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Whisper quiet AC unit recommendations

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Whisper quiet AC unit recommendations

Postby stavrakas » Mon Jul 22, 2019 10:14 am

Hi guys

I am currently building a single room studio in my back garden (approx 30sq mtrs). HVAC has been designed around a wall mounted mini split system. Separate fresh/stale air supply and extraction is taken care of attenuated boxed-in ducting which has been installed on two levels in the ceiling void above.

To my surprise the AC installer brought round a unit with a massive 58db IN/65dbOUT rating (Samsung AR18RXFPEWQN, apparently costing £900). I freaked out when I saw the db figures on the manual so I said to him there is no way I am having this. FYI I am allowing around £2.5-3K for supply and install. Would anyone be able to recommend a reliable whisper quiet (around 20db or thereabouts) model? Would be interested to know what are you guys using.

Your advice on this one would be much appreciated.

Many thanks.

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Re: Whisper quiet AC unit recommendations

Postby Wonks » Mon Jul 22, 2019 1:51 pm

What's the required kW cooling rating?
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Re: Whisper quiet AC unit recommendations

Postby Wonks » Mon Jul 22, 2019 2:05 pm

I see it's 5kW from the manual for that model.

Do you actually need 5kW of cooling?

Smaller indoor units are quieter than big ones. Maybe look at a multi-split system with two or three smaller indoor units connected to one outdoor unit. Maybe a VRV system. Selection of these is not my area of expertise, so I can't really suggest a make or model.

Max (SSG) should be able to recommend some as he's installed quite a few very quiet ones in studios.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Mon Jul 22, 2019 5:42 pm

Thanks for your response Wonks.

Specified unit http://downloadcenter.samsung.com/content/UM/201902/20190225104959600/SERVICE_MANUAL_MALDIVES_EU_190121.pdf
is based on 5KW cooling rating. Cooling rating calculations were based on the following information:

Cooling requirements during regular use:

1 adult
Active monitors Neuman KH310 = 2x300 watts
PC + Screen= 200 watts
Monitor controller and interface= 50 watts
Track LED lighting - Area of room 30 sq.mtrs

Cooling requirements during occasional use (i.e. recording sessions):

As above but with the addition of
2-3 adults
Misc other gear i.e. gtr/bass amps/outboard = 500 watts

OAN the spec sheet that came with the unit showed a 58-65 noise rating which gave me a heart attack. Following more detailed investigation it turns out that the figures on the spec sheet related to sound power ratings (not SPL!). The manufacturer's spec sheet shows the unit's SPL rating as 21db-42db.

So my questions are
1. Is a 5KW unit going to serve my needs? I wouldn't want the unit to be unnecessarily over/under specified
2. Is 21db-42db good noise rating?

Thanks in advance for any help on this one.

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Re: Whisper quiet AC unit recommendations

Postby Wonks » Mon Jul 22, 2019 6:16 pm

Is it an internal room? No windows? Normally heat gain allowances from external walls and windows.

21dB is quiet, 42dB still quiet but noticeable - about the same noise as an average computer makes. The two values are probably low and high-speed fan levels. I think 5kW should be enough for your needs.

I doubt you'll have the monitors at full blast, so that 2x300W will probably be more like 2x100W in practice. A sitting human is normally rated at 80W, but lets say 100W, especially for more active musicians e.g. drummers.

PC on high processing mixing and plug-in load could take more than 200W, so say 300W for that.

Let's allow 300W for the LED lighting.

So that's 1.2kW.

3 more adults and outboard - lets say 1kW.

So that's 2.2kW out of 5kW. Which should mean that the fans should run at low speed almost all of the time, provided that the room doesn't have significant other external heat gains.

The spare cooling capacity will be needed to pull the room down to temperature quickly at the start of the day, if things are left running overnight with the A/C off and the room temperature rises.

