physics), and this is confirmed by plumbers I know.

Does anyone have any experience with these WindWorkers?

[Bushmiller]

JillB

No. No knowledge of Windworker, but most interested.

We have three whirly whatsits on the roof and eight vents in the eaves. The house was hotter than before the whirlys were installed. But we put insulation in the roof too.

That was at the end of last summer. Of course nothing happened in the intervening period as the insulation worked really well for winter.

However after a bout of hot weather I persuaded my builder son to assist in placing some ceiling vents and removing the insulation adjacent to the eaves vents. Actually I assisted the son rather than the other way around.:D

I had reasoned that for the air to exit the roof it had to be able to enter the roof. The insulation was confirmed to be blocking off the free flow of air.

In the rooms themselves the high ceilings on an older style house were trapping air and by mid afternoon the heat front was close to unbearable.

These mods were done today so I will see how they go. I note that Windworker's contention is that the whirly thingos contribute little less than an open hole.

Their device however works on a venturi effect to extract air. There seemed to be a big reliance on the relative opening of doors too, but I will have to look into that further. Although they talk of comparison tests, I couldn't see comparisons with other devices.

Nevertheless I am interested.

Regards
Paul

PS. I trust that was the only significant damage Miss Yasi caused.

[smeds]

One importantant thing to remeber when doing insulation yourself, or by so called proffessionals,never take it out past the frame work of the house, IE never cover over the sefeets or eves's, if you do this you stop anf flow throught the roff cavity dead in its tracks. You nee this cross flow in order to push any hot air upwards, remamber hot air rises, so if you have your whirlybirds or whatever placed at the highest point/s on the roof the the breeze pushing any hot air will automatically got to the hightest point and you have it out of the roof cavity.

Ceiling isulation though, well my jury is still out on that one, we have done the whirly birds and the insulation and actually found it hotter inside the house after it was installed and it wasn't cheap, ( poly wool blend batts ) so you would think they would work. Someone is makinh money it just isn't me.

[IanW]

I probably shouldn't buy into this, but what the heck, a bit of Physics 101 never hurt ....

There seems to be utter confusion amongst the lay public, & even worse, amongst the building/insulating fraternity on how heat is transferred. Heat is transferred by convection (hot air 'rising') conduction (moving through solid objects) and radiation (infra-red, which is what you 'feel' when standing in the sun or near a warm stove, etc.).

The metal roof of most sheds is a beaut conductor & pretty good radiator, so the heat of our tropical sun comes through very easily when there is nothing to stop it. If there is an attic space below, the air in it soon gets pretty warm - enough to cook you in short order, and that heat is soon transferred into the living/working area via the ceiling by conduction & radiation, unless you replace it with air that is less hot. Ceilings are usually made of wood or material that is a relatively poor conductor, so they are better than the roof at keeping your cool, but adding a layer of insulation slows the rate at which heat can transfer into the living or working space, much more. Having a layer of foil each side helps by reflecting the heat on the incoming side, & slowing radiation on the 'cool' side (shiny surfaces are good reflectors & poor radiators, which may sound counter-intuitive).

If you do not provide some way for the air between roof & ceiling or insulation to be replaced regularly by outside air, it gets hotter & hotter (heat coming in faster than it can get out), which speeds up the transfer of heat into the living/work space (the bigger the difference, the more rapidly heat transfers). As observed above, by including adequate ventilation slots, convection will do that for you. Whirlybirds & similar devices should help to some degree, because they do provide a place for the hot air to exit - but you need to put in enough, and provide sufficient vents for the cooler air to enter, if you want to maximise air movement.

With all the best insulation/ airspace venting in the world, you can only hope to keep the living/working area at ambient air temperature - you cannot 'cool' the house below that, though having some way of moving air through the house/shed (breeze, fans) gives a subjective feeling of cooler because you are getting a bit more evaporation off your skin.

Like so many other things in this world, we are cursed by the laws of dimishing returns - it doesn't take much insulation, provided airflow is good, to make a big difference to heat transfer from the roof of a shed. But when it's 40 degrees in the shade, it's going to be bl**dy hot in the shed no matter how much you slow down heat transfer from above.....

Cheers,

[munruben]

When doing roof restoration work I was amazed how many houses had black or dark grey tiles on their roofs.

[Charleville]

I have a concrete tiled roof and I can swear that when I climb up into the ceiling, it is damn hot. "Enough to cook you" as IanW has said.

When I added a couple of Whirlybirds many years ago, I achieved negligible improvement in room coolness and it was only when I added aluminium foil insulation batts in the ceiling that the house became less hot on a hot day.

It was easy to tell which rooms had been insulated and which had not during the installation simply by holding the palm of a hand against the ceiling. In the uninsulated rooms, the ceiling was hot and vice versa in the insulated rooms.

However, where the Whirlybirds pay for themselves imho is in providing ventilation when I am in the ceiling doing maintenance. When I stand on the ladder climbing into the manhole, I can feel a strong updraught of air out of the house into the hot ceiling and exiting through the Whirlybirds. Indeed, when I get really hot up there, I move towards the Whirlybirds for relief from the heat because that is where there is an updraught of cooler air exiting the ceiling.


Soooooo - the point of the story is that I reckon that the Whirlybirds will only be effective if there is a way for air to get into the ceiling from the house. Yes, I know that a tiled roof has plenty of spaces between the tiles for air to come in if it wants to but feeling that updraught in the manhole tells me that a large vent from house into ceiling is what is really required to make the Whirlybirds pay for themselves.



.

[rsser]

Thanks for the physics lesson Ian. Appreciated.

