Outdoor unit in ventilated garage??

[saveasteading]

That's  a  useful link confirming principles with some science.

 

I wonder if I'm missing the point. There isn't a problem, there isn't a complaint and there isn't a planning constraint? You're just trying to do something fancy to minimise noise and nuisance.

 

It needs numbers.

'Too noisy' is subjective. We need a target of a sound level in dB with the appropriate weighting eg dBA or dBB.

This would be measured at the boundary.

 

In caaw of complaint the LA might then measure the sound level. In my experience this has been the difference between current background sound and the new level, so it gets into cost quite early.

 

But you don't seem to have any formal requirement. 

Therefore I suggest you do a good job based on regommendations above and cross your fingers. If nobody complains, that will be the end of it.

 

 

 

[JamesPa]

3 minutes ago, saveasteading said:

But you don't seem to have any formal requirement. 

Therefore I suggest you do a good job based on regommendations above and cross your fingers. If nobody complains, that will be the end of it

I'm not sure I would agree with this approach.  The problem is that, if someone does complain and you don't have planning consent (whether express or under pd), then you haven't got a leg to stand on and, even though you may not be causing a nuisance, your local authority will use planning law as a lever against you to deal with the complaint (because its relatively straightforward whereas dealing with it under nuisance legislation is much more difficult).

 

So unless you are pretty confident that there will be no complaint or know what you would do if there were one, I'd ensure you have planning consent (express or under pd as appropriate).

 

 

[JohnMo]

Outside observation

 

Sounds like a pretty big ASHP you are looking to install, could your efforts be better spent making fabric improvements to the house so you could install a way smaller heat pump and get down to single fan unit?

 

Also without very careful design your proposal could end making the noise worse, rather than better, and end up focussing the noise in a single direction.

 

Choose make or model of heat pump also makes a real difference in noise production and how annoying it is to othes.

[Beelbeebub]

1 hour ago, JohnMo said:

Outside observation

 

Sounds like a pretty big ASHP you are looking to install, could your efforts be better spent making fabric improvements to the house so you could install a way smaller heat pump and get down to single fan unit?

 

Also without very careful design your proposal could end making the noise worse, rather than better, and end up focussing the noise in a single direction.

 

Choose make or model of heat pump also makes a real difference in noise production and how annoying it is to othes.

What if the noise was focused *upwards* 😁

 

If the exhaust duct curved up and exited the roof of the garage then theahority if the sound would go up.

 

More likely a brick "chimney" constructed on the side

 

 

 

 

[JohnMo]

53 minutes ago, Beelbeebub said:

noise was focused *upwards*

What goes up, must come down. Was involved in an offshore wind farm and it had an onshore sub station, the noise at the sub station had been attenuated really well, but the village about 3 miles away had a nice focussed beam of noise coming down on them, apparently way noisier than you would have expected, anyway £1 million pounds later they had it fixed.

[billt]

When we moved to this house the swimming pool had an ASHP built into a brick built shed. The exhaust faced was about 3 inches from a big hole ine the wall. There was no baffle to prevent air bypassing, but it was so close to the wall that air flow was restricted. It seemed to work OK, but it won't really solve any noise issues. If you have a big enough hole for the airflow most of the noise will go out of the hole too.

 

The ASHP we used to replace the original is fitted behind the pump house and is a lot quieter than the original, even though it is external.

 

I have been quite disappointed by the noise that the recently installed ASHP for the central heating makes. I had been expecting something like the You Tube videos which seems to be pretty much white noise (which the pool heat pump produces) but the compressor is pitched and very audible and annoying. The absolute level is within spec and isn't loud enough to be a problem for the neighbours, but it doesn't half irritate me and I lived in a house close to a heat pump like that I would be complaining.

[Archer]

On 18/11/2023 at 08:43, JamesPa said:

As a matter of interest what noise criterion is your planning authority insisting you meet.

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. 

[Archer]

On 18/11/2023 at 09:21, JohnMo said:

 

Sounds like a pretty big ASHP you are looking to install, could your efforts be better spent making fabric improvements to the house so you could install a way smaller heat pump and get down to single fan unit?

 

Also without very careful design your proposal could end making the noise worse, rather than better, and end up focussing the noise in a single direction.

 

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... 

Edited November 19, 2023 by Archer

[JoeBano]

I worked on a bungalow couple months back and was having a ashp fitted. The neighbour bedroom window was 2.5m away for the heat pump location. He paid £1400 for a sound assessment, fitted an acoustic fence (same as a normal fence just twice as thick) and fitted mitsubishi ecodan heat pump. The council accepted that. 

[Archer]

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. 

[JohnMo]

7 minutes ago, Archer said:

also because we want the option of cooling in extreme weather

In another statement you made earlier you stated it was for heat only, but obviously it heat and cool like you expect from an A2A.

 

So are you applying for full planning permission?

 

I have attached the noise data for my A2W and it can be seen distance is your friend. A2A piping isn't that much of an issue for long distances.

[JamesPa]

1 hour ago, Archer said:

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.

If 35/38dBA is the heat pump only (ie it excludes contribution from background) then it's very close or even above pd which is actually 37 dBA excluding background, or 38dBA depending on exactly how you do the calculations.

 

42dBA is often quoted as the PD value but this is wholly misleading as it includes an assumed background of 40dBA (why I don't know, the extra calculation steps merely serve to confuse).

Edited November 19, 2023 by JamesPa

[Beelbeebub]

1 hour ago, JamesPa said:

If 35/38dBA is the heat pump only (ie it excludes contribution from background) then it's very close or even above pd which is actually 37 dBA excluding background, or 38dBA depending on exactly how you do the calculations.

 

42dBA is often quoted as the PD value but this is wholly misleading as it includes an assumed background of 40dBA (why I don't know, the extra calculation steps merely serve to confuse).

Yeah it's really odd to include a calculation step that references a background level (which isn't in itself a stupid thing to do) but then assume the background noise is fixed at 40db.  

 

It explicitly says not to use any other figure.

 

So in effect you will fail the 42db test in any circumstance where your corrected figure is greater than 38db

 

So why not just say that?

[JamesPa]

9 minutes ago, Beelbeebub said:

So in effect you will fail the 42db test in any circumstance where your corrected figure is greater than 38db

 

So why not just say that?

Precisely and not a clue respectively!

 

If you use the MCS official spreadsheet it's 37dBA so far as I can tell.

[Archer]

1 hour ago, JohnMo said:

In another statement you made earlier you stated it was for heat only, but obviously it heat and cool like you expect from an A2A.

 

So are you applying for full planning permission?

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

[Archer]

50 minutes ago, Beelbeebub said:

Yeah it's really odd to include a calculation step that references a background level (which isn't in itself a stupid thing to do) but then assume the background noise is fixed at 40db.  

 

It explicitly says not to use any other figure.

 

So in effect you will fail the 42db test in any circumstance where your corrected figure is greater than 38db

 

So why not just say that?

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

[JamesPa]

9 hours ago, Archer said:

I would rather have the comfort of the PP, it seems daft that the noise threshold doesn't align though

It's completely daft.  My lpa wants me to achieve 27dBA (it's starting point was 10dBA below background which it claims is 30dBA, I've talked them up a bit!).  That's just mad.

[Archer]

11 hours ago, JamesPa said:

It's completely daft.  My lpa wants me to achieve 27dBA (it's starting point was 10dBA below background which it claims is 30dBA, I've talked them up a bit!).  That's just mad.

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