slim duct hvac noise question

[mipa123]

Hi HVAC Experts,

the contractor who build my house installed a low static slim duct hvac in the ceiling of my living room and the (wind) noise it creates, even on low level, drives me nuts.

I've no db meter, so I've used my phone plus an app.. while the classic wall mounted aircon in my bedrooms is around 18dba on low, the one in my living room is 37dba on high and 34dba on low.

The contractor told me that this is normal, so I'm trying to find either validation for that or confirmation that this is not normal - and of course a solution to it.

I've attached a few pictures. The Aircon has 44.000 Btu and 4 huge blowers, while my contractor build a 90 degree wooden elbow right in front of the outlet which includes a funnel to resizes the outlet down to a en even smaller gap than the aircon outlet. In my non-expert-opinion that's way to small and produces back pressure against the fans, which creates noise that the wooden box then amplifies. I've already removed the outlet cover for testing but that didn't change anything regarding wind noise.

 

I've already tried to reach out to the manufacturer "Saijo Denki", but they didn't respond so far.
 

Thanks for any Expert Opinion I can get on that.

Thanks,
Michael

[sometimewoodworker]

1 hour ago, mipa123 said:

I've no db meter, so I've used my phone plus an app.. while the classic wall mounted aircon in my bedrooms is around 18dba on low, the one in my living room is 37dba on high and 34dba on low.

The app is not giving anything remotely close to a true reading, not even a comparative one.

 

at 18dB you would have to be young (under 20) to hear it. The background noise in our quiet bedroom is around 34dB the AC gives a 2dB rise in noise when set on high. So neither of those numbers make much sense. I certainly can’t hear anything as low as 18dB and at 37dB it is a really quiet room. As rise from ambient 18 dB is huge and 37dB rise would probably need hearing protection 
 

I get about a 24dB drop in noise when there is an Issarn concert near us by closing the doors and window, this is an example of that reduction.

 

 

here is an example showing an actual dB meter

 

 

 

 

 

So all this means that you really need a better way of measuring. I have a paid app on my iPad that gives a realistic sound reading, it gives not very different reading differences to the ones showing in the second video with similar sound reduction.

 

 

[tjo o tjim]

I’ve always thought that style of fan coil unit made a lot more noise than the wall mounted or traditional cassette units, but the wooden elbow isn’t going to be doing anything to help you with noise, especially if it is close to the unit.  A starting point would be to screw and glue everything on the elbow, including ceiling attachment, and to make sure you have vibration isolation between the fan-coil and the elbow.  

 

The next remedy is to make the elbow much larger— especially in line with the unit.  That will reduce the airflow noise as it goes around the bend.  Traditionally, you want the first elbow to be at least 6x the height of the air discharge away from the unit (IIRC).

[oldgit]

I've looked up the air volume for that unit on the Saijo Denki website and it's 1450 cubic feet per minute at a noise level of 49 dBA at the unit outlet. That's quite a normal noise rating so I think your problem is the ductwork installation from the unit outlet which is causing the noise. 1450 c,f,m would require a duct size of say 1 metre x 150 mm but the supply air ceiling grille size would have to be approx. 1 metre long x 200mm. This is because the grille has a free area of 70%. The 90 degree wooden bend directly after the unit outlet you describe is a bit worrying as there should be plenum chamber installed on to the fan coil unit with a horizontal duct or ducts leading from the chamber to the supply air grille.

One other point, the intake ceiling grille seems OK in size but is the unit ducted to this grille or is it just drawing air from the ceiling void? The reason is that air inside the ceiling is hotter than the air from your office, so your unit would work much harder to lower the temperature. 

[mipa123]

first thanks to everybody for the response, appreciate it a lot.

 

22 hours ago, sometimewoodworker said:

So all this means that you really need a better way of measuring. I have a paid app on my iPad that gives a realistic sound reading, it gives not very different reading differences to the ones showing in the second video with similar sound reduction.

