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Zammo

There's a hole in my man cave!

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Zammo   

So heading down the final straight with the new house build, and the relatively acoustically sealed man cave is about to get a hole in it. The room has concrete slab floor (which will have underlay and thick carpet), bondek concrete slab roof, and front/side walls core filled block work. The entry is from left rear via a studio grade acoustic door. The rear wall (which backs on to a powder room and laundry, then to the main living space) will be made of the full quiet wave wall system, and other walls and ceiling will be single quiet wave membrane on 12mm boards.

Many pros and cons to such a room, but a big problem my builder has not yet solved is ventilation. We have specified this exhaust fan:

http://www.schweigen.com.au/multipurpose-exhaust-system.html

Advantage is motor is external, so it's extremely quiet. Problem is we need to utilise the rear wall for the grill outlet, and then flexiduct will run through the roof space of the living area before it exits via an external wall to the wall mounted motor.

The flexible duct is 150mm diameter. Query for those more knowledgeable than me. Will this transmit a great deal of noise out of the man cave and through the roof cavity space, and if so will it be limited to mid and high frequencies (due to small grill hole and duct diameter)? If we only have to deal with mids and highs, should be able to wrap something like a tontine acoustisorb insulation material around the duct to deal with majority of noise.

Edited by Zammo

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sthpaul   

Zammo

I am not an acoustician but a mech engineer for HVAC. You can get acoustic flex duct rather than standard duct and wrap it yourself, much easier. But you should also at least have an acoustically lined solid duct with a 90 degree bend coming off the wall behind the grille. Off this bend you may need a length of acoustically lined duct to further assist but you may need someone more acoustically knowledgable to confirm an appropriate length.

Hope this helps.

Sent from my iPhone using Tapatalk

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Zammo   

Thanks sthpaul. Didn't realise there was acoustic flex duct. Will have to check whether it's compatible with the schweigen system. May need to check on the 90 degree bend as well, as schweigen exhaust fans quietness relies on a lack of sharp bends. You've given me a bit explore.

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Tony M   

Hi Zammo

 

My apologies if I've misunderstood something here, but it seems to me that you are putting in an exhaust fan to ventilate an almost-sealed room.

 

I trust there's somewhere for the fresh air to get in? - otherwise the exhaust fan will struggle to do much at all.  Normally this isn't much of a problem as most rooms are leaky, but it seems you are making this fairly tight for acoustic reasons.

 

Any vent where the air gets in will be a potential noise source too so size and placement need to be considered.

 

Cheers

Tony

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sthpaul   

Tony is correct, you can only pull a rabbit out if a hat if the rabbit can get into the hat in the first place. Both air in and air out openings will need to be acoustically treated. If the fan is lacking in grunt you may need to look elsewhere. Fantech is where we source fans from and are quite helpful. Best to work out your duct route and send them a sketch, the pressure drop through the system is what the fan has to cope with. Also the acoustic flex duct shouldn't have any more pressure drop than normal flex, just make sure you have no tight bends and kinks.

Sent from my iPhone using Tapatalk

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:) al   

personally with hvac in a room such as this given the huge effort being gone in zammo. please get in touch with someone like david at wave train. with not a lot of cost he'd do the design for you, once specd and designed anyone else can put in for you.

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Zammo   

Currently exploring options with builders to allow for external air source to get into the cave. Bloody difficult when you have basically an underground room surrounded by reinforced concrete, and you don't want sound to get in or out. We have a footing cavity on one side of the cave which we may be able to utilise - bore a hole in the cave wall, connected by large bore flexible duct to a hole in the external footing wall. I've quoted the Australian Standards to the builder, as their current solution of just an exhaust fan fails to meet them at all. Contract was for the builder to design a ventilation system for the room, so will be interesting to see if they consider such a solution as a variation.

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:) al   

Zammo honestly talk to someone like wave train. This is quite standard in couple of designs I've seen of ht he's done plans for. No need to re in vent the wheel. There's others do design for this kind of thing overseas as well. But all quite standard for a ht room where we are doing hvac but don't want sound leakage

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Gee Emm   

I have experienced a wave train designed room-in-a-room

 

The man knows his stuff

 

This problem is normal business for him.

