@bretix, provided that ASHPs have "breathing" space you can do what you like. Our heat pump has a 2m high log store and fence behind the heat pump and along the sides, and it's open in front where the fan blows outwards. It's all about ensuring that you're not trapping cold air in and around the evaporator.

Did you have something in mind?

I've seen people do this for aesthetic reasons (possibly harming their performance), but what is the motivation behind a protective fence? To protect from wildlife? 

@oswiu the pumps and condensate blow near a path that very quickly turns into an ice rink!

Maybe I need to look into my condensate drainage further but wondered if a picket fence maybe might prevent the path icing. 

If your path is turning into an ice rink there is likely a problem with the condensate drain which the installer should have done properly. The condensate is usually directed into a pipe that goes about a metre deep in a gravel bed.

I have an 'ice rink' by my ASHP simply because the normally adequate drain pipe has frozen.

@morgan My heat pump has some kind of heat wire going into the drain (well it will have when it is redone as at the moment it is hanging over the ground a short distance away from any pipe and it should be vertical over the pipe)

@saz

It's set on a concrete pad with a gravel strip about a meter in front before reaching a path. There's a gravel bed the left of the setup. The installer did mention he was surprised a ?different condensate pad was not included for the installation?

@bretix  This is what it says in the installation manual for your pump.....

'3.5.3 CONDENSE DISPOSAL
The underside of the heat pump has a condensate outlet (refer to
Figure 3-2) that allows any condensate to drain from the heat pump.
Provision must be made to safely collect and dispose of the
condensate.
For example, use 40 mm waste pipe to form a condensate disposal
system into which the condensate flows from the opening in the
bottom of the heat pump casing running to a suitable gulley or
soakaway.
! WARNING !
It is essential that the condensate is able to drain away and
not allowed to run onto any adjacent paths or driveways
where, in winter, this will result in icing and a potential hazard for anyone walking near the heat pump.
The top of the concrete base must be either level with, or
above, the surrounding ground level'

Condensate drains could have been routed through the concrete pad to drain into the hardcore substrate underneath. A 50mm core cutter would have made light work of that to about 12" deep to soak away below the frost penetration line. They did that with my 10kW Aerona and it has worked fine in this cold snap. Is the outdoor unit pipe insulation external grade? At first my installers just put internal grade pipe Armaflex insulation and I insisted on Armacell Tuffcoat waterproof, which is more UV stable, designed for outdoor use and has a weatherproof outer skin. It looks to be different diameter on the RH unit (?)

@allyfish I'll have a look at this closer in daylight.

Thank goodness for this forum for the questions I keep finding.

I'm not sure where I stand legally as out of interest just checked on companies house and the company that installed the system have been liquidated 🤦🏻‍♂️