I've switched to "Decibel X" which is supposed to be the most accurate db meter app..
bedroom AC low: 45 dBA

bedroom AC high: 50 dBA

livingroom AC low: 56 dBA

livingroom AC high: 64 dBA

 

still not sure of course if accurate, but sounds more reasonable. I don't wanna buy an dba meter just for the test.

 

If I compare that to the specification @oldgit found on the Saijo Denki website it's quite more than the 49 dBA (I guess on low?), which would confirm my subjective opinion that "it's way too loud". 

@oldgit do you have a link for me? I wasn't habe to find the exact HVAC model on their webpage.

 

My main concern was, that I don't want to have the contractor rip the plasterboard ceiling open (and of course charge for it) if I'm not sure it will improve anything.. and so far everything I can try would require exactly that. Buf if you guys agree that this installation is not proper,  I would move forward doing that.

 

Based on my google research I thought about replacing the wooden box with a much bigger fiberglass duct/elbow, made of fiberglass duct board. It's easy to cut it myself without special equipment requirement, is light weight and reduces vibration and noise. So win-win .. only problem so far is that I can't find any fiberglass duct board supplier in Thailand. Is there a reason for that? Bad idea?

 

 

The current inlet grill is 170x60cm and the outlet is 120x15cm - so the site of the outlet would be fine for the amount of airflow? @oldgit

 

I also thought about having the identical inlet grille as outlet grille installed by the contractor, so that they cut the ceiling open and install an identical grille thru which I can install my new fiberglass duct myself. I've no experience with working with plasterboard (especial ceilings) at all, so having two grill gates I can open would it make much easier for me to try different solutions and should provide plenty of airflow for the outlet? 

 

My initial plan was to have the AC outlet extended by the contractor straight to the recessed living room ceiling, but unfortunately there is a huge concrete beam in the way (which you can see on the picture of the "wooden box"). There are only 4-5 cm between beam and ceiling, so not really space for air flow... and would have been probably even much louder. My contractor quoted 22.200b for that.

 

19 hours ago, oldgit said:

One other point, the intake ceiling grille seems OK in size but is the unit ducted to this grille or is it just drawing air from the ceiling void? The reason is that air inside the ceiling is hotter than the air from your office, so your unit would work much harder to lower the temperature. 

correct.. they pull the air from the whole ceiling and not via the inlet grill. I've already on my todo to fix that too. 

 

Thanks,

Michael

[oldgit]

1 hour ago, mipa123 said:

first thanks to everybody for the response, appreciate it a lot.

 

I've switched to "Decibel X" which is supposed to be the most accurate db meter app..
bedroom AC low: 45 dBA

bedroom AC high: 50 dBA

livingroom AC low: 56 dBA

livingroom AC high: 64 dBA

 

still not sure of course if accurate, but sounds more reasonable. I don't wanna buy an dba meter just for the test.

 

If I compare that to the specification @oldgit found on the Saijo Denki website it's quite more than the 49 dBA (I guess on low?), which would confirm my subjective opinion that "it's way too loud". 

@oldgit do you have a link for me? I wasn't habe to find the exact HVAC model on their webpage.

 

My main concern was, that I don't want to have the contractor rip the plasterboard ceiling open (and of course charge for it) if I'm not sure it will improve anything.. and so far everything I can try would require exactly that. Buf if you guys agree that this installation is not proper,  I would move forward doing that.

 

Based on my google research I thought about replacing the wooden box with a much bigger fiberglass duct/elbow, made of fiberglass duct board. It's easy to cut it myself without special equipment requirement, is light weight and reduces vibration and noise. So win-win .. only problem so far is that I can't find any fiberglass duct board supplier in Thailand. Is there a reason for that? Bad idea?

 

 

The current inlet grill is 170x60cm and the outlet is 120x15cm - so the site of the outlet would be fine for the amount of airflow? @oldgit

 

I also thought about having the identical inlet grille as outlet grille installed by the contractor, so that they cut the ceiling open and install an identical grille thru which I can install my new fiberglass duct myself. I've no experience with working with plasterboard (especial ceilings) at all, so having two grill gates I can open would it make much easier for me to try different solutions and should provide plenty of airflow for the outlet? 

