MEV vs SRHRV

[calumm]

I need to replace the old fan in my bathroom, and I'm trying to decide between MEV (trickle, with humidistat) and single room heat recovery. My house (ground floor flat) is around 1930, with un-insulated cavities (currently looking at insulating them, and also improving ventilation).

The main benefit of SRHRV is the heat recovery aspect. Additionally, the air coming in can be filtered.

However, I'm also trying to work out what the possible disadvantages of SRHRV could be, so that I can make a more informed decision. Here's what I've come up with so far:

1. More expensive to purchase.
2. MEV would help to ventilate the rest of the house, by pulling in fresh air through trickle vents etc. With SRHRV, would this be reduced, as air is being replaced directly in the bathroom; and would there therefore be less ventilation for the rest of the house? 
3. Air coming into the bathroom, while partly heated, would still be cooler than the air already there, so this could make it cooler after a shower (some reports online mention this).
4. Clearing of moist air would be slower, as the fan is only extracting for 50% of the time (at least, for single-fan units which switch every 70 seconds or so). (Again, mentioned online.)
5. Might clearing of moist air also be slower because some of the air in the vicinity of the fan would be fresh air which had only just been brought in?

These are my speculations as to the downsides of SRHRV. Do they seem valid? Is there anything else?

Thanks - Calum

[JohnMo]

I assume you are referring to to dMEV, not MEV? As MEV is a multi room ducted unit

 

 

If you are installing reversing heat recovery it is normal to install in pairs, one will suck while the other blows then they reverse direction together.  Or you can get single room MVHR, which sucks and blows at the same time.

 

Another alternative is PIV, this takes air normally from the loft and has a single supply point and basically blows air through the house.  The air is also filtered.  You don't need bathroom fans.  Worth looking into also.

[calumm]

Yes, I would have meant dMEV.

I'm looking at the single fan, reversing SRHRV units.

Thinking about installing fans in kitchen and bathrooms, and only going to PIV if we still need it.

Also, I posted in the wrong forum - reposted in Ventilation.

[RobLe]

Those reversing ones are interesting!  Do they reduce humidity as much as a regular SRHRV ?  I ask that, as it seems to me they are a bit more like an ERV.  As they breathe out, I expect moisture will condense into the ceramic core, to evaporate again and come back into the house when it breathes in later?  Anyone know ?  Asking for a friend with humidity issues.

Here’s a random one I found:

https://ventilation-system.com/series/twinfresh-easy

[Nick Thomas]

Huh, I was thinking about one of those for my own bathroom.

 

> Cycle I:

• The polluted warm air is extracted from the room and while passing the ceramic energy regenerator, it transfers the heat and moisture to it. In 70 seconds, as the energy regenerator gets warmed, the ventilator automatically switches to the supply mode. 

> Cycle 2:

• The fresh, but cold outdoor air flows through the heat regenerator and absorbs the accumulated moisture and heat so that the supply air flow has the room temperature. In 70 seconds, when the energy regenerator gets cold, the ventilator switches to the air extract mode. The cycle starts from the beginning. The changeover between the supply and extract modes takes place each 70 seconds

 

Suddenly reads like a bad idea 😅