  We derive an analytical expression for maximum efficiency at fixed power of
heat pumps operating along a finite-time reverse Carnot cycle under the
low-dissipation assumption. The result is cumbersome, but it implies simple
formulas for tight upper and lower bounds on the maximum efficiency and various
analytically tractable approximations. In general, our results qualitatively
agree with those obtained earlier for endoreversible heat pumps. In fact, we
identify a special parameter regime when the performance of the low-dissipation
and endoreversible devices is the same. At maximum power, heat pumps operate as
work to heat converters with efficiency 1. Expressions for maximum efficiency
at given power can be helpful in the identification of more practical operation
regimes.
