Standing condensation water in new MVHR exchanger

[runcyclexcski]

I've installed a new small Boulder MVHR unit and been running it for about a week. It's been around freezing all week, so it was a good chance to check its performance, both in terms of heat-recovery and in terms of condensation. The unit is an older (2x cheaper) version of this:

 

https://ventilationmegastore.co.uk/products/all-products/mvhr-units/auto-bypass-pre-heat/dhv-15b-bph/

 

The drainage hose has remained completely dry for the whole week, even though the quarter of the unit receiving the cold air showed plenty of condensation on the outside, which dripped down about a cup worth (I kept wiping the floor underneath). Since the absence of water in the drainage hose did not make sense, I opened the unit to see what was going on.  I found that the bottom condensation pan was also completely dry. When I pulled out the exchanger, out poured the condensate water, about 2-3 cups worth. This water never made it down into the pan. I do not think the unit was intended to be installed "vertically" which (in prinicple) would allow for the condensate to run off the exchanger faster by gravity -- since this would make the bottom pan vertical, too. It looked as if every plastic channel of the exchanger was "pan-shaped", with water accumulating in every "sub-pan" and not draining out. Perhaps if there was twice as much water in the exchanger (say, a pint), some of it would drain. But it appears that with this design the unit would always have standing water in the cube, which does not sound proper.

 

I know zero about MVHRs, and I bought this unit w/o any research. Based on my new (very limited) experience, I would rotate the cube 90 degrees with respect to the bottom pan (within the unit). Are there units designed like this? Are there units with the exchanger working better for condensate run-off? I do not know... Teflon-coating? A spout in each "fin" to allow run-off? Metal exchangers for better heat conductance? Also, it would make sense if the outside of the unit (at least the respective quarter of it) was insulated on the outside, to prevent the outside condensation. Clearly, none of the above is implemented in this unit, so buyer beware, I guess. 

 

Many thanks in advance! I apologize for weekly postings on this :).

 

 

Edited December 14, 2024 by runcyclexcski

[Mike]

3 hours ago, runcyclexcski said:

the quarter of the unit receiving the cold air showed plenty of condensation on the outside

Is the unit installed the correct way round? Condensation would be expected in the section that exhausts to the outside air - warm moisture-laden internal air sheds water when it's cooled by the incoming air.

 

On the air intake side the cold external air is warmed up, so can hold more moisture, therefore condensation is unlikely.

[runcyclexcski]

The condensation on the outside of the unit is due to the ambient humidity in the room coming into contact with the unit outer metal housing (cooled by the cool incoming air from the inside). I humidify the flat to 45% artificially. The condensation inside the unit, as you say, should be due to the outcoming air coming into contact with the incoming air, and that's the condensate that I can't seem to drain

 

For now, I have tilted the unit by about 5 degree, so that water drips down out of the exchanger and flows towards the spout at the bottom better. Interestingly, the spout is right next to the internal electronic box as well, does not loook like proper placement

[runcyclexcski]

Correction: the exchanger internals are made of aluminum foil, not plastic, I was wrong about that. 

[runcyclexcski]

I have an update on this, after having spent 3 weeks monitotoring the MVHR unit. Learned a lot, which in hindsight I should have anticipated based on the basic laws of physics.

 

These are my personal opinions/observations. TLDR: I think I made it work, but it's not a "plug-in-and-forget" unit.

 

1. Tilting the unit by about 5 degrees towards the drainage spout helped the drainage of condensation water.

 

2. The manufacturer placed the drainage spout on the same corner of the unit as the electrical connection box. This is poor design which caused electrical tripping at least once a week due to dripping water, until I identified additional sources of dripping (hint: not through the built-in spout). The manufacturer had 4 corners to choose from, and picked the worst one.

 

3. My MVHR unit is not insulated on the outside; this is poor design. I note that Boulder now sells the same model that appears insulated and costs 2x, i.e. they may have learned the lesson. About half of condensation that I collect (about 1L per day) forms on the outside of the unit, specifically, the "cold" half. Since the unit needs to be tilted to aid internal condensation drainage, the outside condensation droplets also slide towards the spout corner (following sheet metal bends). Then they drip out of the unit not through the spout, but out of the corner of the unit. So I had to put an additional tray underneath the whole unit to catch the outside condensation.

