More MVHR help please!!

[AppleQueen]

Hello again everyone! Thank you all for your help along the way here.

I'm currently installing the system (and wishing I had just paid someone else to do it) and because I’ve had to re-route the 150mm ducts, I have now run out of the pipework. I’ve just tried to buy some more from somewhere closer than BPC (because it took over a week to arrive last time) and I’ve seen you can get flexible 150mm ducting pipework. This would make it so much easier for me to get the pipework all to fit into the plant room….is there a reason not to use the flexible stuff??

Thanks!

[Mike]

1 hour ago, AppleQueen said:

is there a reason not to use the flexible stuff??

Yes, several reasons!

 

It's much more resistant to airflow than regular duct, so the fans will have to work harder (using more energy, so also louder); condensation can gather in the undulations leading to mould growth; it's not very resistant to being crushed, punctured or ripped; due to these problems it can't be really cleaned internally, should that be needed. The only legitimate use is when using a very short length - e.g. 150mm long for 150mm diameter duct - to connect rigid duct vertically to the MVHR unit, though that seems to be rare.

 

Edited Sunday at 15:25 by Mike

[JohnMo]

7 minutes ago, Mike said:

Yes, several reasons!

Plus it has to be pulled tight, when installed, so almost impossible to install well or correctly.

[AppleQueen]

@Mike @JohnMo Thank you both! I thought there must be a simple reason for it.

Back to it with the rigid stuff then!

[AppleQueen]

Whilst I’m at it…. Does anyone think this design might not pass building regs for ventilation? We have a large open plan family room/kitchen but the part of the ceiling in the kitchen is vaulted and then back down to the family room (pic attached). Because it is vaulted, I can’t get the extract vents to the other side of the kitchen, the closest they can get is where I have put the red crosses. I am also planning to have a hob with recirculating vent. Are building control going to have a problem with that?

[Mike]

The positioning isn't ideal as the air doesn't pass through the kitchen. My guess is that the BCO wouldn't question it, but they may.

[JohnMo]

Air will take path of least resistance. So if your air being supplied at the green X's air will just move to the red X's  and not really wash across the room.

 

Can you get to the vertical face of the vaulted kitchen? I would suspect the dining room supplies make the ventilation in the kitchen worse rather than better. Because the short cut the air can take.  You would actually be better supplying excess air in study and sitting room and having kitchen extract in the vertical face of the vaulted roof.

 

Why two supply and extracts?

 

Have you seen mapped out all the vents on the different floors and tried to understand where the air moves to and from, to make sure the whole house is washed with air?

Edited Sunday at 16:51 by JohnMo

[AppleQueen]

23 minutes ago, JohnMo said:

Air will take path of least resistance. So if your air being supplied at the green X's air will just move to the red X's  and not really wash across the room.

 

Can you get to the vertical face of the vaulted kitchen? I would suspect the dining room supplies make the ventilation in the kitchen worse rather than better. Because the short cut the air can take.  You would actually be better supplying excess air in study and sitting room and having kitchen extract in the vertical face of the vaulted roof.

 

Why two supply and extracts?

 

Have you seen mapped out all the vents on the different floors and tried to understand where the air moves to and from, to make sure the whole house is washed with air?

Thank you, it’s difficult to get to the vertical face of the kitchen because there is a steel beam across the opening. I could go up through the floor into the landing above and then into the vertical face of the kitchen but it’s not ideal because then I would have to box off some of the landing.

BPC did the initial design for me, they put two supplies in the family room (maybe because of size because it’s 6x6m) and they initially said one extract from the kitchen but then I removed a bathroom from upstairs so I thought maybe another in the kitchen to balance it?

I have mapped out the vents but not the air movement - is this difficult to work out myself?

I'm feeling a bit disillusioned because all the companies have said this is a DIY job but even with a professional joiner and my husband helping, this has been horribly stressful to do!

[JohnMo]

1 hour ago, AppleQueen said:

is this difficult to work out myself?

Not really difficult - say you supply 50 l/min at one point, where does it go? It has to go to extract points, so if you have follow the air route. Ideally it will travel across rooms halls etc.

 

Read up on coanda terminals, these will push air across the ceiling in a chosen direction, extract ones will suck it from a direction of your choosing also.