This is very long, so I made it into sections. I hope at least some people read it, or least parts of it, and share feedback. Thanks!
--- On the paper: My interpretation of Figure 6 in the Vaghela/Kapadia paper "The Load Calculation of Automobile Air Conditioning System": this shows net values of loads (positive values) + cooling (negative values). The details are broken out via the lines in Figure 5. The lines reach zero at the steady state on the right of Figure 6. Figure 5 shows overlapped lines, not stacked lines. We can add up each individual line to get to the ~2 kW load that matches the ~2 kW cooling. Also, the horizontal timescales are different between the 2 figures; Figure 6 only covers the first 1/2 hour out of the 3 hours depicted in Figure 5. The paper also assumes an ambient temperature of 35 C. The ambient temperature does not appear to change much in their model, as the contribution to load from the ambient temp is pretty constant, except for a small bump shown in the at the beginning of the black line in Figure 5. It is unclear whether their model puts the vehicle in motion or leaves it parked during the model period. From Figure 5's ambient load line, I think the vehicle has constant airflow over it. The ambient temperature surrounding a stationary car will increase somewhat (making a small heat island). If the air isn't constrained, the heat from a single heat source in a large open air area will rise and mostly be replaced by cooler air close to the original ambient temperature. If there are many closely spaced heat sources, eventually the air in between the closely spaced heat sources will also be warmed. Similar: individual penguin vs a penguin huddling in the middle of the pack in blizzard. Or like the air temps when standing 10 feet from a single bonfire vs being 10 feet from a ring of fire of bonfires (20 foot diameter circle) that surround you. Or perhaps a parking lot (rush hour highway?) full of idling cars running their AC systems.) --- On AC: Air conditioners are heat pumps. Their energy consumption varies according to the temperature gradient between hot and cold. A stationary air conditioner creates a pool of hot air on one side, and a pool of chilled air on the other side. Fans work to dissipate both pools of air, which helps reduce the temperature gradient. Putting a heater (like an ICE) next to the air conditioner's condenser (outside unit) will force the AC to work harder to produce the same amount of cooling. Low airflow will also force the AC to work harder as a heat island builds up. Airflow may come from large fans that dissipate heat and/or from vehicle motion that forces air over the radiator and condenser. Basic air conditioners are either on or off. Their output cannot be varied to match the exact cooling loads, so they cycle on and off to keep a thermostat happy. More advanced electrically-driven AC systems have inverter drives that allow for variable-speed compressor operation that matches the exact load. To my knowledge, mechanically-driven AC compressors as used in most vehicles use a clutch mechanism that turns them on and off as needed. Some cars, like the Prius hybrids, and AFAIK all factory EVs, use an electrically-driven variable-speed compressor. Prius AC can run independent from the ICE, until the traction battery SoC falls low enough that the ICE restarts to recharge the battery up to a reasonable SoC. --- On the topic and premise: I do agree with your general conclusion that an EV running AC will do better than any ICE-driven AC, especially once the self-generated heat island is considered, and doubly so when multiple vehicles are involved. >From prior Gen 2 Prius-as-a-generator testing* and math**, a Prius appears able to turn approximately 15% of gasoline energy to household 120v/240v electrical energy. This is on par with small gensets. Gen 2 Prius 'Ready' mode base load is 316 W (electrical power). Although this value of 15% is quite a bit lower than the 'up to 37%' thermal efficiency of the Gen 2 Prius engine, it does represent the base load overhead and the conversion steps as-measured by bzwilson before reaching 120v/240v. (Fuel -> Prius ICE -> Prius MG1 -> traction battery -> DC/DC converter (200v to 12v) -> 12v to 120v modified sine (square) wave inverter.) For simplicity, I will also use 15% as the efficiency value for driving the Prius AC, even though I know it runs off the traction pack voltage and does not need those same conversion steps. (15% is conveniently the same value seen in one of the referenced documents for tank to wheel efficiency for standard ICE. That also seems like fair for a value for belt-driven AC units.) *Testing: http://hiwaay.net/~bzwilson/prius/priups.html **Math: https://priuschat.com/threads/prius-as-a-generator-revisited.39613/#post-610960 [Note: although below I use power' (kW) instead of 'energy' (kWh)', the math is the same. If it makes more sense to the reader to keep it all as energy units, replace 'W' with 'Wh', 'power' with 'energy', and consider the length of time to be 1 hour.] --- On calculations: Prius AC: let's calculate the engine power requirements. Assuming a COP=4.0 (probably may be generous, but IDK what it really is for the Prius. I am guessing that it is above COP 2.0 at least some of the time), running at 500 W electrical power (to provide 2 kW cooling power) + 316 W electrical power for Prius 'Ready' mode base load = 816 W electrical power needed. 