Air conditioning system - what is its BTU power ?

Romm air conditioners are rated in amount of heat they can suck out
of the room measured in BTU/hour. I wonder, if you compare room A/C
units to car units - how much stronger the car unit has to be ?

Do you know what is an average BTU/hour for a car A/C system?
Just rough number - is is 10000 BTU or rather 50000 or more ?

Pszemol wrote:
> Romm air conditioners are rated in amount of heat they can suck out
> of the room measured in BTU/hour. I wonder, if you compare room A/C
> units to car units - how much stronger the car unit has to be ?
>
> Do you know what is an average BTU/hour for a car A/C system?
> Just rough number - is is 10000 BTU or rather 50000 or more ?

I would say the car air conditioner is a very small capacity since the
interior of the car is very much smaller than even a small room.

> wrote in message oups.com...
> Pszemol wrote:
>> Romm air conditioners are rated in amount of heat they can suck out
>> of the room measured in BTU/hour. I wonder, if you compare room A/C
>> units to car units - how much stronger the car unit has to be ?
>>
>> Do you know what is an average BTU/hour for a car A/C system?
>> Just rough number - is is 10000 BTU or rather 50000 or more ?
>
> I would say the car air conditioner is a very small capacity since the
> interior of the car is very much smaller than even a small room.

I was thinking the same - capacity of car interior is smaller - true.
But ... the insulation of the "walls" and "roof" or the amount of heat
the car interior can absorb from the outside is much, much greater.

Also, I have read the compressor, when operating, can consume
about 10 horsepower from the engine... Why would we want so
much power if the BTU/hour rating is smaller then window AC?
10 horsepower equals to about 7.5 kilowatt of electric power...
If we want to power car compressor from an electric motor
operating on 120V we would have to deliver more than 60 Amps!
Correct me if I am wrong, but this suggests the car A/C units are
either more powerful or more wasteful, less efficient systems :-)

On Thu, 28 Jul 2005 wrote:

> I would say the car air conditioner is a very small capacity since the
> interior of the car is very much smaller than even a small room.

And you'd be quite wrong. Car air conditioners must have very much greater
capacity than room air conditioners, because the heat load is much greater
in a car.

I think the usual engine-driven underhood unit would be rated at 20-30
thousand BTU. This jibes with the rule of thumb that it takes maybe
five hp or 3.8 kW to run the thing. That guesstimate refers to the
modern cylindrical compressors with helical innardds of the
fixed-displacement kind usually used in the US. I think the
old-fashioned ones that looked variously like lawnmower or mini Harley
engines took more like 10-15 hp.


Why so much (2-3x the BTUs of a window unit for the home)? A car may
be small, but it has a lot of glass and tends to be parked and driven
out in the sun, which means a lot of radiative transfer in and a
tendency toward trapping that heat.

(An interesting sidelight, no pun intended and probably not much of one
achieved... Some recent research, oriented toward quantifying how
badly things go wrong and how quickly when you leave your kids or pets
in a parked car, indicates that not only is the heat gain is at least
40-50 deg. F over ambient, but a large part of it happens early on.)

Various companies and institutions like the National Renewable Energy
Laboratory put a lot of research into these things because it's one of
the areas where small improvements in system efficiency or need
reduction, times a large fleet, equal big savings.

Again, that refers to the typical underhood, belt-driven unit.
Auxiliary ones that you see on the top of motor homes are usually about
12-15,000 BTU each, two or three units per vehicle, and run off of 110V
a.c. house current rather than the vehicle's 12 V d.c.

Cheers,
--Joe

Daniel J. Stern wrote:
> On Thu, 28 Jul 2005 wrote:
>
>
>>I would say the car air conditioner is a very small capacity since the
>>interior of the car is very much smaller than even a small room.
>
>
> And you'd be quite wrong. Car air conditioners must have very much greater
> capacity than room air conditioners, because the heat load is much greater
> in a car.

yup... I can only imagine getting in a black car in vegas after it's
been in the sun all day long. Even in Winnipeg it can be 100+ in my
Trans Am if it's been in the sun.

