Utilizing waste heat like that is incredibly difficult, if not impossible. The difference between ambient temperature and heated air expelled by AC is too low to be utilized by mechanical means. Use of piezoelectric and thermoelectric materials is still in infancy and usually tends to end up with negative energy balance when you factor in production and recycling costs against the useful energy generated over their lifetime.
And remember that no energy transfer or transformation is 100% effective. You always end up wasting some in form of heat.
But we should find a way to sell excess heat to third world countries. A useful tech would allow for the creation of different closed systems within the earth
