Outdoor unit in ventilated garage??

[Archer]

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? 

[markc]

Unless you leave the doors open you will be creating a large drive-in fridge, and efficiency will nose dive as the unit tries to extract heat from an ever decreasing air temp.

plus I’m sure there will be regs stating the position requirements.

Edited November 16, 2023 by markc

[Beelbeebub]

I reckon it *might* work with some big caveats...

 

First, you need to makes sure there is no recirculation of air from the inlet to the exhaust.

 

The inlet for heatpumps is the back and one side (usually the left as you look at them). That is where air is sucked in over the heat exchanger coil.

 

The exhaust is the circular (sometimes square) opening at the front.

 

You need to make sure no air ejected out if the exhaust can find it's way back into the inlet.

 

You then also need to make sure there is adequate air flow throught the machine.

 

So *if* you were able to mount the HP so the exhaust blew straight out of the building or the inlet drew from outside, you might have a chance.  Imagine mounting the HP against a partition wall with a hole cut in it.

 

To prevent flow issues, the openings into and out of your building would need to be *at least* as large as you HP, againimagine being able to push your HP easily through the hole.

 

 

[sharpener]

7 hours ago, Archer said:

the engineer says quite reasonably that they have fitted this before in undercrofts or ventilated enclosures without any issues

 

Methinks time for a visit to some of these reference sites and talk to the owners...

[Archer]

6 hours ago, Beelbeebub said:

I reckon it *might* work with some big caveats...

 

First, you need to makes sure there is no recirculation of air from the inlet to the exhaust.

 

The inlet for heatpumps is the back and one side (usually the left as you look at them). That is where air is sucked in over the heat exchanger coil.

 

The exhaust is the circular (sometimes square) opening at the front.

 

You need to make sure no air ejected out if the exhaust can find it's way back into the inlet.

 

You then also need to make sure there is adequate air flow throught the machine.

 

So *if* you were able to mount the HP so the exhaust blew straight out of the building or the inlet drew from outside, you might have a chance.  Imagine mounting the HP against a partition wall with a hole cut in it.

 

To prevent flow issues, the openings into and out of your building would need to be *at least* as large as you HP, againimagine being able to push your HP easily through the hole.

 

 

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

[RichardL]

10 minutes ago, Archer said:

The exhaust would face another similar size....

Air pressure is a thing -  Rather than the cold exhaust fan facing the other opening - can you position the machine so the exhaust is near it - in it almost? i.e. so the path of least resistance (ideally the only path) for the air is out of the building?

(Path of least resistance may well not be a straight line)

I would guess (check with an expert) the exhaust fan is not expecting to generate any pressure - so ducting is probably? not an option.


If that cold air finds a way back to the radiators easier than the relatively warm air from outside you'll have a problem.
 

[Archer]

4 minutes ago, RichardL said:

 can you position the machine so the exhaust is near it - in it almost? i.e. so the path of least resistance (ideally the only path) for the air is out of the building?
 

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

[Beelbeebub]

Preventing recirculation is the key, and the only way to really be sure would be to butt the unit against some sort of enclosure so it sealed (some sort of flexible rubber of foam seal against the face) the two air flows.

 

My worry is that this would also channel the noise out, possibly even acting as megaphone and making it worse!

[sharpener]

8 minutes ago, Beelbeebub said:

My worry is that this would also channel the noise out, possibly even acting as megaphone and making it worse!

 

Also consider access for servicing. A way to address both points is to set the unit back from the walls of the garage and then have a removable housing to cover the gap. I am thinking of 3/4 in chip board lined with 50mm fibreglass insulation which IME will absorb noise quite effectively. And having this inside the garage simplifies the task of keeping it dry.

[Beelbeebub]

7 hours ago, sharpener said:

 

Also consider access for servicing. A way to address both points is to set the unit back from the walls of the garage and then have a removable housing to cover the gap. I am thinking of 3/4 in chip board lined with 50mm fibreglass insulation which IME will absorb noise quite effectively. And having this inside the garage simplifies the task of keeping it dry.

More or less this.

[Archer]

11 hours ago, Beelbeebub said:

 

My worry is that this would also channel the noise out, possibly even acting as megaphone and making it worse!