Now I'm wondering what is the BTU (or ton) capacity of a car A/C system...

Ray

"Pszemol" > wrote in message
...
> Romm air conditioners are rated in amount of heat they can suck out
> of the room measured in BTU/hour. I wonder, if you compare room A/C
> units to car units - how much stronger the car unit has to be ?
>
> Do you know what is an average BTU/hour for a car A/C system?
> Just rough number - is is 10000 BTU or rather 50000 or more ?
Quoted from a poster on eng-tips.com on Aug. 6, 2003: >>The A/C system
on my Acura Type R is rated at 14,000, and it definately puts a good load on
the engine-probably 5 HP at least.<<

Another poster, same site, on July 12, 2002: >>I asked a friend of mine
who works in HVAC at a truck company "Do you happen to know how much heat
the AC system can remove from the truck cab in a given time period" and he
said the following:

20,000 Btu/hr (minimum)
Outside (fresh) air, Panel Vents
90 degF Ambient
50% relative humidity
We actually do a little better than that

This is, of course, in reference to the AC system on a big truck. A car
almost certainly is a bit lower than that.<<

Personally, I don't know; however, a 20Kbtu rating seems reasonable for
a full-sized car, considering the insulation inefficiencies involved. Plus,
that 14Kbtu rating thrown out by the Acura owner has to consider using a
smaller-than-average automobile interior. HTH put us at least in the
ballpark. s

sdlomi2 wrote:
> "Pszemol" > wrote in message
> ...
>
>>Romm air conditioners are rated in amount of heat they can suck out
>>of the room measured in BTU/hour. I wonder, if you compare room A/C
>>units to car units - how much stronger the car unit has to be ?
>>
>>Do you know what is an average BTU/hour for a car A/C system?
>>Just rough number - is is 10000 BTU or rather 50000 or more ?
>
> Quoted from a poster on eng-tips.com on Aug. 6, 2003: >>The A/C system
> on my Acura Type R is rated at 14,000, and it definately puts a good load on
> the engine-probably 5 HP at least.<<
>
> Another poster, same site, on July 12, 2002: >>I asked a friend of mine
> who works in HVAC at a truck company "Do you happen to know how much heat
> the AC system can remove from the truck cab in a given time period" and he
> said the following:
>
> 20,000 Btu/hr (minimum)
> Outside (fresh) air, Panel Vents
> 90 degF Ambient
> 50% relative humidity
> We actually do a little better than that
>
> This is, of course, in reference to the AC system on a big truck. A car
> almost certainly is a bit lower than that.<<
>
> Personally, I don't know; however, a 20Kbtu rating seems reasonable for
> a full-sized car, considering the insulation inefficiencies involved. Plus,
> that 14Kbtu rating thrown out by the Acura owner has to consider using a
> smaller-than-average automobile interior. HTH put us at least in the
> ballpark. s
>
>
I've heard the capacity is in the range of 24K to 30K BTU/hr. The
seemingly oversizing is not so much for maintaining the interior
temperature but rather to get the interior to cooled off fast. Most
manufacturers have acceptance specs on the maximum time allowed to reach
some target temperature. Don't know the details though.

On Thu, 28 Jul 2005 10:00:29 -0500, "Pszemol" >
wrote:

>Romm air conditioners are rated in amount of heat they can suck out
>of the room measured in BTU/hour. I wonder, if you compare room A/C
>units to car units - how much stronger the car unit has to be ?
>
>Do you know what is an average BTU/hour for a car A/C system?
>Just rough number - is is 10000 BTU or rather 50000 or more ?

I'll echo what others have said. I've always understand that the
typical car AC is equivalent in capacity to what's needed to cool a
house. So for small car to small house it would be 15000 btu, big
car, big house, 36,000 btu (3 tons).

Ashton Crusher wrote:
> ... So for small car to small house it would be 15000 btu, big
> car, big house, 36,000 btu (3 tons).

Hmmm...my house is 3000 sq ft and I have a total of 7.5 tons of A/C in
two units. Then again, here in Arizona we need all the capacity we can
get...