Ventilated Seat air movement test

[ernies]

Today I finally have my MX back and time to set up a digital manometer which measures in Pascals down to tenths of Pascals. I tested all three fan settings on the larger portion of the drivers seat. I am attaching a PDF with pictures showing the three fan settings and the pressure differentials at each speed.

The test results are 180 degrees at variance with what I expected. I think that the results I found will be indicative of all other seat ventilation systems installed. While the test was ONLY done on my car (twice with the same results), it is safe to say that all other seats will be the same. The main reason that you cannot "FEEL" air movement is that when suction is moving air away from your hand, the perception of air movement is not even close to what you would "FEEL" if the air movement were toward your hand.

 

[CaliX]

Can you add can feel it?

 

[ernies]

Can you add can feel it?

If someone can tell me how to change the "POLL" options, I will add it. I have never done a poll before.

 

[vandacca]

Thanks for going to the trouble of testing this. Is it at all possible that your fan wiring is reversed, which is causing the suction versus blowing??? Maybe it's like ceiling fans, you need to flip a switch to set the correct fan direction for cooling/heating.

 

[ernies]

Thanks for going to the trouble of testing this. Is it at all possible that your fan wiring is reversed, which is causing the suction versus blowing??? Maybe it's like ceiling fans, you need to flip a switch to set the correct fan direction for cooling/heating.

No, polarity will not change the direction of airflow. IMO. This is all DC electrical.

 

[Hengist]

That's a really really tiny pressure differential. .00113 psi

 

[Hengist]

Or 0.027 inches water column.

 

[ernies]

7.9 Pascals = 0.0317 WC". That is why HVAC engineers use Pascals as PSI is meaningless as it is too high a range and WC" is appropriate for more robust pressure needs.

 

[Dazureus]

Is there a consensus on the efficacy of cooling by pulling air or pushing? 7.9 pascals is a very slight breeze. I was test driving a vehicle this week that had seat cooling and it was actual A/C seat cooling, not just ventilated seats. While the seat did get cold independent of the cabin temperature, it was located strategically on the "bulls-eye" which felt weird. Cooling was lacking elsewhere on the seat and non-existent on the back. Maybe it's a difficult feature to implement.

 

[ernies]

Is there a consensus on the efficacy of cooling by pulling air or pushing? 7.9 pascals is a very slight breeze. I was test driving a vehicle this week that had seat cooling and it was actual A/C seat cooling, not just ventilated seats. While the seat did get cold independent of the cabin temperature, it was located strategically on the "bulls-eye" which felt weird. Cooling was lacking elsewhere on the seat and non-existent on the back. Maybe it's a difficult feature to implement.

If the skin feels air movement, and evaporation from said skin occurs, cooling is the result and resulting perception. Obviously if there is a cooling means such as a cooling coil, and the temperature of the supplied air under positive pressure is below that of surrounding ambient, that is felt as cooling. Positive pressure is how HVAC systems do it best.

Pressure differentials are only part of the equation, with temperature and CFM two other important factors. Under negative (suction) pressure, the ambient would be what it is and the only effect would be the removal of heat building up under the skin over the holes (to a limited degree [no pun intended]). In order to determine CFM you would have to factor in the total area of supplied air. Count the holes, measure the diameter and use the formula pi * r2. Multiply that times the number of holes and you have CFM.

If the skin starts blocking some holes then there will be a change of pressure and airflow out the remaining holes so this is a moving metric. Other restrictions are all the fibers and channels which direct or divert airflow. Anytime you ask any fluid whether water or air to change direction or you lengthen the channel it needs to travel, the velocity changes and the ultimate CFM changes.

Tesla no doubt did a pressure / airflow analysis and were limited by several factors including but not limited to cost and noise. The more airflow needed, the greater the power requirement and the more noise the fan or compressor makes. The current iteration of fan makes a fair amount of noise on the 3 setting.

The bottom line is the occupants’ bottoms feeling cool, then mission accomplished [pun intended]. I believe it is a difficult feature to implement.

 

[goneskiian]

Thanks for testing @ernies!

