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MVHR Research In The News Today


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7 replies to this topic

#1 tennentslager

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Posted 26 April 2016 - 12:16 PM

Snip form the summary
*Well designed, installed, maintained and used MVHR systems are able to make
useful contributions to energy reduction and good ventilation. However, in practice
achieving all these conditions is a challenge for the industry and many of the projects
in the studies had a number of problems that would undermine these benefits.
Common problems included: insufficient system air flow and system imbalance; lack
of appropriate airtightness; poorly designed and installed ductwork; lack of occupant
handover and understanding; inadequate maintenance, in particular filter cleaning or
replacement.*
Report here
http://radar.gsa.ac....L PUBLISHED.pdf


#2 SteamyTea

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Posted 26 April 2016 - 12:41 PM

Are these not the points we have been making ;)

#3 jsharris

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Posted 26 April 2016 - 12:43 PM

The imbalance problem seems widespread. Someone here mentioned that their supplier provided a system that required no balancing, as they'd "calculated it during the duct design" or similar.

I found that balancing was not only needed to show compliance with building regs, but that as installed the system was massively out of balance, despite my best endeavours to get the balancing roughly right by careful design.

The reason, I suspect, that some systems may not be correctly set up and balanced properly is because it is very time consuming, and frankly a complete pain to do. It isn't at all technically demanding or difficult, but it does mean a lot of running around making iterative adjustments, as every time you adjust one terminal you throw out the balance on a handful of others.......................

#4 SteamyTea

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Posted 26 April 2016 - 12:56 PM

It should be possible to design a self balancing system.
Airflow sensors in each duct, some simple valve actuators and very basic software.
If made by the thousands they would not be expensive.

#5 notnickclegg

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Posted 26 April 2016 - 01:02 PM

At least at the system level, some units (Brink, for example) are self-balancing. Of course, if not designed properly, you can end up with quite different fan speeds to obtain "balance".

Jack

#6 ProDave

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Posted 26 April 2016 - 01:11 PM

Interesting that the article on the local lunchtime news up here didn't mention mvhr at all.

It talked about modern homes being "too air tight" and people "not understanding" how to ventilate their homes.

Their example was a modern house which looked like it had half decent double glazed windows, and a representative of the company that built the houses instructing the owner on the fact they should open the trickle ventilators on the windows, and open a bathroom window or turn the fan on when having a shower.

Not exactly rocket science is it?

Edited by ProDave, 26 April 2016 - 01:11 PM.


#7 jsharris

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Posted 26 April 2016 - 01:24 PM

Part of the problem is that the so-called "self-balancing" units aren't any such thing at all. All they do is balance the gross airflow in with the gross airflow out, they don't do any balancing of the system at all.

Balancing is setting the correct room flow rates, one by one, and only having done that do you check the gross flow in and out at the MVHR. If that is in error, then you first go all around the rooms, one by one, adjusting them all in the "right" direction to correct the gross imbalance at the MVHR and also stay within the building regs requirements. Doing this can usually get to within around 4 or 5% of the gross balance at the MBVH, and then you can trim out the small difference by differential adjustment of the fan speeds.

Doing it this way leads to the lowest level of wasted power, by avoiding having the gross imbalance adjusted by a wide variation in MVHR fan speed. It also allows the system to be more efficient overall, and in most cases will allow good ventilation at a fairly low fan speed.

Our system was adjusted like this, and I got the balance such that I only needed to increase one fan by 3% to achieve gross balance.

Edited by jsharris, 26 April 2016 - 01:25 PM.


#8 recoveringacademic

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Posted 26 April 2016 - 01:40 PM

View Postjsharris, on 26 April 2016 - 01:24 PM, said:

Balancing is setting the correct room flow rates, one by one, and only having done that do you check the gross flow in and out at the MVHR. If that is in error, then you first go all around the rooms, one by one, adjusting them all in the "right" direction to correct the gross imbalance at the MVHR and also stay within the building regs requirements. Doing this can usually get to within around 4 or 5% of the gross balance at the MBVH, and then you can trim out the small difference by differential adjustment of the fan speeds.


First: for the original post thanks.

Thank you JSH. That (quoted above) was what worried me.

There was a lack of consideration of key issues at design and construction stages, including the function of the system, integration into the design, quality of installation and commissioning, control systems, and occupant guidance and understanding (point 7.1 page 80)


Point 7.2 deserves repetition and 7.2.2 too (page 82)

Now, how to tackle the obvious conflict of interest when buying an MVHR system from the same company that designs it?