A/C Wattage vs lights

That doesn't sound right. I can't find any figures, but I would have thought that the A/C would be more like a couple of kilowatts.

 

Are you sure that's not the wattage of the blower fans? Toyota seems to use the term "air conditioning" in the most generic sense at times. I could certainly believe that the blower fans consume 200 Watts.

 

Has to be much much more than that. A car requires a lot of BTUs due to the metal and glass making the thing act like a greenhouse with no insulation. A home wall unit that is rated at 12,000 btu/hr uses something like 12-14 amps at 120 volts - that is something like 1440 to 1680 watts. Is it possible they were saying 2,000 watts and a zero got dropped?

 

That sounds more reasonable. Just remember that when you regenerate through braking you earn a little gold star for each 50 Watt-Hours you produce. Well for each hour you run the AC you need to generate 90 of those little stars, so yes it is quite a bit of energy.

 

Not really on subject but a lot of Prius AC info:

http://www.denso.co.jp/AR-e/1998/TW/climate.html

 

Seems to me that anything that consumes electricity will lower mpgs because the ICE will have to run longer to maintain the same charge level in the battery. The air conditioner has a definite toll on mpgs, and leaving the lights on all the time should do too, although to a lesser extent.

 

<div class='quotetop'>QUOTE(thorn\";p=\"110481)</div>

Not really.

450 cubic meters per hour is a lot of air. It works out to 264 cubic feet per minute(CFM).
It's not a perfect comparison, but I looked up the specs of fairly beefy ventilation fan that is rated at 300 CFM. It's like the kind of fan you would put in a bathroom, but at 300 CFM, it would need to be a big bathroom. Anyhow, that fan was rated at 300W. So, a 264 CFM fan in the car, could concievably consume 200W.

That chart you posted kind of sucks in my opinion, because it's not real clear. I suspect the actual power consumption of the compressor is 4500 watts.

First off, look at the heating section. The Prius has an electric heater in addition to using the heat from the engine. If the 200W number was the total power consumption of the A/C, then the 170W number would be the power consumption of the heater. A 170W heater is too small to be worth installing in anything, particularly a vehicle that might have an interior temperature of 10 degrees when you start it. A 5300W heater sounds more reasonable. With that, you really could heat a car from 10 degrees to 65 degrees in five minutes or so.

Secondly, I belive I've read that the Prius battery is a 1.5 kWH battery, meaning to could supply 1.5 kW of power for an hour. That is probably the rating if the entire capacity of the battery is use, however the Prius uses only about 60% of the capacity to prolong the lifespan of the battery. So for practical purposes, lets call it a 1 kWH battery.

If you start with a full charge, and ran the A/C at full power, consuming 4500W, then your battery SOC would go from 8 green bars to 2 pink bars in about 10 minutes. This matches the observed behavior of the car.

 

<div class='quotetop'>QUOTE(Marlin\";p=\"110677)</div>

People are throwing around a lot of numbers without understanding what they mean. 4500 watts of power consumption is too high by at least a factor of 10.

Cooling capacity is how much heat the A/C can remove from the car (or room or house), not how much power the compressor consumes (don't any of you have a/c in your homes???). This is normally measured in Btu/h or tons (1 ton == 12,000 Btu/h). For instance, the downstairs of my house in Las Vegas is cooled with a 3.5 ton heat pump (air conditioner that can run in reverse).

4500 watts of cooling capacity is about 15,300 btu/h, or about the same as a medium size wall a/c unit. Cooling Capacity / Power Consumption = Seasonal Energy Efficiency Ratio.

If you assume an SEER of about 15, that says the Toyota A/C should consume 300 watts. That's pretty far off from the 200 watts in the chart. And I have a hard time believing they achieved an EER above 20, because the highest EER you see in a home A/C unit is around 18, and those units are usually a little on the fragile side, not cost effective, and rely on somewhat "exotic" techniques such as variable speed compressors, etc. But maybe they achieved a SEER of 22.5, and 200 watts is correct.

 

I'm not heating and air conditioning expert, but I'm pretty certain the Prius battery is a 1.5 kWh battery. This is consistent with what I've read that a practical EV car would need a 50 kWh battery. And since the prius uses only 60% of the battery capacity, then the assumption that you really only have 1 kWh available is a reasonable assumption.

A 1 kWh battery could supply 1 kW continuously for an hour. (it's a normalized unit, so it could be capable of 2 kW for 1/2 hour, or 0.5 kW for 2 hours, etc)

So, if the A/C, at full power, only consumes 200 watts of electricity, then a fully charged prius battery could run the air conditioner for 5 hours. With a half charged battery, it could run 2.5 hours.

In reality, if you are sitting in Park with a full battery and the A/C running on MAX COOL, then in roughly 10 minutes, the car has to turn on the ICE to recharge the battery.

That behavior would be consistent with 4500 watts, not 200 watts.

