Monthly Archives: February 2015

The Air Conditioner Effect – Part of the Urban Heat Island Effect

I would point people at this article from 2010 as a starting point.

Think about this:

We wouldn’t put meteorological stations (met stations) right by the exhaust of smoke stacks, would we?  Of course not.  And why not?  The air coming out is HOT.  And what is the air coming out of an air conditioner’s outside compressor unit like?  HOT.

The smokestack effluent is hot because of some heating process.  Normally there is some process in a plant that uses heat and that heat is disposed of out the stack.

Similarly, an air conditioner has a process going on within IT that warms up its exhaust air.  That process is the operating of the compressor unit.  The compressor unit essentially forces a building’s inside air through nozzles, and as the air passes through the nozzle it expands rapidly – which cools THAT air.  But that cooling doesn’t come free.  Compressing that air THROUGH the nozzle means heating it up FIRST.  It has to have a certain velocity in order for the cooling to happen as it exits the nozzle.  So pressure is needed.  And when that coolant is compressed, it heats up and up and up.  Compressors run quite hot, in fact.  And they need to be cooled down.  That is the other side of the air conditioning equation – if you want cool on one side (inside) you have to deal with the heat produced on the other side, and send that heat outside.  The last stage is to run the heated fluid through tubes in front of a fan which blows over them, cooling the fluid in those tubes.  And where does that heat end up going?


(From Notice that orange/yellow arrow representing a heated air plume being sent out into the external atmosphere.  Now do that tens of thousands or hundreds of thousands of times within a city area.  The insides of buildings get cooler, and the outside – what happens to IT? The heat gets dispersed and blended with the ambient air, warming it.  That warming is not zero. Not individually nor collectively.  Collectively those non-zeros adds up.

That is why you don’t put a met station right by the exhaust of an air conditioner – because the air there is HEATED.  So that we can be cool inside, the outside has to get warmer.  In short, the air in our cities is cooler inside and warmer outside.

Now guess where the met stations are – inside or outside?  Right – outside. <i>Where the heated air conditioner exhaust goes.</i> Continue reading