Screening design for heat pump - comments invited

[JamesPa]

I'm finalising the details of my ASHP installation, now scheduled for mid October under PD.  As part of the design there will be a ~2.3m high 750mm wide 'screen' which will provide both sound isolation from the neighbours and, serendipitously, resolve a visual mess visible from one of our windows.  The screen supplements a barrier already provided by a wall of my house and an existing brick wall.

 

Im thinking of an offset 'hit and miss' design built from 20mmx45mm cedar, sketches of location and screen design below. 

 

The requirements are

 

1. Not to reflect too much sound back towards (my) window to the right of the HP
2. Attenuate sound reaching AP2 (mostly its attenuated by my house wall anyway
3. look superb (or at least visually attractive)
4. not cause a problem with air flow

 

I am certain it achieves 2 - 4.  I have a slight worry about 1, but am hoping that the complexity provided by hit and miss will resolve this.  There is probably going to be an element of trial and error, and to be honest I'm not expecting it will cause any problem for the neighbours even without the screen, as the unit itself is the '7kW' (8.5kW in reality at -2/45) Vaillant which is one of the quietest on the market and Quietmark certified.

 

Does anyone wish to/feel able to comment in order to help improve the design?

 

 

 

 

[Big Jimbo]

Don't know where i heard, but i didn't think they were allowed under windows ?

[DanDee]

If I would be installing a HP, I would, in time, try different ways to mass load the unit around the compressor sides/top.

 

1. Iron plates, either scrap or new.

 

2. Sand or soil/flower bed, decorative contraptions, molded around the compressor side.

 

Let your imagination flow, but don't stress it, ideas come best with a glass of wine.

 

https://www.eastdulwichforum.co.uk/topic/325464-how-to-make-an-air-source-heat-pump-fit-into-an-east-dulwich-garden/

[JamesPa]

30 minutes ago, DanDee said:

If I would be installing a HP, I would, in time, try different ways to mass load the unit around the compressor sides/top.

 

1. Iron plates, either scrap or new.

 

2. Sand or soil/flower bed, decorative contraptions, molded around the compressor side.

 

Let your imagination flow, but don't stress it, ideas come best with a glass of wine.

 

https://www.eastdulwichforum.co.uk/topic/325464-how-to-make-an-air-source-heat-pump-fit-into-an-east-dulwich-garden/

Thanks for that.  I was also thinking about putting Cedar cladding on sides and top of the unit as a whole to integrate it visually (there are no side vents). Loading this with sound absorbing material is definitely an option.  However I am guessing that most of the sound comes out of the front with the expelled air, so sceptical top and side loading will make much difference.  Obviously directly loading the compressor is also possibility if that is the dominant noise, although I guess Vaillant might already have done that to get to their published sound power.  Once I have it I can open it up!

 

My preferred tipple is real ale but the point is well taken!

 

1 hour ago, Big Jimbo said:

Don't know where i heard, but i didn't think they were allowed under windows ?

 

There are restrictions on R290 pumps which this is, but there is no restriction (according to the data sheets) on putting them below windows.  Propane falls not rises, so its things to the side and below that matter.  The window to the side doesn't open so isnt a problem..

 

[saveasteading]

The use of alternating planks is crucial  to sound reduction, so that is a great start.

Is it about 5m high as the elevation suggests?

I'd make the panel longer, overlapping the wall position, as noise will bounce through that gap.

 

1 hour ago, JamesPa said:

mostly its attenuated by my house wall anyway

I'm not confident of that: any gap allows a high proportion of sound through.

 

I wouldn't put any roof or insulation in. You need lots of unobstructed air flow.

[Beelbeebub]

The best approach woukd be to "suck it and see" 

 

Install it and see how much the sound bounces about. Having worked with noise attenuation (from roads and industrial sites) itvs really tricky. Sometimes barriers can make things worse! 

 

It may be the noise is perfectly acceptable with no barrier, then the issue is simply visual. 

 

 

[JamesPa]

1 hour ago, saveasteading said:

The use of alternating planks is crucial  to sound reduction, so that is a great start.

Is it about 5m high as the elevation suggests?

I'd make the panel longer, overlapping the wall position, as noise will bounce through that gap.

 

I'm not confident of that: any gap allows a high proportion of sound through.

 

I wouldn't put any roof or insulation in. You need lots of unobstructed air flow.

