Better operation of car air conditioning

The air conditioning in cars is basically a heat pump: heat is transferred from the interior of the vehicle to the outside environment. To do so, energy is consumed - the air conditioning basically increases the load on the car's engine, and thereby increases petrol consumption. Now, I have a few thoughts on how to minimise the build up of heat inside cars, but I'll save that for another post. What I would like to cover here is a more rational way of using air conditioning.

Now, a parked car on a hot - or even warm - day will act as a greenhouse. The effect of the sun will be to heat the air inside the car (and direct radiant heat will further increase any exposed surfaces), and thus heat the seats and anything else inside (which is why it is a criminal offence here, in Victoria, to leave a child unattended in a car (they will heat up more quickly than an adult: think of cooking something in your oven - a smaller object can be cooked quicker, if temperatures are the same [don't like the analogy? Good - that is exactly what people who leave children and animals in cars on warm to hot days are doing), although it is also an offence to leave a child under 15 without adult supervision.

Now, when you go back to your parked car, if you get in, leave it all closed up and then start the engine and the air conditioning, the load your air conditioning has to deal with is:
- the accumulated heat in the interior
- the heat in the air
- the additional heat being put out by the initial air flow from the air conditioner

The second point of these can be dealt with quite easily: turn the fan on high, and open doors or at least windows for a couple of minutes (you should run your engine for at least 30 secionds to get oil circulating before you start driving anyway). For your personal comfort, you can do this while standing outside.

The third heat load is the one that bugs me most. So many people idiotically turn on the air conditioning, and think they MUST close everything up immediately or the air conditioning won't work.

RUBBISH!!!!

If you do close everything up immediately, all you are doing is adding the heat load of the initial warm air that is coming out of the air conditioner to the laod that has to be dealt with by the air conditioner. So, after it deals with the hot air that was in the car initially, it then has to deal with the extra heat load that comes out of the vents when the air conditioner was turned on. You are, in fact, initially INCREASING the air temperature, and then extending the time that will be taken to cool the car. (Of course, this also increases the amount of petrol consumed, and the environmental damage done.)

It's actually quite simple: is the air coming out of the vent warm or cool? If it is still warm (and it can take a few minutes for some air conditioners to start working effectively), then LEAVE THE WINDOWS OPEN.

When the air feels cool, THAT is the time to start closing the car up!