Balancing Query - Replacement MVHR

[TimCx]

I am working through balancing my system now that my replacement MVHR is installed, it replaced a failed system from an defunct manufacturer so I was not able to change the ducting other than near the new unit.

 

I have done some initial tests before doing the proper balancing but I hit a couple of issues and hopefully someone can offer some advice:

 

1) The default setting on the new MVHR (Vent Axia Kinetic Advance S) gave very poor rates, I have now increased these and I am getting better rates without trying to properly balance it yet. The unit it correctly sized for my house but the ducting may be less than ideal. In order to get the flow rates required I may need to run the boost setting at somewhere near 75%. Is the normal or does it indicate a problem?

2) We have a cooker hood in the kitchen, I am not sure how to take that into account with extraction from the kitchen, there is also a vent in the kitchen. Can I keep the vent at a lowish rate and rely on the cooker hood to meet the required kitchen extract figure?

 

Thanks

[TimCx]

Does anyone have any ideas on this, I have been searching elsewhere but I haven't found anything useful especially about the Kitchen situation. Thanks

[JohnMo]

You should not be on boost.

 

First are all the terminals in rooms fully open, if not, open them all.  Start from the furthest thermal, leave that fully open and adjust MVHR speed to get the flow rate you require.  Then work you way back to the mvhr unit adjusting the terminals. Work on supply only or extract only get that one right first.  It will take a few goes to get it correct.

 

When you have both supply and extract correct, set the boost flow rate.

 

The kitchen extract should be circa 45m3/h.  Cooker hood rates can be ignored.

[jack]

5 hours ago, JohnMo said:

You should not be on boost.

 

First are all the terminals in rooms fully open, if not, open them all.  Start from the furthest thermal, leave that fully open and adjust MVHR speed to get the flow rate you require.  Then work you way back to the mvhr unit adjusting the terminals. Work on supply only or extract only get that one right first.  It will take a few goes to get it correct.

 

When you have both supply and extract correct, set the boost flow rate.

 

The kitchen extract should be circa 45m3/h.  Cooker hood rates can be ignored.

 

Also, some MVHR systems adjust per terminal airflow at the manifold. If you have such a system, you should have all terminals wide open while you get as close as you can by adjusting airflow at the manifolds. Once that's done you can make fine adjustments at the terminals if needed. 

[TimCx]

On 27/11/2022 at 10:42, JohnMo said:

You should not be on boost.

 

First are all the terminals in rooms fully open, if not, open them all.  Start from the furthest thermal, leave that fully open and adjust MVHR speed to get the flow rate you require.  Then work you way back to the mvhr unit adjusting the terminals. Work on supply only or extract only get that one right first.  It will take a few goes to get it correct.

Regarding terminals being 'fully open' mine are round screw in things with no markings, I have removed all the screw-in bits to clean them. Am I better off starting with the covers off or should I just connect them as far out as they will go, I am not sure if this would make any difference .

 

I hope to complete the balancing by Sunday., wish me luck ;-)

 

On 27/11/2022 at 10:42, JohnMo said:

 

When you have both supply and extract correct, set the boost flow rate.

 

The kitchen extract should be circa 45m3/h.  Cooker hood rates can be ignored.

I thought I had read somewhere that the required flows for each room e.g. 13ls (45m3) for kitchen could be done on boost and that the normal running could be at a lower rate but I can't find where I read that. From your info I think I need to ensure that the required rates are available on the normal setting and that boost should be higher? 

 

Thanks

[TimCx]

On 27/11/2022 at 16:24, jack said:

 

Also, some MVHR systems adjust per terminal airflow at the manifold. If you have such a system, you should have all terminals wide open while you get as close as you can by adjusting airflow at the manifolds. Once that's done you can make fine adjustments at the terminals if needed. 

Thanks Jack, mine is not that clever, I wish it was it would be a lot easier.

[Blooda]

 

55 minutes ago, TimCx said:

I thought I had read somewhere that the required flows for each room e.g. 13ls (45m3) for kitchen could be done on boost and that the normal running could be at a lower rate but I can't find where I read that. From your info I think I need to ensure that the required rates are available on the normal setting and that boost should be higher? 

 

 

Try this:-

 

Approved Document F: Volume 1 applies to dwellings (publishing.service.gov.uk)

 

 

High rate ventilation [boost]

 

 

Minimum whole dwelling Ventilation - 

 

 

 

 

 

 

 

[JohnMo]

1 hour ago, TimCx said:

Am I better off starting with the covers off or should I just connect them as far out as they will go

Have the cover in position, but wind out as much as possible while still having enough screw engagement to install the lock nut.  Good luck

[TimCx]

45 minutes ago, JohnMo said:

Have the cover in position, but wind out as much as possible while still having enough screw engagement to install the lock nut.  Good luck

Excellent thanks you mentioned lock nuts made me realise I wasn't sure how they are meant to lock, my vents have nuts but they were not locked, most only had 1 but I have now put 2 on each, how should they be locked? Are they to just stop the vent being wound in too far or should they be locked either side of the threaded bit?

Edited December 1, 2022 by TimCx

[JohnMo]

You would have one nut either side of the white threaded part.  Basically lock the first terminal, the other units, move the nuts out of the way, the inner one, screw well out of the way so it doesn't limit adjustment.  When adjusted, pop the terminal out of the ceiling and lock the nuts.

[TimCx]

This balancing is getting very complex in my house !

 

I have 2 small rooms which are essentially plant rooms, one has the indoor part of the ASHP and underfloor heating manifold and the other some plumbing related to solar thermal and a second underfloor manifold, however both of these rooms have extract valves in them.

 

I am also struggling to get the extracts rates right for the kitchen and the system remains unbalanced as the total extract rates are higher than I can achieve for the inlets. 

 

As the 2 plant rooms are not really utility rooms and are small (approx. 2.5 m2 each) and normally don't have people in them can I close both of these valves and not include them in the calculations?

Edited December 3, 2022 by TimCx