MVHR maintenance (condensation and mould)

[runcyclexcski]

I just found this resource; peviously I periodically checked greenbuildingforum, but that may be going belly up.

 

I have recently installed a basic MVHR unit (rated at 150 m³ hr⁻¹). TLDR: How do I make sure I do not get mould in the heat exchange cube due to condensation? I have attached a picture of the MVHR label. It gets to around 0C at night oudroors where I live, so condensation is an issue at my indoor humidity levels (which I maintain at around 50%). 

 

My unit does have a drain hose, and the pan appears to be "proper" (no dead spots in it), but from what I've read online mould can form anyway. Should I replace the cube every winter (can be problematic in the long term if the manufacturer discontinues the unit)? I could make a polycarb window in the unit, to periodically inspect the cube w/o opening the unit. Or, I have some high-power deep UV diodes lying around from other project, so I could potentially implant them inside, but I am not sure if the light can reach deep inside the cube anyway. 

 

 

Thank you all in advance!

[JohnMo]

I assume you are overthinking stuff. Never seen any signs of mould been running for about 3 years.

 

Keep unit on, change or cleaning every six months, open up every year have look clean up. That's it.

 

Airflow rates should be way to high for mould to form.

 

What cube are you talking about?

[MikeGrahamT21]

I’ve had my MVHR running constantly for around 5 years and it still looks like the day I bought it inside, not even a speck of mould.

 

I wash the heat exchanger out once a year (if I remember)

[runcyclexcski]

Thanks, John. It's the heat-exchanger that one pulls out, I may have seen the term "cube" on some other forum. It looks like a beam splitter cube from my laser work.

 

Another issue (I may be over-thinking this) is that I like my flat to be positively pressurized, whereas the MVHR will vent that pressure out. Oh well, I will see how it does.

 

This is what I got from Boulder, they recommend keeping RH at 35-40% which is a bit too low for my liking (below).

 

Quote from Boulder:

>>>>>>>>>>>>

"Ensure Proper Drainage:
Please check that the drainage hose is installed correctly and is free from blockages. This ensures water from condensation is effectively removed.
Adjust Ventilation Rates:
Increasing the airflow slightly can help dry the heat exchanger cube more effectively and reduce the chances of moisture settling.
Lower Indoor Humidity:
While 45% relative humidity is comfortable, lowering it to around 35–40% during the winter can help minimise condensation. If needed, a dehumidifier can assist with this.
Regular Maintenance:
Clean the heat exchanger cube regularly as per the unit's maintenance guidelines. Removing dust and debris will improve performance and help prevent mould growth.
Insulate Ductwork:
Ensure the intake and exhaust ducts are properly insulated to prevent additional cooling and moisture build-up inside the system.
Replacing the Heat Exchanger Cube
If the above measures do not resolve the issue and mould persists, you may need to replace the heat exchanger cube.
In heavy winter use, we would recommend inspecting the cube at the start of the season . You would need to replace it if signs of mould or significant wear are visible." 

Edited December 6 by runcyclexcski

[JohnMo]

26 minutes ago, runcyclexcski said:

is that I like my flat to be positively pressurized, whereas the MVHR will vent that pressure out.

Not sure why you want it pressurised? But you would normally equalise flow and extract, this equalises pressure. If it is pressurised you would struggle to open an inward opening outside door. So I doubt you are actually pressurised, you would also need an airtight house.

 

Any ventilation system will bring your humidity levels down to 35 to 40% in a period of sustained cold outside.

[jack]

1 hour ago, MikeGrahamT21 said:

I’ve had my MVHR running constantly for around 5 years and it still looks like the day I bought it inside, not even a speck of mould.

 

I wash the heat exchanger out once a year (if I remember)

 

I didn't get much mould for the first few years, but as time's gone by, I get increasing amounts building up every year.

 

You've reminded me I need to do my annual clean. If I remember, I'll drop a photo (if it isn't too disgusting!) into the thread.

