frictioncircle
Posts: 123
Joined: Fri Nov 25, 2016 11:23 pm
Location: USA West Coast

Re: Parachute effect, underside of vehicle, undesirable

Wed Mar 18, 2020 10:19 pm

I've similarly read that the engineers were trying to shed weight wherever they could with efficiency as the target.

For example, they added the weight and complexity of a heat pump to the BEV because they realized that those pounds were a worthwhile sacrifice to achieve a range increase.

While I agree that the opening in that panel looks terribly inefficient, it doesn't make much sense they'd leave a big, drag inducing hole that could have been plugged by a BEV-specific $1 vacuum-formed underbody tray.


From Technical training, Product information, I01 Heating and A/C Systems:
The heat pump heat exchanger is installed in series between the coolant pump and electric heater. The energy consumption of the electric heating is reduced effectively by using the heat pump and can be saved under certain circumstances.

In the following efficiency comparison it is clear how high the energy saving is with the heat pump. In order to obtain about 5 kW of heater output, about 5.5 kW of electrical power must be used for the electric heating due to resistor losses.

A system with a heat pump only requires about 2.5 kW of electrical energy in order to provide the same heater output of about 5 kW.

The EKK consumes this electrical energy in order to compress the refrigerant and generate the heater output at the heat pump heat exchanger.

By using the heat pump electrical energy of up to 3 kW can be saved in favorable conditions. This energy can then be used for the electric motor of the vehicle, thereby increasing the range.
The heat pump is not an individual component, but a complex adaptation of a refrigerant circuit with an equally complex control structure.
The highly complex system of the heat pump, adapted to the heating and air-conditioning system, places high demands on the workshop personnel during diagnosis, but when it comes to its application the customer is unable to distinguish it from the conventional heating and air-conditioning system in I01 with the range extender.

panamamike
Posts: 121
Joined: Sat Jan 25, 2020 10:21 am

Re: Parachute effect, underside of vehicle, undesirable

Thu Mar 19, 2020 7:43 am

Is there any proof there's an actual parachute effect? I was more concerned about the crud getting into the engine compartment. I'm thinking it's necessary for some cooling, ability to allow heat to escape.
frictioncircle wrote:
Wed Mar 18, 2020 10:19 pm
I've similarly read that the engineers were trying to shed weight wherever they could with efficiency as the target.

For example, they added the weight and complexity of a heat pump to the BEV because they realized that those pounds were a worthwhile sacrifice to achieve a range increase.

While I agree that the opening in that panel looks terribly inefficient, it doesn't make much sense they'd leave a big, drag inducing hole that could have been plugged by a BEV-specific $1 vacuum-formed underbody tray.


From Technical training, Product information, I01 Heating and A/C Systems:
The heat pump heat exchanger is installed in series between the coolant pump and electric heater. The energy consumption of the electric heating is reduced effectively by using the heat pump and can be saved under certain circumstances.

In the following efficiency comparison it is clear how high the energy saving is with the heat pump. In order to obtain about 5 kW of heater output, about 5.5 kW of electrical power must be used for the electric heating due to resistor losses.

A system with a heat pump only requires about 2.5 kW of electrical energy in order to provide the same heater output of about 5 kW.

The EKK consumes this electrical energy in order to compress the refrigerant and generate the heater output at the heat pump heat exchanger.

By using the heat pump electrical energy of up to 3 kW can be saved in favorable conditions. This energy can then be used for the electric motor of the vehicle, thereby increasing the range.
The heat pump is not an individual component, but a complex adaptation of a refrigerant circuit with an equally complex control structure.
The highly complex system of the heat pump, adapted to the heating and air-conditioning system, places high demands on the workshop personnel during diagnosis, but when it comes to its application the customer is unable to distinguish it from the conventional heating and air-conditioning system in I01 with the range extender.

eNate
Posts: 540
Joined: Mon Sep 09, 2019 5:33 pm

Re: Parachute effect, underside of vehicle, undesirable

Thu Mar 19, 2020 8:02 am

panamamike wrote:
Thu Mar 19, 2020 7:43 am

I was more concerned about the crud getting into the engine compartment. I'm thinking it's necessary for some cooling, ability to allow heat to escape.
Definitely some "crud" getting in there. All of the orange bits on and around my motor are surprisingly dirty, probably a combination of brake and tire dust mixed with assorted road grime. I wonder about the survivability of my fiberglass trunk extension hanging down there near the axle shaft vs. a random rock strike, and whether I should put some sort of rubber coating on the face of it.

As for cooling, I can't really imagine that was much of a design thought, given that there's no outflow. Would a cooling engineer leave a big gaping hole that leads to nowhere, or design a small scoop that direct just the necessary amount of air across whatever requires the airflow, then out?
2 0 1 7   B M W   i 3   9 4 A h   B E V  O a k l a n d
 Wokeby Trunk Extension | Duosida 16A L1 EVSE
 SeaSucker Monkey Bar Roof Rack

jadnashuanh
Posts: 5154
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Parachute effect, underside of vehicle, undesirable

Thu Mar 19, 2020 3:30 pm

Without a wind tunnel, it's really hard to tell whether that gap is producing drag under normal operating conditions. Very small shaping could make the air just wisk by without affecting things. Cars these days spend lots of time in both virtual and real wind tunnels. IF covering it produced a measurable benefit in drag reduction, the cost to cover it would have been done already. IT wouldn't have cost much.

As to potential cooling...keep in mind, you have convection and radiation. Closing it off would diminish both types. IOW, you don't need a lot of wind airflow to affect heat flow, depending on the materials.

One reason they used narrow, tall tires can be seen between the i3 and the i3s. MPGE is 118:112 on the i3 versus the i3s which has wider tires.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

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