 

4. Internal drainage only works well when I switch off the return air flow. When the return air is on, the air flow is against the drainage direction and this prevents the water from draining by gravity (unless there is a cup of standing water in the condenser). As soon as I switch off the motor, there is a burst of water flow in the drainage spout which until then was prevented from draining. If the drainage spout was on the opposite side, the condensation water would flow better (aided by direction of the return air).

 

5. The sheet metal screws in the unit are made of nickel-coated steel. These are now showing signs of rust, after only 3 weeks of operation -- the drainage water has a brownish color which I traced to those screws being in the "flow path" of the drainage water. I will prob get 316 screws and replace the stock ones.

 

5. I ordered 25mm-thick closed-cell PE adhesive insulation foam to cover the the "cold" side of the unit. I hope this directs the condenssation towards the internal condensation tray. Fingers crossed. 

 

6. I inspect the unit daily and pull the "cube" out weekly. If this unit was somewhere in the basement, I can imagine life forms would form in it in a few months, especially if the unit was switched off in the spring and left standing as is through the summer (I saw ghastly pictures on this forum :)). This unit is definitely not of the "connect and forget" type. Maybe there are better manufacturers out there. My unit was 500 quid at the time of purchase; now Boulder wants 1000 quid for it. For 1000 quid for a sheet metal box with two blower fans inside I expected more R&D and less fussy operation.

 

7. The intake air filter is noticeably darker (from the soot of wood-burning neighbors) after 3 weeks of operation. I live in an area with relatively good air quality; in the UK (Leicestershire) I would have collected much more. 

 

At any rate, I consider this an interesting learning experience. If I had to make a unit like this myself, I would prob make it out of transparent polycarbonate -- easier to see what is going on inside.

 

Edited December 30, 2024 by runcyclexcski

[Russdl]

Some interesting observations but are you sure the intake filter is darker through soot? That seems a bit wild after just 3 weeks. 
 

My hunch would be mould is starting to grow considering the wet conditions you describe. 

[Kelvin]

5 minutes ago, Russdl said:

Some interesting observations but are you sure the intake filter is darker through soot? That seems a bit wild after just 3 weeks. 
 

My hunch would be mould is starting to grow considering the wet conditions you describe. 

Possibly but if that filter is getting wet then there’s a serious issue with the MVHR or how it’s installed. Our intake filter was pretty dirty after a couple of months. It cleaned up ok and I replaced it at 6 months. 

[Mike]

6 hours ago, runcyclexcski said:

I note that Boulder now sells the same model that appears insulated and costs 2x, i.e. they may have learned the lesson

Maybe it was originally designed for a warm climate (in China?) & they thought that all they needed to do was add a condensate drain to sell it elsewhere.

[MikeSharp01]

12 hours ago, runcyclexcski said:

5. The sheet metal screws in the unit are made of nickel-coated steel. These are now showing signs of rust, after only 3 weeks of operation -- the drainage water has a brownish color which I traced to those screws being in the "flow path" of the drainage water. I will prob get 316 screws and replace the stock ones.

Good idea and when you fit them make sure there is no rust on the case metal, if there is get a rust killing metal priming paint, paint over the rust and when fitting the screw put a dab of silicon seal in the hole to prevent any water running past the new screws from getting underneath and rusting the case any further.  

[Russdl]

10 hours ago, Kelvin said:

Possibly but if that filter is getting wet then there’s a serious issue with the MVHR or how it’s installed.

For sure, but dirty from soot in three weeks?? They must be right next door to some dark satanic mills if it is soot. 

[Kelvin]

12 minutes ago, Russdl said:

For sure, but dirty from soot in three weeks?? They must be right next door to some dark satanic mills if it is soot. 

Agreed and they’d also likely have the smell of smoke in the house. 

[runcyclexcski]

***My hunch would be mould is starting to grow considering the wet conditions you describe. 

 

Russdl, the "sooty" filter is on the opposite side from the drain, and is much dirtier than the outgoing filter (which is right next to the drain and does get wet). If the mold hypothesis held, it would have been the other way round. So I do not think this is mold. I live an area where people like to burn wood when it goes below 5C to "stay cosy" with their fireplaces, even though everyone has gas heating.

 

I did not mean to say it's "black from soot" -- it's just a noticeable change of colour in to a slight biege. I am used to seeing this slight change of color on 3M P2 respirator before replacement: place the old filter next to the new one and you can see the difference. 

