Roof Ventilator

[chownah]

xerostar,

I wonder why your experience with them is so different from everyone else. Do you think that perhaps there is a company that makes these things to a bad design that doesn't work? It's just about the only explanation I can think of to explain why they seem to work for everyone else but your experience was so bad.

chownah

[Swelters]

xerostar,

I wonder why your experience with them is so different from everyone else. Do you think that perhaps there is a company that makes these things to a bad design that doesn't work? It's just about the only explanation I can think of to explain why they seem to work for everyone else but your experience was so bad.

chownah

Well, sure they work--like Doctor Johnson's dog, walking on its hind legs --"it's not that he does it so well, it's that he does it at all."

The manufacturers' say that they need 5 mph to start working. Note the wind speed in downtown BKK, illustration attached. Also figure the likely 20 cubic meters per minute even when they do work, compared to the recommended one air change per minute for effective ventilation. I think you'll just open the window instead.

[chownah]

xerostar,

I wonder why your experience with them is so different from everyone else. Do you think that perhaps there is a company that makes these things to a bad design that doesn't work? It's just about the only explanation I can think of to explain why they seem to work for everyone else but your experience was so bad.

chownah

Well, sure they work--like Doctor Johnson's dog, walking on its hind legs --"it's not that he does it so well, it's that he does it at all."

The manufacturers' say that they need 5 mph to start working. Note the wind speed in downtown BKK, illustration attached. Also figure the likely 20 cubic meters per minute even when they do work, compared to the recommended one air change per minute for effective ventilation. I think you'll just open the window instead.

Does this conflict with the information you posted in post #24...about the 70 cubic metre per minute 20 inch turbovent?

Chownah

[Swelters]

Does this conflict with the information you posted in post #24...about the 70 cubic metre per minute 20 inch turbovent?

Chownah

Chownah:

I think that was for 15 km/hr wind which rarely occurs as indicated on the figure. I figure that you'd be lucky to get the 20 cm/min with 8 km/hr win. 20 cm/min would at best change the air in a 10mx10mx3m space every 15 min which allows a lot of heat transfer to the air. One air change per minute is the goal for ventilative cooling.

You're going to want the ventilation usually in the late afternoon, you may not have any wind --or any ventilation--then.

I think you worked out some numbers for flow velocity in the turbine, they were not a great deal more than wind velocity. Doesn't this imply that an open window or some cross ventilating louvered vents with say 0.5 sm area would create more air change than the 0.1 sm area turbine? Also, I don't think the velocity you came up with with would translate into much in the way of perceived air movement in the room, consistent with the sceptic's report.

But if the space were well insulated and completely sealed, heat flux into the interior space would be slow but inexorable. In that case any air change would be beneficial and the turbine might well be a big improvement (even though a few passive vents might do as well).

I've got some diurnal data on temperatures inside and around a traditional Thai house which I will post with commentary to the blog in the next day or two. Some interesting problems and possible solutions are apparent.

All of this may seem a bit technical for many readers, but the energy savings for reducing aircon dependence are amazingly high especially in Thailand, so sharpened knowledge (vs doctrines and rules of thumb imported from distant lands and completely different climates, where practices on such matters as vapor barriers should be completely reversed) should yield good dividends. I appreciate your contributions to this dialogue which I hope will produce some significant practical knowledge.

Swelters

Edited November 30, 2006 by Swelters

[chownah]

Well I'm not sure that your discussion is actually to the point raised by xerostar who wrote:

"..............

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. .............."

His description is that it was windy and the ventilator was revolving rapidly and that he got on a ladder and put his head and some tissue at the opening for the vent but there was absolutely no air movement. This seems like a situation that is not consistent with other people's experiences. I have never had one of these vents and don't know how effective they are but it does seem like most people have indicated that they do cause air to move. I could imagine that an improperly designed one could revolve without actually causing any suction.

I'm not advocating these devices but it seems that two advantages they have over a window is that they are on top of the roof where winds should be stronger and a window can capture wind in only certain directions while the ventilators should work for winds in any direction.

My house has a 2.5 square metre louvered vent opening at both ends and and a 15cm wide screened continuous vent on both sides under the eaves next to the wall running the full length of the house. It works ok but since I have no insulation anywhere in the attic space it still gets really hot up there whenever the sun shines.

