Soundproofing a wall with an integrated window aircon

[kreutz]

Hello,

We are renting a few office rooms near a very busy junction in London (its the first floor and there are lots of buses, ambulances, police vehicles passing by all the time). We have recently decided to turn one of them into a video conference room so it has to be very quiet.

Last week we have insulated the windows with isover and recticel, however, to our surprise, the room was still very noisy. We then discovered that there was a working aircon unit integrated above one of the windows and that the noise was coming from there (not the aircon noise but the street noise). The aircon is used by another office and can not be removed. It is basically like having a hole in the wall covered only with plasterboard.

We now have two options:

1. Dropping the project altogether (a very expensive option given all the money that has already been spent)

2. Putting up vertical wooden beams near the section where the aircon is, stuffing them with isover/rockwool and putting plasterboards on top.

Because the room is that noisy, we are wondering whether this would help at all. We need it to be extremely quiet. Do you think it is worth trying to insulate it or should we just leave it? Would you know more efficient ways of how to insulate it?

Thanks.

 

[Deluks]

If the ducting runs in the wall, try and locate exactly where and board over it with a simple timber frame and couple layers of plasterboard. Think of it as a thin spot that you have to 'patch up'

 

[kreutz]

Thanks, Deluks.

Here's a picture of the mess (sorry about the large size):

http://img269.imageshack.us/img269/3608/aircon01.jpg

All this is covered only by a thin sheet of plasterboard.

You can see the ducting on the top, so it isn't the ducting that is causing the trouble. Its the fact that this space for aircon functions like a hole in the wall that can not be stuffed with insulation materials (this would cause the aircon to overheat).

 

[Deluks]

Box round it, you may end up with a bit of wall protruding into the room to accomodate insulation, but a couple of layers of PB will make a big difference.

Maybe frame out a couple of inches, cover with chicken wire (to stop inso from falling into the void and hitting the unit) install rockwool against this, more frame, flush with the insulation, and board over with 2 layers of 12.5mm.

 

[kreutz]

Anybody knows whether it would be safe to stuff the aircon duct with isover? Two cables and an aircon hose go through that duct. I read that isover is not flammable, but I want to double check before I do it.

 

[mointainwalker]

I asked my DIY shed to check on flammability and they rang Isover.

The reply was that it burns around 1200 C,

So should be o.k. unless your offices getr eally warm

 

[0000]

you are not going to get great noise reduction. Noise proof vent will cost you more and that is unlikely to be the end of it.

Retrospective soundproofing is expensive and difficult. For one the glass. The only way that you would get sound proofing from that is if you installed secondary windows 4" or more away from the exterior ones.

In any even you are probably best replacing the whole window/aircon with something designed for the job.

 

[stem]

What a bodge up. The part of the aircon in your photograph looks like an 'Outdoor Unit' so called because it should be mounted outside completely free of any obstruction in order to get a free flow of a large volume of air through the condenser fins, for which it has an integral fan.

I can't see the perspective from your photograph, but I assume it's taken from indoors, so a huge volume of air will be drawn out of your room, through the condenser and blown out into the street. Box it in and you will cut off it's air supply so it will overheat.

BTW, if your office is air conditioned do you not mind all of your expensively cooled air being sucked out into the street? If they use the A/C in the winter (some types produce heat for winter use) then all of your heat will be sucked out too.

BTW what is the piece of white flexible ductwork? is that a vent from a portable A/C unit? or perhaps the extraction from their toilet

 

[masona]

What a bodge up. The part of the aircon in your photograph looks like an 'Outdoor Unit' so called because it should be mounted outside completely free of any obstruction in order to get a free flow of a large volume of air through the condenser fins, for which it has an integral fan.

That's what I thought, I can't see how that is allowed to be inside the room. I don't know if this comes under building regs but I would check with the BCO as it may have to be re-located?

 

[kreutz]

Thanks guys.

Well, the only thing that separates the unit from the outside is a wooden grille, while there is normally a plasterboard nailed from the inside. This way all the air that goes into the aircon comes from the outside (unless there is something that I don't get).

It looks like I will have to build an acoustic wall because nothing else worked. It isn't that expensive and its my last chance.

stem: the hoze that you can see from the picture goes through that duct and I believe that it is there to provide some ventilation to the corridor. It goes right across the room. I have shoved the duct full of isover now so it isn't as noisy, though the noise levels are still unacceptable.

Thanks!
kreutz

 

[stem]

The only thing that separates the unit from the outside is a wooden grille, while there is normally a plasterboard nailed from the inside. This way all the air that goes into the aircon comes from the outside (unless there is something that I don't get).

When the aircon is cooling the office upstairs, the heat that is removed from the office, is transferred to this 'outdoor unit'. A fan then sucks air through the wire grill you can see in your photograph, collects the waste heat from the fins and then, blows it outside. That air has to be pulled in from somewhere.