Edited December 31, 2024 by runcyclexcski

[runcyclexcski]

***Maybe it was originally designed for a warm climate (in China?)

 

Mike, I do not know, I had the impression that Boulder made and sold their units for the UK, but of course I may be wrong.

[runcyclexcski]

***Agreed and they’d also likely have the smell of smoke in the house. 

 

Kelvin, there is noticeable smell of wood smoke outdoors, especially at night. I slightly pressurize the flat, so that the soot does not get inside (and it does not -- apart from the filter). When I test air quality with a laser particle counter, the counts in the 0.3-1 micron range are 10 times higher outside (on the balcony where the air intake is) than indoors, on any day. When I drive on top of a local 1km high hill and test the air quality there, the counts in the 0.3-1 range drop 10x (on the same day/same weather), and one can see from the top that the soot/smoke stays in the valleys.

 

There are more filters downstream from the MVHR (pre-filter with a pleated P2 fabric and a HEPA). The P2 pre-filter is black after 3 months of use and needs to be replaced. The MVHR intake filter is very course and prob does not trap the fine particles anyway. The outgoing MVHR filter, I think, is not needed, since my indoor air is already passed through three HEPAs working 24-7 and is "pretty" clean as is.

Edited December 31, 2024 by runcyclexcski

[runcyclexcski]

Thank you all for the comments. I have also looked at the Brinck system which has been mentioned on this forum, and it seems to have the exchanger cube mounted vertically, consistent with what I discovered with my unit (that having it horizontally restricts the condensation drain). I wonder how well this unit is insulated. Overall, it looks better engineered than the bare-bones unit I've got.

 

https://www.brinkclimatesystems.nl/documenten/flair-450-600-technical-data-sheet-gb-617482.pdf

Edited December 31, 2024 by runcyclexcski

[runcyclexcski]

I have now taken a picture of the HVR unit filters after a month of continous operation (winter air at around 0C outside, wood-burning houses nearby). The outgoing air is on the left, the incoming air is on the right. I'd say, at least 25% of the soot is from New Year's eve. I am thinking to get a roll of generic filter fabric and cut these to size, rather than paying for replacement filters (I would like to replace the incoming filter once a month).

 

 

Edited Thursday at 20:09 by runcyclexcski

[Mike]

On 31/12/2024 at 17:15, runcyclexcski said:

***Maybe it was originally designed for a warm climate (in China?)

 

Mike, I do not know, I had the impression that Boulder made and sold their units for the UK, but of course I may be wrong.

Just taken a look and "Boulder Developments Ltd ... consists of three businesses; SuperFOIL Insulation, Ventilation Megastore and Treefloor" (here). Ventilation Megastore say that they "supply ventilation systems"; no mention of manufacturing.

 

On 31/12/2024 at 17:27, runcyclexcski said:

I have also looked at the Brinck system which has been mentioned on this forum, and it seems to have the exchanger cube mounted vertically, consistent with what I discovered with my unit (that having it horizontally restricts the condensation drain)

There are many units that are designed to be installed either vertically or horizontally, but of course they need to be properly designed to do that.

 

If you're looking for a replacement, the Passivhaus database lists models independently tested to more accurate standards than those required in the UK and those used by manufacturers: https://database.passivehouse.com/en/components/list/ventilation_small

[Russdl]

@runcyclexcski that looks better than the picture you painted in my head.
 

Ours looked similar after about 3 months. I would say it’s unlikely to be just from your neighbours fires unless your MVHR intake is right next to someone’s chimney.
 

Air is generally dirty, there would be no rain without dirt and that’s dirt of any description - pollen, volcanic ash, salt particles, even soot. 
 

It’s certainly worth getting your own filter material but don’t get too wound up about it, it’s doing what it’s supposed to do. 

[jack]

My inlet filter can look very dark after a few months, and we have no houses near enough to us for that to be soot.

[joe90]

3 minutes ago, jack said:

My inlet filter can look very dark after a few months,

Nice to know it’s not on your lungs 🤷‍♂️

[runcyclexcski]

Thank you, all! I am getting a roll of G3/G4 fabric for this. Obviously, I was too naiive to think that my unit was UK-made, but at the time I did not know much about the technology. For 500 quid or whatever I paid for it, it's good learning experience.

 

In principle, one's lungs are designed to deal with the crap in the air, but my lungs no longer can do it properly.