MVHR Performance

[ryder72]

Our MVHR system Airflow Adriot was commissioned in January this year and has been in operation for nearly 12 months now.

 

Last winter Feb-April the display showed the differential between the extract and intake air at around 2-3 degrees with ambient at around 4/5 degrees.

 

Nearly a year into operation, the differential has widened to closer to 4-5 degrees with the same ambient outside temperature.

 

The intake and extract filters were replaced in October (very dirty) and the intake vent metal grille on the outside removed and washed to get rid of all sorts of rubbish (in fact i was pretty surprised at how dirty it was).

 

Is is normal that the differential should grow over a year of operation and what the causes  for this might be. I did wonder if the heat exchanger itself needs to be cleaned out. I can imagine that clogged heat exchange plates (or fins or whatever the appropriate word is) could lead to a deterioration in performance.

[Gone West]

1 hour ago, ryder72 said:

The intake and extract filters were replaced in October (very dirty) and the intake vent metal grille on the outside removed and washed to get rid of all sorts of rubbish (in fact i was pretty surprised at how dirty it was).

 

I found our intake vent got very dirty over the summer. We live out in the sticks and there's a lot of muck thrown up when harvesting. I will keep an eye on it over the winter. It's a good reason for having the vents in an easily accessible place.

[Stones]

1 hour ago, ryder72 said:

Our MVHR system Airflow Adriot was commissioned in January this year and has been in operation for nearly 12 months now.

 

Last winter Feb-April the display showed the differential between the extract and intake air at around 2-3 degrees with ambient at around 4/5 degrees.

 

Nearly a year into operation, the differential has widened to closer to 4-5 degrees with the same ambient outside temperature.

 

The intake and extract filters were replaced in October (very dirty) and the intake vent metal grille on the outside removed and washed to get rid of all sorts of rubbish (in fact i was pretty surprised at how dirty it was).

 

Is is normal that the differential should grow over a year of operation and what the causes  for this might be. I did wonder if the heat exchanger itself needs to be cleaned out. I can imagine that clogged heat exchange plates (or fins or whatever the appropriate word is) could lead to a deterioration in performance.

 

Purely anecdotal, I knew someone who experienced similar reduction in performance who on investigating, found the heat exchange core filled with condensation.  Emptied out, performance returned to what it had been.  

[Jeremy Harris]

Our intake filter, in particular, gets absolutely filthy, and needs regular cleaning/changing to maintain performance.  Someone here posted about their heat exchanger getting dirty, too, which seems to indicate that some MVHR units may not have that good a seal around the filter, or a filter that's not as effective as it should be.  I've no doubt that a dirty heat exchanger may well impact on performance, but if the filter is fitted properly and doing its job the heat exchanger shouldn't get dirty.

 

I took our heat exchanger out to clean it last summer, after it had been working for around 3 years, and found it spotlessly clean, so in our case it looks as if the filters do their job OK.

 

Moisture inside the heat exchanger is an odd one, as there should be a condensate drain, with the heat exchanger arranged internally in a position where any condensation that forms can drain away easily.  Condensation is useful, as it helps a fair bit with efficiency, as long as it can drain away having given up its heat to the heat exchanger plates.

 

I think it's hard to get a clear picture of efficiency from just measuring the temperature differential between the two sides, as it's highly dependent on other factors, like the instantaneous airflow rate (which will probably change a fair bit from minute to minute if there's any sort of a breeze blowing) as well as humidity, with the latter having a significant impact due to the latent heat given up during condensation.

[ryder72]

I have read the manual and it does recommend cleaning (washing out) the heat exchanger every time the filters are replaced. That will teach me to start reading manuals.