 

My initial plan was to have the AC outlet extended by the contractor straight to the recessed living room ceiling, but unfortunately there is a huge concrete beam in the way (which you can see on the picture of the "wooden box"). There are only 4-5 cm between beam and ceiling, so not really space for air flow... and would have been probably even much louder. My contractor quoted 22.200b for that.

 

correct.. they pull the air from the whole ceiling and not via the inlet grill. I've already on my todo to fix that too. 

 

Thanks,

Michael

Hello Michael.

Plenty of points to go through so here goes!

1) Go to the Saijo Denki.co.th website. Click on 'product'. Click on 'duct type air. Click on 'turbo'. Scroll down to 'Duct low static R-410A' specifications. Your unit is the 44,000 BTU/hr. one. The model nos. for the indoor and outdoor unit are at the bottom.

2) Usually, the 49dBA reading is at high speed one metre away from the unit. My opinion is that the unit isn't your problem, it's the ductwork install from the unit to the grille.

3) Perfectly understandable that you don't want to start tearing the plasterboard ceiling about. Did the contractor suggest that an access panel be installed in the ceiling, for maintenance of the unit i.e cleaning the filter? That would give you ideal access to the unit to carry out any alterations.

4) The worry I have with fiberglass board is that, in time, it starts to break up and bits get into the airstream. If you want to go down that road though, line the inside of the duct with something like aluminium foil sheeting, the edges sealed and taped. I much prefer good old fashioned galvanized sheet steel ducting (rectangular or circular) though!

5) The grille sizes are fine for both inlet and outlets but, after altering the duct (make sure it's as straight as possible to the outlet grille with no sharp right angled bends) you still think it's noisy, change the outlet grille to 1200mm x 200mm. You'll get the same airflow into the office but the airflow speed will decrease and the 'throw' will be less. I notice what looks like your desk directly below the unit. Any chance of moving it away a couple of feet to alleviate the problem?

[sometimewoodworker]

3 hours ago, mipa123 said:

I've switched to "Decibel X" which is supposed to be the most accurate db meter app..
bedroom AC low: 45 dBA

bedroom AC high: 50 dBA

livingroom AC low: 56 dBA

livingroom AC high: 64 dBA

 

still not sure of course if accurate, but sounds more reasonable. I don't wanna buy an dba meter just for the test.

 

If I compare that to the specification @oldgit found on the Saijo Denki website it's quite more than the 49 dBA (I guess on low?), which would confirm my subjective opinion that "it's way too loud". 

Those numbers are much more realistic, though if they are accurate is a more difficult question.

 

Without somehow calibrating the numbers I doubt that you can compare them to published numbers and say conclusively that your A/C is louder than the advertised sound level. There are just to many variables involved, and your installation certainly seems to be exacerbating the problem.

 

However the point you can be reasonably confident of is the difference in sound between off, low and high so the sound level when the AC is off it probably important.

 

Our bedroom AC, a Mitsubishi is remarkably quiet and has a difference of about 2dB. In the livingroom our big cassette unit has a 2dB increase from off to on then between 2 & 3 from low to high.

 

so the actual numbers are for our big cassette.

off (extremely quiet room the fridge is the loudest noticeable sound) 36dBA solid

on low 38dBA just

high 40dBA flicking to 41dBA

 

& FWIW the app I use is capable of being calibrated, if I happened to have an SPL meter with known accuracy.

[mipa123]

3) The air inlet grille is already a door to access the AC for maintenance. Unfortunately there is no way to replace or modify the wooden elbow from that side, since it's behind the AC on the other side. But that's actually why I thought about having them installing the same panel/door as air outlet. That wouldn't create as much mess because it's just cutting the right sized hole and fitting the panel in, without the need to put new plasterboard and repaint etc.

 

4) The fiberglass board would be only for the outlet side, so if there come bits loose it gets blown out, not sucked into the blowers. I've seen 2.5cm insulation board here in Thailand which is not meant to be for ducts I guess, but has aluminium foil on both sides, so I would probably go with that. Galvanized sheet is supposed to be not as good for noise reduction, also more complicated to have it made and installed.