So, no guarantees as I really don't know enough about the room construction or location. but 5kW sounds like it should be OK and the fans should run in low speed once the room is at setpoint - given those room loads.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Tue Jul 23, 2019 8:00 am

Thank you Wonks for taking the time to respond, much appreciated.

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Re: Whisper quiet AC unit recommendations

Postby Studio Support Gnome » Tue Jul 23, 2019 10:39 pm

Wonks 's Number crunching estimation is about right IMHO


Typically, In the past, i'd usually start by looking at Daikin, then mitsubishi....

these days , with the benefit of my current day job, I'd actually be looking to get clever with MVHR and some cooling coils , . but you would have needed to make that decision early on and include it in the ventilation strategy

Cheap is a false economy in this game...
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Re: Whisper quiet AC unit recommendations

Postby Wonks » Wed Jul 24, 2019 11:38 am

stavrakas wrote:I am currently building a single room studio in my back garden (approx 30sq mtrs). HVAC has been designed around a wall mounted mini split system.

Somehow I missed this blindingly obvious statement. There will certainly need to be a reasonable allowance made for external heat gains. If you've got room-in-room construction then the U-values

There also needs to be an allowance for the fresh air intake. I don't know what allowance has been made, but 12 l/s per person (fairly standard for a high quality office environment) x 5 people, with cooling down from say 30°C to 22°C, then that's a 560W load.

I'm starting to think that the unit could be working near maximum a lot of the time and won't be as quiet as you'd hope.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Wed Jul 24, 2019 12:44 pm

Thank you both for your helpful responses.

Is there anyway I can get an authoritative opinion on this matter please. Don't mind paying a consultation fee if necessary. Just to reiterate, the current model is a 5KW unit running at 25db-42db (not 21db as I was told initially!). My AC installer has done many studio installs in the past and reckons that 5KW is adequate for my needs. I have seen no calculation figures though, which worries me slightly, so I would like to get a second opinion. I am spending a lot of money on this installation and I would like to get an AC wall unit that will meet my needs.

The studio (professionally designed) is based in Shropshire and is a timber framed construction (approx. 30sq mtrs Image

The external shell is cladded with woodwool boards https://www.savolit.co.uk/products/savolit-plus and then standard plaster render.

The inside is a room within a room construction. Fresh air is brought in via boxed in insulated ducting (long box runs on two levels above internal ceiling) via a fan that can push 50ltrs of air per hour at its lowest setting (model:Manrose MF100). Fanless stale air extraction is taken care once again by boxed in ducting.

Any help would be much appreciated.

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Re: Whisper quiet AC unit recommendations

Postby MOF » Wed Jul 24, 2019 12:57 pm

From what I’ve read over the years the (cooled) air inlet is not routed directly into the studio, it is deliberately sent circuitously and is lined with sound absorbing material to make sure there is no direct path for any external noise.
So an external A/C’s noise will be reduced too in this way.
My caveat, like the other responders, I’m not an expert in these matters.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Wed Jul 24, 2019 1:05 pm

Thanks MOF, as you mention fresh/stale air enters and leaves my studio via many metres of boxed-in insulated ducting that runs on two levels above the internal ceiling.

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Re: Whisper quiet AC unit recommendations

Postby Wonks » Wed Jul 24, 2019 1:26 pm

stavrakas wrote:Fresh air is brought in via boxed in insulated ducting (long box runs on two levels above internal ceiling) via a fan that can push 50ltrs of air per hour at its lowest setting (model:Manrose MF100).

Looking at the data for that fan, that's actually 50 l/s min & 65 l/s max, so in line with my 60 l/s estimate for 5 people. The volumes will probably drop a bit from those figures as there is no extract fan, so the fan also has to push the exhaust air out, increasing the total system pressure drop.

