Thread: Get a roof extractor fan!

Originally Posted by peterpan

I am an engineer LD, by nature an arrogant breed, but I have spent the best part of 30 years designing Heat transfer equipment, air handling equipment and working with thermodynamics

your just the bloke 'im looking for..I would appreciate any advice on the following..
1.QCON blocks and panels as good as the hype
2.Thermal properties of a flat concrete roof
3.Large upstairs room with plenty of through draft 3.4 mtr celing with fan...any need for electric extractor fans close to celing?
cheers

Ok Peterpan, am I wasting my time or is there a better way of cooling my house in Bangkok?

Depends HB on how hot yr house gets, mine has only doors and windows for ventilation and normally will be 2 to 3 Deg C above ambient. Due to a quite favorable orientation, thats low and there would be little I could do to lower the internal temp other than AC.


A wind vent will get rid of some internal heat, but the biggest contributor to house heat is the thermal mass in concrete walls etc. So for a very poorly ventilated house in an area that has regular winds speeds of say above 3 m/s they will provide some extraction but if you regularly get those sort of wind velocities, you get sufficient ventilation just with normal, windows open.
My view as that in the tropics they are a waste of time, maybe for ventilation the above ceiling area, but effective insulation to inhibit ceiling radiation would be far more effective.

Well as someone who is invovled in very big systems (I used to specialise in Hospital operating Theatres of the Ultra Clean Type) my knowledge of them is limited to the fact that I would never consider one in any way shape or form. As I said, you may get some relief, but it needs to be driven by a breeze, the airflow from rising air will not produce the sort of velocities to turn the blades. They also offer no cooling per se, so I consider them pointless for the reasons peterpan has listed.

A lot of buildings in the UK are using passive cooling methods these days, which is cooling the concrete at night, concrete has some interesting thermal properties, but my knowledge of those practices is limited as I haven't done a building of that type only attended seminars etc. I am now out of onsulting and have been for several years at this time. But the practice is to get your structure as cool as possible at night so as to radiate coolth during the day time. Probably not much chance of that working in Thailand....555.

OK, since my interior house temperature, without air con and with windows open, is rarely more than a degree or two above ambient, it seems to make no sense for me to add a turbine fan or other attic ventilation.

Thanks. Saves me some trouble....

So you guys know ALL about ventilation and cooling do you?

Well, all I can say is that my Fan WORKS! The house is definitely cooler now.

And I consider it well worth the 2200bht........

An electrical fan would be better when the winds are low, is true, but mostly where I live, that is only about 20% of the time. Even then the blades revolve quite well, and the very fact that there is a hole in the roof for heat to rise out of is beneficial.....The proof of the pudding, my friends , is in the eating!

^I'd still like to see indoor/outdoor temperature comparisons....

Originally Posted by Bruce

And I've seen them spinning on windless days.

No you haven't.

Just because there isn't any noticeable wind at ground level doesn't mean there isn't any at roof level.

Originally Posted by Bobcock

If you say so...

answer me this though....

If the air you want to move is what is making the 'fan' move, what is the point of that fan????

The job of a fan is to move air from A to B.

If the hot air in A is moving to B on it's own and driving a fan what is the point of the fan??

Clear now?

I suppose the fan is there because if you just put a hole then the rain would come in. Even if it was covered birds etc might get in. There is more wind higher up, so they may work better than just a hole

Also it spins, which looks good. They are probably worth the money as I can't think of a cheaper alternative, but I think there are better ways to ventilate your roof if you were building a new place.

They are popular is Aust, but there's plenty of wind there. If you really want to check on the effectiveness there is probably some Australian research that has the answer.

Originally Posted by Smithson

Also it spins, which looks good.

Yes, so you can look at it and tell yourself "Holy cow, that was a good investment, I can see now how much hot air it is pumping out of my attic" .
And your neighbors will see it, will think "that's a fantastic thing", and then buy one..

Originally Posted by lom

Originally Posted by Smithson

Also it spins, which looks good.

Yes, so you can look at it and tell yourself "Holy cow, that was a good investment, I can see now how much hot air it is pumping out of my attic" .
And your neighbors will see it, will think "that's a fantastic thing", and then buy one..

Impressing friends and neighbors is a big factor when building. If this can be done for 2K+ then it's a good investment.

Iom

I don't have to, that is not my statement, despite you crediting it to me.

^ Quote corrected, sorry

Smithson.

A louvred vent would do the same job in a NO WIND condition. In fact it would do a better job in a NO WIND condition (less resistance to air flow)

As I have said, these will work better in windy conditions than a straight vent, what we are disagreeing with is luckydogs nonsense that in a NO WIND condition his fan is happily spinning away sucking out warm air, which is wrong on two counts.

1. The air flow created by warm air rising is not strong enough to drive this, it is outside wind.
2. If the warm air is driving the fan, then what is the point of the fan? A fan is there to move air NOT vice versa.

It doesn't even need HVAC knowledge to understand this, just common sense.

The reason its better with the ventilator is that without the ventilator the hot air can't escape, but with the ventilator the air can find a path out, so that creates an air current as the hot air rises.
I can look out the first floor back window of my Thai townhouse down onto the roof of the kitchen below, which is between two rows of townhouses so there is little wind movement, and see the ventilator spinning below me, but there is no breeze coming in my first floor window above it.
Its not about whether roof insulation is better than a ventilator. I support both.
Still, if you're happy being hot, stay sceptical.

You are still saying that the air is driving the fan.....what is the point of the fan then?

Louvred upstand, less resistance will perform better in the conditions you say.

Louvres are also good. The ventilator is up high in the roof so empties the hot air out of the roof which is good.

Originally Posted by Bobcock

Smithson.

A louvred vent would do the same job in a NO WIND condition. In fact it would do a better job in a NO WIND condition (less resistance to air flow)

I understand I was only joking.

Originally Posted by Bruce

Louvres are also good. The ventilator is up high in the roof so empties the hot air out of the roof which is good.

You tell 'em Brucey baby. I am bored with all their stupid theoretical utterings.
WE know it works. THEY do not! So WHO BLUDDY WELL CARES?

Cool, over the last week, I too have noticed a 5 degree drop in temperature in my house and I didn't even bother installing an extractor fan.

stupid theoretical utterings

The voice of a Pattaya bar owner.....55555555