816 W/0.15 = 5.44 kW total engine thermal power (0.816 kW electrical output + 4.624 kW thermal output). 4.624 kW thermal (from ICE waste heat) + 2 kW thermal (heat output by AC condenser) + 0.5 kW thermal from AC equipment itself = 7.124 kW thermal power going to increase nearby air temps while getting 2 kW of cooling. [Note: although the Prius engine would cycle on and off at this electrical load level, the average heat output remains the same. A conventional vehicle with a mechanically-driven compressor would not have off periods, thus raising thermal power output numbers, and thus a worse ratio.] For an EV, the ICE heat disappears from the picture, but a different idle draw shows up (assume 160 W idle load in an idle Nissan Leaf, per post by ingineer on mynissanleaf.com forums), leaving 2.5 kW+0.16 kW=2.66 kW thermal power going to grow the ambient heat island while getting 2 kW of cooling. --- Comparisons, non-PHEV Prius to Leaf BEV: COP at 4.0, cooling output power at 2 kW, electrical input at 0.5 kW results in 4.624 kW+2 kW+0.5 kW=7.124 kW thermal (Prius) vs 2 kW+0.5 kW+0.16 kW=2.66 kW thermal (EV) means there is a 2.68:1 ratio. COP at 2.0, cooling output power at 2 kW, electrical input at 1 kW results in 7.46 kW+2 kW+1 kW=10.46 kW thermal (Prius) vs 2 kW+1 kW+0.16 kW=3.16 kW thermal (EV) means there is a 3.31:1 ratio. COP at 4.0, cooling output power at 1 kW, electrical input at 0.25 kW results in 3.21 kW+1 kW+0.25 kW=4.46 kW thermal (Prius) vs 1 kW+0.25 kW+0.16 kW=1.41 kW thermal (EV) means there is a 2.28:1 ratio. COP at 2.0, cooling output power at 1 kW, electrical input at 0.5 kw results in 4.624 kW+1 kW+0.5 kW=6.124 kW thermal (Prius) vs 1 kW+0.5 kW+0.16 kW=1.66 kW thermal (EV) means there is a 3.69:1 ratio. Conclusion: Prius puts out about 3x as much heat as the EV. The difference widens at lower COPs. As more heat is being put out, ambient temperatures can also be expected to increase faster near the Prius, which will lower COP. My guess is other ICE vehicles do worse than the Prius, as they do not have a traction battery that allows the ICE to run intermittently at an decent efficiency point while operating the AC continuously. Regular ICE efficiency suffers at low engine loads. I suggest that if you think the 15% efficiency factor used earlier is not sufficient, then perhaps consider using 2x worse as a rule of thumb number for other ICE vs Prius. One way to do that isa recalculate the Prius numbers using say 22% efficiency, and other ICE at 11%). On Mon, Jul 27, 2020, 10:32 Robert Bruninga via EV <[email protected]> wrote: > A huge advantage of EVs is sitting at an event (or drivein movie) in AC > comfort on a hot day without an engine running. > > Id like to come up with some numbers to describe the total heat generated > by an ICE at idle running its AC compared to an EV. > > Here is a technical paper. > http://www.invisaflects.com/wp-content/uploads/2016/08/vehicleair.pdf > All I can understand is figure 5 and 6. Figure 6 seems to imply that cool > down begins to take about 3 kW but tapers to under 200W as temperature > stabilizes. > > But that conflicts with figure 5 that suggests the 2 PM heat gain is over > 1000 W solar heat gain and 500 W lost due to ventilation. Big difference > between 200 W and 1.5 kW? > > Anyway as a starting point, I am going to assume 1 kW cooling. Now assume > that the AC requires about 500 W electrical to pump about 1 kW of heat out > of the cabin. That 1 kW cooling is then exhausted outside more like 1.5 > kW. > > Now the ICE is assumed to be generating power from an ICE and so WHAT is > the amount of heat exhausted to the outside to achieve the same 1 kW of > cooling? > > This reference shows BEV's are about 75% tank-to-wheels efficient and ICE's > are about 15% for a 5 to one ratio. > http://www.afteroilev.com/Pub/EFF_Tank_to_Wheel.pdf > > But its much worse than that. I am going to assume that running an AC > compressor at Idle is not nearly as efficient as running it when the car is > moving down the road and the ICE is in a more efficient range. And the > compressor is mechanical and with belts. So, I am going to assume it is > 50% worse at idle as electrical. > > So I could claim that the exhaust heat surrounding an ICE parked with the > AC running is TEN times that from an EV. > > Anyone want to refine these assumptions and results? > > Bob > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20200727/6195e7c6/attachment.html > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... 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