whaleshark Posted January 8 Share Posted January 8 Have designed an MVHR system but am struggling with 1 detail. The design has 125mm insulated ducting by the time it reaches the ceiling/wall vents. Isodec/Sonodec to be specific. For the valves I need them: To accept 125mm semi rigid ducting with a good seal (using jubillee clip) To attach to plasterboard, ideally using spring clips/wings rather than screws. Smart looking (spouse approval factor) and that means flat looking valves. I would also like the extracts to have the possibility of adding filters to keep the majority dust/grease out of the ducting. I can't really find any products that fit the bill. The closest I can find are the Vent Axia Uniflex+ valves if used with the optional fixing collar but these don't have the option of extract filters and it doesn't look like the collar has a lot of depth for the duct to 'get on'. There is also a Zehnder Comfovalve which has a filter option but doesn't look like it would take semi rigid duct and a Nuaire Q-Aire valve which is similar. Has anyone else run into the same problem? Link to comment Share on other sites More sharing options...
JohnMo Posted January 8 Share Posted January 8 You need to limit the use of that type of duct as pressure drops could be huge. You really should be doing MVHR to plenum then 75 or 90mm semi rigid duc to outlet. Then a standard 125mm inlet or outlet terminal. 100s of designs available If the duct needs insulation then add that on. Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted January 8 Share Posted January 8 20 minutes ago, JohnMo said: You need to limit the use of that type of duct as pressure drops could be huge. You really should be doing MVHR to plenum then 75 or 90mm semi rigid duc to outlet. Then a standard 125mm inlet or outlet terminal. 100s of designs available If the duct needs insulation then add that on. I think you've got that mixed up, larger ducting wouldn't give a pressure drop, it would just mean the air speed flowing through would be lower for a given flow rate. Pressure drops come from restrictions, filters being blocked etc would give a high pressure drop than a brand new filter as an example. Link to comment Share on other sites More sharing options...
JohnMo Posted January 8 Share Posted January 8 13 minutes ago, MikeGrahamT21 said: think you've got that mixed up, larger ducting wouldn't give a pressure drop, No not mixed up, look at the duct referenced. May be a big diameter but the duct is pretty rubbish and every guide says avoid. Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted January 8 Share Posted January 8 3 minutes ago, JohnMo said: No not mixed up, look at the duct referenced. May be a big diameter but the duct is pretty rubbish and every guide says avoid. Ahh yes thats not MVHR ducting, just ventilation ducting. I had assumed it was this style ducting which is the correct 125mm thermal ducting for MVHR: https://www.i-sells.co.uk/product/kair-self-seal-thermal-ducting-125mm-1-metre-lengths-box-of-6/ The pressure drop with the one above is more to do with unsmooth internal surface and susceptibility of being squashed, bent too sharply etc Link to comment Share on other sites More sharing options...
Mike Posted January 8 Share Posted January 8 2 hours ago, whaleshark said: The design has 125mm insulated ducting by the time it reaches the ceiling/wall vents. Isodec/Sonodec to be specific. That type of duct is totally unsuitable for MVHR use - see also https://forum.buildhub.org.uk/topic/41660-more-mvhr-help-please/ 1 hour ago, JohnMo said: You really should be doing MVHR to plenum then 75 or 90mm semi rigid duct to outlet. Then a standard 125mm inlet or outlet terminal. 100s of designs available If the duct needs insulation then add that on. This. Link to comment Share on other sites More sharing options...
whaleshark Posted January 8 Author Share Posted January 8 I thank you both for the advice and recommendation. I had read the various recommendations that said to avoid that duct however the design needs a branched system and the branch will be mainly running behind an ashlar wall. I have designed the system including static pressure loss, flow rates and air speeds. The critical run pressure loss is around 30-40Pa, with the main variation being on which valves are used. Flow rates have been kept low. I originally agonised over the choice of duct, but I am now satisfied with the choice. By all means, use me as an experiment and I will report back as to how the system has fared when completed. Given that I will be using the 125mm ducting into 125mm valves, does anyone have any recommendations that are a better solution than the Unifllex+ with the collar? (Always aware that it is hard to convey tone in written text: please read this in the best way possible 🙂 ) Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now