Screening design for heat pump - comments invited

[saveasteading]

2 hours ago, SteamyTea said:

hoods for noisy machines

So design one that allows an ashp to operate fully, and make your fortune.

[SteamyTea]

11 minutes ago, saveasteading said:

So design one that allows an ashp to operate fully, and make your fortune.

How to build a sonic crystal

 

1 March 2011

 

What you’ll need: poles or tubes, a saw, measuring tape, a drill, a hammer, nails, two planks of wood (one as a base plate and another as a top plate)

1. Collect poles or tubes (almost any type of pole can be used – metal, plastic or wood, hollow or solid) and decide on the range of frequencies you want to block. The wider the tubes, the broader the range of frequencies the crystal can stop. The pole separation also affects the frequencies you can block so you may want to calculate this now:

Pole separation (a) = speed of sound in air /(2*frequency).

2. Cut the poles into pieces of equal length. To be most effective, the poles should be a long as possible. The crystal should be at least five poles deep to be effective.

3. Mark out a grid on your base plate to show the position of the poles by using the pole separation equation given above.

For example if you want to attenuate low frequencies around 440Hz (this is the frequency of the note A above middle C in the musical scale) you should use cylinders separated by a distance of 39cm and the diameter of each cylinder will need to be 26cm. This structure will be very large!

4. Attach the poles to the base plate. If you’re using solid poles, the simplest option is to nail them to the plate from behind. Depending on the poles you’re using, you may also want to use glue or screws.

5. If the poles are unstable, add a top plate to keep the structure rigid.

6. The best way to test the crystal is with a sound at a single frequency. To create a test tone, you can use a tone generator (like this one available free online) to create a sound file with a specific frequency and duration. Upload this tone to your cellphone.

7. Position your cellphone on one side of the crystal in the centre of the array, roughly 30 cm away from the poles. Play the tone and listen for it on the opposite side of the crystal. You’ll know your structure is effective if the sound is muted.

[sharpener]

12 hours ago, JamesPa said:

Not particularly easy to build though

 

Since you are going to be buying a lot of quite expensive cedar for this your local friendly timber yard will probably rip 4 x 2 into two bits of triangular cross section for a nominal charge. Or you could use arris rail section in treated softwood and stain it to match.

 

Or use fence boards, which are already slightly tapered, and put packing pieces under one edge of them - it's not as though it has to be structural beyond staying upright in the wind.

 

4 hours ago, SteamyTea said:

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.

 

IME this kind of construction works well. The trouble with it out of doors is that almost anything that is a good absorbent for sound is also a good absorbent for water. Though there are some specialist materials which are not badly affected, there was a thread about this in the spring.

 

 

Edited September 1, 2023 by sharpener

[SteamyTea]

6 hours ago, sharpener said:

almost anything that is a good absorbent for sound is also a good absorbent for water.

That is why reticulated foam is used, it is more like a fishtank filter material than a cushion.

[ReedRichards]

You never said what was wrong with this idea:

 

 

Edited September 2, 2023 by ReedRichards

[DanDee]

20 minutes ago, ReedRichards said:

You never said what was wrong with this idea:

 

 

 

Isn't that in the way/closer to space one would use in their garden?

[ReedRichards]

8 hours ago, DanDee said:

 

Isn't that in the way/closer to space one would use in their garden?

 

Yes, but it doesn't get overlooked by two windows, one of which looks out onto the garden.  And it doesn't place the heat pump in a little sound-broadcasting enclosure.

[JamesPa]

9 hours ago, ReedRichards said:

You never said what was wrong with this idea:

 

 

 

1.Visible from AP2 with no practical option for screening so in total poorer according to the MCS analysis

2.The piece of wall against which the HO is sited is <1m long, the heat pump is 1.1m long, thus it would obstruct my patio door or project to the left beyond the wall which is architecturally ugly 

. 

Edited September 2, 2023 by JamesPa

[ReedRichards]

Use trellis with attractive climbing plant grown up it.  Planted in it's own container if it cannot be planted in the ground:

1. Blocks view of heat pump from AP2.  Deflects some noise and muffles it when plant is in leaf.
2. Blocks 10 cm projection of heat pump beyond end of wall.
3. Provides attractive plant to view from Utility window.
4. Cheaper option than complicated sound screen.   

[JamesPa]

1 hour ago, ReedRichards said:

Use trellis with attractive climbing plant grown up it.  Planted in it's own container if it cannot be planted in the ground:

1. Blocks view of heat pump from AP2.  Deflects some noise and muffles it when plant is in leaf.
2. Blocks 10 cm projection of heat pump beyond end of wall.
3. Provides attractive plant to view from Utility window.
4. Cheaper option than complicated sound screen.   

