dMEV and heating

[MarkyG82]

I'm coming back round the houses (pun intended) with the whole ventilation thing. 

BC have commented that we need extract from the ground floor WC (not external walls) and the upstairs wet rooms need new ventilation. 

My plan all along was to retrofit MVHR.  I try to put my money where my mouth is and do things right for all (PV, EV, etc.) and I thought MVHR was the right thing as it would rescue some of the heat lost while still offering some nice fresh air.  I'm now considering dMEV as it's dramatically cheaper and easier to install.  Then combine it with a positive pressure inlet it basically creates a modular MVHR without the R.

 

Long way of asking: how does a dMEV property cope with heat loss through the ventilation?  I don't want to go running the heating only to have it all sucked out by the vents.  We also sleep year round with the windows open but was hoping the MVHR would put a stop to that with the fresh supply.

 

Thinking out loud moment: with the relatively low cost of dMEV, could I install that then swap out to MVHR later if it's not enough?

[JohnMo]

9 minutes ago, MarkyG82 said:

I'm now considering dMEV as it's dramatically cheaper and easier to install.  Then combine it with a positive pressure inlet it basically creates a modular MVHR without the R.

No, do one or the other not both.

 

Wouldn't bother with PIV.

 

dMEV would be my choice or MEV. But you want to make sure it extracts the minimum amount of air - based on internal conditions. You need the following for it perform as required.

 

1. All internal doors need to be undercut (around 10mm clearance to floor covering). This allows cross ventilation.

2. You need inlets in dry rooms, trickle vents or otherwise - but you need these to automatic open and closed based humidity

3.  Your dMEV or MEV unit needs to automatically boost based on humidity. Greenwood CV2GIP are silent, draw next to no power, can by connected and controlled by a 3 core cable only.

 

You can get heat recovery bathroom fans, but they just ventilate the room they are in. You also get reversing fans with heat recovery but start to get expensive, as you need them in every room.

 

Heat losses is minimised by only ventilating at minimal rates as required.

[ProDave]

Well ventilation running 24/7 WILL suck heat out of the house.  That is the whole point of mvhr, that most of the otherwise lost heat, is recovered.

[Alan Ambrose]

Does the Greenwood CV2GIP unit close off the airflow somehow when it's not running, or is that not important?

[JohnMo]

28 minutes ago, Alan Ambrose said:

Does the Greenwood CV2GIP unit close off the airflow somehow when it's not running, or is that not important?

dMEV units run all the time at a low rate.

[JohnMo]

39 minutes ago, ProDave said:

Well ventilation running 24/7 WILL suck heat out of the house

You would be surprised how little a condition based system does. 

 

trickle rate for bathrooms/WC/utility is 5l/sec (21.6m3/h) and kitchen at 8l/s (28.8m3/h). Boost is only in the rooms requiring it

 

So house 3 bathroom, utility and kitchen, trickle rate 115.2m3/h

 

Ventilation heat loss = Q_v = 0.33 × Air volume x ΔT 

0.33 * 115.2 * 24 = 0.9kW at -3 OAT

 

90% efficiency MVHR at Scottish Building regs rates would, be 0.23kW at -3 OAT.  So 670W difference

 

dMEV advantages - No filters, heat exchangers and duct to pump through (supply and extract, only extract fans not supply fans. No filters to replace.

 

Cheap to install, I paid £35 for my fan, used in my summer house.

 

 

 

 

[MarkyG82]

Thanks all.

@JohnMo by don't do both I'm assuming you mean don't do PIV and dMEV together. A couple of articles I read suggested doing them together. I guess it's a way of controlling what air is coming in and gives the option for filter and heat?

I trust your input though. dMEV units are inexpensive to fit so I think that's the way we'll do rather than MVHR.

[OwenF]

FWIW I was swinging between PIV, PIV&MEV or just MEV.

 

I’m now settled on just MEV (probably centralised - Vent Axia multivent) for wet rooms. Plus a ‘dumb’ extract for hob.

 

I like the idea of humidity controlled trickle inlets but 1) they are difficult to source, especially not in window vent form, 2) my house is not airtight (only partial downstairs with good levels of airtightness)

 

Therefore I’m going to bank on enough background intake and the MEV controlling low-rate/boosted extract based on humidity 

[JohnMo]

15 minutes ago, MarkyG82 said:

don't do PIV and dMEV together

Yes choose one system or the other.

 

Not all dMEV units are equal. The Greenwood mentioned above was my second make, the first was quite noisy. Always seem to be plenty of Greenwood units on eBay for good prices.

 

2 minutes ago, OwenF said:

now settled on just MEV

I looked when I was designing my house quite liked the Duco system

 

https://www.duco.eu/uk-ie/products/mechanical-ventilation