A/C units use axial fans (not centrifugal) because they need a high volume of air, but not high pressure, as they are designed to be in open 'free air', not having to pull air through objects that create a resistance such as obstructions, ductwork, walls etc. I would suggest that you get a qualified A/C engineer to examine this installation sooner rather than later.

It looks like I will have to build an acoustic wall.

The wall would probably need to be removed for access to the unit for maintenance (Once or twice a year) but don't obstruct the airflow.

The hoze that you can see from the picture goes through that duct and I believe that it is there to provide some ventilation to the corridor.

Unless it's someone's attempt to introduce a supply of air for the A/C unit, if so, it's nowhere near big enough. Compare the diameter of it with the size of the inlet grille in your photo. Not even considering the pressure loss along its length.

I have shoved the duct full of isover now so it isn't as noisy, though the noise levels are still unacceptable.

"Duct???" The outdoor unit is connected to the indoor unit via a high pressure and a low pressure pipe. There shouldn't be a duct, or is this the air supply?

The idea of these units is that they are mounted outside of the building, in free air, see typical clearances below. Only the two pipes then pass through the building fabric, thus, they can be fully sealed and so no noise enters the premises from outside.

Untitled

• stem
• 6 Sep 2010
• 1

Untitled

• stem
• 6 Sep 2010
• 1

 

[kreutz]

Thanks. Your posts are very helpful.

To be honest, I don't think I will bother arguing with the landlords about this at the moment. I have already bought the materials for an acoustic wall and I have arranged a builder for the weekend, so I'll see where that takes me.

Since you seem to know quite a lot about this type of aircons, would you happen to know the rough procedure for maintaining them? The part that interests me is the side which they are maintained from. Would a maintenance person have to take out the whole unit, or is it enough to just access it from one/both of the sides? The reason why I am asking is that I wonder whether they maintain it from the outside or the inside. Naturally, if they maintain it from the inside then I will need to allow for it when building the acoustic wall. However, if they maintain it from the outside then I won't need to change anything.

Thanks again.

 

[Norcon]

They will need access from the outside. Specifically the right hand side. (When viewed from outside)
The compressor and other components are accessed from a removable panel which wraps around the corner and covers the side partially.

The rear condensor section also needs to be left accessible to clean the fins periodically.
As stem has stated they should ideally be on the outside of the building.
Either mounted on a wall or on a roof or in an area that is very well ventilated.

Can you post up an image of what this looks like from the other side?
Which I assume is the outside of the building.

 

[kreutz]

Thanks very much guys, you've been very helpful.

Norcon: that's the only picture that I could find:

I don't think that it helps much. It looks like one of the windows from the outside, while from the inside the window that is now on the left looks smaller than the one on the right because it is covered with plasterboard.

We have built an acoustic wall and the noise levels are now acceptable. I guess we will have to disassemble the wall before maintenance, unless they can maintain the aircon from the outside.

In any case, my only concern now is ventillation. Anybody could advise on the best methods for ventillation of a small room? Would a portable aircon that chucks out hot air into the corridor be a good idea?

Also, regarding noise, the only thing we can hear now is police/ambulance car sirens. I assume there aren't any materials that would miraculously make that sound disappear?

Thanks again.

 

[stem]

I don't think you will like a portable air conditioner for the following reasons

1. They are noisy. They contain one fan to circulate air inside the room, one fan to blow the waste heat away down the exhaust tube, and a compressor (The thing you've just buried behind an acoustic wall) all contained in one unit sitting at the side of your desk.

2. Also the exhaust hose should vent outside. A considerable amount of waste heat is blown down the exhaust hose when it's cooling the room. If the corridor is enclosed, it will raise the temperature there considerably.

As air is blown into the corridor the existing corridor air will be displaced. The temperature will increase as more hot air is introduced, and as more air is blown in, this will force the warm air out of corridor via windows and doors, which means it could work its way into rooms off the corridor.

3. They are only good for areas like a domestic living room that are fairly small, not exposed to direct sunlight, and not full of heat generating equipment such as lights, computers, and people. Sizes and capacities do vary, so check the manufacturers specifications carefully to see what they are actually capable of doing.

4. The exhaust duct shouldn't be extended, as the fan can't cope with additional resistance. This restricts where they can be located. Most portable conditioners come with a 2-3 metre long hose.

5. Portable units take some of the room air which you have just paid to cool, suck it through a heat exchanger to collect the waste heat and then blow it outside, so they don't make the most efficient use of energy. Having said that, this method of operation does provide for some ventilation of the room via the exhaust hose.

It you want ventilation, then a fan exhausting outside is probably the best solution, unless you have sufficient £££'s for a heat exchanger system that will remove air from the room and also bring fresh air in. At the same time transferring most of the heat from the outgoing air to warm the incoming air in the winter and vice versa in the summer.

For cooling use a spilt air conditioning unit like the one that started this thread (but properly installed)