Solutions for windshield fogging in cold weather?

[tigger19687]

Passed by a Tesla this morning, 19 degrees out but have no idea about humidity .... I looked over to see the driver but I couldn't ................ his window was all fogged up !!

HAHAHAHHAHA Guess it isn't just us, or he is a hot guy

The 'i' was clear. Course I was driving with the heat on the windshield on medium blower. It used up my battery badly so I normally don't do that.

I do NOT have a remote for the car..

 

[PV1]

That's impressive ... What do you do to stay warm (especially your feet)?

Winter coat and Thinsulate gloves. I preheat the car for 30 minutes, so it is usually warm enough to last the 10 miles to work. My shoes are surprisingly decent at keeping in the heat. I'm still cold when I get to work, but I figure that going from a heated house to a heated office building, I can bear 20 minutes of cold. Willingly driving without heat unless necessary helps curb the shock when driving longer distances where the decision between a cold ride and a cold walk is mandatory . That behavior has also prompted endless jokes about not taking the i-MiEV because "it doesn't have heat" :roll: . You take your first 60-mile trip to the city on the third day you own the car and a precedent is set :lol: :roll: .

Heated seat is a must.

 

[jray3]

Though I can't imagine many places with lower humidity than ABQ. ;-p

Normally I would agree with you. But ... No offense meant, but good advice should not be undermined by flip, out of context, remarks.
Aerowhatt

Sorry to be flippant Aero. I spent Christmas skiing north of you in Durango. It felt like my parched amphibian skin would split open, but the chapped lips have finally healed.

I'm not a refrigeration engineer, but here's a psychrometric chart that'll get us pretty close.
http://www.coolerado.com/pdfs/Psychrmtrcs/5000Psychrmtrc11x17.pdf

Since mountains are in our mix, I picked 5000' altitude and saturated air at 50 degrees F (both wet bulb and dry bulb), for an enthalpy of 22.
To achieve comfort and defogging, if we want to hit 69 degrees dry bulb and 50% relative humidity, that's an enthalpy of 27, delta of 5 btu/lb of air and a wet bulb of 58 degrees, smack dab in the middle of the winter comfort zone.

However, if we first cool the air from 50 to 40 degrees dry bulb, that's an enthalpy of 16, delta 6 (down from 22). Assigning a conservative performance coefficient of only 1.5 to the ac compressor brings our change in enthalpy down to 4 btu/lb. (Automotive HVAC COP from http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1734&context=iracc)
Then raise the dehumidified air to 69 degrees and it brings the enthalpy to 17 with a relative humidity of less than 10%. So the net change in enthalpy is 4+1=5 btu per pound of air for ac then heat, making very dry air that will dry the windshield quickly.

Moral of the story: moderate heating alone will suffice for defogging, but using the air conditioner will dry things out more quickly for no more energy.

At 98 cubic feet of interior volume, the iMiEV contains under 7.3 lbs of air, so a full turnover of the cabin would take 36.5 btu in the above example. On the bright side, we could "condition the cabin" 27 times for one kWh (excluding fan consumption and mechanical losses).

Using an ASHRAE average ventilation rate of 10 cfm per person, our little four-seater should get 40 cubic feet per minute of fresh air to keep the occupants fresh. i haven't found flow figures for our blower yet....

 

[kiev]

...
I do NOT have a remote for the car..

wonder if you can track down the previous owner and see if they have it sitting around.

or, go to ready mode with the ignition key while still plugged in/charging with the EVSE and turn on the defroster/heater--will this work similar to what the remote does?
----------------
edit: well i went and tried this and it doesn't seem to work--for one thing it won't go to ready mode, although it does go to 'ON' and the blower fan will operate, but i'm not sure that the water heater was actually heating. Need to do a longer duration test of this...

 

[jsantala]

No, it doesn't run the electric heater while charging, unless you have the remote to turn it on. With the french versions there is no remote, so we're stuck with no heat during charging. Unless one has a fuel heater installed, since it will still blow air thru the heat exchanger and the fuel heater has it's own water pump (at least mine does).

Sadly my fuel heater's fuel pump crapped out right now that we have toasty -25˚C mornings on end.

 

[Aerowhatt]

Sorry to be flippant Aero. I spent Christmas skiing north of you in Durango. It felt like my parched amphibian skin would split open, but the chapped lips have finally healed.

One of my favorite haunts used to be Purgatory Ski area. Much more fitting name than it's current Durango Mountain moniker IMO.

I'm not a refrigeration engineer either. Just a Physics major (the science of engineering). I'm fairly certain that no one here cares about the humidity discussion in detailed scientific terms. They just want repeatable good results. Just a couple of points then my end of it rests.

1. The tables and graphs are apples and oranges compared with the systems working in our cars. Many factors, but just a couple for examples.

1. The AC coil in a vehicle is very small which leads to reintroduction of significant amounts of moisture to the airflow condensed on it as air recirculation continues.

2. Occupants add significant humidity to the mix breathing etc.

3. Refrigeration units suffer considerable stress when operating in a very cold environment (it's not what they are optimized for).

That said, something PV1 said got me wondering about how the system actually works. It does indeed have a damper that is actuated by the temperature selection. They thought it prudent to have the air flow bypass the heating coil when in the selector is in cool (down of the green dot). However in any mode the airflow still passes through the AC coil. So it's, filter first, then AC coil and then heating coil only if the selector is in heat mode.

