Hello Green Builders,

Any recommendations on which brands/models to look at or avoid?
Naturally, I want all the good stuff, like high ACTUAL efficiency, low cost etc.
Recondemations along this line are helpful.

But, thinking people here can provide guidance to the less google-able aspects.
Like, reliability, service support, flexibility/ability to interface with third party controls etc.

Any tips appreciated!

I was recommended (by a sales guy) to go for Nuaire AB WM1 but I haven't made any decisions yet. £800-£1k ish

Default would be vent axia hr100r which is very basic. £250ish


Some high end options here https://database.passivehouse.com/en/components/list/ventilation_small

I am extremely happy with my Komfovent unit from BPC especially in this cold weather as it has not needed to be switched off due to freezing (it would have been off for about 3 days).

I can connect it to my HomeAssistant (HA) locally.

I have fitted CO² monitoring to it, but manage the fan speed by HA rather than feeding the value into it. I'd recommend some form of CO² monitoring as it is more important in my situation than RH.

Efficiency is good if the figures reported by it are correct.

Posted By: Chendyhttps://database.passivehouse.com/en/components
Is the data here from testing or from the manufacturers?

The manufacturers pay a passivhaus-accredited lab to do the assessment and the database contains the certified results from the labs.

If a manufacturer chooses not to have a unit assessed, then it won't appear.

The minimum standard for all units is that they should meet EN 308:1997.

Unfortunately, anything marketed as intended for PH, tends to have an extra grand added to the price tags. It's still a niche market in the UK, you might be able to import something from Europe cheaper.

Don't forget to price for the ducts, manifolds, valves etc and any controllers, and the labour fitting them, it can add up to quite a lot. Once you invest on all that, the extra price of a good fan unit compared to a cheap one, might not seem so bad.

There are actually some different methods in which % heat recovery can be calculated. Some say that the SAP Q method favours the manufacturers by making the performance look better, and that the PH method is more demanding. So if you have % recovery numbers quoted from different sources they might not be directly comparable, that's an advantage of the PH database.

The elephant in the room is humidity - when you draw air through the house it gets warm (sensible heat) and it carries away humidity (latent heat). MHRV units might recover 90% of the sensible heat, and their sales people talk about that a lot, that's what the testing figures measure. They don't recover (condense) much of the latent heat at all, some recover only a little condensation and some actually recover no condensation at all. (Think of this like how a condensing boiler is more efficient, only at lower temperatures so the condensing is relatively more important for mhrv). So the difference between claimed 80% sensible heat recovery and claimed 90% sensible heat recovery is less significant than it may seem, if neither is recovering much evaporative heat.

... does the PH database testing methods ignore latent heat and any other nicher forms of heat as well??

Posted By: WillInAberdeenIt's still a niche market in the UK

It is. Here in France you can buy a selection of lower-spec units from larger DIY stores, from around €750.

Posted By: WillInAberdeen...you might be able to import something from Europe cheaper.

It is worth considering this. I may well buy a PH-assessed Zehnder unit for my current project and prices - for the same unit - range from €1,750 to €3,297, depending on the supplier and the country. You may also find that model names (and their stock codes) differ between countries, so some research may be needed to hunt down the best deal, and to make sure that the prices are for the same piece of hardware.

Posted By: WillInAberdeenfactors like noise

Particularly important for a flat, if it's going to be above your ceiling or in a cupboard, Chendy.

Posted By: ChendyThe efficiency of the fans is ignored?!

No, passivhaus certification requires that the total electrical power consumption of all fans, controls and any essential external systems do not exceed 0.45 W/m³/h when operating at (passivhaus's assessed) full throughput, with an external pressure of 100 Pa. The best units use less than half of that, as you can see from their database.

Posted By: Chendyelectrical efficiency isn't factored into the declared efficiency numbers?

The passivhaus 'efficiency ratio' does take into account electrical efficiency, and other factors, to show 'the amount by which the energy demand caused by ventilation can be reduced.' For full details, you can read the assessment criteria yourself: https://passivehouse.com/downloads/03_Reqs_and_testing_procedures_ventilation_en.pdf

Outside the Passivhaus scheme, getting reliable numbers for either of the above is difficult.

I bought a load of temperature sensors a few years ago so I could monitor my sentinel kinetic plus B; still haven't got around to fitting them, but I really should as I've always wondered about its efficiency

Posted By: cjardps.. "MHRV; Mechanical Heat with Recovery Ventilation"?

It's MVHR..

IIRC we had a long discussion about that previously...

The matrix always seemed really small to me, and I still wonder why it isn't made of metal

Posted By: WillInAberdeenIf 1kg of outside air at (say) 7⁰/80%RH is drawn into a house at 21⁰/60%RH, then it needs:

14kJ of sensible heat (80-90% of this is recoverable by a MHRV)

11kJ of latent heat (not much of this is recoverable by a MHRV)

I don't understand this. What is the latent heat for? Where is water being evaporated? What I would expect is that the air in the building will not be at 60% but more like 40-50% where the reduction due to fresh air is balanced by emissions from breathing, washing etc etc.

Posted By: jms452It's the latent heat of water vapour condensed from the outgoing air into the heat exchanger.

When it's 'very cold' outside some of this becomes available.

Right, but in WiA's chosen scenario it doesn't. But it's not energy consumed anywhere or lost so I'm not sure how it fits in to an MVHR 'efficiency' calculation.