Heat loss calculation check

[JohnMo]

On 21/12/2024 at 00:31, Gordo said:

As air is blown in it is sucked out at a measured / adjusted rate to be left "slightly" pressurise in the house

Sorry this is incorrect. The MVHR in and out flows, are balanced - same is taken out as brought in, so house is neither pressurised or depressurised by MVHR. 

 

MVHR also slowly decreases house temp (assuming colder outside) as the efficiency of the heat exchanger within the MVHR unit will never be 100%. Ventilation heat loss will be based on approximately 10 to 20% of the overall flow rate of the MVHR unit, plus natural ventilation heat losses based on house airtightness. So airtight house, ventilation losses are almost all losses produced by MVHR, leaky house plus MVHR, are MVHR losses plus natural air leakage losses.

[Russdl]

6 hours ago, JohnMo said:

The MVHR in and out flows, are balanced

Our supply is always slightly higher than extract, so theoretically we are slightly over pressured. 
 

[G and J]

53 minutes ago, Russdl said:

Our supply is always slightly higher than extract, so theoretically we are slightly over pressured. 
 

And what percentage accuracy are the air volume measurements do you think?  

[JohnMo]

2 hours ago, Russdl said:

Our supply is always slightly higher than extract, so theoretically we are slightly over pressured. 
 

Why? You will always get less heat recovery!

[Russdl]

6 hours ago, G and J said:

And what percentage accuracy are the air volume measurements do you think?

Absolutely no idea, it’s what the Brink is reporting and I’ve no reason to question the accuracy thus far. 
 

5 hours ago, JohnMo said:

Why? You will always get less heat recovery!

As for the “why” that’s the way it operates and always has but being slightly ‘over pressure’ seems like a good thing to me. Isn’t it? We’re quite airtight but not a sealed box. 
 

I haven’t given this a huge amount of thought until now but surely that slight over pressure will act as an air barrier to any small air leaks we have  - ensuring the air leaks out and not in - so we’d be giving away a little bit of pre warmed cold air instead of welcoming in the little bit of cold air that hadn’t been pre warmed. 

[G and J]

Ummm, what’s wrong with it being balanced? Less leakage either way unless I guess it’s blowing a hooley. 
 

I would look at those readings and, unless I knew their accuracy was better than +/-1%, I’d conclude that the difference is too close to call. 

[Russdl]

7 minutes ago, G and J said:

Ummm, what’s wrong with it being balanced?

Until I gave it a bit of thought a few minutes ago I would have said “nothing” but now having given it a bit of thought I’d say “air curtain”. 
 

Like I say, it’s always been like that, the supply has always been slightly higher than the extract. I have no reason to doubt the data the machine is giving me so perhaps the manufacturer thinks it’s a good thing?

 

Standing by for the contrary views.