Air Conditioning Unit the same on BEV and REx?

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cornfieldcraig

Member
Joined
May 14, 2015
Messages
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Do all i3s use the same technology for air conditioning? For heating I know that REx units use resistant heating and most BEVs use a heat pump. Since heat pumps can both heat and cool, my assumption would be that vehicles with heat pumps would use them for both heating and cooling, which means that the REx-equipped vehicles would use something different and likely less efficient.
 
I'm pretty sure that while yes, one unit could heat and cool, that doesn't work well in a car where you may need to do both at the same time to remove humidity or defrost the windows. So, I think you'll find the a/c units are the same, and on the BEV with a heat pump, that is only used for heat, and both might run when trying to defrost the windows.
 
They REx and BEV use the exact same A/C compressor. The Heat Pump functionality is achieved completely and solely by valving in the A/C system. Electronic Expansion valves(EXV) are used along with shutoff valves to control amount and direction of refrigerant flow in a BEV, while the REx uses a much simpler Thermo-expansion valve setup with shutoff valves built-in(ETXV).
 
GodFollower said:
They REx and BEV use the exact same A/C compressor. The Heat Pump functionality is achieved completely and solely by valving in the A/C system. Electronic Expansion valves(EXV) are used along with shutoff valves to control amount and direction of refrigerant flow in a BEV, while the REx uses a much simpler Thermo-expansion valve setup with shutoff valves built-in(ETXV).
Click to expand...
How does an i3 BEV dehumidify the cabin air while heating? Does it use the heat pump in cooling mode to dehumidify while using resistance heaters to heat the air? I assume that's how the REx works, but the BEV is supposed to be more efficient in heating mode.
 
alohart said:
GodFollower said:
They REx and BEV use the exact same A/C compressor. The Heat Pump functionality is achieved completely and solely by valving in the A/C system. Electronic Expansion valves(EXV) are used along with shutoff valves to control amount and direction of refrigerant flow in a BEV, while the REx uses a much simpler Thermo-expansion valve setup with shutoff valves built-in(ETXV).
Click to expand...
How does an i3 BEV dehumidify the cabin air while heating? Does it use the heat pump in cooling mode to dehumidify while using resistance heaters to heat the air? I assume that's how the REx works, but the BEV is supposed to be more efficient in heating mode.
Click to expand...

That is incorrect, in most cases. See the below quote from the training manual:

If�the�heat�pump�is�used�in�the�mixed�operation,�the�shutoff�valves�with�the�numbers�17,�20�and�21�are
open.�The�shutoff�valve�with�the�number�18�is�closed�as�there�should�be�no�reverse�flow.�This�results
in�a�division�of�the�hot,�high-pressure�refrigerant.
On�the�one�hand,�cooling�of�the�high-voltage�battery�unit�and�dehumidification�of�the�passenger
compartment�can�be�realized�by�the�cooling�at�the�evaporator,�on�the�other�hand,�the�divided�heat
transported�with�the�refrigerant�is�used�for�the�heat�pump�heat�exchanger.
Click to expand...


Basically, it still uses the A/C compressor to chill the evaporator, but uses the heat absorbed by that evaporation to heat the coolant in the resistive heater circuit. So, it is still using the same resistive heater circuit; but generating the heat with the heat pump rather than from the resistive heater.
 
GodFollower said:
If the heat pump is used in the mixed operation, the shutoff valves with the numbers 17, 20 and 21 are
open. The shutoff valve with the number 18 is closed as there should be no reverse flow. This results in a division of the hot, high-pressure refrigerant. On the one hand, cooling of the high-voltage battery unit and dehumidification of the passenger compartment can be realized by the cooling at the evaporator, on the other hand, the divided heat transported with the refrigerant is used for the heat pump heat exchanger.
Click to expand...

Basically, it still uses the A/C compressor to chill the evaporator, but uses the heat formed by that evaporation to heat the coolant in the resistive heater circuit. So, it is still using the same resistive heater circuit; but generating the heat with the heat pump rather than from the resistive heater.
Click to expand...
Clever!

Thanks for posting the explanation! However, I think your restatement of the heating function is not accurate in that evaporation doesn't generate heat that warms the coolant in the resistive heater circuit. The hot compressed liquid refrigerant is split into two streams. As you stated, one stream is fed into the evaporator where its conversion from a liquid to a gas takes heat from the surroundings (i.e., it lowers the temperature of the cabin air which dehumidifies it). The other hot compressed liquid refrigerant stream is passed through a heat exchanger that transfers heat from the hot refrigerant to the coolant in the resistive heater circuit which then warms the dehumidified cabin air.

It seems like pretty clever technology to make it all work under varying conditions. The hot liquid refrigerant in the dehumidifier stream won't evaporate in the evaporator if its temperature is too low or its pressure is too high, so the compressor speed and how the refrigerant is split into two streams are probably critical. The heating stream seems less critical since its heat is just being transferred to the resistive heater circuit coolant with no phase change occurring (i.e., the refrigerant remains a liquid). How these two streams are recombined for another pass through the compressor probably involves some clever engineering.
 
alohart said:
GodFollower said:
If the heat pump is used in the mixed operation, the shutoff valves with the numbers 17, 20 and 21 are
open. The shutoff valve with the number 18 is closed as there should be no reverse flow. This results in a division of the hot, high-pressure refrigerant. On the one hand, cooling of the high-voltage battery unit and dehumidification of the passenger compartment can be realized by the cooling at the evaporator, on the other hand, the divided heat transported with the refrigerant is used for the heat pump heat exchanger.
Click to expand...

Basically, it still uses the A/C compressor to chill the evaporator, but uses the heat formed by that evaporation to heat the coolant in the resistive heater circuit. So, it is still using the same resistive heater circuit; but generating the heat with the heat pump rather than from the resistive heater.
Click to expand...
Clever!

Thanks for posting the explanation! However, I think your restatement of the heating function is not accurate in that evaporation doesn't generate heat that warms the coolant in the resistive heater circuit. The hot compressed liquid refrigerant is split into two streams. As you stated, one stream is fed into the evaporator where its conversion from a liquid to a gas takes heat from the surroundings (i.e., it lowers the temperature of the cabin air which dehumidifies it). The other hot compressed liquid refrigerant stream is passed through a heat exchanger that transfers heat from the hot refrigerant to the coolant in the resistive heater circuit which then warms the dehumidified cabin air.

It seems like pretty clever technology to make it all work under varying conditions. The hot liquid refrigerant in the dehumidifier stream won't evaporate in the evaporator if its temperature is too low or its pressure is too high, so the compressor speed and how the refrigerant is split into two streams are probably critical. The heating stream seems less critical since its heat is just being transferred to the resistive heater circuit coolant with no phase change occurring (i.e., the refrigerant remains a liquid). How these two streams are recombined for another pass through the compressor probably involves some clever engineering.
Click to expand...

You are correct, I typo'd. It is using the heat absorbed by the evaporation, not created by ;)
 

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