 

... maybe, but either its not a solid barrier (plants are not a solid barrier) so cant reasonably be assumed to block sound, or its a third reflective surface within 1m, thus restoring the penalty for reflective surfaces.  Also it doesn't make sense visually in context (this isn't obvious from the plan, you have to see it on the ground).  Plus it doesn't do what my planned screen does ie. resolve a long standing visual problem which anyway needed resolving (thus justifying the cost of using cedar wood).

 

Thanks for the suggestion all the same, they all add to the thought process.

 

I'm not intending to make the sound screen complex, just hit and miss in the first instance, which because it is solid and obstructs the view meets the MCS requirement and is genuinely reasonably 'sound' from a sound perspective. 

 

The principal risk with this simple design is, I think, reflection into my house not towards the neighbours house; the basic sound trajectory, given the orientation of the heat pump and barriers, is going to be 'down the garden'.  Since I am unlikely to be running it even for DHW in summer as I have solar PV, I really don't think that noise in the garden matters much (and anyway the neighbours have a heat pump for their swimming pool about 15m down the garden, so they cannot legitimately complain too much about garden noise).  My intent therefore is to prototype it in cheap wood, see if there is a problem in my house.  If there is , see if rotating it as @sharpenersuggests makes a difference and if so somehow angle the slats on the production version of the hit and miss.     

 

Its a pity that this area appears to be so 'experimental'  There must surely by now be acoustic modelling software which would allow these sorts of things to be designed.  I guess that uncertainties in the materials would still impose limitations, and its (apparently) already pushing expectations to expect plumbers to become heating engineers without also expecting them to become acoustic engineers as well!

[JamesPa]

17 hours ago, SteamyTea said:

That is why reticulated foam is used, it is more like a fishtank filter material than a cushion.

I googled reticulated form and fish tank filters was what appeared top.  I had to add sound absorber to the search term to get foam specifically for this purpose.

 

Im not particularly keen on foam between the two sides of the hit and miss panel because it will obstruct air flow for the heat pump, although there is an argument that its anyway far enough away and also air from above is pretty unrestricted because its a single storey building so this wouldn't matter much.  

[SteamyTea]

5 hours ago, JamesPa said:

Im not particularly keen on foam between the two sides of the hit and miss panel because it will obstruct air flow for the heat pump,

Reticulated foam is what we made the air filters from.  These could be tiny ones for old Minis to huge ones for mining.

Take the air filter off your car and see how noisy it gets.

 

If you want a cheap fish tank filter, use a bit of Scotchbrite, it is the same stuff.

[sharpener]

9 hours ago, JamesPa said:

I'm not intending to make the sound screen complex, just hit and miss in the first instance, which because it is solid and obstructs the view meets the MCS requirement and is genuinely reasonably 'sound' from a sound perspective. 

 

9 hours ago, JamesPa said:

... and if so somehow angle the slats on the production version of the hit and miss.  

 

On further thought this may not work. At wavelengths much shorter than the slat width it might be OK (say 4 ins == 3kHz) but around the 3kHz mark it will act as a diffraction grating and might give you quite marked side lobes (think Yagi antenna) - you could model it and see what you get!

 

For reflections at significantly lower frequencies I think the detail will be unimportant and the orientation of the overall screen surface will be dominant.

 

So it very much depends on the nature of the noise. I remember reading somewhere that Vaillants have an annoying whine resulting directly or indirectly from the inverter drive, I will be asking my prospective installer for a reference site with the same model to check this aspect as well as for general comparison purposes, did you do the same?

[JamesPa]

2 hours ago, sharpener said:

 

 

On further thought this may not work. At wavelengths much shorter than the slat width it might be OK (say 4 ins == 3kHz) but around the 3kHz mark it will act as a diffraction grating and might give you quite marked side lobes (think Yagi antenna) - you could model it and see what you get!

 

For reflections at significantly lower frequencies I think the detail will be unimportant and the orientation of the overall screen surface will be dominant.

 

So it very much depends on the nature of the noise. I remember reading somewhere that Vaillants have an annoying whine resulting directly or indirectly from the inverter drive, I will be asking my prospective installer for a reference site with the same model to check this aspect as well as for general comparison purposes, did you do the same?

Hmm, thanks for this thought.  The slat width is 45mm, so I guess that's 6kHz.  I would have thought that it was the slat pitch that matters though, but that's only a bit larger.  I'm definitely not going to model it, I'm going to build a prototype and see what happens.

 

I was aware of the (alleged) whine, I haven't asked for a refence site and many report a good experience.  In I haven't asked because, to be honest, I've had a pretty exhausting 2 year journey with the difficulty of all of this, and the many obstructions that both the industry and my LPA put in the way.  I am thus grateful to have a solution which fits within PD rules (they don't consider Yagis) so the LPA doesn't need to get involved with. 