 

<div class='quotetop'>QUOTE(priusenvy\";p=\"110701)</div>

People are throwing around a lot of numbers without understanding what they mean. 4500 watts of power consumption is too high by at least a factor of 10.

Cooling capacity is how much heat the A/C can remove from the car (or room or house), not how much power the compressor consumes (don't any of you have a/c in your homes???). This is normally measured in Btu/h or tons (1 ton == 12,000 Btu/h). For instance, the downstairs of my house in Las Vegas is cooled with a 3.5 ton heat pump (air conditioner that can run in reverse).

4500 watts of cooling capacity is about 15,300 btu/h, or about the same as a medium size wall a/c unit. Cooling Capacity / Power Consumption = Seasonal Energy Efficiency Ratio.

If you assume an SEER of about 15, that says the Toyota A/C should consume 300 watts. That's pretty far off from the 200 watts in the chart. And I have a hard time believing they achieved an EER above 20, because the highest EER you see in a home A/C unit is around 18, and those units are usually a little on the fragile side, not cost effective, and rely on somewhat "exotic" techniques such as variable speed compressors, etc. But maybe they achieved a SEER of 22.5, and 200 watts is correct.[/b][/quote]

Sorry Priusenvy but you missed the boat big time. You say that 4500 watts gives 15,300 BTU/Hr and that might be ballpark correct, and that is about how much cooling you would need in a car this size. The 200-300 watts is just to run the fan, the compressor will consume that 4500 watts of power easily. Think about this logically, a hair dryer uses about 1500 watts, so we are talking about the same amount of energy as three hairdriers. Sure it is cooling, but a btu is a btu and the energy figure in the thousands of watts per hour is a valid number.

 

As far as "fragile" high efficiency A/C systems, I had the Bryant Evolution in my former house in the Burbs, and I have the same system at the hobby farm.

http://www.bryant.com/corp/details/0,2938,...ETI8275,00.html

I have almost 5 years experience with Bryant's premium efficiency A/C and have never had any problems. True my cooling season only lasts 3 months max, but then the condenser has to sit there the rest of the year.

Including the middle of winter at -40.

I used to only get 4-5 years out of a cheapie system under such conditions. Usually the compressor will seize sitting so long, and the -40 winters will cause cheap brazed fittings at the compressor to develop cracks and you lose all the Freon. My Bryant Evolution systems have been a pleasant surprise, and they're way quieter when running too.

If these systems are so "fragile" why do Bryant, Carrier, Lennox, and Trane offer the longest warranties on their Premium Efficiency series A/C? I have friends in Mesquite, NV and St George, UT, with premium units and even since 1997 they have had zero problems.

You look around where they live and the "contractor special" units have already been replaced because they quit. So much for "fragile" premium A/C.

In a climate like Palm Springs, CA, Las Vegas, NV, Mesquite, NV, Phoenix, AZ, St George, UT, etc, when you compare an A/C rated SEER 10 to one rated SEER 18, the ROI is usually 3 years or less.

The biggest mistake I have seen, and this is where the homeowner has to do a LOT of research, is in not properly matching the air handler, the evaporator, and the outside condenser. It might cost you 10-15% more with a variable speed air handler and good insulated, cased evaporator coil, but it pays in long life and good performance.

The only way to know how much power the Prius variable speed compressor uses is to put an Amp Clamp on the cable while it's running Max A/C. Stuck in traffic I've gone from SOC all blue to pink in 5 mins, so I'd guess 4.5 KW minimum. Don't forget you're also running the radiator fan at maximum speed too, as you need a lot of airflow over the condenser.

Most car and pickup A/C are 2 ton minimum. The A/C in my 2000 GMC Sierra extended cab was rated something like 20,000 btu cooling, and the Suburban is almost 4 ton capacity, around 42,000 btu.

You need a lot of cooling capacity in a car and especially an SUV. Think about it: it's basically a greenhouse on wheels, with single pane windows and poor insulation.

 

Jayman - Well said -that was the exact point I was trying to get across before.

The only exception I have with anything you said has to do with the high eff home units. I have had one for 13 years - its 95% eff condensing gas furnace. I also have an old standing pilot furnace for the other part of the house. The high eff one is the only product I have ever paid for a maintenance contract on. I have them to the house at least twice a year to work on it as it is constantly eating circuit boards.

The A/C part of the system is only rated at 12, as to go higher in northern NJ just does not make sense - you don't run the system long enough to payback the huge premium you pay for the systems - at least I don't.

 

<div class='quotetop'>QUOTE(kirbinster\";p=\"110740)</div>

Sounds like a power problem to me. My Bryant in the former Burb house was trouble free, so is the current one at the hobby farm:

http://www.bryant.com/corp/details/0,2938,...ETI8341,00.html

Though I have a surge arrestor mounted in the panelboard. It doesn't take much of a glitch to make them latch up.

I would shudder to think of finding a qualified tech to work on a complicated electronic condensing furnace. It would be like the horror stories we have here finding Prius techs.

