Roof Ventilator

[P76]

I just put a motorised roof ventilator on my house in Sydney and the difference in inside temperature is amazing.

I would like to put one in my house in Thailand, just wind powered, no motor. I have only seen large industrial types. They would be OK but I think they are only suitable for flat roofs.

Anyone have expierience with these?

[Naam]

I just put a motorised roof ventilator on my house in Sydney and the difference in inside temperature is amazing.

I would like to put one in my house in Thailand, just wind powered, no motor. I have only seen large industrial types. They would be OK but I think they are only suitable for flat roofs.

Anyone have expierience with these?

a wind powered fan does not give you any energy saving no matter what some "experts" claim. the only way to cool down your attic and avoid heat transmission to your home is an electric exhaust fan. i am not sure what size of home you have but i use a roof fan drawing at full power ½HP = ~365 watt for a roofed home of approximately 600m². you don't have to go my expensive way (15k baht for the fan and 13k baht for a phase-shifting regulator which is thermostatically controlled) but a normal exhaust fan for 2-3.000 baht / 100-120 watts manually switched or by timer (1.200 baht) should do the trick and reduce your electricity bills. if you don't have (like me) a hip roof but gables the installation should be a breeze. make sure the fan is mounted on one side of the attic and there is an opening to draw fresh air from the opposite side.

if you need more technical assistance don't hesitate to PM me.

Edited November 15, 2006 by Dr. Naam

[Jai Dee]

I am considering installing one in my place too... in Thailand... as the insulation under the tiles is not very effective.

I used to have one installed in my place in Perth, WA, and the temperature difference is incredible.

They can be mounted on both flat and pitched roofs, somewhere near the apex to get good wind flow.

In Australia you can get them powder coated to any colour you want to match your tiles, but in Thailand I have only seen them in a galvanized finish.

All sizes (both domestic and industrial) are freely available here.

[tutsiwarrior]

from where I sit I can see that some of the neighbors got the wind turbine type ventilators mounted on pitched roofs...don't seem to be a problem as the ventilators stay vertical and the roof sealing arrangement appears to be routine...

recently in Vietnam I observed that these turbine ventilators are widely used with many sidewalk vendors having them on display by the kerbside. VN is a lot poorer than Thailand and the people there are a lot more resourceful. I'd say go for it but check the installation to yer own satisfaction...a simple sun-light test should do to insure that there shall be no rain water ingress...these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

myself, I make do with 6" fiberglass blankets available at HomePro...the wife (who is the boss) is loathe to cut holes in the roof...

[tutsiwarrior]

to follow on, I found these ventilator units to be available on the outskirts of small towns usually where building materials people have their premises...you can usually see them on display out by the road. Don't know about BKK...but if you purchase in the Smoke it's bound to be more expensive. A good tip is to have the thai wife/girlfriend do the deal while you hunker down in the back of the vehicle, unseen...sorta like buying mangoes/bananas/sweet corn from a roadside stall...

these folks usually deliver within a certain radius so don't worry about that...you would have to make your own installation arrangements, though...most competent local builders can whip it into place in no time, cheap as well in most cases...

[Naam]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

[Pink Mist]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

thank god another scientist arrives, had this argument with yorkie yesterday, there is no such thing as suction, or centifugal force for that matter.

[chuchok]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

thank god another scientist arrives, had this argument with yorkie yesterday, there is no such thing as suction, or centifugal force for that matter.

I beg to differ.

(yeah,yeah I know.....it's all air pressure!)

[astral]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

If there is a wind blowing, the flow of air passed the unit will indeed suck the hot air out.

Pure physics - I believe Bernoulli defined the effect.

[Swelters]

thank god another scientist arrives, had this argument with yorkie yesterday, there is no such thing as suction, or centifugal force for that matter.

It's a good thing that the auto industry never learned this important news in the age of the carburetor.

The performance of these devices could be rationally evaluated if their capacity, say in terms of cubic meters of air moved per minute, were known. Never been able to find anything on this myself.

[scotsman]

If you dont like to cut holes in your roof and stick a ugly metal thing on your roof, get a electric one installed in the roof space with it vented to the ouside that goes off when it reaches a pre set temp. I got one installed over 7 years ago and its still working great.

[samran]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

If there is a wind blowing, the flow of air passed the unit will indeed suck the hot air out.

Pure physics - I believe Bernoulli defined the effect.

It's all hot air....

boom boom!!!

