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Old 05-12-2021, 12:39 PM   #1 (permalink)
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Air Conditioning Load impact on cooling system

An additional puzzle piece involved in a vehicles cooling system and drag is associated with the heat load imposed upon the radiator by the heat rejected from the air conditioning condenser, upstream of the radiator; which is a function of the total cooling load of the cabin.
The total cooling load for the cabin will include heat flux associated with conduction, internal sensible and latent heat sources, direct solar gain, infrared radiation, outside air ventilation sensible and latent heat, and HVAC system heat.
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* Conductive loads will have to do with the area of all cabin exterior surfaces, the inverse of all their individual R-factors, the design indoor/ outdoor temperature differential, including an engine compartment firewall ( when applicable ).
* Working temperatures for USA vehicles would be 75F-indoor, 122F- outdoor.
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* Internal loads would involve passenger occupancy density and both their sensible and latent heat contribution.
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* Direct solar gain would involve insolation value for Furnace Creek, Death Valley, California, USA, full sun, peak summer, solar noon, glazing area, selective coatings ( shading coefficients ), greenhouse effect.
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* Infrared radiation emitted from solar- UV absorbing/ long-wave re-radiating surfaces.
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* Indoor cabin volume and outdoor, fresh-air, ventilation, air-exchange volume rate cooling load based upon sensible/ latent enthalpy differential with indoor design air enthalpy.
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* HVAC heat load involves air handler electric motor losses and air handler fan losses when developing cfm and total pressure (Pt)
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1) cabin 'size' and 'volume' makes a difference
2) cabin 'construction' makes a difference
3) cabin 'glazings' makes a difference
4) whether or not there's an engine compartment firewall makes a difference
5) whether there's two-passengers, or eleven makes a difference
6) the AC system must perform to specification while parked, idling, no wind, all accessories 'ON'
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* Under the worse-case scenario, the radiator must handle not only engine/motor/battery/regeneration heat flux, but also navigate the additional worse-case scenario air conditioning heat load.
* As cooling system drag is related to radiator shutter position and ' blower-assisted' dynamics, the role the air conditioning system plays on overall cooling system performance needs to be appreciated.
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* With respect to the Porsche 911 Carrera cooling drag, consider its surface area, interior volume, and that it is a 2-passenger coupe, compared to the 1st-gen, Tesla Model S sedan surface area, interior volume, and that it is rated to carry up the seven (7) passengers, also lacking any facility to lose powertrain heat from an 'exhaust' system.

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Last edited by aerohead; 05-14-2021 at 12:36 PM.. Reason: add data
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Old 05-12-2021, 12:56 PM   #2 (permalink)
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* The radiator must accommodate blockage from the air conditioning condenser when it is inoperative.
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Old 05-12-2021, 06:22 PM   #3 (permalink)
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radiator / condenser

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Originally Posted by freebeard View Post
* The radiator must accommodate blockage from the air conditioning condenser when it is inoperative.
Some exceptions would be past iterations of the V-10 powered Dodge RAM pickup. These trucks had parallel radiator and condenser. Side by side.
Each was unobstructed with respect to the forward stagnation point.
The first-gen Honda CIVIC CRX HF was also configured this way. They came from Japan without AC, which was added as an option at the dealer.
For series heat exchangers, the condenser is fully exposed to the dynamic pressure of the stagnation point, however, it's flow volume in the recent past, would be governed ( or not ) by the presence ( or not ) of radiator shutters, modulating airflow, as a function of coolant temperature sensor data to the CPU portion governing shutter positioning and it's output signal.
Same for 'blower-assisted' operations.
During winter arctic conditions the shutters might never open, except to allow for compressor-assisted sub-cooling dehumidification, plus reheat, to clear away windshield condensation.
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Old 05-12-2021, 07:01 PM   #4 (permalink)
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I don't quite see the point of the post.

Cooling loads of a car involve all cooling loads - isn't that obvious? That's why I (usually, at least) talk about car 'heat exchangers', not just 'the radiator'.

For example, you could add here the cooling load of the transmission cooler in cars with auto trans, the cooling load of the engine oil cooler (where fitted), and the cooling load of the intercooler (where fitted).

As I say, it just seems to be stating what is obvious.
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Old 05-12-2021, 07:54 PM   #5 (permalink)
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Quote:
Originally Posted by aerohead View Post
Some exceptions would be past iterations of the V-10 powered Dodge RAM pickup. These trucks had parallel radiator and condenser. Side by side.
Each was unobstructed with respect to the forward stagnation point.
The first-gen Honda CIVIC CRX HF was also configured this way. They came from Japan without AC, which was added as an option at the dealer.
I remember some Volkswagens with longitudinal engine had a similar setup too.


Quote:
For series heat exchangers, the condenser is fully exposed to the dynamic pressure of the stagnation point, however, it's flow volume in the recent past, would be governed ( or not ) by the presence ( or not ) of radiator shutters, modulating airflow, as a function of coolant temperature sensor data to the CPU portion governing shutter positioning and it's output signal.
Same for 'blower-assisted' operations.
No wonder most buses, and even trucks, have the condenser assembled out of the engine bay. IIRC some Asian forward-control vans had the condenser assembled below the floorboard of the driver's compartment, between the radiator and the front axle, in a horizontal position which seemed quite bad as it would be somewhat prone to damage from road debris.
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Old 05-14-2021, 10:08 AM   #6 (permalink)
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below the floorboard

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I remember some Volkswagens with longitudinal engine had a similar setup too.




No wonder most buses, and even trucks, have the condenser assembled out of the engine bay. IIRC some Asian forward-control vans had the condenser assembled below the floorboard of the driver's compartment, between the radiator and the front axle, in a horizontal position which seemed quite bad as it would be somewhat prone to damage from road debris.
My 1970 Karmann Ghia had an add-on AC system, with a horizontal condenser coil ' under the engine.' It had already lost all its charge, and was the first thing to go to the wrecking lot.
When Toyota came out with it's first van, it had the condenser under the front. Some genius at the dealership had hosed the whole thing down with asphaltic undercoating. Caveat emptor.
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Old 05-14-2021, 09:19 PM   #7 (permalink)
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Quote:
Originally Posted by aerohead View Post
My 1970 Karmann Ghia had an add-on AC system, with a horizontal condenser coil ' under the engine.'
I don't remember seeing any horizontal condenser being fitted under the engine on classic Volkswagens with add-on air conditioners.


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When Toyota came out with it's first van, it had the condenser under the front. Some genius at the dealership had hosed the whole thing down with asphaltic undercoating. Caveat emptor.
I guess you mean the US-spec versions of the LiteAce, of which I have only seen one in Amazon some 12 years ago. The other vans fitted with a horizontal condenser I refered to were mostly Chinese copies of the 4th-generation HiAce.

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