 

5) I definitely still need an 90 degree elbow but I would move it as far away from the AC as possible - which is unfortunately max 90cm, because there comes the concrete beam. So if I make a 120x20 cm opening that's 70cm straight.. and then the bend. Not sure if with 70cm distance of fiber glass duct and a bigger opening the AC is really less noisy and if it's worth all the hassle.

 

I don't sit underneath but 5-6m away where I still get 56dBA on low.. in my opinion that wooden box is like a subwoofer box that amplifies the noise evenly ????

 

I've just also checked for Cassette style ACs as replacement, but my ceiling is only 40cm and all that cassette things are at least 70-80cm deep...

 

[mipa123]

13 minutes ago, sometimewoodworker said:

so the actual numbers are for our big cassette.

off (extremely quiet room the fridge is the loudest noticeable sound) 36dBA solid

on low 38dBA just

high 40dBA flicking to 41dBA

 

good idea about comparing the difference. I've

off 46dBA solid at my work desk about 4-5m away from the AC

on low 56 dBA (which is plus 10 dBA to off) at my desk

on high 62 dBA (which is plus 16 dBA to off) at my desk

 

compared to your 2-4 dBA difference.. that's A LOT.. and Saijo Denki sells this things as "super quiet" - but that's what they all say...

 

On days I've the AC running the whole day (working from home) I feel like I've spent the whole day sitting next to a highway.

[mipa123]

finally found one... it's actually for lining to reduce noise.. but for a small duct like I require it should be totally fine to build the whole duct out of the board - I guess...

 

https://www.scgbuildingmaterials.com/th/products/SCG-Thermal-Insulation-FPO-Series-Thickness-25-mm/8852424068447

[sometimewoodworker]

49 minutes ago, mipa123 said:

 

good idea about comparing the difference. I've

off 46dBA solid at my work desk about 4-5m away from the AC

on low 56 dBA (which is plus 10 dBA to off) at my desk

on high 62 dBA (which is plus 16 dBA to off) at my desk

 

compared to your 2-4 dBA difference.. that's A LOT.. and Saijo Denki sells this things as "super quiet" - but that's what they all say...

 

On days I've the AC running the whole day (working from home) I feel like I've spent the whole day sitting next to a highway.

With any kind of background noise, like the radio, you can’t hear that the A/C is on if it’s on low, you only know because the room is cool also the fans (MrKen) are super quiet and on number 3 ( 1/2 speed) again they are barely audible.

 

so with those numbers there may be something wrong. It could also be that those kinds of units are loud and this could be the reason that cassette units for large areas and splits are the standard.

 

it could also be that so few (relatively) of the kind of unit you have are installed that the fitters don’t know how to set them up.

 

this is our big A/C it’s probably a 48,000 BTU unit

 

 

Edited November 4, 2019 by sometimewoodworker

[mipa123]

6 minutes ago, sometimewoodworker said:

it could also be that so few (relatively) of the kind of unit you have are installed that the fitters don’t know how to set them up.

that's exactly what I think

 

I've also MrKen fans and rarely used the AC the last year but started using it more recently to get rid of humidity, which results in being super annoyed because of the loud noise all the time. I need to turn the AC off to understand the TV when watching Netflix... so I'm not over sensitive I guess.. it's just loud as f'ck.

 

Unfortunately I can't install a cessette system like you have, because lack of depth in the ceiling ????

 

[sometimewoodworker]

5 minutes ago, mipa123 said:

Unfortunately I can't install a cessette system like you have, because lack of depth in the ceiling ????

Probably not what you want to hear, but there are low profile high BTU splits that you can get. It may be simpler to give up on the hidden unit and get something like this

[mipa123]

I've tried to reach out to the manufacturer again if it's probably possible to replace the blower motors with slower ones to create less air flow and less air pressure once the room is cold. Because that would be easy doable without ripping the ceiling open.

 

On High setting it takes about 5-10 minutes to make the whole room (about 9 x 7.5 x 2.4 meters) cold like a fridge, so having the blower run on lower speeds afterwards should be totally fine - but currently not possible, because even on low the wind speed at the outlet is super high... and of course noisy.

