Vent axia advance old house

[Noodle]

Hi all,

 

So we have a 16thC farmhouse, we renovated it 5 years ago, new windows, extern insulation etc but obviously still not hugely air tight. 

We just replace our old old Duplexvent with a new Vent Axia Advance as old one died and callout are half the amount of a new unit!

 

So, we've never balanced the system properly just used it to control condensation and fresh air. So obviously it won't be working quite right.

 

I had a few questions anyway on its operation and peoples thoughts.

 

 

1- design was by BPC and we have more of a positive pressure system,  3 supplies in hallways ( that are high flow) and normal extracts. So our 209m3/h translates to approx 60l/s flow rates (screenshot of flow rates from bpc desogn) This technically should be what we have set on the unit correct?  This turns into quite aloud gale at supplies and really we still get a large air flow at vents at half that.... 

Question is is it really bad to run the supply at say 30l/s but keep extracts high to control condensation in.our bathrooms? Does the system just not work that way and just ramping up extract wont work or will mess up air temps.

 

2 - on the app, is the internal temp the temperature inside the mvhr unit? Its in the attic. The 1st day i turned the system on the supply temp was more like 17 degrees and now far lower around 13? It's really cold outside so do people think its because its so cold outside and in the attic that my supply has dropped so much or is because I'm faffing around with the fans and unbalanced the system so much? I assume with such a low internal unit temp the heat exchanger can only do so much in say sub 5 degrees external temp?

 

I know I need to balance the system properly but any thoughts on the above greatly appreciated.

 

Thanks.

 

 

 

[Noodle]

Oh, our house is approx 220m2 and 5 bedrooms, 3 bathrooms as well.

[MJNewton]

3 hours ago, Noodle said:

2 - on the app, is the internal temp the temperature inside the mvhr unit? Its in the attic.

 

Could well be, and intended to represent the 'ambient' temperature of the surroundings. 5.9°C sounds reasonable for a cold roof space with an outside temperature of 3.4°C. (Mine is currently 4.1°C in the loft, 1.3°C outside so broadly similar)

 

Quote

The 1st day i turned the system on the supply temp was more like 17 degrees and now far lower around 13? It's really cold outside so do people think its because its so cold outside and in the attic that my supply has dropped so much or is because I'm faffing around with the fans and unbalanced the system so much? I assume with such a low internal unit temp the heat exchanger can only do so much in say sub 5 degrees external temp?

 

With a supply:extract ratio of 13.1°C:17.8°C that gives a 74% heat recovery efficiency which whilst on the low side is still within the realms of what might expect, particularly if the flow is on the high side (harder to recover the heat) and the loft is cold. Tweaking the flow down a bit and adding some insulation to the unit might help. Also, make sure any ducting in the loft is insulated too - I imagine your house isn't actually at 17.8°C, particularly at ceiling level, and so there's some heat loss along the way in the extract ducting. All very common for a retrofit in my view.

 

Incidentally, whilst it'd be worth experimenting to see if you can up the efficiency do remind yourself that even 13.1°C is considerably better than the 3.4°C that you'd have coming through window trickle vents that you otherwise should have!

Edited February 12, 2021 by MJNewton