MVHR commissioning

[CC45]

Hi all,

 

looking for some advice.

 

just commissioning the MVHR - a Vent Axia Sentinel Kinetic plus.  Supply and extract target 172m3.

 

With both the supply and extract set to 30%, the supply actually measured 161m3 and extract was 199m3.  I was surprised at the difference.  There are more supply valves and there's Q a bit more duct.

 

I increased the fan speed on the supply up to 33% - it then measured a wee bit below 172m3. Sorted.  I then went around and set the valves. All good.

 

The extract I reduced a bit and then remeasured and then reduced again and then a bit more.  At 24% I got down to 182m3 - I think at 22% it would be close to target.  Is a 11% difference between supply & extract OK?  It seems a lot to me.  At 22% it is only 2% above the normal overnight / low ventilation rate.  I've also got issues with the balance between valves - some are closed down all the way and still over supplying.....

 

I didn't expect it to be such a challenge....

 

I just hope the anemometer is reading reasonably close to right .........

 

Any thoughts?

 

Cheers

 

CC

 

 

 

[Gone West]

11 hours ago, CC45 said:

Any thoughts?

Our fan settings are 30% supply and 45% extract for normal use. I've also got a large difference in valve openings but that is because of the difference in room volumes, but everything balanced out ok eventually.

[CC45]

Thanks Peter - what are the fans set at for boost and then overnight?

[Gone West]

12 minutes ago, CC45 said:

Thanks Peter - what are the fans set at for boost and then overnight?

Ours stays the same 24/7 on level 2. The only time the supply fans increase is if the built in EASHP pushes out warm air when it goes to 100% for a few seconds and then modulates down to whatever flow is required. Level 4 is boost which is 100%, we don't change the setting for overnight. Level 1 is for unoccupied and level 3 is a party setting both of which we have never used.

[Russdl]

I have a question regarding MVHR commissioning and Approved Document F. 
 

Document F, Table 5.1a is titled ‘Extract Ventilation Rates’.  
 

Document F, Table 5.1b is titled ‘Whole Dwelling Ventilation Rates’. 
 

To my mind ‘Ventilation’ is extract + supply and not extract only. 
 

It seems most on here are hitting the 5.1b ‘ventilation’ requirement by upping the extract rate to hit the 0.3 l/s per m2 of internal floor area.

Is that necessary?

 

What am I missing?

 

Thanks in advance. 

[dpmiller]

extract and supply should match, near as.

[Russdl]

@dpmiller yep, mine are pretty much balanced. 
 

My question is in relation to Table 5.1b which specifies ’Ventilation’ rates (not ‘Extract Ventilation’ rates, that is in table 5.1a)

 

Note ‘a’ of table 5.1b requires minimum ‘ventilation’ rate (not ‘extract ventilation’ rate) to be 0.3 l/s per m2 of internal floor area which would be 57.9 l/s for us. 
 

So the question is, do I combine my extract rate and supply rate to get to a figure above 57.9 l/s or do I have to ramp up the extract rate so that my extract total is above 57.9 l/s

 

My view is that ‘ventilation’ is air in/air out whereas ‘extract ventilation’ is just air out. 

[dpmiller]

I'd opine that ventilation is flow *through* so wouldn't be adding them, no.

[Russdl]

@dpmiller so you reckon ‘ventilation’ in 5.1b is the same as ‘extract ventilation’ in 5.1a?
 

I guess you’re right, I think most people here who refer to the “0.3 l/s per m2” section have all bumped up their extract rates to hit the target, and many of them are far wiser than me.