Mitigate noise from the ASHP

[Tony K]

Evening all. 

Having researched it to death in advance, after one month living in the SB I've now got a better idea of noise levels from my ASHP. As can be seen in the photo, my garden is small, includes a tiny office (to the left of the photo) and is unfinished, as is the external wall of the house (summer jobs). 

 

I was extremely limited as to where I could put the ASHP. It is near bedroom windows, and perhaps closer to the wall than is ideal in terms of rebound echo. 

 

Anyway, up until this week the noise has been fine. Obviously, the windows are closed in the evening, which helps. I have always intended to apply various noise mitigations as appropriate once living with it. 

 

This week, once the temperature dropped close to, and then below, zero, the ASHP became really, really noisy. It is quite noticeable indoors, and almost overpowering outdoors. I have seen it complete its defrost cycle (I presume. It kicks out a load of steam) and there is little or no ice settling on it, and I've no reason to think it's faulty. When the temperature returned to normal briefly one night, the noise from the ASHP reduced considerably, only to increase again when the cold snap returned. 

 

I am thinking of pinning some sort of sound proofing to the wall behind the unit, partly to lessen noise inside the house but mostly to affect echo. The garden will have six to eight inches of topsoil and then grass on it in due course, and the office will be clad in timber, all of which I think might help. I have considered building some sort of acoustic enclosure, but not yet researched any details. 

 

Does anyone have any experience of attempting these things, and/or other suggestions? 

 

Cheers 

[sharpener]

If you search amongst @JamesPa's posts about a year ago there was a lot of discussion about various possible measures including commercially available enclosures (v expensive) and mats behind the HP.

Also as you have found, the most objectionable noise only occurs in the top 10 - 15% or so of the power range. Is there any way of limiting the output power somewhat whilst still leaving enough to keep you warm, perhaps with slightly longer heating times? Might be labelled Current Limit or Noise Reduction Mode.

 

 

Edited Saturday at 22:58 by sharpener

[PhilT]

The speeded up fan whooshing caught me by surprise during the first freezing night after installation. But I can barely hear that inside the house. What kind of walls and windows are those?

Edited Saturday at 22:58 by PhilT

[Tony K]

31 minutes ago, PhilT said:

The speeded up fan whooshing caught me by surprise during the first freezing night after installation. But I can barely hear that inside the house. What kind of walls and windows are those?

 

Standard cavity walls, block, insulation, block. Double glazed windows. 

[Tony K]

1 hour ago, sharpener said:

If you search amongst @JamesPa's posts about a year ago there was a lot of discussion about various possible measures including commercially available enclosures (v expensive) and mats behind the HP.

Also as you have found, the most objectionable noise only occurs in the top 10 - 15% or so of the power range. Is there any way of limiting the output power somewhat whilst still leaving enough to keep you warm, perhaps with slightly longer heating times? Might be labelled Current Limit or Noise Reduction Mode.

 

 

 

Thanks, I think I've found the discussion in question. 

 

Something I've never been clear about is which part of the ASHP unit the noise emerges from (if it comes from one part in particular). If the noise comes from the front then would I achieve anything by adding acoustic matt to the wall behind the unit? 

[JohnMo]

Your trouble is the noise is bouncing about. The noise is in principle projected forwards, there is a hard surfaces in front, that deflects the noise towards the house.

 

You may find getting rid of all the mess may help, allowing the noise escape easier. Then some soft planting, shrubs and bushes to absorb noise.

[Beelbeebub]

That outbuilding is going to bounce the sound stright back at the house.

 

Drive along with your window down and note how much reflected noise you get driving pet a wall vs hedge vs open fields.

 

Have a really good look at what you can do to that structure to reduce reflections. Climbing plants, cladding, hedge etc.

 

One idle thought, the sound is most likely getting in via the windows etc. The sound will be a very consistent "droning". Ideal for some sort of active nose cancellation system? Do they do ones that fit to windows? They used to have transducer that would fit to glass to make them into speakers and could use them as mics.

[Beelbeebub]

Found this, absolutely no idea how much it is, if it works or is. Just snake oil.

 

https://denoize.com/

[Pocster]

I deliberately placed mine away from the house but 1 metre away from a stone wall.

 

When it's real cold and it kicks in ( to defrost maybe ) it can be surprisingly noisy.

[Tony K]

2 hours ago, Pocster said:

I deliberately placed mine away from the house but 1 metre away from a stone wall.

 

When it's real cold and it kicks in ( to defrost maybe ) it can be surprisingly noisy.

 

Both in terms of volume and pitch, I would describe the noise from my ASHP in the very cold evening as more than enough to scare most people away from buying one. It's certainly not something I'd be happy to live with moving forward. 

 

Thanks for your comments all, general view seems to be that the reflective surfaces are a key issue. They will all be addressed as part of the landscaping etc anyway. 

 

Has anyone experimented with home made acoustic enclosures, acoustic mats etc? I should probably think about them before I finish the landscaping, rather than after. 

[Beau]

I've messed about with making sound dampening enclosures in the past but inside

 

The usual 3 options 

 

Containment. Clearly not a great option for the heat pump 

 

Absorption. In the case of my project this required acoustic rockwool which is much denser. Again not easy in that space

 

Diffraction. This is breaking up the sound waves. The ivy on that hedge is probably doing that pretty well plus probably some absorption. Could you grow a creeper up the wall of the outside shed and fence?