[sometimewoodworker]

9 minutes ago, mipa123 said:

On High setting it takes about 5-10 minutes to make the whole room (about 9 x 7.5 x 2.4 meters) cold like a fridge, so having the blower run on lower speeds afterwards should be totally fine - but currently not possible, because even on low the wind speed at the outlet is super high... and of course noisy.

From what you say I am virtually certain that your A/C unit is oversized for your conditioned space.  We would fit a 33,000 BTU unit for an area that size, if we were going to get a non inverter.
 

For an inverter a 33% oversized unit may not be a problem, I haven’t seen enough information on oversizing of inverters to know when oversized units become a problematic.
 

For most Thai calculations it would be said to be a little undersized.

[mipa123]

I'm thinking about replacing my indoor unit with a cassette one, in the hope it's compatible with the outdoor unit.. need feedback from manufacturer to figure that out.

 

@sometimewoodworker what are the dba specs of your cassette, just to have a comparison?

 

Most calculation tools suggest at least 40-46.000 btu for my space, since it's west side and one side of the room is fully glass panels.

 

So I would probably go with the 44.000 cassette sanjio denki offers, which is 44dba - which is already 5 dba less than the slim duct one (if properly installed) ..

and I've learned 3 dba = double the noise

[oldgit]

23 minutes ago, mipa123 said:

I'm thinking about replacing my indoor unit with a cassette one, in the hope it's compatible with the outdoor unit.. need feedback from manufacturer to figure that out.

 

@sometimewoodworker what are the dba specs of your cassette, just to have a comparison?

 

Most calculation tools suggest at least 40-46.000 btu for my space, since it's west side and one side of the room is fully glass panels.

 

So I would probably go with the 44.000 cassette sanjio denki offers, which is 44dba - which is already 5 dba less than the slim duct one (if properly installed) ..

and I've learned 3 dba = double the noise

Just looked at the Mitsubishi PLY-SP42EA (42,000BTU's/hr) cassette indoor unit and they require a minimum depth of 298mm inside the false ceiling space.

[mipa123]

2 minutes ago, oldgit said:

Just looked at the Mitsubishi PLY-SP42EA (42,000BTU's/hr) cassette indoor unit and they require a minimum depth of 298mm inside the false ceiling space.

I've about 40mm and the existing one is 350mm, so the cassette with 325mm should fit here without problems.

 

Just need to figure out if its compatible with the outdoor unit since changing all of it would be a pain.. or even more pain than replacing the indoor unit already is.

But I figured if I have the pain and costs of re-doing the ceiling anyways, let's put in the proper device instead of building dirty hacks around the wrong AC unit.

 

I'm also not sure if the pricing of about 48.000 thb for the cassette on dealer websites includes the outdoor unit? Bought my existing one with the house.

 

dBa wise the Mitsubishi seems to have quite identical values as Saijo Denki, while Saijo is even more quiet on low.

[sometimewoodworker]

42 minutes ago, mipa123 said:

 

 

I'm also not sure if the pricing of about 48.000 thb for the cassette on dealer websites includes the outdoor unit? Bought my existing one with the house.

 

dBa wise the Mitsubishi seems to have quite identical values as Saijo Denki, while Saijo is even more quiet on low.

That price will not include the outdoor unit. 
 

While I don’t read Thai the chart you posted lists a minimum of 44dB? The Mitsubishi is a minimum of 38dB if so the sound level would be about ¹/₄ of the Saijo so I don’t know where your figures are coming from.

[mipa123]

1 minute ago, sometimewoodworker said:

While I don’t read Thai the chart you posted lists a minimum of 44dB? The Mitsubishi is a minimum of 38dB if so the sound level would be about ¹/₄ of the Saijo so I don’t know where your figures are coming from.

 

The 44 dba is the maximum noise. 