Thanks.

 

Its about 2.3m high in order that assessment point (1m in front of the window) is not visible from any position 25cm from the pump.  Thats just a bit less than the height of the (single storey) wall that it abuts (which obscures most of the view) - elevation below (panel being the arrangement of vertical rectangles)

 

I intend to have no gap between wall and panel however the planks will have gaps between them (because the horizontal member holding them together passes between them to let air through (including wind!) but without any direct line of sight.

 

(edit, by wall did you mean the boundary wall not the house wall?)

 

 

1 hour ago, Beelbeebub said:

The best approach woukd be to "suck it and see" 

 

Install it and see how much the sound bounces about. Having worked with noise attenuation (from roads and industrial sites) itvs really tricky. Sometimes barriers can make things worse! 

 

It may be the noise is perfectly acceptable with no barrier, then the issue is simply visual. 

 

 

Pretty much my intent.  I may even build a prototype out of cheap wood first (I happen to have plenty kicking around) before committing £300 worth of cedar)

Edited August 31, 2023 by JamesPa

[saveasteading]

22 minutes ago, JamesPa said:

did you mean the boundary wall

yes. noise will bounce of the house wall and door and through the gap.

 

 

[JohnMo]

You should really should go through the noise assessment for MCS. From your sketch you appear to have 4 walls to reflect the noise.

 

Have you considered moving else where, like where it says Existing wall.  Way less surfaces to bounce noise off.

[JamesPa]

37 minutes ago, JohnMo said:

You should really should go through the noise assessment for MCS. From your sketch you appear to have 4 walls to reflect the noise.

 

Have you considered moving else where, like where it says Existing wall.  Way less surfaces to bounce noise off.

Thanks for the comment.  Two walls and the ground within 1m = 3 reflective surfaces according the MCS noise assessment which has of course been done.

 

'Existing wall' is the boundary wall so not allowed because within one metre of boundary.  The words themselves are in the middle of the route from patio to garden and would definitely be visible from ap2.  It might just pass the MCS criterion but by a smaller margin than proposed location without visibility.

2 hours ago, saveasteading said:

yes. noise will bounce of the house wall and door and through the gap.

Thanks also for the comment.  The thin line below the wall in the diagram is a fence which, according to MCS, is a barrier because there is not visibility (although I have my doubts MCS is correct, but that's generally the case!).  More importantly I can't see the trajectory to which you refer.  Can you clarify?  The barrier design currently ends more or less level with the end of the wall (based on a projected perpendicular from the house).  This   gives a 'solid and massive' overlap of 100mm due to the fence ending with a concrete post.  

Edited August 31, 2023 by JamesPa

[sharpener]

6 hours ago, JamesPa said:

 

1. Not to reflect too much sound back towards (my) window to the right of the HP

 

If there is scope to cant the screen outwards (i.e. rotate anticlockwise in plan) then any reflections would miss the window on the right.

 

In other respects I think you have a good chance of it working. The hit and miss screen will give rise to multiple internal reflections between wood surfaces which should absorb a lot. I don't think scrap iron would be very effective, you have the mass but OTOH the surfaces are reflective and it has virtually no internal damping.

 

Now if only I could remember the handle of the acoustics consultant who was posting on here in the spring...

[saveasteading]

2 hours ago, JamesPa said:

I can't see the trajectory to which you refer. 

It's not like snooker where the bounce is precise and predictable. Sound waves will bounce off the wall in multiple directions, and probably make it between your new screen and the existing wall.

 

There is also a science to the dimensions of the planks you use, hit and miss, but I have long forgotten any details.

You clearly know to  adopt hit and miss so perhaps have info on plank sizes too?

[SteamyTea]

7 hours ago, saveasteading said:

There is also a science to the dimensions of the planks you use, hit and miss, but I have long forgotten any details.

I wish I had learnt them.

I missed one lecture at university, it was the one on sound waves.

https://en.wikipedia.org/wiki/Wave_equation

 

[ReedRichards]

Isn't it going to obstruct the door?  Why not move it up and to the right (on the plan view).  Or is that a bay window shown on the side elevation?   

[Dave Jones]

put it on the flat roof ?

[Big Jimbo]

I used to frequent a lot of music studios when i was pretending to be the next Smokey Robinson. From what i remember the vocal area was always covered in those foam tiles that looked a bit like egg boxes on steroids.

