Air Con single vs multi unit efficiency?

[ashthekid]

I have air con pipework setup ready for installation of a new AC system into two bedrooms.

My question is what is more efficient to run as I have two options:

 

2x outdoor units (5kw & 2.5kW units)

or 

1x multi outdoor unit 8kW (this is approx £1000 more than the 2 unit quote)

 

And from a noise point of view is double the noise for two units or are they quieter if being smaller kW units?

If i were to go for 2 outdoor units, what is the minimum gap I can get away with if they are positioned one behind the other? The space I designed for just one units means if i squeeze two in there is only 15cm gap - is this enough?

[crispy_wafer]

 I suspect individually that either of the 2 smaller units will modulate down lower than the single higher capacity unit.  The manufacturers bumf should reveal all.

[RichardL]

Something for the mix based on experience of my house install:

If you're UK and you go for more than one outside unit its outside permitted development and will need planning permission.

Noise is virtually zero - certainly if theres a closed window, and/or 1.5m or so distance from the compressor.
Often the fan rather than the compressor is the only thing you can hear.

Bedroom - are you going to run aircon overnight - i.e. does the internal or external unit noise matter?
Again I don't know your location, but I run aircon to take the room to a good sleeping temp around 10:30 pm then turn off when I'm actually in it.

A larger single unit may be better here - i.e. work it less for much of the year - but care is needed, if its too big then you're into start/stop territory which isn't great.

Personally I went for 2x outside units because of pipe/trunking run distances on a whole house install.

[pudding]

Also, you prob wont need an 8kW unit, 5 or 6 would be fine. Theres very small chance that both internal units will be running and max capacity at the same time, and even if that is called for, it would be for a short time until they throttled down and demanded less. I've got a 2.5/2.5/3.5kW system runnning from a 5kW outdoor unit, all good. In the back of the Daikin manuals and specs you can see what the 5kW outdoor unit can actually provide if all 3 units are running and what they're effectively derated to.

[markocosic]

1:1 units will modulate / control better.

 

 

Might option 3 work?

 

Single head system and duct it to both rooms:

https://www.saturnsales.co.uk/Fujitsu-Slim-Ducted.html

 

 

In terms of outdoor units one behind the other - that's a no - they have to be next to each other. Can be quite close to a wall / quite close to each other top/bottom / fairly close to each other on the sides; but the fan must face ay from the wall not into another unit.

 

 

I wouldn't expect to hang 2.5 / 5 kW heads off an 8 kW outdoor unit. Probably hang that off a 5 kW outdoor unit.