With the heat on, one can use the AC to precondition the air before it gets heated. Mistu was pretty smart about how this whole system works. When making a selection all you are doing is telling the software what you want, or think you want. Then it decides what settings to actually implement to deliver the perceived desired result. I was able to find a couple of combinations that result in less than optimal adjustments by the software. But overall it is a very good and comprehensive system. Bottom line, if you simply can't get adequate results with defogging windows with the NON AC strategies, given previously by me and others, then just turn the dial to the defrost only mode. (Full right on the airflow selector) The system will turn on the AC in a limited way, for you.

Does it use more or less power to defrost with or without AC? That is a question that can only be answered for a specific set of conditions. Under most of them it will use more. There are also cases where it would use less. So do what works for you and get it off the full defrost setting as soon as conditions allow.

Canion fans can track all three usages, side by side, to see how things are working out AC/heater/summary(which of course includes all usage).

Interesting side note:
When you adjust the temperature controls in an ICE you adjust how much fresh cool outside air and how much is heated by the relatively stable temperature of the heater coil. Cooler settings more outside air less hot air and vice versa.

The 'i' controls the hot air temperature by controlling the water temperature (not by mixing hot and cold air). The very logistics of the system insures that an ICE will defog somewhat more easily than the 'i' will.

Aerowhatt

 

[jray3]

.... how the system actually works. It does indeed have a damper that is actuated by the temperature selection. They thought it prudent to have the air flow bypass the heating coil when in the selector is in cool (down of the green dot). However in any mode the airflow still passes through the AC coil. So it's, filter first, then AC coil and then heating coil only if the selector is in heat mode. .....
The 'i' controls the hot air temperature by controlling the water temperature (not by mixing hot and cold air). The very logistics of the system insures that an ICE will defog somewhat more easily than the 'i' will.

Aerowhatt

Thanks A.- it's a good discovery that the system is routed and controlled differently than most ICE hvac, and that manual control could be counterproductive. My takeaway is to not fight the factory programming.

but... has anyone identified the main exit points for cabin air? I'm wondering if one could set it to exhaust from the floor in winter, and from a higher point in summer (other than driving with the windows cracked). Using natural stratification could help in both seasons.

 

[PV1]

The cabin vents are located underneath the taillights. Inside, these are behind the slots in the C pillars.

I guess I need to research our HVAC system some more.

 

[Aerowhatt]

I guess I need to research our HVAC system some more.

Some things I observed seem a bit quirky. For instance when you have the fan running, temp on green dot, fresh air selected. Then you move the temp selector to cool. Of course the AC comes on but also the fresh air/recirculate "hood" (for lack of a better term) behind the glove box changes positions. Opening up part way to make part (perhaps as much as half) of the feed air into the blower to come from the cabin (partial recirculated).

Same thing happens if you have the flow set to any combination of floor and defrost. Temp in the heating position, set on fresh air and you manually push the AC button. This seems counter productive to me if windows are fogging already?

Aerowhatt

 

[PV1]

I've noticed that. It would be helpful to do the opposite, mix part fresh with mostly recirculated air.

 

[PV1]

I've experimented with running heat and AC at the same time, but I'm not convinced that the AC runs at all, let alone making any difference. Also, I don't believe that the ductwork allows mixing heat and AC.

I stand corrected. Air does flow through the AC coil regardless of the temperature knob. The airflow damper only directs air toward or away from the heater core.

It took some patience, but I managed to get my AC compressor to run enough to tell how the air flowed. It doesn't like to run in cold weather.

I still wish that the recirculator could be set for a mix of fresh and cabin air.

 

[Aerowhatt]

I've experimented with running heat and AC at the same time, but I'm not convinced that the AC runs at all, let alone making any difference. Also, I don't believe that the ductwork allows mixing heat and AC.

I stand corrected. Air does flow through the AC coil regardless of the temperature knob. The airflow damper only directs air toward or away from the heater core.

It took some patience, but I managed to get my AC compressor to run enough to tell how the air flowed. It doesn't like to run in cold weather.

I still wish that the recirculator could be set for a mix of fresh and cabin air.

I still have my Jeep Comanche PU I bought in 1985 (86 model year). I miss the old manual controls. Everything run by cables. Infinite heat/cool mixture settings. Infinite fresh/recirculate settings. Straight forward and they all still work smoothly and easily 31 hard years later. How many of these new servo actuated computer controlled dampers will still function as intended 30 years from now?? Don't get me started on the difference in costs.

Aerowhatt

 

[haviton]

Hi everyone, ive had my citroen c-zero for a year now, and love it! and I have created my own solution for keeping the windscreen clear all the time, without having any effect on the range at all. if anyone is still monitoring this thread I will share my solution with pictures. So let me know if anyone is interested.

 

[PV1]

Yes, please.

 

[FrostyCanada]

Yes

 

[acensor]

Hi everyone, ive had my citroen c-zero for a year now, and love it! and I have created my own solution for keeping the windscreen clear all the time, without having any effect on the range at all. if anyone is still monitoring this thread I will share my solution with pictures. So let me know if anyone is interested.

Hi!

I'm still interested.

What did you come up eith?

Alex