Archer

That's helpful @severnside and also a bit worrying from my perspective. We are still waiting on planning (looooonnnnngggg story) but will be retro-fitting warm air in a similar way to you. How has the cost compared with your old oil fired system out of interest?

This unit does look perfect as a direct replacement. You still have an outdoor and indoor unit by the looks of things but it's very design led. The wall units are some of the nicest I've seen. Having gone through the mill on this with the current gas warm air providers (including J&S etc), I'd be a little wary of an unproven American import. The warranties all seem quite weak and you wouldn't get great aftercare support etc. The commercial A2A products are a bit niche, but Daiken, Mitsubishi etc do sell products with decent warranties and engineers that know what they are doing with them. Government should look again at A2A systems, they are not getting the support that A2W does and it makes no sense. HVAC has additional benefits to air quality etc that could really improve uptake imo

Your post on the other website that you linked further up was incredibly useful. Good luck with it, sounds stressful

I've completed the MCS assessment using software and didn't clock that was going on. It makes perfect sense though, now you've mentioned it, it was confusing how many different iterations of most modeling were coming out bang on 42 db (obviously because of the background adjustment). Well that makes a lot more sense now

I don't think I stated in this thread that it was for heat only, not intentionally anyway. It will be primarily for heat, but it's an A2A system so can be used for either (probably just our upstairs zone, not downstairs which will have un-insulated metal ducts). Yes, full planning although PD is an option (not for cooling obviously). I would rather have the comfort of the PP, it seems daft that the noise threshold doesn't align though

Meant to say as well, have already explored fabric improvements and it's not amazing but we have 70-80mm of mineral wool throughout in walls and ceilings and 270mm in the loft/roof. Further improvements are possible but we would lose space and have a very long pay back.

There don't seem to be many ducted A2A units on the market that are significantly quieter, we've looked around and the lowest (max) Sound Power is around 66/67. We did look at 2x smaller units but the planning assessment adds a 3db noise penalty. Obviously A2A have some other advantages- namely that they won't be run at random times for hot water demand (and generally should run less overall). We need this system because we are replacing a gas warm air and have the ducts already. Our system is oversized for heat (covered in other threads). Essentially because A2A units have a good modulation ratio of around 6:1 and also because we want the option of cooling in extreme weather and A/C is sized differently to heat (I think you need something like 40% more output to cool because of heat gains). So our room heatloss is c.8 kw @ -2degrees. The twin fan we've gone for is 14kw max in heating (12kw cooling), but I also feel like it should be running a lot under it's stated max sound power most of the time, hopefully helped by the extra juice. On our proposals / the starting point of this thread... I've gone back to a simpler approach - pump out in the open in a U shaped enclosure with a full, acoustic screen facing the closest neighbour and a full height timber louvre opposite the pump fan discharge/ outlet. This complies with the manufacturers guidance and should hopefully be ok for sound (the neighbour facing the fan louvres has window about 20m away with a brick wall between us and them). We've got an online acoustic engineer working it up for our planning app so hopefully this one gets us through...

They have a requirement for 35db at the assessment window which is challenging to say the least and inconsistent with the PD rights @ 42db. Through conversations with them - which were painfully teased out - they have indicated that they would accept 38db if we can show mitigations. It all feels horribly unfair, we've a neighbour who has built right along our boundary with rooms that are not even noise sensitive, but still affect what we can do. I have to say that I fear for a national roll out unless the system is made easier. 99% of people won't jump through the hoops that I have (whilst paying twice the cost for the privilege). Our council is the Green Party as well and it's still been no easier.

Weird, I looked at the link above and can see the price you said, it's coming out much lower (£700). Maybe my quote was for installation as well

I've got a quote from them already - £1600 for 2m x 2.4m (!!!). Where are you that price from? Also It doesn't have a ventilation value (free air) like some of the louvre options. In the other location that we are looking at we can keep the barrier 50cm away from the fan which is technically ok but it feels like performance might be better with a louvres / hit and miss your option than a solid barrier. Can I ask a question, in practice how often do the heat pumps run at their max sound power? Ours will be a bit oversized (which you need if using for cooling) so very rarely running full tilt (we'll use for cooling very rarely as well, just want the option). Just trying to get a gauge on it

I'm leaning towards this - keep it simple, show the acoustic louvres, build something hit/miss to allow airflow and help with noise, and then if there is a real problem down the line we can look at the "proper" (expensive) solutions

It is high and that's part of the issue. But we haven't been able to find a ducted A2A unit that is significantly quieter. We were looking at 2x smaller units but they add a noise penalty of 3db so it doesn't help. There isn't doesn't seem to be the domestic market for them yet so no quietmark products or anything similar. It's ridiculous really and made it so hard. But we've looked at all the main manufacturers. Re: hit and miss, yes that's an option and the steel acoustic louvres are all rated for noise and airflow. But they are pricy (£c. £200 per meter +) we might end up having to go that route though

Yes all good points, a louvered fence is an option in a different location that would work. The premade units are quite expensive and we need an acoustic report to back up the reduction (because it's not permitted development). Definitely an option though. I don't know it will be noisy, it's the planning team creating issues. It's an A2A so will only run on the winter when windows are closed anyway but the sound power is 70db - that's the max noise output but the figure used for assessment. That's obviously quite loud but you adjust it to get to a sound pressure at various assessment points (ie neighborhood windows)

Again this is pretty much exactly what I was envisaging... I'll put a sketch up to illustrate how it could look... I was expecting Buildhub to call this plan crazy and be done with it, but it sounds like you think it could actually work... Do you think it's sensible to try and speak to the technical team at Mitsubishi HI and run it past them (mainly for warranty purposes)?

It's a quirk of where our garage is that the end of it basically faces out on nothing much residential, so no major noise issues there but it's the "nicest" bit of the conservation area so I'm worried about neighbours and planners if we try and locate it outside the garage. It's a very attractive brick garage 😅