Comments on: Defogging Your Car Windshield with Psychrometrics

By: Andrew Lane

Andrew Lane — Sun, 03 Mar 2019 06:41:05 +0000

In reply to chris. Indeed Chris...currently I
Indeed Chris...currently I get my electrons from the Grid which is infinitely more efficient than burning anything under the hood! The sheer size of the Grid Generation clearly makes anything one does under the hood quite small and horribly inefficient in comparison! Indeed with EVs that have HVACed Batteries there is also no silly sad messy maintenance with which to contend. Ahhh and with EVs many Car Dealerships give away free fuel some even 24/7 as electricity is so cheap some folks just give it away. Ohhh and when was the last time someone spilled electricity in the Gulf of Mexico, Alaska, or the Kalamazoo River in Michigan? Of course EVs are the only cars that get more efficient as they get cleaner as the Grid gets cleaner! Hmmmm oil burning cars seem to get worse with age!

By: chris

chris — Wed, 27 Feb 2019 16:16:09 +0000

In reply to Andrew Lane aka Captain PLaneT. Andrew Lane, where do you get
Andrew Lane, where do you get your electrons from? PVs or Dinos? There is no escaping it, if we burn energy outside of independent alternative generation, we are using fossil fuels. Possibly more efficiently but fossil fuels nonetheless. And if your utility is hydro power, additional load usually consumes electrons that would be exported on the grid to displace the most carbon rich generation elsewhere.

By: Andrew Lane aka Captain PLaneT

Andrew Lane aka Captain PLaneT — Wed, 27 Feb 2019 14:17:03 +0000

Ahhh Good and Honorable Folks
Ahhh Good and Honorable Folks,

As the driver of EVs now for 6 years(done with petroleum fur the sake of Global Warming and National Security…Hmmmm last year we got 11% of our Oil from Saudi)…I really like the crack the two front windows a bit(in Georgia) to allow the outside air and the just inside the windshield air be one the same? Using the HVAC in EVs visually penalizes the range per Charge. Adding the wind deflectors seems like a good idea to get that outside air inside and keep the rain out!

By: JC

JC — Tue, 22 Jan 2019 16:26:10 +0000

Excellent. I can't tell you
Excellent. I can't tell you how many people I see this time of year driving with fogged up windows. It's amazing that this isn't common knowledge.

By: Leigha Dickens

Leigha Dickens — Tue, 22 Jan 2019 13:48:43 +0000

I was once intrigued by a
I was once intrigued by a separate mystery of car windshield physics, whose answer came to me as I starting thinking about building science more regularly. I used to wonder why on some cold winter mornings one of our family cars would have ice on the windshield but the other car windshield would be dry, when both are parked next to each other and conditions seem mostly the same. The way our driveway is set up, the one that does not have ice in these situations is parked in front of our house, the one that does have ice is parked in front of our yard. I've now realized that the windshield of the car in front of our house must be partially shielded from the cold night sky, as our driveway is on a hill and the silhouette of the house looms above and roughly normal to the angle of the windshield. Thus, that windshield experiences less radiative heat loss and does not get quite as cold as the windshield of the car with only open sky in front of it, which in some conditions can mean the difference between condensation or not.

By: Mac Sheldon

Mac Sheldon — Sun, 20 Jan 2019 21:58:21 +0000

In reply to abailes. Yep, I cite your article
Yep, I cite your article frequently, and agree that the video is generally useful and hopefully sparks curiosity in your readers. Yours is the most valuable blog in cyberspace and deserves to be shared with all who enjoy learning about the way our world around us really works.

By: abailes

abailes — Sun, 20 Jan 2019 14:54:17 +0000

In reply to Mac Sheldon. Thanks, Mac. We're

Thanks, Mac. We're definitely on the same page regarding air's inability to hold water vapor. I wrote about this a few years ago in an article titled, Are You Making This Mistake With Humidity? (That article annoyed a couple of readers, who accused me of obfuscation because I tried to make the case using condensation on grass, but my larger point was still valid.) In the article here, I did talk about air with relative humidity but was careful not to associate any holding capacity with the air. And I wrote, "The amount of water in the vapor phase depends on temperature and availability of water." As you say, the dry air components have nothing to do with how much water goes into the vapor phase.

And yeah, Rober didn't really explain why the AC setting helps. Still, I thought it was a good video for general audiences.

By: DCE

DCE — Sat, 19 Jan 2019 16:56:19 +0000

Most vehicles sold in the USA
Most vehicles sold in the USA since the late ’80s automatically turn on the AC when you turn on the defrost setting – EXCEPT when the air temps go below a certain pre-set (varies between makes/models but is typically just above freezing). The problem with turning on the AC is that the conditioned air only goes through the passenger face/foot vents – which is fine for dehumidification but can preclude the defrost air blast on the inside of the windshield as these functions are sometimes connected to each other. A stop-gap solution if this is a great issue is to have an auxiliary fan plugged into a 12V outlet and directed to the windshield (maybe by sitting on the dash). Now when you change the passenger settings the cabin air can be directed to the windshield instead of trying to get the OEM controls to cooperate.

By: dta

dta — Fri, 18 Jan 2019 20:19:12 +0000

Whether or not it indicates
Whether or not it indicates it, every car I've owned built since the late '90s turns on the AC when on defrost. And by the way, if it's cold enough for condensation, PLEASE let your car warm up for a minute or two before turning the AC on. AC parasitic loads can be as much as 10%, and the last thing your cold engine needs is more load. Besides, you won't get any heat until your engine comes up to temperature and starts circulating warm water into the heater core.

By: Richard

Richard — Fri, 18 Jan 2019 19:51:30 +0000

In reply to RoyC. Here in the UK we have cold
Here in the UK we have cold damp days and rain at 4c. This calls for the air con compressor to be running. Modern cars however disable the compressor below 5c. Ford do this on my car and their response is you don't need air con when it's cold! For demisting you do.