Browse Forums Heating, Cooling & Insulation 1 May 28, 2012 1:12 pm Hi H1 We recently commissioned 2 A/C units (ducted) in our house. We have a reasonably complex build so we have a ducted Daiken system on the top floor and a second ducted system on the bottom 2 floors (living and basement) (built on a side of a hill). Both units are single phase daikin inverters upstairs about 13kw and downstairs a about 14kw. The unit on the top floor is fine, conventional installation, fan coil in roof cavity, return air grill in corridor and outlets into each bed room etc. Downstairs the fan coil sits under the house behind the basement and routes air up through cavities between rooms etc with the air return being between joists across under the floor outputing to a side wall return vent. I'm speaking with the installers about my issue but I also wanted some indepentant throughts on the topic. the problem is the noise at the grill on the air return on the downstairs unit is I think quite excessive; I used a dB reader (iPhone app) - on the unit upstairs the air return (standing below the grills) is 45dB on the downstairs standing near the side wall air return it is 65dB (4 times as loud) - and loud enough that you say "Hey thats really loud" and it is a obvious and ongoing noise in the living areas. What can cause this; my thoughts are possibly constricted return air flow (as I mentioned it is a tricky install) the fan coil unit is also connected about 2m behind the vent so am I getting noice feeding back into the house from the fan coil? Any thoughts on what/why how? Let me know what critical information I've missed in this post and I'll add it, I'm keen to get it resolved but also keen for some independent feedback. Cheers! Mark Re: Noise from Air Return Grill - Daikin 2May 29, 2012 5:49 am 2m of return air duct is not a lot... I'd suspect you're getting quite a bit of noise from the fancoil... also check that this duct is acoustic sound reducing duct... sounds like you have a FDYQ160 there which will move 1,000 litres of air per second... to keep the return air airflow under 2m/s you'll need a return air grille with a surface area of at least 0.5m2... Re: Noise from Air Return Grill - Daikin 3May 30, 2012 11:02 am Hi Iceman I think that has hit the nail on the head - is this right: The air return is travelling between floors using the space between 3 joists as the air path. This path isn't lined or insulated. The path length is about 2.5m and at the end of that there is a box made of that A/con foil clad foam interfacing to the fan coil unit. The joists are 24x45 with some minimum obstructions on 1 of them, 3 joists are being used for the return. Based on a quick calc we have 2500-2800cm2 of area, but from you email we 5000 cm2 of space. Would it be fair to say that the unit isn't breathing correctly? Daikins site suggests the fan coil creates 51dB of noise, however I'm reading 70 directly at the grill (it's like it amplified). (knowing little about A/c design) I take it that if you restrict the return the unit will suck harder, forcing air at a higher speed and creating noise? I assume the answer is to add more air return capacity? It's a complex install but in thinking I believe we could probably bring at least 1 additional return into another area (with atleast 30cm round duct or more) - that would add another 800cm2 odd of return capacity. Still short by the sounds of it but would that improve things much? Do you have any suggestions to improve sound - or is it just m2 capacity of return? cheers MArk Nope, only on the inside, I've literally has my ears to the brick outside and can't hear anything. I can sort of 'reset' the noise by pressing firmly on the studs. This… 10 11701 Upgrading your windows to soundproof ones, like triple-glazed, can make a significant difference. While changing window… 4 11624 How do you remove one of these ceiling air con vents? And is it possible to disconnect the duct joined to the vent from inside the house, without going into the roof cavity? 0 5835 |