Tuesday, 31 October 2006

Climate Control

The weather is being peculiar. Here at the end of October, it’s been ludicrously warm, interspersed with high winds and lashing rain. All of which conspires to give me a problem: windscreen fogging. The warmth means that as soon as it rains, and the outside temperature plummets, the residual warm air in the car (and this is with the heater on cool) hits the cold glass and - POW! - instant loss of visibility. Usual response - to put the blower on the windscreen - fails miserably, only causing more fogging. I try turning the heat up, as I do in winter - it just gets worse.

I try to approach this logically.

Fogging is caused by condensation - warm, moisture laden air passing over a cold surface, the water condenses out onto the surface. It’s meteorological.

I need to equalise the temperature somehow.
To clear the rear window, you put the inbuilt heating element on - this heats up the glass and stops the condensation. Heating up the windscreen - by using the hot air blower - does not have the same effect. It doesn’t prevent the condensation, it makes it worse, except for a thin strip at the bottom, which clears a bit. Hmmm. OK - so there’s even more moisture in the air now, with it being warmer. (And I’m melting…) So I need to take the moisture out of the air - dry it out. I stick on the air conditioning and the air recycling, whizzing the moist warm air through the drier, in effect, and not letting any new damp stuff in. This isn’t very effective, but does reach halfway up the windscreen. Something is working, I’m just not sure what.

SO - if heating up the screen fails, try the opposite! Cool the air down.

Turn down the heater, and blow cold air across the screen. This still fails to give me visibility. Take it down a notch - I stick on the air conditioning, turn up the blower, and wheee! The screen clears almost immediately. I freeze, but I can now see where I’m going.

So the answer, at least in warm-ish weather, is to cool down the air that’s actually hitting the windscreen - effectively putting a thin layer of icy air between the screen and the moist air. Now that’s quite logical, but given the meteorology involved, it leaves me with one question. When the moist warm air hits the icy layer, why doesn’t it condense out? My guess is that the cold air is moving too much - but I still wanna know - why aren’t there clouds forming just above my head?

Vehiculonimbus!

7 comments:

mackie said...

"why aren’t there clouds forming just above my head?"

there aren't??? how disappointing. :-P

this really makes me glad i am usually riding a bike :-D

LOL :smooch:

Anonymous said...

Mad, this made me think of a character in the old cartoon who had a permanent rain cloud above his head. LOL!

Do you have a air intake with a inside/outside air option? Sometimes just having it on "inside" helps.
There is also a product you can get to spray on your windsheild that is SUPPOSED to prevent fogging up.

Be careful out there! :-)

Jude

GfM said...

It's your car. Mine does not do that :p hehe, no really, I have no idea why this happens, usually it happens when I drive into an underground parking. But frantic windshield wiping and turning on the aircon to full blow onto the windshield usually does the trick.
I wish I had your enquiring mind, I just look at stuff like this and go: huh.

Tats said...

You're obviously a weather goddess with your own personal weather system, m'dear!

Another thought - is your car unusually moist for some reason? Not casting any aspersions of a personal nature (honest!), I'm just remembering that my old car got this problem after I ferried a lot of trees around, and the moisture got into the upholstry.

Mackie - the bike works, but I then have Mad's problem with my glasses when I walk into a warm building. Hard to look cool with fogged specs.

Sue D said...

Mad - you should be a cartoon character!

I was just thinking that...alas...my car does not have air-conditioning, but then realised in a way it does...because it must be the same effect as when I just put the windows down...making the inside the same temperature as the outside; with added advantage of even if windows still misty, can see out of side window.

My chap's new car has a heated front windscreen as well as rear; very handy to see and not freeze.

Just wondering if the moisture is being stored by your car and when it gets really cold, will it snow inside?

mad said...

I suspect it may be partially caused by hot flushes :blush: which fog out the car every so often (Tats can vouch for this! - remember the taxi?) Weather goddess? - too much Douglas Adams, me dear!!!

I probably am a cartoon character somewhere, Sue! And I can just see the snowfall.... must draw that, maybe!

mackie said...

"Mackie - the bike works, but I then have Mad's problem with my glasses when I walk into a warm building. Hard to look cool with fogged specs."

Tats, i am at a point where i realise that i will have to wear glasses or lenses soon, and i do NOT like the idea. örgs.

of course Mad is a weather goddess. there can't be any doubt about it, and since mosts gods have made it into comics, she certainly is a cartoon, too. :-P