[JamesPa]

8 hours ago, saveasteading said:

It's not like snooker where the bounce is precise and predictable. Sound waves will bounce off the wall in multiple directions, and probably make it between your new screen and the existing wall.

 

There is also a science to the dimensions of the planks you use, hit and miss, but I have long forgotten any details.

You clearly know to  adopt hit and miss so perhaps have info on plank sizes too?

Re the wall/reflections fair enough.  The house walls are rendered with 10mm stone chips in slurry, creating something about as far from a plane surface as you can imagine.  I'm hoping this turns out to be a good thing not bad.

 

Interesting, re plank sizes, I don't have the info but I'll try a search for it.  I did find a company that sells a slatted wall sound insulation product for interior use, I might take a closer look and see if it tells me anything.

 

1 hour ago, ReedRichards said:

Isn't it going to obstruct the door?  Why not move it up and to the right (on the plan view).  Or is that a bay window shown on the side elevation?   

Sorry about that, the door was long ago changed to a fixed window, the elevation is out of date.

 

36 minutes ago, Dave Jones said:

put it on the flat roof ?

That was the original plan that got abandoned when I thought I might have to install under express consent and installation on the flat roof is simply incapable of achieving anywhere near to the (quite ridiculous) LPA noise spec, because distances are similar or less and there is no realistic possibility of barriers that look anything other than completely ridiculous.

 

I could in principle reinstate the plan now I'm installing under PD, but the thought process and preferences have moved on.

 

21 minutes ago, Big Jimbo said:

From what i remember the vocal area was always covered in those foam tiles that looked a bit like egg boxes on steroids.

Yes, like anechoic chambers.  If I could find a small exterior rated version I might consider it!

 

11 hours ago, sharpener said:

If there is scope to cant the screen outwards (i.e. rotate anticlockwise in plan) then any reflections would miss the window on the right.

I had considered this.  I don't think the whole screen can be canted enough but maybe the individual slats can.  I think it needs an angle of about 30 deg.  I'll play with the CAD, but most likely just experiment with a prototype screen and dehumidifier (as the sound source).

[AliG]

17 hours ago, DanDee said:

f I would be installing a HP, I would, in time, try different ways to mass load the unit around the compressor sides/top.

 

I can stand a couple of feet away from my parents' Panasonic 7kW ASHP and barely tell if it is on.

 

I'll try again on a really cold day in winter, but I think the issue of noisy ASHPs is a thing of the past and not a concern nowadays.

[DanDee]

36 minutes ago, AliG said:

 

I can stand a couple of feet away from my parents' Panasonic 7kW ASHP and barely tell if it is on.

 

I'll try again on a really cold day in winter, but I think the issue of noisy ASHPs is a thing of the past and not a concern nowadays.

 

Agree, yet the topic was started and is actively being discussed/debated.

 

I suppose the best answer that everyone has is to install first and see how it goes from there.

Edited September 1, 2023 by DanDee

[JamesPa]

13 hours ago, sharpener said:

If there is scope to cant the screen outwards (i.e. rotate anticlockwise in plan) then any reflections would miss the window on the right.

 

Something like this might be possible.  At 30degrees slat rotation the reflected sound in principle misses the window and the wall and there is still no line of sight through. Reflections from the rear slats still head towards the window but through a fairly small aperture.

 

Not particularly easy to build though - I think I'm going to suck it and see.

 

[Big Jimbo]

I like it, but to make it even harder to make, i would have every angle different. Totally mess with the sound waves.

[JamesPa]

16 minutes ago, Big Jimbo said:

I like it, but to make it even harder to make, i would have every angle different. Totally mess with the sound waves.

And my mind when I look at it from the window...  I guess it could become a conversation piece.

[saveasteading]

2 hours ago, Big Jimbo said:

Totally mess with the sound waves.

+1.

 

 

 

[Beelbeebub]

Randomness helps with sound attenuation. Regular structures can create peaks and troughs in the sound distribution.

[SteamyTea]

We used to make acoustic hoods for noisy machines.

If I remember correctly, the inside, the noisy side, was 30% open sheet (just loads of 40mm holes.

Then 50mm of reticulated acoustic foam, not that dense.

Then the composite outer cover, which was just a 1300 g/m² grp layup.