Chownah

P.S. The chart you posted doesn't enlarge when I click on it....could you repost it or see if someone can fix it?.........Chownah

Edited November 30, 2006 by chownah

[Swelters]

My house has a 2.5 square metre louvered vent opening at both ends and and a 15cm wide screened continuous vent on both sides under the eaves next to the wall running the full length of the house. It works ok but since I have no insulation anywhere in the attic space it still gets really hot up there whenever the sun shines.

Chownah

P.S. The chart you posted doesn't enlarge when I click on it....could you repost it or see if someone can fix it?.........Chownah

I can see that you are really seeking some practical improvement for your house. Is there an afternoon breeze of 5 mph or more in your parts? Do you have a dropped ceiling so that there is a ventilated attic-like space between the room (I assume second story) and the roof? I take it that the roof is convertional cement tile and the ceiling is say some kind of half-inch-thick fiberboard material? Your roof is delivering a lot of power, maybe 100 watts per square metrer, to the air below. I'm going to set up a simple numerical model for the heat transfer which would allow for some simulation of this situation. Since you already have so much ventilation (but not enough to handle the big thermal load) I have to question whether the turbine increment would do anything at all. I would think that a few rolls of the standard glass insulation or comparable fluffy stuff would do wonders, cut the heat transfer by 90 percent, preferably stuck under the roof but on top of the dropped ceiling would be ok too. Foil, shiny side down, glued to the underside of the roof will cut the transfer by about 40 percent by eliminating the radiant transfer from roof to ceiling.

This is exactly the situation I had in a Bangkok office, it was intolerable. I solved it by suspending one of those black plastic nets (two layers) like they use in nurseries a meter above the roof because I couldn't easily get into or work in the "attic" space. Worked like a charm--in effect, an artificial tree --but would hardly be suitable for a house.

The chart you asked about is now posted at:

http://www.thaivisa.com/forum/blog/swelters/index.php?

Swelters

[chownah]

Actually I'm not urgently seeking practical improvement.....if I was I would just do it....the attic gets hot but the living space is liveable with just a fan in the hot spells. I see that we agree on the effectiveness of batt insulation....if/when I get around to installing some I'll probably put it right on the top surface of the ceiling and expect that will be sufficient....if not then I'll add some more under the roof but my experiences with fibre batts is that 4 inches or more of fibreglass batt right on the top surface of the ceiling should do just fine. Sometimes when its hot I use the back of my hand (it is more sensitive than the palm) to feel how hot the walls, ceiling, and floor are....I feel around the edges and in the middle sort of all over to see where the warmest areas are and the ceiling is by far the warmest spot and especially in certain areas so this back hand diagnostic is what I'll use to guide my insulation efforts.

Chownah

P.S. You seem to be heavily promoting your blog....what's up with that?

Chownah

Edited November 30, 2006 by chownah

[Swelters]

The manufacturers' say that they need 5 mph to start working. Note the wind speed in downtown BKK, illustration attached. Also figure the likely 20 cubic meters per minute even when they do work, compared to the recommended one air change per minute for effective ventilation. I think you'll just open the window instead.

Frustrated at the lack of performance data, I obsessively seached the web and found the following

for turbine vents. These are assorted manufacturers' claims.

diam inch, wind km/hr, capacity cm/min

6, 6, 3

6, 16, 8,

12, 8, 10

14, 24, 38

18, 6, 14

18, 16, 28

20, 6.4, 48

20, 15, 75

32, 6, 35

32, 16, 77

The turbine is about as efffective as an open cross ventiliating windows or wall vents of the same size.

Conclusion: for a big turbine, you can get 50-75 cubic meters per min exhaust if the wind is good. This is enough to change the air in a small bedroom every minute, which should suffice to keep the air in the room from heating much even in a room that is not insulated. But no wind, no air movement except for what I suspect is a small amount of exhaust due to the "stack effect."

But insulation, preferably some kind of fluffy stuff, is the less complicated and more reliable way to go.

Swelters

Edited December 9, 2006 by Swelters

[elkangorito]

Having previously worked as an antenna installer in Australia, I can certainly say that these "whirlies" are very effective.

My co-worker & I used to argue over who's turn it was to go in the roofspace on a hot summer day...unless we saw roof ventilators. On many occasions, we had to take turns of about 10 minutes each in an unventilated roofspace due to the extreme heat build up (60 to 80 degrees Celsius). But with roof ventilation (the wind assisted rotating kind) the temperature was markedly cooler & tolerable. In other words, they worked well.

