Pardon the pun but how much power does the power steering use on a engine?

I have Ford focus 1.8 petrol titanium (08 plate) and have noticed recently that when driving and slow down on approach and turn into corners I feel a draught and drop in the internal cabin temperature.

Also when idling and I turn the steering wheel the rev’s dip slightly. I assume this must be power steering related issue?

When I switch the A/C on it doesn’t seem to affect the power or dip the rev counter.

If this is normal then so be it but was wondering if anyone had experienced similar problems as I was thinking of dropping it back into Ford for a check.

Thanks