We have a concrete tile pitched roof and shredded seagrass insulation above the ceiling.

I put one cheap rotary ventilator in the ceiling and the effect on the rooms closest to it was striking. Then I added a 2nd and a 3rd with diminishing returns. The house is about 18 squares.

There's enough air gaps around the tiles for outside air to be drawn in, up and out so I haven't bothered with soffit vents (the soffits are AC sheet so you can imagine why).

When the insulation subsidy was on offer, it did seem attractive to remove all the seagrass and get help with installing foil topped blanket but too late now.

I have a spare roll or two of sarking (? .. sheet with one foil surface) and wonder whether it would really help just to lay this over the seagrass shiny side up. With due attention to electrical wiring of course.

[Chris Parks]

I have always wondered why we build stupid houses that don't suit the climate. What is really needed is a two layer roof, the outer skin cops the radiant heat and the inner skin seals the roof in a conventional manner. between the two should be an air gap through which convection moves cooling air. If the sun can't heat the inner skin then it can't heat up and the roof cavity is thus cooler and no insulation required in the roof. Beats me why it can't be done.

[rsser]

You can, and to some extent we do, build houses to suit the climate, esp. re insulation.

If you do a google on insulation, .gov sites, you'll find a very useful gov't guide to insulation options acc to location in Australia.

The roof is just part of the picture.

[Chris Parks]

You miss the point I made, stop the sun hitting the roof and insulation is not needed. Insulation is a band aid solution for a problem that should not exist.

[rsser]

Your point was about the value of a dual skin roof; not about stopping the sun hitting it.

Dual skinning Jill's roof would be a more expensive proposition than one of the varieties of heat control. Up north, dual sided foil is a much better proposition than firbreglass or polyester blanket.

Down here in Melb. the picture is different. We need batts or blankets in winter as well as a reflective surface in summer.

Design follows climate and building characteristics, and anyway with retrofits you have limited choices.

[Chris Parks]

Your point was about the value of a dual skin roof; not about stopping the sun hitting it.

It was not! It was the stupidity of building houses that need insulation. Where did I ever suggest that Jill do it? What I said was houses are built wrong for our climate.

[TTIT]

I....... He said the whirlybird cannot cool the space below (by the laws of physics), and this is confirmed by plumbers I know........?I would agree that the whirlybirds don't help cool a tin shed much but if you really want to cool the 'space below' easily and relatively cheaply, whack on a coat of Thermashield 2000 or one of the equivalents - makes a huge difference instantly without any re-construction or messing about inside the shed at all. :2tsup: Best thing I ever did to my shed.

[Bushmiller]

A few things have been introduced here

1. As you go further north the difference between night and days temperatures lessens. Some techniques that work well in Melbourne will not work in Cairns for example.

2. As you vent hot air from the roof, it will be replaced with cooler air. Unless you are drawing it from underground (some passive solar houses use this simple technique) it will be ambient air. This means as has been already stated, you cannot cool down to a lower temperature than this. If ambient is 40 deg C, that is the best you can hope for. It is better than the 60 deg C you might have been experiencing in your roof cavity.

3. Light colour reflect better than dark colours and absorb less heat

4. There is the heat that accumulates in the roof space.

5. There is the heat that accumulates beneath the ceiling. Both accumulations have to be dealt with.

6. Insulation retains temperature. This can be hot temperature or cold temperature. Your vacuum flask will keep cold drinks cold or hot drink hot. Similar story in your house.


Lots of different effects going on here. Plenty more that I hope may not see the light of day in this post. By all means start a new thread. I love this topic and may have again been guilty of starting a digression.

However, Jill wanted to know if the "Windworker" would offer a significant improvement in performance over the conventional whirly thing that was damaged in the cyclone. Anybody got one?

Regards
Paul

[Dengue]

However, Jill wanted to know if the "Windworker" would offer a significant improvement in performance over the conventional whirly thing that was damaged in the cyclone. Anybody got one?


Thanks Paul :wink:

[smeds]

Hi there Jill
just so we get your question back on track i have founf this for you to read, very interesting actually and makes your choice sound very good
Windworker (http://forums.permaculture.org.au/showthread.php?353-Windworker)
hope this maked your decision a bit easier

smeds

[smeds]

Google windworker and cyclones and you get some pretty good answers that make them sound better than the old whirlybids

[Bushmiller]

A couple of extracts from the Windworker site
"
The primary function of the WINDWORKER was to reduce the built-up pressure from within the interior of structures in the event of cyclones, hurricanes and destructive storms as a means of assisting the prevention of loss of roof cladding from buildings."

and

"
As this air transfer process is continuous 24 hours per day, every day, through suction and convection, a cool air insulation is registered between roof and ceiling causing the temperature within the ceiling cavity to reduce substantially. Tests have shown that by POSITIVE VENTILATION the internal temperature in both ceiling space and rooms will reduce to external shaded ambient levels, that being the coolest possible temperature without refrigeration."

I don't think in terms of cooling it will offer much advantage over the conventional cyclones, although it is possible it may have a better airflow. It will not ultimately make a house cooler.

It may indeed have benefits in a storm situation by being able to create a resistance against the roof being ripped off. Most houses that lose their roof do so by it being sucked off rather than blown off. A negative pressure is created above the roof resulting in lift. It is the same principle with an areoplane wing that allows a plane to fly. We seem to prefer house that stay put. Windworker claims to be able to minimise the roof removal effect.

Possibly cost will be the factor in the end and the likelihood of cyclone damage in your area.

Still nobody with direct knowledge of Windworker. Hmmmm.

Regards
Paul