[tutsiwarrior]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

hmmmm...dunno...these units appear to rotate faster when there is a breeze than when there isn't, and the turbine 'bucket' design indicates that outside airflow should be the driving mechanism... although I accept your point that rising volumes of hot air can contribute to the machines effectiveness...

but to get to the point YOU MESSIN' WID ME??? FORGET HEAVY SABRES AND BACKYARDS...I SAY SAWED OFF PUMP ACTION WEAPONS AND TAKE IT TO THE STREET WHERE IT BELONGS...

Edited November 16, 2006 by tutsiwarrior

[Naam]

If there is a wind blowing...

*****

"if" = then suction, "if not" = then one has to pay for suction

[Naam]

I SAY SAWED OFF PUMP ACTION WEAPONS

******

AGREED! expect my seconds to knock on your door tomorrow morning @ 0600hours sharp to throw the glove across your threshold.

ahmmm... are we going to use blanks or real ammunition?

[chuchok]

these simple tin units act as an induced draft fan that sucks the hot air out of the roof space...cheap and effective...

------

i most humbly beg to differ Tutsi-Warrior and comrade in arms. these "simple units" do not suck hot air out of the roof space but they are driven by the expanding hot air. simple law of physics applies.

if disagreement should prevail i suggest a duel with heavy sabres coming sunday morning at dawn in my backyard.

If there is a wind blowing, the flow of air passed the unit will indeed suck the hot air out.

Pure physics - I believe Bernoulli defined the effect.

no such thing as suction I believe.I think that even mr bernoulli would call it a difference in air pressure.

[lopburi3]

I installed two 25" stainless steel units last year and they indeed do work very well. There is no hole cutting as they mount on fiberglass tile shape base made for them so only a couple of roof tiles are removed and replaced by the fiberglass unit and the turbine installed vertical on it. But you do have to make sure they seal it well. As can be verified at any store front display the units do indeed rotate with the slightest air flow. Can not verify temperature change but it is enough so that standing with head in air space is comfortable rather than the sweat box it was before.

[lannarebirth]

I installed two 25" stainless steel units last year and they indeed do work very well. There is no hole cutting as they mount on fiberglass tile shape base made for them so only a couple of roof tiles are removed and replaced by the fiberglass unit and the turbine installed vertical on it. But you do have to make sure they seal it well. As can be verified at any store front display the units do indeed rotate with the slightest air flow. Can not verify temperature change but it is enough so that standing with head in air space is comfortable rather than the sweat box it was before.

Hi lopburi3,

Do you have a picture of how the wind turbines look on your house? I'm finalizing plans of a house design and I'd certainly rather use a non electric ventilating option, but I'm cocerned it's appearance might detract too much from a home that is designed more along the lines of traditional Thai architecture.

[lopburi3]

I can not view them as are mounted on back side of roof so only house behind us can see them.

[chownah]

At this link:

http://www.greenhouse.gov.au/yourhome/technical/fs02.htm

I found this:

"Myth: Roof ventilators will keep your house significantly cooler.

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."

For me the operative principle here is "insulation is a better investment".

Chownah

[Swelters]

At this link:

http://www.greenhouse.gov.au/yourhome/technical/fs02.htm

I found this:

"Myth: Roof ventilators will keep your house significantly cooler.

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."

For me the operative principle here is "insulation is a better investment".

Chownah

Yes, insulation is the best, but not reflective insulation. The Australian statement is correct in most respects, but I claim that "fiberglass or the like" should be substituted for "reflective". I think that the foil industry, always aggressive, snuck that one through. Further proof to follow.

Swelters

Edited November 19, 2006 by Swelters

[lopburi3]

While insulation may make good sense in cooler areas as it works both ways' for heat buildup the vents make a huge difference; especially with the normal ceiling of cement board which becomes a very good radiator of heat. When Microfiber first opened production in Thailand I did cover ceiling but never did feel much of an improvement. I have felt the improvement with turbine vents. Normal passive roof vents do not move anywhere near the same amount of air however and the article mentioned does not specify what type they are talking about and I am sure they are not talking about cement board ceilings.

[chownah]

Swelters,

I agree. Long ago I read somewhere that reflective insulation rarely provides the benefit it claims....I don't know where I read this so I'm not trying to convince anyone of this. I have never used reflective insulation except for the times when I bought fiberglass batts and the kraft paper which holds the fibres into a batt was aluminized and this only by coincidence, not by choice. I have used fiberglass batts quite alot (for cold weather climate) and I find them to work really really well when installed properly (no gaps and edges neatly tacked and in combination with a sheet plastic moisture barrier).

