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 ?

Reply to
Pszemol
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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.

Reply to
marks542004

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 :-)
Reply to
Pszemol

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.

Reply to
Daniel J. Stern

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

Reply to
Ad absurdum per aspera

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

Reply to
ray

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.>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.

Reply to
sdlomi2

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.

Reply to
dyno

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).

Reply to
Ashton Crusher

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...

Reply to
M.M.

Only in cooler regions (Flagstaff maybe, but definitely not Phoenix!), or small cottages or apartments, would 15,000 BTU be considered a whole house's worth of air conditioning.

A very broad rule of thumb for home air conditioning in most parts of the US is a ton (12,000 BTU) per 500 square feet. To get a bit more scientific about it, see for instance

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(especially if you want a fairly technical discussion of how peopleend up oversizing their home air conditioner through simplisticfloor-space-based rules of thumb, what's wrong with that, and how toavoid it)
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Cheers,

--Joe

Reply to
Ad absurdum per aspera

Interesting. Thanks for the pointers...

Reply to
M.M.

OH no! I just bought 40 acres in Snowflake (yes on a road) but milder there.

Bush

Reply to
Bushleague

I'm in the same area and get by with 5.5 tons (2 ton & 3.5 ton units) for 4400 sq. ft., max about $100 a month, but the house was especially designed for minimum energy useage (high mass, every room zoned).

Reply to
rantonrave

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