House too hot?

[PeTe33]

While trawling through endless pages and web-sites WRT ventilation etc, I stumbled across the following site which I found highly interesting.

Thought I'd pass it on

[Mary Fisher]

Mary

[Andy Champ]

Apparently not.

I'm amazed by how many people open their windows wide on a hot day, when the best thing to do is to shut all the windows and curtains until it gets dark.

Of course, leaving the windows open at night can be a security risk...

My grandparent's house in Brisbane was designed as first floor only - with a clear air path underneath, lifted away from the hot ground and wide verandahs to shade the windows. This was common practice before aircon was invented.

Andy

[David]

In article , Andy Champ writes

Why would the ground be hot? do they live in a volcanic area? better to insulate the roof

[Sam Nelson]

The almost-to-the ceiling `real Georgian' sash windows were designed to be opened bottom and top to expel warm air at the top and replace it with cooler air from below.

Australian houses are often built with a significant gap underneath them, as well as with other measures on the supports, to keep ground-crawling things of various unpleasantnesses out of the house.

[David]

In article , Sam Nelson writes

Yes, I know... but the hot ground??

[jacob]

It is possible that you really mean this, or are you being ironical?

[manatbandq]

It's even better to have the curtains on the outside (shutters) to stop the heat getting through the glass in the first place.

MBQ

[Mary Fisher]

Very difficult with bay windows ...

Mary

[jacob]

And get in bed with some thick pyjamas on - that'll keep the heat out!

[jacob]

And get in bed with some thick pyjamas on - that'll keep the heat out!

[Andy Champ]

Because the sun shines on it. For an extreme example, touch tarmac on a sunny day.

Andy

[Andy Champ]

I really mean it. Sunshine approximates to 1Kw/M^2. Work that out on your glass area. The curtains - especially if they have pale linings - reflect much of that out. When we had that hot spell the house stayed 5 degrees C below midday peak. This was helped by keeping an eye on the outside temperature, and opening all the windows and curtains upstairs as soon as outdoors temperature met indoor temperature. (but not downstairs - we don't live in *that* nice an area...)

Of course, as has been pointed out, shutters on the outside work even better.

Running a PC indoors can mess this all up of course, 500W all day adds up. My son's bedroom was usually hotter than outdoors!

Andy

[The Natural Philosopher]

But..the ground under the house doesn't get any sun shining on it....

[Weatherlawyer]

Closed glass edifices are called greenhouses colloquially. There is a reason for that.

Blue end spectra passes through glass but toward the red end it is reflected back into or out of the room. So once all the available sunlight is admitted in a closed room the radiation tends to stay in it untill conduction or convection removes it.

However, closing the curtains, along with helping you to miss out on the summer, will enable you to keep temps down a little. You may need to put the lighs on instead though.

[David]

The sun shines on it under a house? that's a clever trick unless its a glass house with no floor

[manatbandq]

I always thought it was the other way round. Blue end spectra is blocked (that's why you don't get a tan indoors from the UV) and red end gets through. The IR warms up the surfaces which then warm the room by conduction or convection. That's why closing curtains doesn't work as well as shutters on the outside. The curtains just warm up and then warm the air in the room through convection.

MBQ

[Bob Mannix]

No I believe Weatherlawyer is correct. Most of the UV comes through the glass, warms the contents of the room which then emit the heat via convection or infra-red which is trapped by the glass. The world acts the same way - if it didn't the atmosphere would be hotter higher up (nearer the heat source). Adiabatic cooling (colder higher) occurs because the UV from the sun hits the ground and is re-emitted as IR, which warms the air. Atmospheric conditions determine how much UV gets in and how much IR gets out - the "greeenhouse effect". In any case we are all correct in the end - shutters on the outside are definitely best!

Bob Mannix

[jacob]

Yebbut if you have air change and ventilation the inside air temp will be at least as high as outside except for short periods of catching up and the buffering effect of thermal mass. Inside temp will also increase due to heat generated within the house and solar gain from windows. If you have closed windows and no ventilation you are likely to die a slow death due to suffocation and severe overheating! Curtains will function as solar panels and will loose gained heat to the room - so making no difference overall. Would have local effect though of keeping sunlight from the immediate area but turning the heat gained into higher air temp. I think you have got it exactly wrong but I can see the logic - you could argue that wearing a woolly hat and gloves will keep the heat off your body - wrong, but a parasol will help. The french have the best answer - high ceilings, and windows fully opened inwards on hot days with the external louvred shutters closed on the outside - i.e. keeping sunlight out and allowing air circulation.

[Rob Summers]

I think (and certainly IME and a google-search agree)) most glass used in domestic situations blocks most UV. I burn very very easily in the sun but not when I'm sat behind the front-room window on a sunny day in the sun.

Rob