I'd appreciate anyone's thoughts on this, having read in one or two posts (I now can't find...) that longer hoses can reduce/eliminate vibrations travelling through the primary pipework elsewhere.

Yes.  Where would the optimal position and method of stepping down?  I assume nearest the unit, so at the unit's inlet/outlet - but not sure how.

You protect the outside pipework and the pump either by having glycol so the water can just sit at very cold temperatures, or you circulate the warm water in the pipes to keep the outside parts from freezing – the anti-freeze valves are a fail-safe should you be unable to power the water circulation. You would not want to be dumping glycol.

Thank you.

Full bore valves are isolating valves...

From the BES component diagram in the OP (relevant section below), it shows 'isolator valves' and 'full bore valves' - though, having just looked at it again, I've just noticed the isolator valves are inside the property:

The isolator valves I mentioned describing my install are Inta lever ball valves - I assume these should be full bore to maximise flow rate and be positioned as the primary pipework exits the brickwork outside?  Is there any value in having a second set at the unit's inlet/outlet too?

I also don’t have any hydraulic separation, and I have 400mm clear to the rear of the evaporator.

If you are having vibration issues at the heat pump then it might be an equipment issue rather than a pipework issue. I have noise inside introduced by the circulation pumps, but only small amounts of occasional mechanical noise and the sound of the air being moved from the outside unit. The units weigh around 100kg so you wouldn't want any slight vibration to be converted into sound or transmitted to the rigid, fixed pipework, but they aren't going to move around like washing machines.

You ask a few questions:

28mm pipework should run as far as you can take it into the house - you need volume of water in the system to cover defrosts.

You protect the outside pipework and the pump either by having glycol so the water can just sit at very cold temperatures, or you circulate the warm water in the pipes to keep the outside parts from freezing – the anti-freeze valves are a fail-safe should you be unable to power the water circulation. You would not want to be dumping glycol.

Full bore valves are isolating valves...

hi SKD,

What model are you referring to please? The R32 only refers to the refrigerant. I’ve posted here the data sheet for the current r32 models and the clearance quoted is a minimum of 300mm at the back of the product. Where did you see 140mm?

Yes that's right. I remember reading about this when we were ordering ours.  The 5kW has a smaller enclosure than the 6, 8.5 and 11.2kW versions.  Our enclosures are 150mm deeper than the 5kW and have a larger internal air volume. The 5kW is similar in depth to the earlier Ecodans which also required 300mm at the rear.

@derek-m, would you think a larger distance is practical for performance or noise reasons?

Probably both.

The heat pump requires a good flow of 'fresh' air through the evaporator coils, which are located at the rear and one side of the unit. Noise levels can be affected by distance as well as nearby surfaces.

Can full-bore valves provide that 28mm->22mm conversation?  If not, how would it be best done?