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Zammo   

Building company project manager is discussing with mechanical contractor to come up with solutions. May be a bit late in the day to get someone like wave train involved, as we really are in the home straight. We should be able to come up with a solution, as lots of products out there for acoustic insulation of the ducts used in residential and commercial applications. Stuart from SGR suggested a pretty handy product. So many things to get right building a house - this was one of those we just left a bit late, but should be able to solve. Thanks again guys. Will update once I get feedback from builder and architect.

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Zammo   

Thanks Peter. Well aware of that mate. Wish we had thought about this way back at design stage, but so many things going on with the build we all left it a bit late. Project manager in discussions with mechanical engineer now. External vent solution I thought of has problem of heat/cold transfer, so need either internal fresh air source or heat exchanger. 

Edited by Zammo

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Zammo   

post-109000-0-63625000-1410578538_thumb.

 

Ok, here's a rough schematic to avoiding asphyxiation in the man cave. Going with the ERV unit you suggested Pete. Thanks very much - builder was very happy to see such a narrow profile unit that would easily fit in bulkhead over powder room/laundry/kitchen. We are going to actually place the unit a bit further right in the picture in the laundry, so slightly longer run to cave with some gentle 90 degree bends in the flexiduct.

 

Two perforations of rear quietwave wall for inlet/outlet. We're going to use acoustic 150mm duct for all limbs, and additionally pack with acoustisorb or similar, particularly at the perforations. Inlet and outlet are external wall, so no need for dead vent.

 

Have done calculations, and can run ERV unit at it's lowest setting of 40l/sec - this will provide over 10% air turnover per hour, and runs at 38dB at 1.5m from unit. The room is all underground and should stay at a reasonably constant comfortable temp, so at this stage no plans to add heating or cooling to the ERV unit. Will re-assess once we've lived with it for a bit.

 

Thanks to all for input, and will keep updated on Man Cave thread.

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Good stuff. Can you dump the supply and returns into an insulation lined box in say a soffit? that would be best. Then use something like one of these http://www.holyoake.com/product-details/LD1200_item.html?ref_cat_id=Linear-Bar-Diffusers

 

When I say best, that's what I am doing :D

 

Basically you want to keep stepping up the size of the supply/return as you get near the room to being the air velocity down = quieter

 

Edit: ideally you'd run the supply to the front of the room in a soffit

Edited by Peter the Greek

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Zammo   

Hey Peter. We did look into a soffit, but for reasons of expediency we've held off for the moment. Kinda hoping the bulkhead where the ERV and flexiduct go will do most of the acoustic damping. Won't be too difficult to add a soffit later (at rear, sides or even all the way through to front of room) if required.

Edited by Zammo

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Fair enough, see how you go.

 

Its just better to flow the air from one end to the other for obvious reasons.

 

Its good your using acoustic duct. Mine is currently half and half - well half a line box, so basically acoustic duct, and a 3-4m run of 150mm pvc pipe (just because I had it lying around), the pvc pipe acts like a horn. so its a little audible. I'll swap it out before the room is done.

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Tony M   

Zammo, looking at your diagram, I'd really be worried about the airflow short-circuiting as Peter has alluded to.  I appreciate that you can add a bulkhead later to take the air supply to the other end of the room if necessary.  But t might be easier and more realistic to factor this in from the beginning - it's almost certainly going to be needed to get good ventilation levels without excessive air movement in the room. 

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Zammo   

Have discussed short-circuiting with the ERV supplier (airchange), which have a local office. They seem pretty confident won't be an issue considering room dimensions and flow rates. Again, we have considered a soffit and moving inlet/outlet to opposite ends of room, but honestly it won't be a big deal to retrofit if we run into problems with current setup.

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Tony M   

Sounds like you have it under control, Zammo.  And it's always worth trying the easiest solution first.

 

The end to end option would allow the same level of ventilation to be achieved with a lower velocity airflow, which might be nice in a music room.  But I do understand your strategy of keeping it as a potential improvement down the track if the planned set-up proves less than ideal.  Until you try these things you never know for sure how they will perform in the real world..  

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Zammo   

Thanks for feedback Tony. I'm quite impressed by the ERV unit. Locally made, and at the flow rates we're going to start with, whisper quiet.

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Jventer   

A question from a novice. With air movement - are the in and out vents at the same level? Do they need to be high , low or  the one high and the other low?

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