They seemed to be very effective in roofspaces that had a vapour barrier under the roofing material & also ceiling insulation. But as another poster indicated, these ventilators won't work well if there is not an air intake into the roofspace.

I think they're a great idea & I would never pay to use an electric fan (plus the ongoing maintenance costs) to ventilate a space that can otherwise be easily, efficiently & naturally ventilated.

[RubbaJohnny]

Any recet advice

Am building now and see the aluminium unpowered whirlygigs around 1000baht

Plan to use foil insulation under tile on 20cm superblock walls

all tips gratefully received

Even you know more than my builders who are wearing 3 lkayers as I drip with sweat in C Rai

[jaideeguy]

3 yrs ago, I installed 2 of those round 'spinner' ventilators and can say that they do ventilate my roof and cool a little [every degree helps] and best of all, they are free to run and maintenance free [except to lubricate them occasionally...I haven't had to in 3 yrs, so must be good bearings] and my observation is that the hotter it gets, the faster they spin, which leads me to beleive that they are not controled by passing wind, but escaping hot air from attic.

and I would have to disagree to a previous post regarding insulation. foil type is best as it reflects the heat....simple test is just to hold a sheet of foil above your head on a sunny day and you will feel the difference. fiberglass sandwiched foil is best, but provides a good nesting place for birds, rats etc.......had to remove some once and it was a real mess to remove.

Just my experience....i'm no scientist

[pete_r]

my observation is that the hotter it gets, the faster they spin, which leads me to beleive that they are not controled by passing wind, but escaping hot air from attic.

Interesting and that may explain some glass pyramids I've noticed in Hanoi, installed under the "whirlies" (see example below): The glass could be there to raise the temperature of the air below the rotor. As the hot air goes up, it would increase the speed of the rotor and the extraction efficiency of the system.

[Naam]

my observation is that the hotter it gets, the faster they spin, which leads me to beleive that they are not controled by passing wind, but escaping hot air from attic.

Interesting and that may explain some glass pyramids I've noticed in Hanoi, installed under the "whirlies" (see example below): The glass could be there to raise the temperature of the air below the rotor. As the hot air goes up, it would increase the speed of the rotor and the extraction efficiency of the system.

fact is that without a breeze driving the rotating fan the airflow is hampered = less efficiency.

[londonthai]

glass is for getting light inside for the dark attic - roof ventilator should be at the highest point, where air is the hottest.

us to the 'sucking' of air - it exists in the chimney (the higher the chimney the more sucktion) due to the air pressure difference (higher pressure near the ground - lower pressure high above the roof). But placing ventilators very high above the roof would be impractical and ugly.

[jaideeguy]

The truth is that they never stop spinning....even during the winter months, the attic is always hotter than the house and heat rises....simple as that!!

Wind may play a part in increasing the effeciency, but just passive heat escaping thru the highest part of your roof will increase the speed accordingly.

Admittedly, they are not the most beautiful things to look at, but they do their job on the back side of my house where i don't have to look at them.

[mrsmith]

hi there is a company called atco www.atco.co.th that makes exactly what you want.they have different sizes. we are planing to put several on house in roi-et in sept

hope this helps. mr smith[/b]

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?

[mrsmith]

an additional note; these can be used with flat or angled roofs. they come with their own roof

panel-just replace one of your existing roof panels.[/b]

hi there is a company called atco www.atco.co.th that makes exactly what you want.they have different sizes. we are planing to put several on house in roi-et in sept

hope this helps. mr smith[/b]

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?

[longball53098]

Just viewed the ATCO site and if I see this correctly,,,,,,,,,,,,,,,,in the gallery all you see are commercial structures,,,,,,,,,,,,no residential roof,,,,,,,,,,,,,,,,,reason? Who wants one of these big, ugly things on their roof? Not me for sure,,,,,,,,,,,,,,,,,,there are better solutions out there.

[dotcom]

Atco say they are waterproof. I just have a hard time believing that. One a year we get rains that are just unbelievable. A few inches in an hour.

Having it in stainless would be excellent. My ceilings are plaster board & any kind of leak would be a disaster.

[DtemJai]

This working great in Isaan.

[DtemJai]

This works great for me in Isaan

[Kwasaki]

This works great for me in Isaan

A good proven old ancient system.