<div class='quotetop'>QUOTE(kirbinster\";p=\"110740)</div>

Not too sure about that. At my former Burb home I got a package deal with the entire Evolution system, around $2,500 more than a regular system.

To me the biggest gain was in improved comfort and *much* improved indoor air quality.

I used to have a house -back in the early 90's - with a SEER 8 or 10 A/C. On a muggy Winnipeg summer day that 1.5 ton system (18,000 BTU) would easily use 50 kwh/day. My home I had built in the Burbs was almost twice as large, and it had a 2 ton (24,000 btu) Bryant Puron two-speed A/C. It would use at most 18 kwh/day under similar operating conditions, and kept MUCH better humidity control.

Overall I've had good luck with premium Bryant HVAC up here, and premium Carrier HVAC in Mesquite, NV and St George, UT. Good luck trying to find a qualified contractor though. That's where the problems start.

Jay

 

<div class='quotetop'>QUOTE(jayman\";p=\"110742)</div>

Sounds like a power problem to me. My Bryant in the former Burb house was trouble free, so is the current one at the hobby farm:

http://www.bryant.com/corp/details/0,2938,...ETI8341,00.html

Though I have a surge arrestor mounted in the panelboard. It doesn't take much of a glitch to make them latch up.

I would shudder to think of finding a qualified tech to work on a complicated electronic condensing furnace. It would be like the horror stories we have here finding Prius techs.

<div class='quotetop'>QUOTE(kirbinster\";p=\"110740)</div>

Not too sure about that. At my former Burb home I got a package deal with the entire Evolution system, around $2,500 more than a regular system.

To me the biggest gain was in improved comfort and *much* improved indoor air quality.

I used to have a house -back in the early 90's - with a SEER 8 or 10 A/C. On a muggy Winnipeg summer day that 1.5 ton system (18,000 BTU) would easily use 50 kwh/day. My home I had built in the Burbs was almost twice as large, and it had a 2 ton (24,000 btu) Bryant Puron two-speed A/C. It would use at most 18 kwh/day under similar operating conditions, and kept MUCH better humidity control.

Overall I've had good luck with premium Bryant HVAC up here, and premium Carrier HVAC in Mesquite, NV and St George, UT. Good luck trying to find a qualified contractor though. That's where the problems start.

Jay
[/b][/quote]

Jay you are right about finding someone that knows anything about the high eff furnace. I have the contract with the gas company - and have the direct line for the head of service who knows the equipment. One of these years I will replace it with something that is less of a pain in the nice person.

You sort of made my point that the high eff A/C does not pay. You say the difference in cost is about $2500, but you only save 32 kwh per day. If we assume roughly 15 cents a kwh and 90 days a year of A/C then the savings is only $450/year. Subtract from that the roughly $125 a year you would earn on the $2500 at 5% and you get savings of only $325/yr which is a payback of almost 8 years. I agree that if you live in FL, AZ, MS,....etc then it makes sense, but where I live it is a marginal investment.

 

<div class='quotetop'>QUOTE(thorn\";p=\"110745)</div>

Again, I'm certainly not an A/C expert, but...

If you look back at the chart you posted, you should see the footnote that 4500W is when the compressor is running at it's maximum speed. I imagine it only does that when the maximum cooling demand exists, such as when you first start the car and it's 110+ inside. It would normally run at much less.

Another difference to note between a home central air conditioning system and a car central air conditioning system, is that a home system's output is typically 20 degrees cooler than the air that enters the unit. That's what they design the systems for. If you let your house heat up to 110 degrees, and then turned on the A/C, the temperature of the air coming out of your vents would be around 90 degrees. Eventually, as the house cools down, the air comes out cooler and cooler, because the air going in is cooler. When you house gets down to 70 degrees, the air coming from the vents would be 50 degrees. I've tested this, because I had trouble with my central A/C's compressor intermittently not turning on, so I spent a couple of weeks with a temperature probe in one of the registers until I got it fixed.

I don't know about you, but I'm pretty sure that the air that comes out of the vents in my car is far cooler than 80-90 degrees shortly after turning on the car, even when the car has been sitting in the sun on a 95 degree day. This tells me that the car A/C was designed to give a greater temperature delta when servicing a maximum cooling demand, than a home system is designed for. If I set my A/C for max cool then within about 30 seconds I'm getting air from the vents that feels like it's in the 50's, so we're talking about a 50 or so degree temperature delta. That takes more power.

It should be also noted that a home system is always in "recirc" mode, in that it typically cools down the air from inside the house that is already near the target temperature. A car, on the other hand, typically utilizes outside air, which again requires a high temperature delta between the air going in and the air coming out.
I haven't tried it, but I would imagine that the Prius would kick you out of recirc mode if you left it on too long. Maybe not, since it has a variable speed compressor, but that's what other cars do. My wife's Chevy Malibu will only allow the recirc mode to be on for 5 to 10 mintues before it kicks it off. This is because if allowed to remaing in recirc, the condenser fins would get too cold and you run the risk of forming ice on them.