Efficiency of an engine:

η

= 1 -

Qc Qh

The efficiency η must be less than 1!

Performance coefficient of a refrigerator:

Κ

=

Qc W

=

Qh W

- 1

The performance coefficient κ may be greater than 1!

Both a heat engine and a refrigerator must have an exhaust. This loss is an inescapable fact of thermodynamics.