Your builder will have to have done U-value calcs for building regs (though they are mainly about heating, not cooling), so worth asking them what the external cooling load on a design day is. You also need to know what that cooling design day external temperature is. In London, it was 28°C for a long time, but fairly recently, 30°C has normally been used. Which means that the systems are designed to work up to 30°C ambient and maintain the internal design conditions. Above that temperature, internal temps will rise, but there is also a risk of A/C units shutting down on high pressure due to overload. With high heatwave temps like we have at the moment, you may not be able to use the studio - at least with lots of people and equipment running.

Hopefully the external part of the A/C unit is on a north-facing wall (otherwise east is better), as the sun can warm up the walls, heat the air and the ambient conditions for the external unit can easily be 3-4°C higher than ambient temps. There will also be a certain amount of recirculation of the hot air discharge from the unit's fan, so having as much free space around it will help.

I would suggest dropping Studio Support Gnome a PM. He may have the time to look at the design and the calcs and maybe recommend some changes, or he may know some others who could help.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Wed Jul 24, 2019 2:16 pm

Wonks wrote: Looking at the data for that fan, that's actually 50 l/s min & 65 l/s max, so in line with my 60 l/s estimate for 5 people.

That's correct 50 l/s min (not 50 l/s ph!)

Wonks wrote: Your builder will have to have done U-value calcs for building regs (though they are mainly about heating, not cooling), so worth asking them what the external cooling load on a design day is. You also need to know what that cooling design day external temperature is. In London, it was 28°C for a long time, but fairly recently, 30°C has normally been used. Which means that the systems are designed to work up to 30°C ambient and maintain the internal design conditions. Above that temperature, internal temps will rise, but there is also a risk of A/C units shutting down on high pressure due to overload. With high heatwave temps like we have at the moment, you may not be able to use the studio - at least with lots of people and equipment running.

This obviously worries me but without getting an expert opinion I can't be sure.

Wonks wrote: Hopefully the external part of the A/C unit is on a north-facing wall (otherwise east is better), as the sun can warm up the walls, heat the air and the ambient conditions for the external unit can easily be 3-4°C higher than ambient temps. There will also be a certain amount of recirculation of the hot air discharge from the unit's fan, so having as much free space around it will help.

The external part of the AC unit is south facing but it is screened by a tall thick hedge so no sun gets to it thankfully.

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Re: Whisper quiet AC unit recommendations

Postby Mike Stranks » Wed Jul 24, 2019 3:16 pm

Just to be clear...

Max aka Studio Support Gnome is an expert. He has designed and built many pro-grade studios - incl outdoor new builds.

If Max says 'This is OK' then it is OK. On the other hand...
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Wed Jul 24, 2019 8:24 pm

Thanks to all who have taken the trouble to reply to my post.

My AC installer sent me a breakdown of his calculations for my studio, see below (right click open link in new tab will enlarge image). Breakdown shows a requirement for a 5.5KW unit. If you spot anything that hasn't been taken into account then please let me know.

Regards

Stavros

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Re: Whisper quiet AC unit recommendations

Postby Wonks » Wed Jul 24, 2019 10:05 pm

That form doesn't look to be filled in properly e.g window size - height is 0! (so no window heat gain allowed for).

100w/m2 for LED lighting? I'd expect it to be a lot less otherwise it's going to be pretty blinding.

Equipment gains seem low compared to precious discussions.

Can't see any wall/roof thermal gains. It may not be too much with room-in-room construction but something should be there with space for a U-value for each wall and the roof.

Also, will you only ever have 3 people plus yourself in there?

Whilst the overall figure may be approx. correct, the calculation sheet should be filled in correctly to prove it, otherwise they are laying themselves wide open for a professional negligence suit.

A 5kW unit may well be underpowered and will almost certainly be runing in high speed and so producing the loudest noise levels available.

You need professional help here.
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Re: Whisper quiet AC unit recommendations

Postby stavrakas » Wed Jul 24, 2019 10:33 pm

Thank you once again Wonks. You have spotted things I don't have a clue about. i have contacted Max here as per people's suggestions and I am waiting for his reply.

