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Windshield/Windscreen Drafts/Draughts in 2.5

Discussion in 'Roadster' started by Slackjaw, Nov 17, 2011.

  1. Slackjaw

    Slackjaw Member

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    I've noticed that above approx 50 mph I get a steady flow of cold air from the vents at the base of the windscreen. This is with the Heating/AC off and the dashboard vents closed. It doesn't seem to matter if I have the "circulate internal air" mode active. It is most noticeable as the outside temp [according to the car] approaches 40 F or below.

    Is this a fault, or a known problem? Can it be fixed other than by stuffing socks into the vents?

    My drive is a minimum of 125 miles per day, which means I use about 150 ideal miles because I'm on the NJ Turnpike at 70+ mph. For my own confidence level I'd probably start charging in Range mode if I had to run the heater on max for the whole drive as I've found that costs me approx 25 ideal miles per round trip... And I really don't want to have to charge in Range every day. I'm more likely to start driving in a hat, scarf and gloves, then I won't look so impressive when people pull alongside to wave and give a thumbs up (as happens almost every trip!). Any advice appreciated... Thanks!

    [I've searched for this topic but not found any good matches; please redirect/move if I missed something.]
     
  2. Dragon

    Dragon Lightning Green Fairytale

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    That is normal on my car too. It helps a bit directing the air blow to the feet.
     
  3. Slackjaw

    Slackjaw Member

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    Just to be clear, this is still true with the fan set to "0"? I'll try that, then the socks. ... Thanks
     
  4. Dragon

    Dragon Lightning Green Fairytale

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    Jep, still true with the fan to 0.
     
  5. NigelM

    NigelM Recovering Member

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    Checked it out on my 2.5 today. With the fan set to "0" and the air direction set on the passenger cabin, there is a very light air flow; when I closed the vents I don't feel anything. With the air diverted to the windscreen, I do feel a light air flow when I put my fingers over there but fortunately we don't have the cold temperatures to bother us (it's a cool 78F today). I didn't feel anything when the car is still so it's probably something to do with the air pushing past the fans when the car is moving.
     
  6. strider

    strider Active Member

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    Many of my cars have done this - especially the ones w/ manual HVAC controls. Even with the fan at 0 you get a "ram air effect" where air is being pushed into the cabin from the outside. You could even adjust the temp of this air via the temp control. You shouldn't need to run the heater at max - just try running it w/ the temp in the middle and fan at 1.
     
  7. Slackjaw

    Slackjaw Member

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    OK... Thanks for the feedback. I'll experiment on the way home today. It's colder than it was this morning so I may still have to choose between being warm and being fast! Tough choice.
     
  8. Doug_G

    Doug_G Lead Moderator

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    The Roadster won't run the heater at max if the fan is at 1, even if you turn the dial all the way up. It limits the heater current based on the fan setting.
     
  9. Doug_G

    Doug_G Lead Moderator

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    Use the seat heater instead. It takes a lot less power than the cabin heat.
     
  10. hcsharp

    hcsharp Active Member

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    That's not consistent with my heater usage. I find if I use recirculate the heater will only use a lot of power for the first couple of minutes, then it drops to about 1 amp and the impact on a long drive is very small. Rain will impact your range much more than the heater.

    Like Dragon I also find that directing the air to the feet will slow the draft from the vents. According to the owners manual about 10% of the air comes from the outside even with recirculate set.
     
  11. Slackjaw

    Slackjaw Member

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    OK... Well, I tried all of the above (redirecting to feet, fan set to 1, heat on max, recirculate ON) and it was a lot more comfortable on the way home; not toasty but OK. Speed was about the same [probably a bit slower on the homeward leg because the trip back is in the dark], but I used an additional 2.15 kWh coming home:

    Trip out: 16.94 kWh net energy, 60.3 miles ==> 280.9 Wh/mile
    Trip back: 19.09 kWh net energy, 61.7 miles ==> 309.4 Wh/mile

    I also know these numbers can vary a lot based upon weather, traffic, etc., but if 1 ideal mile is approx 221 Wh (assuming 53 kWh = 240 miles?) then using the heater on the whole trip would have cost me in the region of 5 kWh which is 20+ ideal miles, roughly in line with my previous ballpark figure of 25.

    Maybe this doesn't apply so much at high speeds? I'm basically on cruise control at 70 mph for approx 51 miles of this 61 mile trip.

    Thanks again for the input. I'll still plan that if I want the heating on for my whole (2.5 hrs, 121 real miles) daily round trip, I need to budget 25 ideal miles of juice, or maybe it's as simple as saying 10 ideal miles per hour driven under these conditions. Luckily I can still do that trip in Standard mode if I don't mind getting Power Limit a few miles from home. It doesn't scare me as much as it used to...
     
  12. doug

    doug Administrator / Head Moderator

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    Perhaps this is obvious, but if you cruised at 65 mph instead of 70 mph for that 51 miles, you'd save about 14% of the energy (20% of the power) that you lose to wind resistance while only adding about 3 minutes to your travel time.
     
  13. Slackjaw

    Slackjaw Member

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    Yeah... 65 is about the slowest you can possibly go on this stretch of the NJ Turnpike. I try to keep it on the slow side but I can only allow so many Priuses to pass me before I have to do me some educatin'. You should see them all - I'm pretty sure there's a thread on some Prius forum somewhere where all these guys laugh about how they "blew past this little black Tesla on I-95".

    On a related note, I was giving someone a ride & drive in the Roadster a few weeks ago and we were talking about how to save energy/increase range when driving. I said something about the power cost to overcome air resistance scaling as the cube of the speed and after a short pause (just long enough for me to regret my remark) she said "Woah. You'd think Tesla could do better than that...". :biggrin:
     
  14. VolkerP

    VolkerP EU Model S P-37

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    Well, fools help tell the truth. With Model S Cd~.22 surely they do better but they can't beat v cube. Or can they? That would require Cd to decrease with v - the air suspension should help here.
    Conclusion: Tesla did better, much better than any other car maker. There's still some room left for improvement:
    - cover body panels with "shark skin"
    - hide wheels with skirts that deploy at higher speeds
    - get rid of these side mirrors
    - deploy aerodynamic tail
    - any other change of vehicle geometry that can be performed safely at higher speeds but is impractical in city traffic
     

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