[lucioperca]

isn't that used when decompressing the air, i.e. closed loop

[jagged-chisel]

You just pull that from the atmosphere.

Compress to store [potential] energy, take the heat generated during compression and use it, decompress at time of need and let the [hot?] atmosphere supply energy to the decompressing gas.

I wouldn’t call it a closed loop, but maybe a lack of deficit.