 

So I'm now taking the view that any further challenges (of which there are bound to be some) will just have to be ironed out experimentally.  In extremis I will move the pump 20m down the garden, or revert to putting it on the garage roof (which is MCS-020 compliant without any barrier, albeit has no chance of meeting my LPA demands).  Both are 'solutions' that I want to avoid if at all possible, but not much is actually lost if I am eventually forced to adopt them.

 

Sadly, after this 2 year journey, I can't currently see how heat pumps have got any chance of being adopted by the mass market in the UK.  The industry and in particular the gatekeeper, MCS, and my LPA at any rate, simply doesn't understand (and, so far as I can tell, doesn't want to understand), the challenges of the customer experience.  Perhaps I (like many on this forum) understand too much and would have an easier time as a 'dumb' customer, with perhaps an 80% chance of getting a workable installation and a 20% chance of getting rubbish (which in the latter case they have no chance of understanding enough to fix and which the industry will close up around its protective regulations to justify ignoring). 

 

Unless the government steps in seriously, bothers actually to understand the industry, and forces it to fix itself up (which currently would entail disbanding MCS, which appears to be the root of much of the problem, or as a minimum taking it out of the PD loop), I predict that the political hurdles will be too great and the transition will be watered down or abandoned.  I'm really quite depressed about it, because I fear that the civil service has been diminished to the point where it can no longer do the work that would be necessary to fix up the situation, even if ministers had the will.

Edited September 3, 2023 by JamesPa

[saveasteading]

Can i return to basics?

Your design is good. Planks hit and miss on opposite sides is good practice....look at motorway sound barriers.

Do it and see how it works.

[SteamyTea]

39 minutes ago, saveasteading said:

Do it and see how it works

You can also add random spot mass to it, that can be used to tune the absorption.

 

I wonder how hard it would be to add a sound cancelling system to a heat pump.

 

eBay have some noise cancelling headphone for less than 20 quid.

But of modification and an old Amstrad stereo from a car boot sale should do it.

Can always play your Bowie collection if not.

[Conor]

I really wouldn't bother, you get used to the look and low hum in no time. They are much quieter than you think. Stick the unit in and then see if/what bothers you. 

[saveasteading]

1 hour ago, SteamyTea said:

can be used to tune the absorption.

And then you can write the definitive book on the subject.

I don't think this fence is down to mass, just blocking and breaking up the sound waves.

If it looks good and purposeful, the neighbour won't be seeking problems.

[JamesPa]

1 hour ago, SteamyTea said:

Can always play your Bowie collection if not.

Perhaps somebody should design a combination heat pump/juke box with directional sound, able to broadcast different tunes on each of the sides.

 

For what it's worth I have regular experience of resonance effects when taking my narrow boat through a tunnel.  Get the angle precisely right, and the person steering (ie me) can be deafened by the reflected, resonant noise of the exhaust.  Fortunately the window for the effect is very narrow, the tinyest of angles completely kills it.  Hopefully too with the heat pump.

Edited September 3, 2023 by JamesPa

[Timedout]

Every morning and frequently through the day and evening I can hear to chorus of my own and many of my neighbours oil boilers. I find it hard to believe that the ASHP makes more noise than an oil boiler.
 

 Why is planning law putting up unnecessary barriers? Is this MSC employing another market control strategy?

[JamesPa]

30 minutes ago, Timedout said:

Every morning and frequently through the day and evening I can hear to chorus of my own and many of my neighbours oil boilers. I find it hard to believe that the ASHP makes more noise than an oil boiler.
 

 Why is planning law putting up unnecessary barriers? Is this MSC employing another market control strategy?

Its 'NEW' technology used mostly by FOREIGNERS and follows FRENCH laws of physics.   Just like unvented cylinders, which might BLOW UP.

 

...therefore it must be bad, and thus you have to burden it/its an opportunity to burden it with unnecessary regulation (all done in the name of consumer protection).

 

With apologies for the Daily Mail style reporting!

 

In fairness some light touch rules on noise only are probably justified both for oil burners and ASHPs.  LPAs should then be prohibited from imposing more severe noise restrictions, but allowed to permit more relaxed ones eg in noisy areas..

Edited September 3, 2023 by JamesPa

[SteamyTea]

47 minutes ago, JamesPa said:

FRENCH laws of physics

Does that account for all the problems at CERN.

The protons travel perfectly though the part in Switzerland, clockwork precision even, then grind to a halt and have lunch, some light sex with a mistress, a snooze and half a bottle of cheap brandy when they hit the French part.

 

Probably why we left the maths to the French, they can only (expletive deleted) up a napkin.

 

Oh shit, just remembered half my family is French.

Edited September 3, 2023 by SteamyTea