I am worried about the prospect of spending a considerable amount of money on something that may or may not be fit for purpose.

If anyone else can recommend a specialist company I can consult about this I would be most grateful.

Thanks in advance.

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Re: Whisper quiet AC unit recommendations

Postby Studio Support Gnome » Wed Jul 24, 2019 10:54 pm

I don't seem able to open the image, but ignoring the air con for a moment.

I'm not particularly inclined to get directly involved.
it's someone else design,and I have spent too many years fixing other peoples cock ups.
I just don't need the hassle any more. as an independent contractor or consultant, which is why I'm not one any more.
... and if it came in to my employer for my day job, for air handling is what we do.... , This project falls below the normal scope of my current role..... even if it came to us, and management allowed it to be accepted, it's unlikely I would be tasked with it , I tend to deal with higher profile , higher value jobs....

but some pointers.

10 l/s per person is the absolute minimum required supply, as per building regs .. would achieve IDA3 more than likely, although it can just scrape in to IDA2 in some circumstances, to achieve IDA1 then the default calculation value is 20l/s per person , and required minimum would be greater than 15l/s/person

to maximise work productivity , creativity, and stamina , IDA1 is advised.

and this would also require filtration. anywhere between G4 and F7 would be adequate



and there is reason Manrose do not often publish proper performance pressure/flow graphs. (draw your own conclusions)

you would likely be better off with a product from other companies, like S&P ,(TD silent range) or Airflow (Aventa Silent range ) , who at least publish data you can practically use to calculate achieved performance

or any number of other manufacturers....

anyone who will actually publish a graph of the actual achieved airflow against a given system pressure. rather than someone who simply tells you the maximum airflow with no back pressure, and the maximum pressure any air will move against at all.... with no clue as to what happens between, or what the resulting noise figures will actually be, in flow and outside of duct... or indeed predict the SFP with any degree of accuracy./



I would need to review your duct design, in detail, to give any idea of correct spec.

If this is a domestic situation, whoever has specified your ventilation should be certified as being competent to do so.... at very least NICEIC Part F certification.


I would also hope, that CIBSE guide B, (2016 is still the current edition ) has been referenced for heating, ventilation and cooling design specification.


The sensible thing would, as I hinted at earlier, to have used an MVHR design to help minimise the heating and cooling loads , maintain air quality

and if insisting on only one fan, then extracting makes more sense ..... noise tends to travel with airflow.... putting your only mechanical in to your supply airflow means you have to work harder to reduce the noise in the incoming airflow,


although frankly, I'd put one in each.... because you have to consider the system pressure from inlet on exterior, to outlet on exterior, as being driven by that one fan.


fans in series will not increase fundamental rate, but will increase ability to overcome system pressure.

thus, one on inlet, one on outlet, would help maintain the target flow rate, but cope with the pressure, potentially with lower noise as it won't have to work so hard to achieve the actual flow rate

don;t be fooled into thinking there is a direct straight line relationship between fan speed, and flow volume ... this is only true when there is no resistance to flow , such as would be imposed by a duct system .
at which point, the internal friction coefficient of the duct surfaces, and the smoothness of the design, turbulence or lack thereof, cross sectional area, and a whole raft of other parameters have an effect on the actual achieved airflow....

when a fan speed says it can do say 61 l/s with no pressure reference point, AT 61 l/s then the speed spec is in to open air...

if a fan says it's maximum pressure is 200 Pascals.... at the blade rotation speed that gives 61l/s in to open air.... then 200Pa is the maximum pressure against which so much as one molecule will make forward motion.... achieved flow rate 0.00001 l/s sort of thing....

here endeth the lesson.
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Re: Whisper quiet AC unit recommendations

Postby Wonks » Thu Jul 25, 2019 6:00 am

I found that opening the image in another window worked for me.
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Re: Whisper quiet AC unit recommendations

Postby Wonks » Thu Jul 25, 2019 7:56 am

This should be better. I think the other images are thumbnails.

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