Archer

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 😅

That was the plan essentially, the unit would be 300mm or less from the louvre (the exhaust) and the engineer would calculate the free flow. It does seem like in theory it could work, it's just that everything you read online and in the technical literature says keep them outside with free flow air. But if you look at the ISO accredited acoustic enclosures, they basically do the same as our engineer is suggesting - ie. A small, ventilated box. I don't know if I have the courage to push the trigger on it though

This is along the lines we were thinking... It's hard to illustrate without drawings but in that photo above - the window would be taken out and a timber louvre put in instead (approx 1m x 1.2m) that would line up directly with the side intake... The exhaust would face another similar size timber louvre and we'd box the edge of the unit to stop the air mixing. It sort of feels like it should work on paper, but I still don't know if it's a good idea, I guess it would mean a gale howling through the garage and not sure whether the provider would warranty the installation of there was a problem. Fitting it outside on the garage wall is also an option but we're in a conservation area so the appearance comes into play

I think I know the answer to this one before starting... but... One option for us to address a noise issue with our heat pump location (planning app) seems to be to locate the outdoor compressor unit in the garage. The proposal from our engineer is for the fan to be in the corner 30cm from a large 1m x 1m louvred opening and a separate side vent discharging the exhaust air from the side of the air to outside. See photo of location below... So everything I've read online seems to say this is a bad idea but the engineer says quite reasonably that they have fitted this before in undercrofts or ventilated enclosures without any issues. What are the thoughts... If there is a performance drop is this likely to be major or minor? Does the main fan suck new air from the front and discharge cold air from the back (or is it from the side only?

Hahaha The worst part is that it's usually our young girls walking me up bit this time I don't even have an excuse... Just insomnia muscle memory! I'll go to sleep I think, enjoy the trip!

I was worried about this when we moved in March but honestly hasn't been an issue at all. We get noise from footsteps through the ceilings but no conversation audible from the ducts. That was a nice surprise, it might just be the way our system was designed though

I don't know if this is helpful or not because our A2A system hasn't been installed yet (gas warm air currently...) But... We've specced a Mitsubishi unit, and gone for one considerably larger than the expected heat loss. For a few reasons. 1. All the AC engineers seem to recommend it based on experience (but this may just be natural caution) 2. A2A units have reasonably good modulation ratio's so short cycling should be less of an issue. Ours is around 6;1 (so 1.4kw to 9.5kw 3. You get lower output in extreme temperatures, as much as a 25% drop @ -10 degrees on our unit 4. There seem to be some efficiency advantages to HP's running in the middle/ lower end of their capacity so long as they don't excessively cycle. This is also true for unit noise 5. On the Mitsubishi range, the COP increases quite a lot for the larger units over some of the the smaller ones. On the positioning of the outlet grille and return duct - there are some brilliant resources from the US online. I'll try and post one I found later on

Our (70's) house has a combination of floor and wall gratings. Apart from looking a bit dated they are mostly fine in the floor if you know your room layouts. We've noticed that all sorts of stuff falls down the grates, but it's easy to lift out and vacuum clean. This is one of the advantage of the lift out grates, albeit they don't look as good as flush linear slot diffusers. I'll send some pictures of ours in carpet later if that helps. We're actually doing the opposite to you and moving some floor ones to the ceiling on the first floor where we have a loft above. This isn't for aesthetic reasons though, they look fine in bedrooms - for us it's technical, around our heat pump installation.

Thanks everyone, yes I'm coming around to the keep it simple view as well, definitely

My powers of sketch are worse than my technical knowledge but here we go... The below shows a very simplified sketch of the proposed system. Pump A serves the top floor and fancoil unit C; Pump B serves the ground floor and fan coil unit D also in the loft). My OP was asking whether it's potentially possible to have 2x refrigerant lines into each fan coil, so C+D are served jointly by A+B with a control to make B the dominant one and A to only kick in past a certain output (ie. in very cold weather if needed). Sorry I don't have circuit sketches or anything like that, just querying whether this is ever done? I think I may have answered my only question and the fan coil units might not be set up for multiple refrigerant lines

Sorry, this is another annoying, niche question that I have on our install... I'll ask our engineer as well but using this as a safe space first in case it's a really daft question... Current plan for our refurb is 2x outdoor units and 2x ducted indoor A2A units. The total capacity seems to be well over what's needed based on heat loss (but the pumps have a 1:6 modulation ratio so less of an issue than with an A2W system). The smaller of the two outside units has a significantly worse COP @ 7degrees than the larger - something like 15% worse. Does anyone know if it's possible to set a two pump system up so that one is the primary unit and the second pump acts as a backup/ only kicks in if the heat demand exceeds a certain threshold? There would be several advantages to this if possible - the minimum output would be reduced to reduce cycling; COP increased; noise reduced by sharing the load in cold weather; backup capacity for extreme cold snap etc. From what I can work out with our proposed system, it should be technically fine to run 2x indoor air handler units off a single outdoor. It's just whether there's a way to set them up in series? Obviously you'd need twice the refrigerant runs which would add cost and maybe be a bit ugly... But anything else, or stupid idea?!

That was my understanding of it as well