Lossnay

[Andy AC]

Can any one help me with sizing a lossnay unit? I've got involved with a project which needs a new fresh air/ventilation setup and needs to be very quiet. The room is 9.4 x 8.4 x 2.7m. It is going to be converted to a superquiet video teleconferencing room with approx 12 people max at any one time. The room is going to have much more soundproofing on the walls and the ceiling tiles are also to be changed. The room also has 2 x mitsi 7 kw cassettes with zubadan outdoor units, these are also quite noisy- fan motors whine quite a bit.
They have asked for maxiumum of 36dba measured at 1m from outlet, I think I will struggle to achive this.
I am thinking of changing the cassettes for ducted indoor units and maybe install them outside the room along with a new lossnnay system.
The reason I need a lossnay unit is that the existing fresh air inlet and return to the room is too noisy for what they require - it's noisier than both the cassettes running at full speed. The existing fresh air is from a rooftop unit far far away. I can pick up fresh air for the lossnay from just a few meters from the room.

Any help greatly appreciated, I've never had to deal with fresh air systems before - I was only asked to quiet down the a/c, now it's turning into a big can of worms.

[Brian_UK]

You're going to need isolated ductwork and plenty of sound attenuators.

Ductwork needs to be sized for low velocity with low noise air terminals.

Also consider any hard mechanical noise that may get transmitted through the structure from any equipment that you mount.

[r.bartlett]

a 500 will be big enough and upsize the ducting from the spigots to reduce the air speed. these units are very quiet so you won't need any attenuation just make sure there are enough outlets. - I would use 4 x 595 ceiling tile replacements in/out.But you should size it correctly yourself.

[Neddy]

Could you use a Mitsubishi electric Guf ? It's basically a lossnay with a heat exchanger you can pipe to an outdoor.

[Andy AC]

Thanks for the input chaps. Looks like i'm going to run out of space for all the grilles - at least 2 supply and return for each for the a/c and a couple for the fresh air. Looks like the ceiling void above the room is gonna need total gutting and start from scratch. Beginning to wish I didn't get involved now.
Neddy - if thats the things I think they are, they are the size of a smart car. The building does have some of them littered about in a random fashion, but there is not enough space anywhere in the ceiling void of the basement- would solve the problem though.

[The Viking]

Andy,
Another thought.

As Neddy said, use a GUF but put it outside and only run 2 over-sized ducts in.

[Slim R410a]

We have just installed a very similar job. Room with varied occupancy depending on meeting type 8.4m x 8.4m x 2.55m height.
2No. SEZ-KD71 ducted and 1No. LGH-65 Lossnay.
We upsized the duct - Used 1No. 300dia x 300 long acoustic silencer after each supply air plenum to 3No. 595 (200dia neck) swirl diffusers and 250dia x 300 long silncers on the lossnay fresh air supply and stale air return.
2No. 595 swirl diffusers used for the lossnay supply (200dia neck) and 10% of the indoor units duty (125dia) went onto the return air filter on each indoor unit.
Used the ceiling void as a return for the 2 indoor units and the return (stale air) on the lossnay.
Sensor on the PAR-31 used for the setpoint. (within the room at 1.2m ffl)