[Mike]

On 06/12/2024 at 14:43, runcyclexcski said:

Another issue (I may be over-thinking this) is that I like my flat to be positively pressurized

Not a good idea - unless your flat is perfectly airtight the excess pressure pushes moist internal air through any gaps in the structure, where it can condense and cause problems.  Always go for equally balanced.

[runcyclexcski]

John -- I like to keep the flat pressurized, b.c. it prevents passive diffusion of odors (my neghbor's weed and cigarettes, ozone in the summer etc )and particulate pollution from the outside. I do notice the pressure when I open the entry door, there is resistance to it. The pressure is perhaps 0.1 bar, nothing major, just like I had in my clean-room optics labs when they were certified. Once I pressurized, I have noticed significant drops in particulate counts indoors (at least 3-fold) compared to before pressurization. Thus I do not expect the MVHR to work perfectly, but anything helps. The place has gaskets at each door, all-metal doors etc. so they seemed to care about this. I will prob hire the same contractor when it's time to build my own place.

[runcyclexcski]

Jack -- would be nice to hear about your MVHR performance. I will make sure to wash the exchanger at the end of the winter, and will also bleach the inside of the unit with non-chlorine (peroxide-based) bleach.

[G and J]

3 minutes ago, runcyclexcski said:

The pressure is perhaps 0.1 bar, nothing major

Wow.  Do the doors sound like the doors on the USS Enterprise?   (Being serious I’m with @Mike on this one, running a positive pressure sounds like an invitation to trouble, and running balanced should keep smells out just as well - all down to the quality of the extra carbon filter you may have fitted).

[JohnMo]

45 minutes ago, runcyclexcski said:

pressure is perhaps 0.1 bar

No way are you pressurised that high.

 

In the 10s of Pascal's, maybe. 10kPa - no.

 

Are you sure you don't mean 0.1psi maybe, not sure I would want to open a door against that.

[runcyclexcski]

I have an always-on bathroom extractor which I cannot switch off, and that used to pull my neighbors' weed smell under the door in and also would pull in the odor traps from the shower basins. With the positive pressure in place, these issues were gone. Now I have a seal on the metal entry door all around as well.

 

Alright, I admit, I pulled the 0.1 bar (0.1 atm) number out of nowhere. I need to measure it properly, need to dig up my 1 bar range barometer. When I open the entry door, there is resistance and the air blows out through the gap, and this is what I am used to having in my optics labs. The input air is at 150 cubic meters per hr (that I did measure), and, before I installed the MVHR, I let the air "find its way" out, probably through the only bathroom exhaust shaft which I measured at 10% of my input rate. The latter is prob where my 0.1 atm wild guess came from, but of course it's wrong.

[MikeSharp01]

1 hour ago, runcyclexcski said:

The pressure is perhaps 0.1 bar,

That's is an awful lot of pressure. 1.5psi = 6000 Pa = 120 x the passive house test pressure = massive load on a door (3000lb @ 72inch x 33inch x 1.5lb) 

[runcyclexcski]

MIke -- yes, I obviously got this wrong. I will measure it properly and post. My background is from chromatorgraphy systems in which 1 bar (1 atm) is considered low pressure :).

[JohnMo]

58 minutes ago, runcyclexcski said:

chromatorgraphy systems in which 1 bar

Are you talking 1 Barg or 1 Bara? (as in gauge or absolute).

[runcyclexcski]

1 bar == 1 atm. This is what we use to measure liquid pressure in chromatography systems which have pumps etc to move liquids around and purify chemicals. 0 bar would mean no pressure applied to the system.

[JohnMo]

8 minutes ago, runcyclexcski said:

1 bar == 1 atm

Near but not quite

 

1 atm = 101325 pascals (Pa)

1 bar = 100000 pascals (Pa)

atm value x 101325 Pa = bar value x 100000 Pa

atm value = bar value x 0.986923

[runcyclexcski]

1 bar = 100000 pascals (Pa) 

1 atm = 101325 pascals (Pa)

 

OK, I did not know this, thanks!