Does the air disruption truely affect energy usage in this particular situation?

I was reading the comments in this Ible: http://www.instructables.com/id/Parasitic-Wind-Turbine/ and they said that having the turbine in the way of the airflow would create more of a load on the A/C thereby causing it to use more energy. I don't understand it in this case. I can see how putting it in line, mounted to the exhaust port, thereby blocking the exhaust would restrict the airflow. I don't see how using the already exhausted air would restrict the airflow. That, IMO, would be like saying that when you are stopped at a red light and another car is behind you, your engine is working harder because that car is behind your exhaust. Am I thinking right on this?

Comments

[NachoMahma]

. The fan (and any restriction/obstruction) will increase backpressure, even though it is out of the shrouded area of the fan. No matter how you look at it, if the turbine is putting out X amount of power, it is robbing that much power (more, actually) from the fan. As mounted in the first pic of the iBle, the extra backpressure will be very low and you'll probably never notice it - and you won't get much power out of it - but it's there.

[Zippomanonfire]

My thought would be as if it were a standalone wind turbine. It would catch the wind generated and the air would be deflected to the sides and around the obstruction as opposed to going back to the source. There might be a little bit that heads back to the source, but it seems that would be miniscule at best. I was just wondering if the comments had merit. In this comment-- "_soapy_ says: That's exactly right. See Treb's accurate explanation in the thread. I'll paraphrase it: You don't get anything free, because by putting something in the way of the airflow, the fan has to work harder to do the same cooling it was doing before you put the new fan on top and reduced the airflow." -- the assumption is that the motor has to work harder to cool the condenser because the airflow is restricted. I can see how his rig would restrict the airflow slightly, but even so it would not cause any significant loss of throughput ergo minimal extra load. This obviously wouldn't recapture everything lost. But it seems it would pick up at least the ability to light some LED's out of waste.

[NachoMahma]

. Unless the cooling unit is already on it's last leg, the little extra load you will introduce to drive an LED won't matter. The effect will be very small, but it won't be zero. . You won't be getting anything for free ("out of waste"). Your electric bill will be higher. Maybe only a few cents, but you will be using more energy to drive the generator.

[lemonie]

If the air-con fan is transferring energy to the turbine (via the air) it will be working a little bit harder (a few LEDs to power). The exhaust is obstructed a bit. Since the author is still around, I advise that you either post a comment on the I'ble or Private Message him - pretty sure he'll give you a good answer.

L