MVHR long term efficeincy - drop off after 3 years

[Simon R]

It looks as though the efficiency of my MVHR is diminishing and I've not a clue why so I thought where better to get some input than BuildHub.

 

I'm running a Blauberg SB 550 unit which is possibly a little oversized for our build. When commissioned  the air flow temperatures suggested I was getting pretty much 94%, today, three years later it looks as though its running at about 80%. The filters are clear(newly fitted), the heat exchanger core and internals of the unit and clean and indeed look like new.

 

When commissioned the air entering the house was less than 3.3C colder than the air leaving the house.  

 

 

 

Now it's pretty much 5.3C cooler. That's a big enough difference to notice as a draft. The figures looks like it has to be the heat exchange unit unless I'm getting a lot more air into the house than is leaving it through the MVHR. Our build ACH of 0.6 was, testing the flows should let me know if this has changed.

 

I've contacted Blauberg who made some suggestions about possible causes. Imbalanced flows,  dirty filters, dirty heat exchanger etc. I also asked them if they monitored and kept efficiency data for the long term operation of their units, they don't (or won't share it?).

 

I've added myself to the anemometer wait list so I can check flows and compare them to those at the time of commissioning, however as no settings have been changed I'd be surprised if it's a factor.

 

There must be a good number of BuildHub members who have long term data of the efficiency of their MVHR systems heat exchangers. I'd like to know if others have seen a drop off and indeed if they haven't.

 

Here is a copy of the heat exchanger washing instructions:Cleaning Poly brochure_EN.pdf

 

 

[ProDave]

When mine (different make) started to seem non optimum, investigation showed the stainless steel inlet vent has a Gauss filet on the input that had become almost entirely blocked with dust.  Cleaning that out restored normal operation and is now on my annual maintenance list.

[Simon R]

4 minutes ago, ProDave said:

When mine (different make) started to seem non optimum, investigation showed the stainless steel inlet vent has a Gauss filet on the input that had become almost entirely blocked with dust.  Cleaning that out restored normal operation and is now on my annual maintenance list.

Thanks, that's one area I've not checked. I'll take a look and report back......only snag is it's 7M up so I'll need to get the staging out.

[Hastings]

Did you manage to improve things?

 

My system is 5 years old and one thing that's clear from reading this forum topic (MVHR) is that not enough thought, attention and design is applied to how to keep all the myriad parts of the airflow path clean.

 

In particular, positioning of the external intake vent (mine is on a slate roof two storeys high and I don't know whether it has a mesh within it) and cleaning of the heat exchange core unit.

[MJNewton]

Just stumbled across this thread and happened to have been looking at some charts for our MVHR system covering the five years since first installed and thought them worth posting as it looks like performance has remained fairly consistent with no apparent degradation:

 

 

 

The overall average efficiency rating of 89% (or 74% using a slightly different calculation method) doesn't seem too bad, particular given the annual drops over the summer as the bypass kicks in an out thus throwing all the figures out. The supply-intake delta (difference in temperature between the outside air and what is being supplied to the rooms) has similarly remained consistent over the years.

 

In terms of maintenance, all I've ever done is replace the heat exchanger filters every 6-12 months. I haven't cleaned any ducts, external grilles, the heat exchanger itself etc.

 

[Oz07]

4 minutes ago, MJNewton said:

Just stumbled across this thread and happened to have been looking at some charts for our MVHR system covering the five years since first installed and thought them worth posting as it looks like performance has remained fairly consistent with no apparent degradation:

 

 

 

The overall average efficiency rating of 89% (or 74% using a slightly different calculation method) doesn't seem too bad, particular given the annual drops over the summer as the bypass kicks in an out thus throwing all the figures out. The supply-intake delta (difference in temperature between the outside air and what is being supplied to the rooms) has similarly remained consistent over the years.

 

In terms of maintenance, all I've ever done is replace the heat exchanger filters every 6-12 months. I haven't cleaned any ducts, external grilles, the heat exchanger itself etc.

 

Do you change or clean the filters? Mine were washable 

[MJNewton]

5 minutes ago, Oz07 said:

Do you change or clean the filters? Mine were washable 

 

Change. Ours came with G4 filters and for their replacement I've just been using a giant roll of cheap generic filter material that I cut and fit into the stock frames.

 

 

They are certainly always very dirty each time, particularly the incoming filter which is black and full of various insects! The extract is cleaner, but still quite dusty.

 

 

Edited 11 hours ago by MJNewton

[Oz07]

Yeh my incoming was dirty, the outgoing I just found dusty. It is satisfying seeing all the crap its catching. Expensive satisfaction though