running MVHR in the summer

[runcyclexcski]

I have been running a basic MVHR during the winter which I installed in Novemeber'24 -- upstream from a forced air filtration system (150 m^3/hr). I am mostly happy with the system, although it took some trial and error to set up a condensation run-off tray (for both internal and internal condenstation) -- in the coldest winter months, when the temps fell below freezing overnight, I would collect up to 1 L of condenste per night. I also replaced the input filter every month (using a helpful link to an RS item I got on this forum), wiped the insides of the unit and washed the exchanger under tap water. With this regular maintenance, it did not look filthy at all, so I am not terrified to open it now.

 

In the summer, I typically run a split AC unit and the same 150m^3/hr forced air ventilation system (I am severely allergic to pollen). The AC seems to keep up with the ventilation. Should I bypass the MVHR unit during the summer, or should I keep it running? I expect there to be condensation from the input air (it gets +30C and 80% RH outside here). In principle, it sounds like a good idea to keep it running, but in my experience there can be surprises. E.g. I wonder if there will be mold growing on the input filter, given the warmth and the high humidity of the input air. But then it also it can grow on my HEPA pre-filters, but in my experience it was not an issue the previous summer (with no MVHR installed).

[Mike]

You'll still want to keep a healthy indoor air quality, so you'll need it running to ensure that the air stays fresh. And if there is condensation within the unit, the fresh air running through it is more likely to help to keep it free from mould compared to stagnant moist air in the unit if you switch it off. So I'd keep it running.

[JohnMo]

39 minutes ago, runcyclexcski said:

replaced the input filter every month (using a helpful link to an RS item I got on this forum), wiped the insides of the unit and washed the exchanger under tap water

Why so often, change my filters every six months or so open it up once a year.

 

39 minutes ago, runcyclexcski said:

Should I bypass the MVHR unit during the summer, or should I keep it running

Keep it running - it's ventilation Aircon isn't!

 

39 minutes ago, runcyclexcski said:

mold growing

Mould is a product of humidity, temperature and lack of ventilation, so if the ventilation is on why do you get mold.

[runcyclexcski]

Thank you, John and Mike. Good point re: lack of ventiilation as the reason for mold growth. I hope the movement of air, even if the humidity is 70% (in the summer) is enough to make mold unhappy and dry it out. 

 

I did not mean to stop ventilation altogether in the summer, I meant whether I should bypass the MVHR in the summer. Ventilation is on at all times.

 

I tried changing the filter less frequently, and I noticed that after I replaced the filter after only 2 months, the air flow increased by 25%. The filter became dark brown in colour. Must be the wood burning in my area (we have issues with air pollution in air valley when it gets cold). The filters are cheap. I bought two square meters following a link which I believe was from you;  each filter is onlly 180 mm x 220 mm. So I do not mind opening the thing up to make sure everything is OK inside and get better air flow in return. I have seen some horrifying pictures of insides of MVHR units on this forum.

 

There are also bugs that like crawling into the vents in the summer and autumn. So if there is a wasp nest being built inside, or a bunch of stink bugs, I would prefer knowing it early. I do have a coarse mesh in the untake, but somehow there is always a kind of bug that can make it through. I am also thinking to make a transparent window in the MVHR so I can look inside.

Edited Tuesday at 14:50 by runcyclexcski

[Mike]

5 hours ago, runcyclexcski said:

I hope the movement of air, even if the humidity is 70% (in the summer) is enough to make mold unhappy and dry it out.

This will give you a clue:

 

https://www.researchgate.net/figure/sopleths-for-growth-of-various-fungus-species-and-the-lowest-isopleth-for-mould-LIM-0_fig1_272886603