Newby Heat-Pump question - runs in the winter?
Air Conditioners and Heat Pumps and  are just refrigeration systems. The following are the differences:

Air Conditioners

Dedicated cooling only systems are often referred to as Air Conditioners and have a single usage cycle that dehumidifies and cools the interior air in the living space. These are turned off in winter time for the obvious reason that you no longer need cool air inside and so often are winter-proofed to also prevent air leakage and precipitation intrusion.

Heat Pumps

Dual purpose heating/cooling systems are referred to as Heat Pumps and have a reversible cycle. They can be used to both Air Condition and Heat the living space by switching the direction of refrigerant flow. 

In the summer time, they cool the interior by heating the outside atmosphere. In winter time, they heat the interior by cooling the outside atmosphere. Hence the name Heat Pump.

They run year around and therefore must have free airflow through them year around (not be winter-proofed with air-tight coverings). Having some sort of roof with clearance to allow free airflow and to keep the snow out would be a really good idea.