 

After spending about the whole day I've found that one http://www.saijo-denki.co.th/index.php?route=document/documents/Catalog_All_Round_Cassette

 

Sound Pressure Level Indoor Unit (Turbo/HiHi/Hi/Med/Low): 45 / 43 / 41 / 36 / 33

[sometimewoodworker]

1 hour ago, mipa123 said:

The 44 dba is the maximum noise. 

So what is the second number 120dBA?

[mipa123]

27 minutes ago, sometimewoodworker said:

So what is the second number 120dBA?

Outside. But doesnt make much sense because way to loud.. the other pdf says 60 for outside

Edited November 5, 2019 by mipa123

[oldgit]

1 hour ago, sometimewoodworker said:

That price will not include the outdoor unit. 
 

While I don’t read Thai the chart you posted lists a minimum of 44dB? The Mitsubishi is a minimum of 38dB if so the sound level would be about ¹/₄ of the Saijo so I don’t know where your figures are coming from.

Phew! That would be very expensive for just doing the indoor unit. The prices they usually quote are for the supply, installation and commissioning of the complete installation.

[sometimewoodworker]

24 minutes ago, oldgit said:

Phew! That would be very expensive for just doing the indoor unit. The prices they usually quote are for the supply, installation and commissioning of the complete installation.

You are getting wall mounted units confused with cassette units. The price for a cassette in the 42,000 BTU range complete from Mitsubishi is going to be around 75,000 Baht, fitting for cassette units runs around 10,000 Baht so you need to add that, and not many places include fitting in the price

Edited November 5, 2019 by sometimewoodworker

[sometimewoodworker]

3 hours ago, mipa123 said:

 

@sometimewoodworker what are the dba specs of your cassette, just to have a comparison

 

don’t forget that the real world numbers are virtually certain to be higher for all A/C units as the specs are from an anechoic room.

[mipa123]

2 minutes ago, sometimewoodworker said:

don’t forget that the real world numbers are virtually certain to be higher for all A/C units as the specs are from an anechoic room.

thanks. I just compare it to your "I can't hear the AC when the TV is on" to my "I can't hear the TV when the AC is on". So if the Saijo cassette has 33 dba on low I should be able to hear my TV too ????

[sometimewoodworker]

3 hours ago, mipa123 said:

thanks. I just compare it to your "I can't hear the AC when the TV is on" to my "I can't hear the TV when the AC is on". So if the Saijo cassette has 33 dba on low I should be able to hear my TV too ????

Apart from the fact that it’s the radio that is on, often playing gently through the 7 sets of speakers in the house (I have that many so I can have quiet music or books or podcasts playing without having to have any one loud) and there is a TV though SWMBO only uses it occasionally for YouTube.
 

So yes as long as the A/C is installed correctly it will be virtually unnoticeable.
 

One point is that we have had the outdoor units mounted well away from any of the living room or bedroom walls it cost a little more as the pipe run is significantly longer than the 4 metres that is included in the standard install price. It was well worth the cost as the outdoor units, while not very loud, can definitely be heard in the workshop.

 

 

[tjo o tjim]

8 hours ago, sometimewoodworker said:

(I have that many so I can have quiet music or books or podcasts playing without having to have any one loud)

Sonos or a traditional amplifier?

[sometimewoodworker]

4 hours ago, tjo o tjim said:

Sonos or a traditional amplifier?

Not Sonos nor yet a traditional amplifier but airplay using these

 

and you can connect powered speakers or any system that can work with a line in connection.

Edited November 6, 2019 by sometimewoodworker

[mipa123]

9 hours ago, tjo o tjim said:

Sonos or a traditional amplifier?

I've Sonos. Love the physical (and audio) quality, but the Software is a pain sometimes - not improved for 5 years.. no new features even everybody complains.

 

 

On 11/5/2019 at 5:00 PM, sometimewoodworker said:

That price will not include the outdoor unit. 

Seems Saijo Denii only sells in bundles (indoor+outdoor) so they price would be for both. Still trying to get only the indoor replaced, but if they dont sell them separately I may have to replace both or find a good trade-in deal with the contractor. Would be a waste to throw my 2 year old duct AC on the trash...

Edited November 6, 2019 by mipa123