Chownah

[Swelters]

Here's another piece of information for the quantitative-minded:

One manufacturer

http://www.windmaster.co.za/tornado_tech_info.htm

claims tested ventilation capacity of its 20 inch (big!) wind turbine of 4500 cubic meters per hour with a 15 km/hr wind. That's about 70 cm/min, which will produce an air change every minute in a smallish (5mx5mx3m )hot uninsulated attic or upper room, which should be just right to prevent air temperature buildup. It would take a fairly good power fan, say 12 inch, to compare with this.

The midday temperature in Bangkok is in fact typically 15 km/hr, but it drops to about half that rate in the afternoon, say 3 pm, which is when the heat is worst. This is reportedly just enough to keep a turbine going, with maybe only about a third of the 70 cm/min.

All things considered, I would go with 12 inches of fiberglass or rockwool insulation (not foil) combined with screened louvred vents for enclosed attic spaces (ie dropped ceilings).

If you want to add a wind turbine to exhaust any remaining hot air, I'd check to see whether you have a 5 mph wind when you want it (April afternoons?). You can get daily weather data for many places in Thailand on Weather Undergound.

Swelters

[chownah]

I did some calcs and it works out that a 15 km/hr wind moving that much air through a 20 inch throat would mean a 23 km/hr air speed through the throat....is that the way these things work?...they create a greater velocity through the throat than the wind that is powering them?...just wondering.

Chownah

[Swelters]

.... midday temperature in Bangkok is in fact typically 15 km/hr........

That should read "midday wind velocity in Bangkok".

Chownah, I don't understand the physics of those things atall, atall....

I just looked at a couple of roofs from the skytrain, they are using what look like 20 or 24 inch turbines, rather densely placed, maybe 3 meters apart on a grid. This seems to confirm the need for a lot of turbine capacity if you don't insulate. I haven't worked out the arithmetic, but I suspect that more insulation and less turbines is a better way to go.

[xerostar]

I live in Perth Australia.

I installed a couple of the rotating roof ventilators on my shed.

I bought them at the local hardware store.

On a hot windy afternoon the ventilators were really getting some revs up.

However the air inside the shed remained very hot, despite insulation under the corrugated iron sheets. I got on a ladder and stood with my head under the opening to the ventilator.

I could not feel any air moving. Even a piece of tissue paper failed to rise with the apparently invisible air current.

In principle these ventilators are as effective as a free wheeling toy propeller mounted on a bicycle.

At best they allow some hot air to escape from under the roof, equal to the size of the hole.

What's missing from these devices is a horizontal impeller mounted underneath to actually move air upwards by harnessing the rotating motion of the device.

I think a large electric exhaust fan would have been very effective for cooling but I didn't try it.

After that I installed a 2.5 HP reverse cycle air conditioner.

Cool at last, and warm in the winter too!

[Swelters]

Notice the spacing of these 20 inch (approx) turbine ventilators

[Jai Dee]

I live in Perth Australia.

I installed a couple of the rotating roof ventilators on my shed.

I bought them at the local hardware store.

On a hot windy afternoon the ventilators were really getting some revs up.

However the air inside the shed remained very hot, despite insulation under the corrugated iron sheets. I got on a ladder and stood with my head under the opening to the ventilator.

I could not feel any air moving. Even a piece of tissue paper failed to rise with the apparently invisible air current.

In principle these ventilators are as effective as a free wheeling toy propeller mounted on a bicycle.

At best they allow some hot air to escape from under the roof, equal to the size of the hole.

What's missing from these devices is a horizontal impeller mounted underneath to actually move air upwards by harnessing the rotating motion of the device.

I think a large electric exhaust fan would have been very effective for cooling but I didn't try it.

After that I installed a 2.5 HP reverse cycle air conditioner.

Cool at last, and warm in the winter too!

For them to work effectively there must be some form of ventilation under the eaves as well... to allow fresh cool air to replace the hot air that is being expelled by the fan.

Installing them on a tin shed without any additional ventilation is just not gonna work.

[xerostar]

For them to work effectively there must be some form of ventilation under the eaves as well... to allow fresh cool air to replace the hot air that is being expelled by the fan.

Installing them on a tin shed without any additional ventilation is just not gonna work.

Yes I forgot to mention that the door was in the open position when I did the test.

If there was any "suction" effect, I should have been able to detect

an upward breeze just under the "Whirlybird".

I had two on a shed 9M x 3M

In any case I would never bother with them again.

They are more of a gimmick than an effective ventilator.

It's a pity they didn't put a fan blade on the bottom end of the shaft.

That would have actually pulled the air upward, the same way as an electric exhaust fan,

although no where near as effectively, because the revs needed would be 1000's of rpm.

A hole in the roof would be just as effective except that the "Whirlybird" stops the rain getting in.