I don't recall what made me think it was actually pulling the air. Someone's comment somewhere. Interesting to see my thought was correct. Makes sense though. Glad to see confirmation they are actually workng.

 

[vandacca]

However, pulling/sucking the air makes no sense to me. I would expect that pushing the air through the holes would have a more noticeable effect. i.e. Directing small amounts of air out through small holes would generate more air over the body than trying to suck in an equal amount over a huge volume. Something just doesn't make sense here...

 

[SolarRoof]

My wife's Ford Explorer Platinum has AC seats and you can feel the air pushing through the ventilated seats - feels great, esp here in Phoenix. I feel nothing from the X.

 

[K-MTG]

Why is it pulling air, it should be pushing. I don't feel any benefit when I am using it

 

[ernies]

Why is it pulling air, it should be pushing. I don't feel any benefit when I am using it

K-MTG....that of course is a rhetorical question and probably not answerable by anyone other than the design team for that element of the X. However, answers are often not 100% truthful [I can't handle the truth] OR helpful.

The air is simply going down into the seat pulled by the fan as attested to by another Sig owner who put a funnel on the seat and did a smoke test.

They might know something I don't, but the "feel" of moving air is helpful from a mental standpoint and for my money it makes sense from a physics standpoint.

From the lack of response to this posting, most do not seem to care...which is fine with me, but if I lived in Phoenix I might feel differently.

 

[systemcrashed]

Why is it pulling air, it should be pushing. I don't feel any benefit when I am using it

The only reasonable answer to this would be for efficiency. By using the A/C return as the source of suction, there would be two less motors necessary, an easy way to conserve power and still produce some ventilation. Unless there are actual motor driven fans in the seats and I am way off. Then I would suspect this might be a mistake.

Does the speed of the A/C fan increase the amount of suction through the seats with the seat vent setting on high?

 

[ernies]

The only reasonable answer to this would be for efficiency. By using the A/C return as the source of suction, there would be two less motors necessary, an easy way to conserve power and still produce some ventilation. Unless there are actual motor driven fans in the seats and I am way off. Then I would suspect this might be a mistake.

Does the speed of the A/C fan increase the amount of suction through the seats with the seat vent setting on high?

The three tested pressure were on 1, 2 and 3 settings. It is an independent fan and not part of the AC.

 

[goneskiian]

I don't know if this makes sense, but I'll say it anyway. Evaporative cooling happens when moisture evaporates and is pulled away from the skin. With a fan blowing on your sweaty a$$ sitting on a seat, (in my thinking anyway) you wouldn't get as much evaporation as if a fan was pulling air away from said sweaty a$$ sitting in the seat.

Would you actually feel it as much as nice cold AC'd air blowing on you? Maybe not. But maybe it would actually be as effective. Yes, more testing needs to happen to verify this theory.

Or maybe it was a last minute addition (Elon's already admitted to trying to stuff too much tech into the X from the gun), and as such wasn't well thought out. Maybe they just threw some fans under there and said "Right, well that's good enough, back to these damn doors and would you just look at those seats! F'in sculptural works of art they are!"

 

[systemcrashed]

I don't know if this makes sense, but I'll say it anyway. Evaporative cooling happens when moisture evaporates and is pulled away from the skin. With a fan blowing on your sweaty a$$ sitting on a seat, (in my thinking anyway) you wouldn't get as much evaporation as if a fan was pulling air away from said sweaty a$$ sitting in the seat.

Would you actually feel it as much as nice cold AC'd air blowing on you? Maybe not. But maybe it would actually be as effective. Yes, more testing needs to happen to verify this theory.

Or maybe it was a last minute addition (Elon's already admitted to trying to stuff too much tech into the X from the gun), and as such wasn't well thought out. Maybe they just threw some fans under there and said "Right, well that's good enough, back to these damn doors and would you just look at those seats! F'in sculptural works of art they are!"

Not to mention sweaty a$$ vapors and other biological gases getting sucked into your sculptural works of art!

 

[Lucidor]

I find the whole concept of ventilated seats confusing, regardless of the direction of the fan. Wouldn't the air pass through the holes in the seat that are not covered by your behind? How does your body get exposed to the air at all if the perforation beneath it is blocked?