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 😅

[Archer]

11 hours ago, sharpener said:

 

Also consider access for servicing. A way to address both points is to set the unit back from the walls of the garage and then have a removable housing to cover the gap. I am thinking of 3/4 in chip board lined with 50mm fibreglass insulation which IME will absorb noise quite effectively. And having this inside the garage simplifies the task of keeping it dry.

 

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)?

 

[saveasteading]

The expulsion side of it is a rather undirected blast of cold air, so really needs to be to completely free space.

In your case this would be immediately inside the wall at the big opening.

But that's almost outside as regards noise.

The inlet side will find air to replace it if you have loads of openings, or a very big but leaky garage.

 

There isn't much point in an underperforming heat pump.

 

Why can't you build a louvred fence around it to absorb the sound? Or a hedge?

 

Lastly, do you know how noisy it will be and if it is really an issue?

 

 

[Archer]

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)

[saveasteading]

70dB seems very high.

Have you time to change the machine?

 

Surely someone has designed and proven an acoustic fence already.

I know what I would do but proving it would be tricky.

I'm thinking it is planks vertically  hit and miss ie one outside, one inside.  That doesn't just bounce the sound back but kills it.

But a right size of plank will work best for the frequency....someone somewhere has done this.

 

 

[saveasteading]

Acoustic fence for air conditioner works on Google. 

I can't see a diy one yet.

But that will be enough for the planners.

Show a commercial one with numbers.

[Archer]

36 minutes ago, saveasteading said:

70dB seems very high.

Have you time to change the machine?

 

Surely someone has designed and proven an acoustic fence already.

I know what I would do but proving it would be tricky.

I'm thinking it is planks vertically  hit and miss ie one outside, one inside.  That doesn't just bounce the sound back but kills it.

But a right size of plank will work best for the frequency....someone somewhere has done this.

 

 

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

[Archer]

34 minutes ago, saveasteading said:

Acoustic fence for air conditioner works on Google. 

I can't see a diy one yet.

But that will be enough for the planners.

Show a commercial one with numbers.

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

[Blooda]

Noistop Essential - Permanent Acoustic Barrier - Ikoustic Soundproofing

 

Essentially some galvanised weld mesh with waterproof rockwool

 

£279 -  2.4m x 1m x 6cm 

 

Plenty of downloads to send [bore] the Planners with.  Including a case 30 page case study on ASHP.  

 

 

[Archer]

1 hour ago, Blooda said:

Noistop Essential - Permanent Acoustic Barrier - Ikoustic Soundproofing

 

Essentially some galvanised weld mesh with waterproof rockwool

 

£279 -  2.4m x 1m x 6cm 

 

Plenty of downloads to send [bore] the Planners with.  Including a case 30 page case study on ASHP.  

 

 

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

[Archer]

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

[sharpener]

There was a recent thread which is highly relevant to all this, maybe @JamesPa can provide a link as it was his IIRC.

[JamesPa]

14 hours ago, sharpener said:

There was a recent thread which is highly relevant to all this, maybe @JamesPa can provide a link as it was his IIRC.

I think @sharpenermay be referring to this thread about noise in another forum.

 

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/noise-planning-expert

 

It does discuss some of the issues encountered in depth, based around the experience of someone apparently facing enforcement action under nuisance law.  Unfortunately the individual in question is definitely in violation of planning regulations and the local authority are probably using this to conflate the two entirely separate branches of law in a way which is not entirely helpful.  

 

I will shortly be posting on the same thread the best statement I can get out if my eho on the criteria for noise nuisance.  Its sort of helpful, and sort of useless.

Edited November 18, 2023 by JamesPa

[JamesPa]

17 hours ago, Archer said:

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

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

 

I have an ongoing argument with mine over their wholly unreasonable requirement if express consent is sought, and I think they now recognise that they have a problem because they have advised me to find a way to install under pd if at all possible (even though they will not accept pd noise levels, or anything close to them, when determining an application for express consent).

Edited November 18, 2023 by JamesPa

[JohnMo]

12 minutes ago, JamesPa said:

advised me to find a way to install under pd if at all possible (even though they will not accept pd noise levels, or anything close to them, when determining an application for express consent).

Different sheet of paper, with different tick boxes. Can't get away from those tick boxes.